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science_qa_input_label_prep

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Can one bit of light bounce off another bit of light?	Yes, one bit of light can bounce off another bit of light, but not directly, and the effect is very rare. Light is made out of small quantum objects called photons. When you turn on a lamp, the light bulb begins creating and emitting trillions upon trillions of photons. Photons are in a class of quantum particles known as bosons. Bosons are special because many bosons can occupy the exact same quantum state at the same time. Light being made of bosons is what makes a laser beam possible. A laser beam is a collection of many photons all in the same quantum state. In contrast, particles that are not bosons cannot occupy the same state at the same time. This is one of the effects that keeps the atoms in an object from collapsing to a single point. The principle that dictates that non-bosons cannot be in the same state is called the Pauli Exclusion Principle. Non-bosons are also called fermions. The fact that bosons such as light can occupy the same state means that they don't get in each other's way. Also, light dominantly interacts with objects that have electric charge. Since light itself does not have electric charge, one photon cannot directly interact with another photon. Instead, they just pass right through each other without being affected. Because they are bosons and because they carry no electric charge, one photon cannot directly bounce off another photon. If you point one jet of water towards another jet of water, then at the point where they cross you will get a mess of water spraying all over due to the collisions. In contrast, if you shine one light beam such that it crosses another light beam, they will just pass through each other unaffected. However, two photons heading towards each other can indeed collide indirectly. The process goes like this. A photon can spontaneously degenerate into a particle with mass and its antiparticle in a process known as pair production. In this process, the energy of the photon is completely transformed into the mass of the two particles. For example, a photon can turn into an electron and an anti-electron. If two photons head towards each other and they both turn into electron/anti-electron pairs at about the same time, then these particles can interact. The anti-electron from one photon will collide with an electron from the other photon, and turn back to light. The same thing happens to the other anti-electron and electron. The overall effect is that you get two photons going into the interaction and you get two photons coming out of the interaction, so it looks like the photons simply bounced off each other. In a sense, the one bit of light did indeed bounce off the other bit of light, but only indirectly by transforming into other particles. This interaction is shown in the diagram. The red squiggles represent photons, the e+ blue lines are anti-electrons (positrons), and the e- blue lines are electrons. A photon comes from the left of the diagram and decays into an electron and an anti-electron. At the same time, another photon comes from the right and turns into an electron and an anti-electron. Each anti-electron collides with an electron, they mutually annihilate and turn back into a new photon. Photon-photon scattering is therefore possible through an indirect mechanism, but it is rare. There are two reasons that it is rare. First, light can only turn into other particles if it has enough energy to create the mass needed for the new particles, according to E = mc2. Because c is such a huge number, it takes a large amount of energy to make a little bit of mass. In order to turn into an electron and an anti-electron, the photon must have at least as much energy as the equivalent energy of their combined masses. Only gamma rays (one step higher than X-rays) have enough energy to do this. Secondly, the photons have to transform at just the right moment in order for the new particles from both photons to collide. For both of these reasons, light-light scattering is very rare. In fact, light-light scattering has never been conclusively observed. All the steps in light-light scattering have been observed (pair production and pair annihilation), so that we know that it is possible. The whole effect is just so rare that it has never been observed. However, the Large Hadron Collider (LHC) has both the ability to create high-energy light, and the ability to create a lot of it, making the rarity of light-light scattering more manageable. It is only a matter of time before the LHC observes light bouncing off light.	tag/antimatter/	context: tag/antimatter/ question: Can one bit of light bounce off another bit of light?	Yes, one bit of light can bounce off another bit of light, but not directly, and the effect is very rare. Light is made out of small quantum objects called photons. When you turn on a lamp, the light bulb begins creating and emitting trillions upon trillions of photons. Photons are in a class of quantum particles known as bosons. Bosons are special because many bosons can occupy the exact same quantum state at the same time. Light being made of bosons is what makes a laser beam possible. A laser beam is a collection of many photons all in the same quantum state. In contrast, particles that are not bosons cannot occupy the same state at the same time. This is one of the effects that keeps the atoms in an object from collapsing to a single point. The principle that dictates that non-bosons cannot be in the same state is called the Pauli Exclusion Principle. Non-bosons are also called fermions. The fact that bosons such as light can occupy the same state means that they don't get in each other's way. Also, light dominantly interacts with objects that have electric charge. Since light itself does not have electric charge, one photon cannot directly interact with another photon. Instead, they just pass right through each other without being affected. Because they are bosons and because they carry no electric charge, one photon cannot directly bounce off another photon. If you point one jet of water towards another jet of water, then at the point where they cross you will get a mess of water spraying all over due to the collisions. In contrast, if you shine one light beam such that it crosses another light beam, they will just pass through each other unaffected. However, two photons heading towards each other can indeed collide indirectly. The process goes like this. A photon can spontaneously degenerate into a particle with mass and its antiparticle in a process known as pair production. In this process, the energy of the photon is completely transformed into the mass of the two particles. For example, a photon can turn into an electron and an anti-electron. If two photons head towards each other and they both turn into electron/anti-electron pairs at about the same time, then these particles can interact. The anti-electron from one photon will collide with an electron from the other photon, and turn back to light. The same thing happens to the other anti-electron and electron. The overall effect is that you get two photons going into the interaction and you get two photons coming out of the interaction, so it looks like the photons simply bounced off each other. In a sense, the one bit of light did indeed bounce off the other bit of light, but only indirectly by transforming into other particles. This interaction is shown in the diagram. The red squiggles represent photons, the e+ blue lines are anti-electrons (positrons), and the e- blue lines are electrons. A photon comes from the left of the diagram and decays into an electron and an anti-electron. At the same time, another photon comes from the right and turns into an electron and an anti-electron. Each anti-electron collides with an electron, they mutually annihilate and turn back into a new photon. Photon-photon scattering is therefore possible through an indirect mechanism, but it is rare. There are two reasons that it is rare. First, light can only turn into other particles if it has enough energy to create the mass needed for the new particles, according to E = mc2. Because c is such a huge number, it takes a large amount of energy to make a little bit of mass. In order to turn into an electron and an anti-electron, the photon must have at least as much energy as the equivalent energy of their combined masses. Only gamma rays (one step higher than X-rays) have enough energy to do this. Secondly, the photons have to transform at just the right moment in order for the new particles from both photons to collide. For both of these reasons, light-light scattering is very rare. In fact, light-light scattering has never been conclusively observed. All the steps in light-light scattering have been observed (pair production and pair annihilation), so that we know that it is possible. The whole effect is just so rare that it has never been observed. However, the Large Hadron Collider (LHC) has both the ability to create high-energy light, and the ability to create a lot of it, making the rarity of light-light scattering more manageable. It is only a matter of time before the LHC observes light bouncing off light.
Does the negative mass of antimatter mean that it's gravitationally repelled from stars?	Antimatter does not have negative mass. In our universe, there is no such thing as negative mass. Mass only comes in positive form. In contrast, electric charge can be positive or negative. The nonexistence of negative mass has profound consequences. First, gravity is always attractive and never repulsive. Presumably, if negative mass existed, it would be repelled by objects with positive mass such as the earth or sun. A cup made out of negative mass would fall up and not down when you let it go. As interesting as this sounds, negative mass does not exist, so heavier objects always fall down. Second, the lack of negative mass means that gravitational fields can never be shielded, blocked, or canceled. In contrast, electric charge comes in both positive and negative varieties. An electric field created by a positively charged object can therefore be blocked by a wall of negative charges. This is the principle used in metal shielding, which keeps the microwaves in a microwave oven from cooking everything in the kitchen. But there is no negative mass to cancel out gravity. If negative mass did exist, you could use it as a form of anti-gravity. If you built a floor on earth out of negative mass of sufficient size, then people above that floor would feel no gravity and would float around. Again, negative mass does not exist, so genuine anti-gravity is not possible. Gravity permeates every cell of every creature, and into the deepest dungeon with the thickest walls. Antimatter is a physical entity with positive mass that is identical to regular matter in every way except that the charge and some other properties are flipped. Every bit of matter in the universe has a potential antimatter counterpart. Every fundamental particle of regular matter has an antimatter version. For instance, the antimatter version of the electron is the positron. Electrons and positron have the exact same mass, the same spin, and the same charge magnitude. The only difference is that electrons are negatively charged and positrons are positively charged (positrons should not be confused with protons which are completely different particles) and a few other properties are flipped. When an electron meets a positron, they annihilate each other and their combined mass is converted completely into energy in the form of gamma rays. This effect is used routinely in medical PET scans. In general, antimatter annihilates its regular matter version when they meet. Antimatter can be thought of as regular matter traveling backwards in time. In this picture, a particle-antiparticle annihilation event can be thought of as a forward-time-traveling particle being knocked by gamma rays so that it becomes the same particle, but just traveling backwards in time. Note that this time travel concept applies only to specific antimatter events that obey the conservation of energy and does not open up the possibility for humans to travel back in time, which would violate the conservation of energy. Although antimatter comes in very small quantities in our universe, it is not as exotic or unnatural as once thought. Every minute of every day, high energy cosmic rays from distant supernovas are slamming into earth's atmosphere and creating a very small amount of antimatter. Also, the natural radioactive decay that takes place constantly in earth's rocks creates small amounts of antimatter. But this antimatter does not stick around for long because it quickly bumps up against regular matter and destroys itself in the process.	tag/antimatter/	context: tag/antimatter/ question: Does the negative mass of antimatter mean that it's gravitationally repelled from stars?	Antimatter does not have negative mass. In our universe, there is no such thing as negative mass. Mass only comes in positive form. In contrast, electric charge can be positive or negative. The nonexistence of negative mass has profound consequences. First, gravity is always attractive and never repulsive. Presumably, if negative mass existed, it would be repelled by objects with positive mass such as the earth or sun. A cup made out of negative mass would fall up and not down when you let it go. As interesting as this sounds, negative mass does not exist, so heavier objects always fall down. Second, the lack of negative mass means that gravitational fields can never be shielded, blocked, or canceled. In contrast, electric charge comes in both positive and negative varieties. An electric field created by a positively charged object can therefore be blocked by a wall of negative charges. This is the principle used in metal shielding, which keeps the microwaves in a microwave oven from cooking everything in the kitchen. But there is no negative mass to cancel out gravity. If negative mass did exist, you could use it as a form of anti-gravity. If you built a floor on earth out of negative mass of sufficient size, then people above that floor would feel no gravity and would float around. Again, negative mass does not exist, so genuine anti-gravity is not possible. Gravity permeates every cell of every creature, and into the deepest dungeon with the thickest walls. Antimatter is a physical entity with positive mass that is identical to regular matter in every way except that the charge and some other properties are flipped. Every bit of matter in the universe has a potential antimatter counterpart. Every fundamental particle of regular matter has an antimatter version. For instance, the antimatter version of the electron is the positron. Electrons and positron have the exact same mass, the same spin, and the same charge magnitude. The only difference is that electrons are negatively charged and positrons are positively charged (positrons should not be confused with protons which are completely different particles) and a few other properties are flipped. When an electron meets a positron, they annihilate each other and their combined mass is converted completely into energy in the form of gamma rays. This effect is used routinely in medical PET scans. In general, antimatter annihilates its regular matter version when they meet. Antimatter can be thought of as regular matter traveling backwards in time. In this picture, a particle-antiparticle annihilation event can be thought of as a forward-time-traveling particle being knocked by gamma rays so that it becomes the same particle, but just traveling backwards in time. Note that this time travel concept applies only to specific antimatter events that obey the conservation of energy and does not open up the possibility for humans to travel back in time, which would violate the conservation of energy. Although antimatter comes in very small quantities in our universe, it is not as exotic or unnatural as once thought. Every minute of every day, high energy cosmic rays from distant supernovas are slamming into earth's atmosphere and creating a very small amount of antimatter. Also, the natural radioactive decay that takes place constantly in earth's rocks creates small amounts of antimatter. But this antimatter does not stick around for long because it quickly bumps up against regular matter and destroys itself in the process.
How can you tell a black hole made out of antimatter from a black hole made out of matter?	According to our current understanding, there is no way to distinguish an antimatter black hole from a regular-matter black hole. In fact, there is no difference between an antimatter black hole and a regular-matter black hole if they have the same mass, charge, and angular-momentum. First of all, antimatter is just like regular matter except that its charge and some other properties are flipped. Antimatter has positive mass just like regular matter and experiences gravity the same way. Antimatter is exotic in the sense of being very rare in our universe, but it is not exotic in how it obeys the laws of physics. An antimatter cookie would look just like a regular-matter cookie. Therefore, adding the concept of antimatter to the discussion does not really lead to anything new or exotic. We could just as easily ask, "what is the difference between a black hole made of hydrogen and a black hole made of helium?" The answer is that there is no difference (as long as the total mass, charge, and angular-momentum are the same). According to the No-Hair Theorem, a black hole has the interesting property that all information and structure that falls into a black hole becomes trapped from the rest of the universe, and perhaps even destroyed, except for its effect on the total mass, charge, and angular momentum of the black hole. The overall mass of a black hole is what determines the strength of its gravity. When scientists talk about large or small black holes, they are actually talking about the mass of the black hole. Large black holes have more mass, more gravity, and therefore more effect on their surroundings. When matter falls into a black hole, it increases the overall mass of the black hole. The overall electric charge of a black hole determines the strength of the electric field that it creates. When matter with electric charge of the same polarity as the black hole falls in, it increases the charge of the black hole. The overall angular momentum of a black hole describes how fast it is spinning. When matter falls into a black hole with a swirling motion (as opposed to falling straight in), it can increase the black hole's total angular momentum if the matter swirls in the same direction, or decrease the black hole's total angular momentum if it swirls in the opposite direction. In the book The Nature of Space and Time by Stephen Hawking and Roger Penrose, Hawking states: The no-hair theorem, proved by the combined work of Israel, Carter, Robinson, and myself, shows that the only stationary black holes in the absence of matter fields are the Kerr solutions. These are characterized by two parameters, the mass M and the angular momentum J. The no-hair theorem was extended by Robinson to the case where there was an electromagnetic field. This added a third parameter Q, the electric charge... What the no-hair theorems show is that a large amount of information is lost when a body collapses to form a black hole. The collapsing body is described by a very large number of parameters. These are the types of matter and the multipole moments of the mass distribution. Yet the black hole that forms is completely independent of the type of matter and rapidly loses all the multipole moments except the first two: the monopole moment, which is the mass, and the dipole moment, which is the angular momentum. We don't know exactly what goes on in a black hole. The matter inside a black hole could be condensed down to an indistinguishable blob. Or the matter could retain some structure but remain trapped in the black hole by the black hole's intense gravity. The problem is that a black hole's center is so small that the theory of General Relativity, which describes gravitational effects, becomes inaccurate. We need quantum theory to accurately describe physics on the very small scale. But we have not yet developed a correct theory of quantum gravity. Therefore, we won't have a good idea of what goes on inside a black hole until we have an accurate theory of quantum gravity. The fact that the inside of black holes is shielded from all experimental observations makes the task even more difficult.	tag/antimatter/	context: tag/antimatter/ question: How can you tell a black hole made out of antimatter from a black hole made out of matter?	According to our current understanding, there is no way to distinguish an antimatter black hole from a regular-matter black hole. In fact, there is no difference between an antimatter black hole and a regular-matter black hole if they have the same mass, charge, and angular-momentum. First of all, antimatter is just like regular matter except that its charge and some other properties are flipped. Antimatter has positive mass just like regular matter and experiences gravity the same way. Antimatter is exotic in the sense of being very rare in our universe, but it is not exotic in how it obeys the laws of physics. An antimatter cookie would look just like a regular-matter cookie. Therefore, adding the concept of antimatter to the discussion does not really lead to anything new or exotic. We could just as easily ask, "what is the difference between a black hole made of hydrogen and a black hole made of helium?" The answer is that there is no difference (as long as the total mass, charge, and angular-momentum are the same). According to the No-Hair Theorem, a black hole has the interesting property that all information and structure that falls into a black hole becomes trapped from the rest of the universe, and perhaps even destroyed, except for its effect on the total mass, charge, and angular momentum of the black hole. The overall mass of a black hole is what determines the strength of its gravity. When scientists talk about large or small black holes, they are actually talking about the mass of the black hole. Large black holes have more mass, more gravity, and therefore more effect on their surroundings. When matter falls into a black hole, it increases the overall mass of the black hole. The overall electric charge of a black hole determines the strength of the electric field that it creates. When matter with electric charge of the same polarity as the black hole falls in, it increases the charge of the black hole. The overall angular momentum of a black hole describes how fast it is spinning. When matter falls into a black hole with a swirling motion (as opposed to falling straight in), it can increase the black hole's total angular momentum if the matter swirls in the same direction, or decrease the black hole's total angular momentum if it swirls in the opposite direction. In the book The Nature of Space and Time by Stephen Hawking and Roger Penrose, Hawking states: The no-hair theorem, proved by the combined work of Israel, Carter, Robinson, and myself, shows that the only stationary black holes in the absence of matter fields are the Kerr solutions. These are characterized by two parameters, the mass M and the angular momentum J. The no-hair theorem was extended by Robinson to the case where there was an electromagnetic field. This added a third parameter Q, the electric charge... What the no-hair theorems show is that a large amount of information is lost when a body collapses to form a black hole. The collapsing body is described by a very large number of parameters. These are the types of matter and the multipole moments of the mass distribution. Yet the black hole that forms is completely independent of the type of matter and rapidly loses all the multipole moments except the first two: the monopole moment, which is the mass, and the dipole moment, which is the angular momentum. We don't know exactly what goes on in a black hole. The matter inside a black hole could be condensed down to an indistinguishable blob. Or the matter could retain some structure but remain trapped in the black hole by the black hole's intense gravity. The problem is that a black hole's center is so small that the theory of General Relativity, which describes gravitational effects, becomes inaccurate. We need quantum theory to accurately describe physics on the very small scale. But we have not yet developed a correct theory of quantum gravity. Therefore, we won't have a good idea of what goes on inside a black hole until we have an accurate theory of quantum gravity. The fact that the inside of black holes is shielded from all experimental observations makes the task even more difficult.
Is there any difference between antimatter, dark matter, dark energy, and degenerate matter?	Yes. Although the names sound vague and almost fictional, the types of matter called antimatter, dark matter, dark energy, and degenerate matter are all different, specific entities that really exist in our universe. Antimatter is just regular matter with a few properties flipped, such as the electric charge. For example, the antimatter version of an electron is a positron. They both have the same mass, but have opposite electric charge. Antimatter is not as exotic as science fiction makes it out to be. For starters, antimatter has regular mass and accelerates in response to forces just like regular matter. Also, antimatter is gravitationally attracted to other forms of matter just like regular matter. For every particle that exists, there is an antimatter counterpart (some particles such as photons are their own anti-particles). What makes antimatter unique is that when antimatter comes in contact with its regular matter counterpart, they mutually destroy each other and all of their mass is converted to energy. This matter-antimatter mutual annihilation has been observed many times and is a well-established principle. In fact, medical PET scans routinely use annihilation events in order to form images of patients. Antimatter is therefore only distinct from regular matter in that it annihilates when meeting regular matter. For instance, a proton and a positron are somewhat similar. They both have regular mass. They both have a positive electric charge of the same strength. They both have a quantum spin of one half. But when a proton meets an electron, it forms a stable hydrogen atom. When a positron meets an electron, they destroy each other. The key difference is that a positron is antimatter and a proton is not. Antimatter is very rare in our universe compared to regular matter, but there are small amounts of antimatter all over the place in the natural world, including inside your body. Antimatter is created by many types of radioactive decay, such as by the decay of potassium-40. When you eat a banana, you are eating trace amounts of antimatter-producing atoms. The amount is so small, that it does not really affect your health. But it is still there. Why doesn't antimatter build up in your body? The key is that our universe is mostly made of regular matter, so antimatter cannot stick around for very long. Very soon after antimatter is created, it bumps into regular matter and gets destroyed again. Antimatter is also produced by lightning and cosmic rays. It is well understood by physicists, and is predicted by standard particle physics theories. Dark matter is matter that does not interact electromagnetically, and therefore cannot be seen using light. At the same time, dark matter does interact gravitationally and can therefore be "seen" through its gravitational effect on other matter. It is common throughout the universe and helps shape galaxies. In fact, recent estimates put dark matter as five times more common than regular matter in our universe. But because dark matter does not interact electromagnetically, we can't touch it, see it, or manipulate it using conventional means. You could, in principle, manipulate dark matter using gravitational forces. The problem is that the gravitational force is so weak that you need planet-sized masses in order to gravitationally manipulate human-sized objects. There remains much unknown about dark matter since it is so hard to detect and manipulate. Dark matter is not predicted or explained by standard particle physics theories but is a crucial part of the Big Bang model. Dark energy is an energy on the universal scale that is pushing apart galaxies and causing the universe to expand at an increasing rate. Like dark matter, dark energy is poorly understood and is not directly detectable using conventional means. Several lines of evidence make it clear that our universe is expanding. Not only that, our universe is expanding at an increasing rate. Dark energy is the name of the poorly understood mechanism that drives this accelerating expansion. While dark matter tends to bring matter together, dark energy tends to push matter apart. Dark energy is weak and mostly operates only on the intergalactic scale where gravitational attraction of dark matter and regular matter is negligible. Dark energy is thought to be spread thinly but evenly throughout the entire universe. Dark energy is also not predicted or explained by standard particle physics theories but is included in modern versions of the Big Bang model. Dark energy may have a connection with the vacuum energy predicted by particle physics, but the connection is currently unclear. Degenerate matter is regular matter that has been compressed until the atoms break down and the particles lock into a giant mass. Degenerate matter acts somewhat like a gas in that the particles are not bound to each other, and somewhat like a solid in that the particles are packed so closely that they cannot move much. A white dwarf star is mostly composed of electrons compressed into a state of degenerate matter. A neutron star is mostly composed of degenerate neutrons. Further compression of a neutron star may transform it to a quark star, which is a star composed of quarks in a degenerate state. But not enough is known about quarks to determine at present whether quark stars really exist or are even possible. These concepts are summarized in the list below. Regular Matter Antimatter Dark Matter Dark Energy Degenerate Matter	tag/antimatter/	context: tag/antimatter/ question: Is there any difference between antimatter, dark matter, dark energy, and degenerate matter?	Yes. Although the names sound vague and almost fictional, the types of matter called antimatter, dark matter, dark energy, and degenerate matter are all different, specific entities that really exist in our universe. Antimatter is just regular matter with a few properties flipped, such as the electric charge. For example, the antimatter version of an electron is a positron. They both have the same mass, but have opposite electric charge. Antimatter is not as exotic as science fiction makes it out to be. For starters, antimatter has regular mass and accelerates in response to forces just like regular matter. Also, antimatter is gravitationally attracted to other forms of matter just like regular matter. For every particle that exists, there is an antimatter counterpart (some particles such as photons are their own anti-particles). What makes antimatter unique is that when antimatter comes in contact with its regular matter counterpart, they mutually destroy each other and all of their mass is converted to energy. This matter-antimatter mutual annihilation has been observed many times and is a well-established principle. In fact, medical PET scans routinely use annihilation events in order to form images of patients. Antimatter is therefore only distinct from regular matter in that it annihilates when meeting regular matter. For instance, a proton and a positron are somewhat similar. They both have regular mass. They both have a positive electric charge of the same strength. They both have a quantum spin of one half. But when a proton meets an electron, it forms a stable hydrogen atom. When a positron meets an electron, they destroy each other. The key difference is that a positron is antimatter and a proton is not. Antimatter is very rare in our universe compared to regular matter, but there are small amounts of antimatter all over the place in the natural world, including inside your body. Antimatter is created by many types of radioactive decay, such as by the decay of potassium-40. When you eat a banana, you are eating trace amounts of antimatter-producing atoms. The amount is so small, that it does not really affect your health. But it is still there. Why doesn't antimatter build up in your body? The key is that our universe is mostly made of regular matter, so antimatter cannot stick around for very long. Very soon after antimatter is created, it bumps into regular matter and gets destroyed again. Antimatter is also produced by lightning and cosmic rays. It is well understood by physicists, and is predicted by standard particle physics theories. Dark matter is matter that does not interact electromagnetically, and therefore cannot be seen using light. At the same time, dark matter does interact gravitationally and can therefore be "seen" through its gravitational effect on other matter. It is common throughout the universe and helps shape galaxies. In fact, recent estimates put dark matter as five times more common than regular matter in our universe. But because dark matter does not interact electromagnetically, we can't touch it, see it, or manipulate it using conventional means. You could, in principle, manipulate dark matter using gravitational forces. The problem is that the gravitational force is so weak that you need planet-sized masses in order to gravitationally manipulate human-sized objects. There remains much unknown about dark matter since it is so hard to detect and manipulate. Dark matter is not predicted or explained by standard particle physics theories but is a crucial part of the Big Bang model. Dark energy is an energy on the universal scale that is pushing apart galaxies and causing the universe to expand at an increasing rate. Like dark matter, dark energy is poorly understood and is not directly detectable using conventional means. Several lines of evidence make it clear that our universe is expanding. Not only that, our universe is expanding at an increasing rate. Dark energy is the name of the poorly understood mechanism that drives this accelerating expansion. While dark matter tends to bring matter together, dark energy tends to push matter apart. Dark energy is weak and mostly operates only on the intergalactic scale where gravitational attraction of dark matter and regular matter is negligible. Dark energy is thought to be spread thinly but evenly throughout the entire universe. Dark energy is also not predicted or explained by standard particle physics theories but is included in modern versions of the Big Bang model. Dark energy may have a connection with the vacuum energy predicted by particle physics, but the connection is currently unclear. Degenerate matter is regular matter that has been compressed until the atoms break down and the particles lock into a giant mass. Degenerate matter acts somewhat like a gas in that the particles are not bound to each other, and somewhat like a solid in that the particles are packed so closely that they cannot move much. A white dwarf star is mostly composed of electrons compressed into a state of degenerate matter. A neutron star is mostly composed of degenerate neutrons. Further compression of a neutron star may transform it to a quark star, which is a star composed of quarks in a degenerate state. But not enough is known about quarks to determine at present whether quark stars really exist or are even possible. These concepts are summarized in the list below. Regular Matter Antimatter Dark Matter Dark Energy Degenerate Matter
Are there nuclear reactions going on in our bodies?	Yes, there are nuclear reactions constantly occurring in our bodies, but there are very few of them compared to the chemical reactions, and they do not affect our bodies much. All physical objects are made of molecules. A molecule is a series of atoms linked together by chemical (electromagnetic) bonds. Inside each atom is a nucleus which is a collection of protons and neutrons linked together by nuclear bonds. Chemical reactions are the making, breaking, and rearranging of bonds between atoms in molecules. Chemical reactions do not change the nuclear structure of any atoms. In contrast, nuclear reactions involve the transformation of atomic nuclei. Most of the processes surrounding us in our daily life are chemical reactions and not nuclear reactions. All of the physical processes that take place to keep a human body running (blood capturing oxygen, sugars being burned, DNA being constructed,etc.) are chemical processes and not nuclear processes. Nuclear reactions do indeed occur in the human body, but the body does not use them. Nuclear reactions can lead to chemical damage, which the body may notice and try to fix. There are three main types of nuclear reactions: Note that nuclear fission and radioactive decay overlap a little bit. Some types of radioactive decay involve the spitting out of nuclear fragments and could therefore be seen as a type of fission. For the purposes of this article, "fission" refers to large-scale nucleus fragmentation events that can clearly not be classified as radioactive decay. Nuclear fusion requires high energy in order to be ignited. For this reason, nuclear fusion only occurs in stars, in supernovas, in nuclear fusion bombs, in nuclear fusion experimental reactors, in cosmic ray impacts, and in particle accelerators. Similarly, nuclear fission requires high energy or a large mass of heavy, radioactive elements. For this reason, significant nuclear fission only occurs in supernovas, in nuclear fission bombs, in nuclear fission reactors, in cosmic ray impacts, in particle accelerators, and in a few natural ore deposits. In contrast, radioactive decay happens automatically to unstable nuclei and is therefore much more common. Every atom has either a stable nucleus or an unstable nucleus, depending on how big it is and on the ratio of protons to neutrons. Nuclei with too many neutrons, too few neutrons, or that are simply too big are unstable. They eventually transform to a stable form through radioactive decay. Wherever there are atoms with unstable nuclei (radioactive atoms), there are nuclear reactions occurring naturally. The interesting thing is that there are small amounts of radioactive atoms everywhere: in your chair, in the ground, in the food you eat, and yes, in your body. Radioactive decay produces high-energy radiation that can damage your body. Fortunately, our bodies have mechanisms to clean up the damage caused by radioactivity and high-energy radiation before they become serious. For the average person living a normal life, the amount of radioactivity in his body is so small that the body has no difficulty repairing all the damage. The problem is when the radioactivity levels (the amount of nuclear reactions in and around the body) rise too high and the body cannot keep up with the repairs. In such cases, the victim experiences burns, sickness, cancer, and even death. Exposure to dangerously high levels of radioactivity is rare and is typically avoided through government regulation, training, and education. Common causes of human exposure to high radioactivity include: Note that if you have a single medical scan performed that requires drinking or being injected with a radioactive tracer, you do indeed end up with more nuclear reactions in your body than normal, but the level is still low enough to not be dangerous, and therefore was not included on this list. Low levels of radioactive atoms are constantly accumulating in every person. The ways we end up with radioactive atoms in our bodies include: eating food that naturally contains small amounts of radioactive isotopes, breathing air that naturally contains small amounts of radioactive isotopes, and being bombarded with cosmic rays that create radioactive atoms in our bodies. The most common natural radioactive isotopes in humans are carbon-14 and potassium-40. Chemically, these isotopes behave exactly like stable carbon and potassium. For this reason, the body uses carbon-14 and potassium-40 just like it does normal carbon and potassium; building them into the different parts of the cells, without knowing that they are radioactive. In time, carbon-14 atoms decay to stable nitrogen atoms and potassium-40 atoms decay to stable calcium atoms. Chemicals in the body that relied on having a carbon-14 atom or potassium-40 atom in a certain spot will suddenly have a nitrogen or calcium atom. Such a change damages the chemical. Normally, such change are so rare, that the body can repair the damage or filter away the damaged chemicals. The textbook Chemistry: The Practical Science by Paul B. Kelter, Michael D. Mosher and Andrew Scott states: Whereas potassium-39 and potassium-41 possess stable nuclei, potassium-40 is radioactive. This means that when we consume a banana, we get a measurable amount of radioactive potassium-40. How much? The natural abundance of potassium-40 is only 0.012%, or approximately 1 atom in 10,000. A typical banana has approximately 300 mg of potassium. Therefore, with each banana that we eat, we ingest approximately 0.036 mg of radioactive potassium-40. The natural occurrence of carbon-14 decay in the body is the core principle behind carbon dating. As long as a person is alive and still eating, every carbon-14 atom that decays into a nitrogen atom is replaced on average with a new carbon-14 atom. But once a person dies, he stops replacing the decaying carbon-14 atoms. Slowly the carbon-14 atoms decay to nitrogen without being replaced, so that there is less and less carbon-14 in a dead body. The rate at which carbon-14 decays is constant and well-known, so by measuring the relative amount of carbon-14 in a bone, archeologists can calculate when the person died. All living organisms consume carbon, so carbon dating can be used to date any living organism, and any object made from a living organism. Bones, wood, leather, and even paper can be accurately dated, as long as they first existed within the last 60,000 years. This is all because of the fact that nuclear reactions naturally occur in living organisms.	tag/atom/	context: tag/atom/ question: Are there nuclear reactions going on in our bodies?	Yes, there are nuclear reactions constantly occurring in our bodies, but there are very few of them compared to the chemical reactions, and they do not affect our bodies much. All physical objects are made of molecules. A molecule is a series of atoms linked together by chemical (electromagnetic) bonds. Inside each atom is a nucleus which is a collection of protons and neutrons linked together by nuclear bonds. Chemical reactions are the making, breaking, and rearranging of bonds between atoms in molecules. Chemical reactions do not change the nuclear structure of any atoms. In contrast, nuclear reactions involve the transformation of atomic nuclei. Most of the processes surrounding us in our daily life are chemical reactions and not nuclear reactions. All of the physical processes that take place to keep a human body running (blood capturing oxygen, sugars being burned, DNA being constructed,etc.) are chemical processes and not nuclear processes. Nuclear reactions do indeed occur in the human body, but the body does not use them. Nuclear reactions can lead to chemical damage, which the body may notice and try to fix. There are three main types of nuclear reactions: Note that nuclear fission and radioactive decay overlap a little bit. Some types of radioactive decay involve the spitting out of nuclear fragments and could therefore be seen as a type of fission. For the purposes of this article, "fission" refers to large-scale nucleus fragmentation events that can clearly not be classified as radioactive decay. Nuclear fusion requires high energy in order to be ignited. For this reason, nuclear fusion only occurs in stars, in supernovas, in nuclear fusion bombs, in nuclear fusion experimental reactors, in cosmic ray impacts, and in particle accelerators. Similarly, nuclear fission requires high energy or a large mass of heavy, radioactive elements. For this reason, significant nuclear fission only occurs in supernovas, in nuclear fission bombs, in nuclear fission reactors, in cosmic ray impacts, in particle accelerators, and in a few natural ore deposits. In contrast, radioactive decay happens automatically to unstable nuclei and is therefore much more common. Every atom has either a stable nucleus or an unstable nucleus, depending on how big it is and on the ratio of protons to neutrons. Nuclei with too many neutrons, too few neutrons, or that are simply too big are unstable. They eventually transform to a stable form through radioactive decay. Wherever there are atoms with unstable nuclei (radioactive atoms), there are nuclear reactions occurring naturally. The interesting thing is that there are small amounts of radioactive atoms everywhere: in your chair, in the ground, in the food you eat, and yes, in your body. Radioactive decay produces high-energy radiation that can damage your body. Fortunately, our bodies have mechanisms to clean up the damage caused by radioactivity and high-energy radiation before they become serious. For the average person living a normal life, the amount of radioactivity in his body is so small that the body has no difficulty repairing all the damage. The problem is when the radioactivity levels (the amount of nuclear reactions in and around the body) rise too high and the body cannot keep up with the repairs. In such cases, the victim experiences burns, sickness, cancer, and even death. Exposure to dangerously high levels of radioactivity is rare and is typically avoided through government regulation, training, and education. Common causes of human exposure to high radioactivity include: Note that if you have a single medical scan performed that requires drinking or being injected with a radioactive tracer, you do indeed end up with more nuclear reactions in your body than normal, but the level is still low enough to not be dangerous, and therefore was not included on this list. Low levels of radioactive atoms are constantly accumulating in every person. The ways we end up with radioactive atoms in our bodies include: eating food that naturally contains small amounts of radioactive isotopes, breathing air that naturally contains small amounts of radioactive isotopes, and being bombarded with cosmic rays that create radioactive atoms in our bodies. The most common natural radioactive isotopes in humans are carbon-14 and potassium-40. Chemically, these isotopes behave exactly like stable carbon and potassium. For this reason, the body uses carbon-14 and potassium-40 just like it does normal carbon and potassium; building them into the different parts of the cells, without knowing that they are radioactive. In time, carbon-14 atoms decay to stable nitrogen atoms and potassium-40 atoms decay to stable calcium atoms. Chemicals in the body that relied on having a carbon-14 atom or potassium-40 atom in a certain spot will suddenly have a nitrogen or calcium atom. Such a change damages the chemical. Normally, such change are so rare, that the body can repair the damage or filter away the damaged chemicals. The textbook Chemistry: The Practical Science by Paul B. Kelter, Michael D. Mosher and Andrew Scott states: Whereas potassium-39 and potassium-41 possess stable nuclei, potassium-40 is radioactive. This means that when we consume a banana, we get a measurable amount of radioactive potassium-40. How much? The natural abundance of potassium-40 is only 0.012%, or approximately 1 atom in 10,000. A typical banana has approximately 300 mg of potassium. Therefore, with each banana that we eat, we ingest approximately 0.036 mg of radioactive potassium-40. The natural occurrence of carbon-14 decay in the body is the core principle behind carbon dating. As long as a person is alive and still eating, every carbon-14 atom that decays into a nitrogen atom is replaced on average with a new carbon-14 atom. But once a person dies, he stops replacing the decaying carbon-14 atoms. Slowly the carbon-14 atoms decay to nitrogen without being replaced, so that there is less and less carbon-14 in a dead body. The rate at which carbon-14 decays is constant and well-known, so by measuring the relative amount of carbon-14 in a bone, archeologists can calculate when the person died. All living organisms consume carbon, so carbon dating can be used to date any living organism, and any object made from a living organism. Bones, wood, leather, and even paper can be accurately dated, as long as they first existed within the last 60,000 years. This is all because of the fact that nuclear reactions naturally occur in living organisms.
Are two atoms of the same element identical?	No. Two atoms of the same chemical element are typically not identical. First of all, there is a range of possible states that the electrons of an atom can occupy. Two atoms of the same element can be different if their electrons are in different states. If one copper atom has an electron in an excited state and another copper atom has all of its electrons in the ground state, then the two atoms are different. The excited copper atom will emit a bit of light when the electron relaxes back down to the ground state, and the copper atom already in the ground state will not. Since the states of the electrons in an atom are what determine the nature of the chemical bonding that the atom experiences, two atoms of the same element can react differently if they are in different states. For instance, a neutral sodium atom (say, from a chunk of sodium metal) reacts with water much more violently than an ionized sodium atom (say, from a bit of salt). Chemists know this very well. It's not enough to say what atoms are involved if you want to fully describe and predict a reaction. You have to also specify the ionization/excitation states of the electrons in the atoms. Even if left alone, an atom often does not come with an equal number of protons and electrons. But what if two atoms of the same element both have their electrons in the same states. Then are they identical? No, they are still not identical. Two atoms of the same element and in the same electronic state could be traveling or rotating at different speeds, which affects their ability to chemically bond. Slower moving atoms (such as the atoms in solid iron) have time to form stable bonds, while faster moving atoms (such as the atoms in liquid iron) cannot form such stable bonds. A slow moving tin atom acts differently from a rapidly moving tin atom. But what if two atoms of the same element both have their electrons in the same states, and the atoms are both traveling and rotating at the same speed. Then are they identical? No. Although two such atoms are essentially chemically identical (they will chemically react in the same way), they are not completely identical. There's more to the atom than the electrons. There's also the nucleus. The nucleus of an atom contains neutrons and protons bonded tightly together. The same chemical element can have a different number of neutrons and still be the same element. We refer to the atoms of the same element with different numbers of neutrons as "isotopes". While the particular isotope involved does not affect how an atom will react chemically, it does determine how the atom will behave in nuclear reactions. The most common nuclear reaction on earth is radioactive decay. Some isotopes decay very quickly into other elements and emit radiation, while other isotopes do not. If you are doing carbon dating, the fact that a carbon-12 atom is not identical to a carbon-14 atom is essential to the dating process. Simply counting the number of carbon atoms in a sample will not give you any information about the age of a sample. You will have to count the number of different isotopes of carbon instead. But what if two atoms are the same element, have electrons in the same state, are traveling and rotating at the same speed, and have the same number of neutrons; then are they identical? No. Just like the electrons, the neutrons and protons in the nucleus can be in various excited states. In addition, the nucleus as a whole can rotate and vibrate at various speeds. Therefore, even if all else is identical, two gold atoms can have their nuclei in different excited states and behave differently in nuclear reactions. To state the case succinctly, it is very hard to have two atoms of the same element be exactly identical. In fact, succeeding in coaxing a group of atoms to be very close to identical was worthy of a Nobel Prize. With that said, don't think that atoms have individual identities beyond what has been mentioned here. If two carbon atoms are in the exact same molecular, atomic, electronic and nuclear states, then those two carbon atoms are identical, no matter where they came from or what has happened to them in the past.	tag/atom/	context: tag/atom/ question: Are two atoms of the same element identical?	No. Two atoms of the same chemical element are typically not identical. First of all, there is a range of possible states that the electrons of an atom can occupy. Two atoms of the same element can be different if their electrons are in different states. If one copper atom has an electron in an excited state and another copper atom has all of its electrons in the ground state, then the two atoms are different. The excited copper atom will emit a bit of light when the electron relaxes back down to the ground state, and the copper atom already in the ground state will not. Since the states of the electrons in an atom are what determine the nature of the chemical bonding that the atom experiences, two atoms of the same element can react differently if they are in different states. For instance, a neutral sodium atom (say, from a chunk of sodium metal) reacts with water much more violently than an ionized sodium atom (say, from a bit of salt). Chemists know this very well. It's not enough to say what atoms are involved if you want to fully describe and predict a reaction. You have to also specify the ionization/excitation states of the electrons in the atoms. Even if left alone, an atom often does not come with an equal number of protons and electrons. But what if two atoms of the same element both have their electrons in the same states. Then are they identical? No, they are still not identical. Two atoms of the same element and in the same electronic state could be traveling or rotating at different speeds, which affects their ability to chemically bond. Slower moving atoms (such as the atoms in solid iron) have time to form stable bonds, while faster moving atoms (such as the atoms in liquid iron) cannot form such stable bonds. A slow moving tin atom acts differently from a rapidly moving tin atom. But what if two atoms of the same element both have their electrons in the same states, and the atoms are both traveling and rotating at the same speed. Then are they identical? No. Although two such atoms are essentially chemically identical (they will chemically react in the same way), they are not completely identical. There's more to the atom than the electrons. There's also the nucleus. The nucleus of an atom contains neutrons and protons bonded tightly together. The same chemical element can have a different number of neutrons and still be the same element. We refer to the atoms of the same element with different numbers of neutrons as "isotopes". While the particular isotope involved does not affect how an atom will react chemically, it does determine how the atom will behave in nuclear reactions. The most common nuclear reaction on earth is radioactive decay. Some isotopes decay very quickly into other elements and emit radiation, while other isotopes do not. If you are doing carbon dating, the fact that a carbon-12 atom is not identical to a carbon-14 atom is essential to the dating process. Simply counting the number of carbon atoms in a sample will not give you any information about the age of a sample. You will have to count the number of different isotopes of carbon instead. But what if two atoms are the same element, have electrons in the same state, are traveling and rotating at the same speed, and have the same number of neutrons; then are they identical? No. Just like the electrons, the neutrons and protons in the nucleus can be in various excited states. In addition, the nucleus as a whole can rotate and vibrate at various speeds. Therefore, even if all else is identical, two gold atoms can have their nuclei in different excited states and behave differently in nuclear reactions. To state the case succinctly, it is very hard to have two atoms of the same element be exactly identical. In fact, succeeding in coaxing a group of atoms to be very close to identical was worthy of a Nobel Prize. With that said, don't think that atoms have individual identities beyond what has been mentioned here. If two carbon atoms are in the exact same molecular, atomic, electronic and nuclear states, then those two carbon atoms are identical, no matter where they came from or what has happened to them in the past.
Can sound waves generate heat?	Yes, sound waves can generate heat. In fact, sound waves almost always generate a little bit of heat as they travel and almost always end up as heat when they are absorbed. Sound and heat are both macroscopic descriptions of the movement of atoms and molecules. Sound is the ordered movement of atoms and molecules in rapid waving patterns. Heat is the disordered, random, movement of atoms and molecules. Therefore, all you have to do in order to turn sound into heat is transform some of the ordered movement of the atoms and molecules into disordered movement. This effect always happens to some extent. This effect happens a lot whenever the sound wave encounters irregularities as it travels. For instance, dust particles in air are irregularities that randomly interfere with the vibrating motion of some of the air molecules that make up the sound wave. The dust particles mess up some of the ordered motion, and therefore convert some of the sound to heat. As another example, the rough surface of an object constitutes a collection of irregularities that the sound wave encounters. Therefore, when a sound wave hits a rough surface, the motion of the air molecules gets scrambled up a bit. Note that the air molecules already have a motion that is somewhat disordered. In other words, air through which sound is traveling already contains some amount of heat. When some of the sound wave is converted to heat, the motion of the air molecules becomes more disordered and the amount of heat increases. The ordered movement of atoms is also made more disorderly when sound travels through acoustically absorbent materials. Materials can be made absorbent by embedding an array of little irregularities directly into the material, such as air bubbles. For this reason, materials that are soft and porous, like cloth, are good at converting sound to heat. The sound is said to be "absorbed" or "lost" when it is converted to heat inside a material. Even without irregularities, a material can be highly absorbent if the atoms and molecules that make up the material cannot slide past each other smoothly. In this case, an atom or molecule that is trying to participate in the ordered vibrational motion of the sound wave roughly slides past the neighboring atoms or molecules that are off to the side, such that motion gets diverted in sideways directions rather than continuing in the forward direction as part of the sound wave. The ordered motion therefore becomes disordered. You can think of it as a kind of internal friction that all materials posses to some extent. In this way, some of the sound energy is converted to thermal energy. All materials, even air, have some amount of resistance to smooth atomic/molecular sliding and therefore are somewhat absorbent to sound. In summary, sound waves always generate a little heat as they travel and they ultimately almost always end up completely as heat when they are absorbed by materials. However, the amount of energy carried by sound waves is very small, so that the amount of heat they generate is typically insignificant. In short, cranking up the volume on your speakers is a terrible way to try to heat up your room. Yelling at your soup does indeed warm it up, but the amount is far too small to be noticeable.	tag/atom/	context: tag/atom/ question: Can sound waves generate heat?	Yes, sound waves can generate heat. In fact, sound waves almost always generate a little bit of heat as they travel and almost always end up as heat when they are absorbed. Sound and heat are both macroscopic descriptions of the movement of atoms and molecules. Sound is the ordered movement of atoms and molecules in rapid waving patterns. Heat is the disordered, random, movement of atoms and molecules. Therefore, all you have to do in order to turn sound into heat is transform some of the ordered movement of the atoms and molecules into disordered movement. This effect always happens to some extent. This effect happens a lot whenever the sound wave encounters irregularities as it travels. For instance, dust particles in air are irregularities that randomly interfere with the vibrating motion of some of the air molecules that make up the sound wave. The dust particles mess up some of the ordered motion, and therefore convert some of the sound to heat. As another example, the rough surface of an object constitutes a collection of irregularities that the sound wave encounters. Therefore, when a sound wave hits a rough surface, the motion of the air molecules gets scrambled up a bit. Note that the air molecules already have a motion that is somewhat disordered. In other words, air through which sound is traveling already contains some amount of heat. When some of the sound wave is converted to heat, the motion of the air molecules becomes more disordered and the amount of heat increases. The ordered movement of atoms is also made more disorderly when sound travels through acoustically absorbent materials. Materials can be made absorbent by embedding an array of little irregularities directly into the material, such as air bubbles. For this reason, materials that are soft and porous, like cloth, are good at converting sound to heat. The sound is said to be "absorbed" or "lost" when it is converted to heat inside a material. Even without irregularities, a material can be highly absorbent if the atoms and molecules that make up the material cannot slide past each other smoothly. In this case, an atom or molecule that is trying to participate in the ordered vibrational motion of the sound wave roughly slides past the neighboring atoms or molecules that are off to the side, such that motion gets diverted in sideways directions rather than continuing in the forward direction as part of the sound wave. The ordered motion therefore becomes disordered. You can think of it as a kind of internal friction that all materials posses to some extent. In this way, some of the sound energy is converted to thermal energy. All materials, even air, have some amount of resistance to smooth atomic/molecular sliding and therefore are somewhat absorbent to sound. In summary, sound waves always generate a little heat as they travel and they ultimately almost always end up completely as heat when they are absorbed by materials. However, the amount of energy carried by sound waves is very small, so that the amount of heat they generate is typically insignificant. In short, cranking up the volume on your speakers is a terrible way to try to heat up your room. Yelling at your soup does indeed warm it up, but the amount is far too small to be noticeable.
Can the decay half-life of a radioactive material be changed?	Yes, the decay half-life of a radioactive material can be changed. Radioactive decay happens when an unstable atomic nucleus spontaneously changes to a lower-energy state and spits out a bit of radiation. This process changes the atom to a different element or a different isotope. Since radioactive decay is a spontaneous event, you may think that the half-life of the decay process is completely fixed and cannot be altered by outside influences. However, this statement is not completely true. First of all, it is worth pointing out that the time when an individual radioactive atom decays is completely random. It is impossible to predict when an individual radioactive atom will decay. The half-life of a certain type of atom does not describe the exact amount of time that every single atom experiences before decaying. Rather, the half-life describes the average amount of time it takes for a large group of atoms to reach the point where half of the atoms have decayed. The half-life of a radioactive material can be changed using time dilation effects. According to relativity, time itself can be slowed down. Everything that experiences time can therefore be given a longer effective lifetime if time is dilated. This can be done in two ways. Traveling at a speed close to the speed of light causes time to slow down significantly, relative to the stationary observer. For instance, a number of radioactive atoms shot through a tube at high speed in the lab will have their half-life lengthened relative to the lab because of time dilation. This effect has been verified many times using particle accelerators. Time can also be dilated by applying a very strong gravitational field. For instance, placing a bunch of radioactive atoms near a black hole will also extend their half-life relative to the distant observer because of time dilation. The half-life of radioactive decay can also be altered by changing the state of the electrons surrounding the nucleus. In a type of radioactive decay called "electron capture", the nucleus absorbs one of the atom's electrons and combines it with a proton to make a neutron and a neutrino. The more the wavefunctions of the atom's electrons overlap with the nucleus, the more able the nucleus is to capture an electron. Therefore, the half-life of an electron-capture radioactive decay mode depends slightly on what state the atom's electrons are in. By exciting or deforming the atom's electrons into states that overlap less with the nucleus, the half-life can be increased. Since the chemical bonding between atoms involves the deformation of atomic electron wavefunctions, the radioactive half-life of an atom can depend on how it is bonded to other atoms. Simply by changing the neighboring atoms that are bonded to a radioactive isotope, we can change its half-life. However, the change in half-life accomplished in this way is typically small. For instance, a study performed by B. Wang et al and published in the European Physical Journal A was able to measure that the electron capture half-life of beryllium-7 was made 0.9% longer by surrounding the beryllium atoms with palladium atoms. In addition to altering the chemical bonds, the half-life can be altered by simply removing electrons from the atom. In the extreme limit of this approach, all of the electrons can be ripped off of a radioactive atom. For such an ion, there are no longer any electrons available to capture, and therefore the half-life of the electron capture radioactive decay mode becomes infinite. Certain radioactive isotopes that can only decay via the electron capture mode (such as rubidium-83) can be made to never decay by ripping off all the electrons. Other types of radioactive decay besides electron capture have also been found to have the decay half-life depend on the state of the surrounding electrons, but the effects are smaller. The change in half-life due to changing the electron environment is generally very small, typically much less than 1%. Lastly, the half-life of a radioactive material can be changed by bombarding it with high-energy radiation. This should not come as a surprise since radioactive decay is a nuclear reaction, and inducing other nuclear reactions at the same time as the decay can interfere with it. However, at this point, you don't really have stand-alone radioactive decay. Rather, you have nuclear reaction soup, so this approach may not really count as "changing the half-life". When reference books list values for the half-life of various materials, they are really listing the half-life for the material when its atoms are at rest, in the ground state, and in a particular chemical bonding configuration. Note that most changes to the half-life of radioactive materials are very small. Furthermore, large changes to a half-life require elaborate, expensive, high-energy equipment (e.g. particle accelerators, nuclear reactors, ion traps). Therefore, outside of specialized labs, we can say that as a good approximation radioactive decay half-lives don't change. For instance, carbon dating and geological radiometric dating are so accurate because decay half-lives in nature are so close to constant.	tag/atom/	context: tag/atom/ question: Can the decay half-life of a radioactive material be changed?	Yes, the decay half-life of a radioactive material can be changed. Radioactive decay happens when an unstable atomic nucleus spontaneously changes to a lower-energy state and spits out a bit of radiation. This process changes the atom to a different element or a different isotope. Since radioactive decay is a spontaneous event, you may think that the half-life of the decay process is completely fixed and cannot be altered by outside influences. However, this statement is not completely true. First of all, it is worth pointing out that the time when an individual radioactive atom decays is completely random. It is impossible to predict when an individual radioactive atom will decay. The half-life of a certain type of atom does not describe the exact amount of time that every single atom experiences before decaying. Rather, the half-life describes the average amount of time it takes for a large group of atoms to reach the point where half of the atoms have decayed. The half-life of a radioactive material can be changed using time dilation effects. According to relativity, time itself can be slowed down. Everything that experiences time can therefore be given a longer effective lifetime if time is dilated. This can be done in two ways. Traveling at a speed close to the speed of light causes time to slow down significantly, relative to the stationary observer. For instance, a number of radioactive atoms shot through a tube at high speed in the lab will have their half-life lengthened relative to the lab because of time dilation. This effect has been verified many times using particle accelerators. Time can also be dilated by applying a very strong gravitational field. For instance, placing a bunch of radioactive atoms near a black hole will also extend their half-life relative to the distant observer because of time dilation. The half-life of radioactive decay can also be altered by changing the state of the electrons surrounding the nucleus. In a type of radioactive decay called "electron capture", the nucleus absorbs one of the atom's electrons and combines it with a proton to make a neutron and a neutrino. The more the wavefunctions of the atom's electrons overlap with the nucleus, the more able the nucleus is to capture an electron. Therefore, the half-life of an electron-capture radioactive decay mode depends slightly on what state the atom's electrons are in. By exciting or deforming the atom's electrons into states that overlap less with the nucleus, the half-life can be increased. Since the chemical bonding between atoms involves the deformation of atomic electron wavefunctions, the radioactive half-life of an atom can depend on how it is bonded to other atoms. Simply by changing the neighboring atoms that are bonded to a radioactive isotope, we can change its half-life. However, the change in half-life accomplished in this way is typically small. For instance, a study performed by B. Wang et al and published in the European Physical Journal A was able to measure that the electron capture half-life of beryllium-7 was made 0.9% longer by surrounding the beryllium atoms with palladium atoms. In addition to altering the chemical bonds, the half-life can be altered by simply removing electrons from the atom. In the extreme limit of this approach, all of the electrons can be ripped off of a radioactive atom. For such an ion, there are no longer any electrons available to capture, and therefore the half-life of the electron capture radioactive decay mode becomes infinite. Certain radioactive isotopes that can only decay via the electron capture mode (such as rubidium-83) can be made to never decay by ripping off all the electrons. Other types of radioactive decay besides electron capture have also been found to have the decay half-life depend on the state of the surrounding electrons, but the effects are smaller. The change in half-life due to changing the electron environment is generally very small, typically much less than 1%. Lastly, the half-life of a radioactive material can be changed by bombarding it with high-energy radiation. This should not come as a surprise since radioactive decay is a nuclear reaction, and inducing other nuclear reactions at the same time as the decay can interfere with it. However, at this point, you don't really have stand-alone radioactive decay. Rather, you have nuclear reaction soup, so this approach may not really count as "changing the half-life". When reference books list values for the half-life of various materials, they are really listing the half-life for the material when its atoms are at rest, in the ground state, and in a particular chemical bonding configuration. Note that most changes to the half-life of radioactive materials are very small. Furthermore, large changes to a half-life require elaborate, expensive, high-energy equipment (e.g. particle accelerators, nuclear reactors, ion traps). Therefore, outside of specialized labs, we can say that as a good approximation radioactive decay half-lives don't change. For instance, carbon dating and geological radiometric dating are so accurate because decay half-lives in nature are so close to constant.
Do atoms ever actually touch each other?	The answer depends on what you mean by "touch". There are three possible meanings of touch at the atomic level: 1) two objects influence each other, 2) two objects influence each other significantly, or 3) two objects reside in the exact same location. Note that the everday concept of touch (i.e the hard boundaries of two objects exist at the same location) makes no sense at the atomic level because atoms don't have hard boundaries. Atoms are not really solid spheres. They are fuzzy quantum probability clouds filled with electrons spread out into waving cloud-like shapes called "orbitals". Like a cloud in the sky, an atom can have a shape and a location without having a hard boundary. This is possible because the atom has regions of high density and regions of low density. When we say that an atom is sitting at point A, what we really mean is that the high-density portion of the atom's probability cloud is located at point A. If you put an electron in a box (as is done in quantum dot lasers), that electron is only mostly in the box. Part of the electron's wavefunction leaks through the walls of the box and out to infinity. This makes possible the effect of quantum tunneling, which is used in scanning tunneling microscopes. With the non-solid nature of atoms in mind, let us look at each of the possible meanings of touching. 1. If "touching" is taken to mean that two atoms influence each other, then atoms are always touching. Two atoms that are held a mile apart still have their wavefunctions overlapping. The amplitude of one atom's wavefunction at the point where it overlaps with the other atom's center will be ridiculously small if they are a mile apart, but it will not be zero. In principle, two atoms influence each other no matter where they are in the universe because they extend out in all directions. In practice, if two atoms are more than a few nanometers apart, their influence on each other typically becomes so small that it is overshadowed by the influence of closer atoms. Therefore, although two atoms a mile apart may technically be touching (if we define touching as the overlap of atomic wavefunctions), this touching is typically so insignificant that it can be ignored. What is this "touching"? In the physical world, there are only four fundamental ways for objects to influence each other: through the electromagnetic force, through the strong nuclear force, through the weak nuclear force, and through the force of gravity. Neutrons and protons that make up the nucleus of an atom are bound to each other and undergo reactions via the two nuclear forces. The electrons that make up the rest of the atom are bound to the nucleus by the electromagnetic force. Atoms are bound into molecules, and molecules are bound into everyday objects by the electromagnetic force. Finally, planets (as well as other large astronomical objects) and macroscopic objects on the planet's surface are bound together by gravity. If two atoms are held a meter apart, they are touching each other through all four fundamental forces. However, for typical atoms, the electromagnetic force tends to dominate over the other forces. What does this touching lead to? If two atoms are too far apart, their interaction is too weak compared to other surrounding bodies to amount to anything. When the two atoms get close enough, this interaction can lead to many things. The entire field of chemistry can be summed up as the study of all the interesting things that happen when atoms get close enough to influence each other electromagnetically. If two atoms are non-reactive and don't form covalent, ionic, or hydrogen bonds, then their electromagnetic interaction typically takes the form of the Van der Walls force. In the Van der Walls effect, two atoms brought close to each other induce electric dipole moments in each other, and these dipoles then attract each other weakly through electrostatic attraction. While the statement that "all atoms on the planet are always touching all other atoms on the planet" is strictly true according to this definition of touching, it is not very helpful. Instead, we can arbitrarily define an effective perimeter that contains most of the atom, and then say that any part of the atom that takes extends beyond that perimeter is not worth noticing. This takes us to our next definition of touching. 2. If "touching" is taken to mean that two atoms influence each other significantly, then atoms do indeed touch, but only when they get close enough. The problem is that what constitutes "significant" is open to interpretation. For instance, we can define the outer perimeter of an atom as the mathematical surface that contains 95% of the atom's electron mass. As should be obvious at this point, a perimeter that contains 100% of the atom would be larger than the earth. With 95% of the atom's electron probability density contained in this mathematical surface, we could say that atoms do not touch until their 95% regions begin to overlap. Another way to assign an effective edge to an atom is to say it exists halfway between two atoms that are covalently bonded. For instance, two hydrogen atoms that are covalently bonded to each other to form an H2 molecule have their centers separated by 50 picometers. They can be thought of as "touching" at this separation. In this approach, atoms touch whenever they are close enough to potentially form a chemical bond. 3. If "touching" is taken to mean that two atoms reside in the exact same location, then two atoms never touch at room temperature because of the Pauli exclusion principle. The Pauli exclusion principle is what keeps all the atoms in our body from collapsing into one point. Interestingly, at very low temperatures, certain atoms can be coaxed into the exact same location. The result is known as a Bose-Einstein condensate. Again, atoms never touch in the everyday sense of the word for the simple reason that they don't have hard boundaries. But in every other sense of the word "touch" that has meaning at the atomic level, atoms certainly touch.	tag/atom/	context: tag/atom/ question: Do atoms ever actually touch each other?	The answer depends on what you mean by "touch". There are three possible meanings of touch at the atomic level: 1) two objects influence each other, 2) two objects influence each other significantly, or 3) two objects reside in the exact same location. Note that the everday concept of touch (i.e the hard boundaries of two objects exist at the same location) makes no sense at the atomic level because atoms don't have hard boundaries. Atoms are not really solid spheres. They are fuzzy quantum probability clouds filled with electrons spread out into waving cloud-like shapes called "orbitals". Like a cloud in the sky, an atom can have a shape and a location without having a hard boundary. This is possible because the atom has regions of high density and regions of low density. When we say that an atom is sitting at point A, what we really mean is that the high-density portion of the atom's probability cloud is located at point A. If you put an electron in a box (as is done in quantum dot lasers), that electron is only mostly in the box. Part of the electron's wavefunction leaks through the walls of the box and out to infinity. This makes possible the effect of quantum tunneling, which is used in scanning tunneling microscopes. With the non-solid nature of atoms in mind, let us look at each of the possible meanings of touching. 1. If "touching" is taken to mean that two atoms influence each other, then atoms are always touching. Two atoms that are held a mile apart still have their wavefunctions overlapping. The amplitude of one atom's wavefunction at the point where it overlaps with the other atom's center will be ridiculously small if they are a mile apart, but it will not be zero. In principle, two atoms influence each other no matter where they are in the universe because they extend out in all directions. In practice, if two atoms are more than a few nanometers apart, their influence on each other typically becomes so small that it is overshadowed by the influence of closer atoms. Therefore, although two atoms a mile apart may technically be touching (if we define touching as the overlap of atomic wavefunctions), this touching is typically so insignificant that it can be ignored. What is this "touching"? In the physical world, there are only four fundamental ways for objects to influence each other: through the electromagnetic force, through the strong nuclear force, through the weak nuclear force, and through the force of gravity. Neutrons and protons that make up the nucleus of an atom are bound to each other and undergo reactions via the two nuclear forces. The electrons that make up the rest of the atom are bound to the nucleus by the electromagnetic force. Atoms are bound into molecules, and molecules are bound into everyday objects by the electromagnetic force. Finally, planets (as well as other large astronomical objects) and macroscopic objects on the planet's surface are bound together by gravity. If two atoms are held a meter apart, they are touching each other through all four fundamental forces. However, for typical atoms, the electromagnetic force tends to dominate over the other forces. What does this touching lead to? If two atoms are too far apart, their interaction is too weak compared to other surrounding bodies to amount to anything. When the two atoms get close enough, this interaction can lead to many things. The entire field of chemistry can be summed up as the study of all the interesting things that happen when atoms get close enough to influence each other electromagnetically. If two atoms are non-reactive and don't form covalent, ionic, or hydrogen bonds, then their electromagnetic interaction typically takes the form of the Van der Walls force. In the Van der Walls effect, two atoms brought close to each other induce electric dipole moments in each other, and these dipoles then attract each other weakly through electrostatic attraction. While the statement that "all atoms on the planet are always touching all other atoms on the planet" is strictly true according to this definition of touching, it is not very helpful. Instead, we can arbitrarily define an effective perimeter that contains most of the atom, and then say that any part of the atom that takes extends beyond that perimeter is not worth noticing. This takes us to our next definition of touching. 2. If "touching" is taken to mean that two atoms influence each other significantly, then atoms do indeed touch, but only when they get close enough. The problem is that what constitutes "significant" is open to interpretation. For instance, we can define the outer perimeter of an atom as the mathematical surface that contains 95% of the atom's electron mass. As should be obvious at this point, a perimeter that contains 100% of the atom would be larger than the earth. With 95% of the atom's electron probability density contained in this mathematical surface, we could say that atoms do not touch until their 95% regions begin to overlap. Another way to assign an effective edge to an atom is to say it exists halfway between two atoms that are covalently bonded. For instance, two hydrogen atoms that are covalently bonded to each other to form an H2 molecule have their centers separated by 50 picometers. They can be thought of as "touching" at this separation. In this approach, atoms touch whenever they are close enough to potentially form a chemical bond. 3. If "touching" is taken to mean that two atoms reside in the exact same location, then two atoms never touch at room temperature because of the Pauli exclusion principle. The Pauli exclusion principle is what keeps all the atoms in our body from collapsing into one point. Interestingly, at very low temperatures, certain atoms can be coaxed into the exact same location. The result is known as a Bose-Einstein condensate. Again, atoms never touch in the everyday sense of the word for the simple reason that they don't have hard boundaries. But in every other sense of the word "touch" that has meaning at the atomic level, atoms certainly touch.
Does an atom have a color?	The answer really depends on how you define "having a color". The term "color" refers to visible light with a certain frequency, or a mixture of visible light frequencies. Therefore, the word "color" describes the frequency content of any type of visible light. Anytime visible light is present, we can describe it as having a certain color. With this in mind, there are many different ways an object can reflect or emit visible light. Thus, there are many ways an object can "have a color". While a single, isolated, atom can reflect or emit visible light in several of these ways, it does not participate in all the ways. If you define "having a color" very narrowly such that it only includes certain mechanisms, then atoms do not have color. If you define "having a color" more broadly, then atoms do have a color. Let us look at the different ways an object can reflect or emit visible light and apply each one to an atom. 1. Bulk reflection, refraction, and absorptionThe most common, everyday manner in which objects can send visible light to our eyes is through bulk reflection, refraction, and absorption. These three effects are all part of the same physical mechanism: the interaction of an external beam of light with many atoms at the same time. When white light, which contains all colors, hits the surface of a red apple, the light waves that are orange, yellow, green and blue get absorbed by the atoms in the apple's skin and converted to heat, while the red waves are mostly reflected back to our eyes. Some of the light is also transmitted through the apple skin and bent slightly as it goes through. We call this bent transmission of light "refraction". Some materials such as glass transmit a lot of the light while other materials such as apples transmit very little. The key point here is that traditional reflection, refraction, and absorption constitute a bulk phenomenon where each ray of light interacts with dozens to millions of atoms at the same time. This makes sense when you consider that visible light has a wavelength that is about a thousand times bigger than atoms. Visible light waves have a wavelength from 400 nanometers to 700 nanometers, depending on the color. In contrast, atoms have a width of about 0.2 nanometers. This discrepancy is why you can't see individual atoms using an optical microscope. The atoms are far smaller than the light you are trying to use to see them. The color of an object that results from traditional bulk reflection, refraction, and absorption is therefore a result of how several atoms are bound together and arranged, and not a result of the actual color of individual atoms. For example, take carbon atoms and bind them into a diamond lattice, and you get a clear diamonds. In contrast, take carbon atoms and bind them into hexagonal planes and you get gray graphite. The nature of the bonds between many atoms is what determines the traditional color of a material and not the type of atoms themselves. If you have no bonds at all between any atoms, you get a monoatomic gas, which is invisible (at least according to traditional reflection, refraction, and absorption). The color of most of the everyday objects around us, from apples to pencils to chairs, arises from traditional bulk reflection, refraction, and absorption. This mechanism of light delivery is so common and intuitive that we could define "having a color" narrowly to only include this mechanism. With this narrow definition in mind, therefore, a single atom is too small to have a color. 2. Thermal radiationHeat up a bar of iron enough and it glows red. You could therefore say that the color of a hot iron bar is glowing red. The red color of the iron bar in this case, however, is due to thermal radiation, which is a mechanism that is very different from bulk reflection, refraction, and absorption. In the mechanism of thermal radiation, the atoms of an object knock into each other so violently that they emit light. More accurately, the collisions cause the electrons and atoms to be excited to higher energy states, and then the electrons and atoms emit light when they transition back down to lower energy states. Since the collisions due to thermal motion are random, they lead to a wide range of energy excitations. As a result, the thermal radiation emitted contains many colors that span a broad band of frequencies. The interesting thing about thermal radiation is that its color is more a result of the temperature of the object and less a result of the material of the object. Every solid material glows red if you can get it to the right temperature without it evaporating or chemically reacting. The key to thermal radiation is that it is an emergent property of the interaction of many atoms. As such, a single atom cannot emit thermal radiation. So even if we expand the definition of "having a color" to include thermal radiation, individual atoms still have no color. 3. Rayleigh scatteringMore informatively called "long-wavelength scattering", Rayleigh scattering is when light does bounce off of single atoms and molecules. But because the light is so much bigger than the atoms, Rayleigh scattering is not really the "bouncing" of a light wave off of a small particle such as an atom, but is more a case of immersing the particle in the electric field of the light wave. The electric field induces an oscillating electric dipole in the particle which then radiates. Because the mechanism is so different, Rayleigh scattering of white light off of small particles always creates the same broad range of colors, with blue and violet being the strongest. The color of Rayleigh scattering is always the same (assuming the incident light is white) and is mostly independent of the material of the scattering object. Therefore, a single atom does have a color in the sense that it participates in Rayleigh scattering. For example, earth's atmosphere is composed mostly of small oxygen molecules (O2) and nitrogen molecules (N2). These molecules are far enough apart that they act like single, isolated molecules. When the daytime white sunlight hits isolated air molecules, it scatters according to Rayleigh scattering, turning the sky whitish-bluish-violet. The fact that we can see the daytime sky attests to the fact that small, individual molecules can exhibit some form of color. While we are talking about small molecules when it comes to the sky, the same principle applies to single atoms. Properly understood, the color in Rayleigh scattering belongs more to the interaction itself than to the actual types of atoms involved. Just because the sky is blue does not necessarily mean that nitrogen atoms are blue. Raman scattering is much rarer than Rayleigh scattering, but is nearly identical in the context of this discussion. Raman scattering is different in that some of the energy of the incident light is lost internally to the particle so that the scattered light is shifted lower in frequency. 4. Gas DischargeGas discharge (e.g. a Neon light) is perhaps the mechanism that would best fit the notion of an individual atom "having a color". Gas discharge is what happens when you take pure atoms, isolate them from each other in a low-density gas state and then excite them using an electric current. When the atoms de-excite, they emit visible light. The key here is that a particular atom can only being excited, de-excited, and emit light in certain ways. This leads to the color of an atom during gas discharge being very strongly tied to the type of atom involved. The frequency spectrum of an atom during gas discharge is considered the color "fingerprint" of that particular type of atom. For instance, true neon signs are always red because neon atoms themselves are red under gas discharge. Argon atoms are lavender under gas discharge, while sodium atoms are yellow and mercury atoms are blue. Many of the colors generated by "Neon" lights are attained by mixing different gases together. The "flame test" used in chemistry to detect certain atoms is essentially a less-controlled, less-pure version of a gas discharge lamp. Note that florescence (such as in a florescent light bulb), phosphorescence, and gas laser emission are all similar to gas discharge in that they involve exciting electrons in single atoms or simple molecules. As opposed to gas discharge, which forces an atom to emit all of its characteristic colors; florescence, phosphorescence, and laser emission all involve exploiting certain transitions so that only certain atomic colors are emitted. They can be considered special cases of gas discharge, as far as atomic color characterization is concerned. There are many other ways an object or material can emit or reflect visible light; such as through semiconductor electron-hole recombination (in LED's), Cherenkov radiation, chemical reactions, synchrotron radiation, or sonoluminescence; but all of these involve the interaction of many atoms or no atoms at all, and so are not pertinent to the current discussion. In summary: in the sense of traditional reflection, refraction, absorption, and thermal radiation, individual atoms are invisible. In the sense of Rayleigh scattering and gas discharge atoms do have a color.	tag/atom/	context: tag/atom/ question: Does an atom have a color?	The answer really depends on how you define "having a color". The term "color" refers to visible light with a certain frequency, or a mixture of visible light frequencies. Therefore, the word "color" describes the frequency content of any type of visible light. Anytime visible light is present, we can describe it as having a certain color. With this in mind, there are many different ways an object can reflect or emit visible light. Thus, there are many ways an object can "have a color". While a single, isolated, atom can reflect or emit visible light in several of these ways, it does not participate in all the ways. If you define "having a color" very narrowly such that it only includes certain mechanisms, then atoms do not have color. If you define "having a color" more broadly, then atoms do have a color. Let us look at the different ways an object can reflect or emit visible light and apply each one to an atom. 1. Bulk reflection, refraction, and absorptionThe most common, everyday manner in which objects can send visible light to our eyes is through bulk reflection, refraction, and absorption. These three effects are all part of the same physical mechanism: the interaction of an external beam of light with many atoms at the same time. When white light, which contains all colors, hits the surface of a red apple, the light waves that are orange, yellow, green and blue get absorbed by the atoms in the apple's skin and converted to heat, while the red waves are mostly reflected back to our eyes. Some of the light is also transmitted through the apple skin and bent slightly as it goes through. We call this bent transmission of light "refraction". Some materials such as glass transmit a lot of the light while other materials such as apples transmit very little. The key point here is that traditional reflection, refraction, and absorption constitute a bulk phenomenon where each ray of light interacts with dozens to millions of atoms at the same time. This makes sense when you consider that visible light has a wavelength that is about a thousand times bigger than atoms. Visible light waves have a wavelength from 400 nanometers to 700 nanometers, depending on the color. In contrast, atoms have a width of about 0.2 nanometers. This discrepancy is why you can't see individual atoms using an optical microscope. The atoms are far smaller than the light you are trying to use to see them. The color of an object that results from traditional bulk reflection, refraction, and absorption is therefore a result of how several atoms are bound together and arranged, and not a result of the actual color of individual atoms. For example, take carbon atoms and bind them into a diamond lattice, and you get a clear diamonds. In contrast, take carbon atoms and bind them into hexagonal planes and you get gray graphite. The nature of the bonds between many atoms is what determines the traditional color of a material and not the type of atoms themselves. If you have no bonds at all between any atoms, you get a monoatomic gas, which is invisible (at least according to traditional reflection, refraction, and absorption). The color of most of the everyday objects around us, from apples to pencils to chairs, arises from traditional bulk reflection, refraction, and absorption. This mechanism of light delivery is so common and intuitive that we could define "having a color" narrowly to only include this mechanism. With this narrow definition in mind, therefore, a single atom is too small to have a color. 2. Thermal radiationHeat up a bar of iron enough and it glows red. You could therefore say that the color of a hot iron bar is glowing red. The red color of the iron bar in this case, however, is due to thermal radiation, which is a mechanism that is very different from bulk reflection, refraction, and absorption. In the mechanism of thermal radiation, the atoms of an object knock into each other so violently that they emit light. More accurately, the collisions cause the electrons and atoms to be excited to higher energy states, and then the electrons and atoms emit light when they transition back down to lower energy states. Since the collisions due to thermal motion are random, they lead to a wide range of energy excitations. As a result, the thermal radiation emitted contains many colors that span a broad band of frequencies. The interesting thing about thermal radiation is that its color is more a result of the temperature of the object and less a result of the material of the object. Every solid material glows red if you can get it to the right temperature without it evaporating or chemically reacting. The key to thermal radiation is that it is an emergent property of the interaction of many atoms. As such, a single atom cannot emit thermal radiation. So even if we expand the definition of "having a color" to include thermal radiation, individual atoms still have no color. 3. Rayleigh scatteringMore informatively called "long-wavelength scattering", Rayleigh scattering is when light does bounce off of single atoms and molecules. But because the light is so much bigger than the atoms, Rayleigh scattering is not really the "bouncing" of a light wave off of a small particle such as an atom, but is more a case of immersing the particle in the electric field of the light wave. The electric field induces an oscillating electric dipole in the particle which then radiates. Because the mechanism is so different, Rayleigh scattering of white light off of small particles always creates the same broad range of colors, with blue and violet being the strongest. The color of Rayleigh scattering is always the same (assuming the incident light is white) and is mostly independent of the material of the scattering object. Therefore, a single atom does have a color in the sense that it participates in Rayleigh scattering. For example, earth's atmosphere is composed mostly of small oxygen molecules (O2) and nitrogen molecules (N2). These molecules are far enough apart that they act like single, isolated molecules. When the daytime white sunlight hits isolated air molecules, it scatters according to Rayleigh scattering, turning the sky whitish-bluish-violet. The fact that we can see the daytime sky attests to the fact that small, individual molecules can exhibit some form of color. While we are talking about small molecules when it comes to the sky, the same principle applies to single atoms. Properly understood, the color in Rayleigh scattering belongs more to the interaction itself than to the actual types of atoms involved. Just because the sky is blue does not necessarily mean that nitrogen atoms are blue. Raman scattering is much rarer than Rayleigh scattering, but is nearly identical in the context of this discussion. Raman scattering is different in that some of the energy of the incident light is lost internally to the particle so that the scattered light is shifted lower in frequency. 4. Gas DischargeGas discharge (e.g. a Neon light) is perhaps the mechanism that would best fit the notion of an individual atom "having a color". Gas discharge is what happens when you take pure atoms, isolate them from each other in a low-density gas state and then excite them using an electric current. When the atoms de-excite, they emit visible light. The key here is that a particular atom can only being excited, de-excited, and emit light in certain ways. This leads to the color of an atom during gas discharge being very strongly tied to the type of atom involved. The frequency spectrum of an atom during gas discharge is considered the color "fingerprint" of that particular type of atom. For instance, true neon signs are always red because neon atoms themselves are red under gas discharge. Argon atoms are lavender under gas discharge, while sodium atoms are yellow and mercury atoms are blue. Many of the colors generated by "Neon" lights are attained by mixing different gases together. The "flame test" used in chemistry to detect certain atoms is essentially a less-controlled, less-pure version of a gas discharge lamp. Note that florescence (such as in a florescent light bulb), phosphorescence, and gas laser emission are all similar to gas discharge in that they involve exciting electrons in single atoms or simple molecules. As opposed to gas discharge, which forces an atom to emit all of its characteristic colors; florescence, phosphorescence, and laser emission all involve exploiting certain transitions so that only certain atomic colors are emitted. They can be considered special cases of gas discharge, as far as atomic color characterization is concerned. There are many other ways an object or material can emit or reflect visible light; such as through semiconductor electron-hole recombination (in LED's), Cherenkov radiation, chemical reactions, synchrotron radiation, or sonoluminescence; but all of these involve the interaction of many atoms or no atoms at all, and so are not pertinent to the current discussion. In summary: in the sense of traditional reflection, refraction, absorption, and thermal radiation, individual atoms are invisible. In the sense of Rayleigh scattering and gas discharge atoms do have a color.
Does an electron in an atom move at all?	First of all, I assume you meant to ask the question, "Does an electron in a stable (non-transitioning) atomic state experience any movement?" Obviously, an electron that is transitioning between states is moving from one state to the other. But for an electron that is just staying in one stable state in an atom, the question is more interesting. Does it move? The answer could be yes or no depending on how we define motion and what form of the electron we consider to be truly real. The problem is that an electron is not a solid little ball that we can watch zip around. An electron is a quantum object. As such, an electron is partially particle-like and partially wave-like, but is really something more complex that is neither a simple wave nor a simple particle. The electron is described by a probabilistic quantum wavefunction, which spreads out through space and vibrates, but in such a way that it still has certain discrete properties such as mass. When bound in a stable state in an atom, the electron wavefunction spreads out into a certain shape called an "orbital". The orbital does not contain the electron or describe the average location of a little hard electron orbiting around. Rather, the orbital is the electron. When bound in a stable state in an atom, an electron behaves mostly like an oscillating three-dimensional wave, i.e. the orbital vibrates. It's a bit like a vibrating guitar string. When you pluck a guitar string, you get the string shaking, which is what creates the sound. Scientifically, we would say that you have excited a standing wave in the string. The guitar string is not moving in the sense of shooting off to the other side of the room. In this sense, the guitar string is not moving at all, but remains clamped to the guitar. But the guitar string is moving in the sense that it is vibrating when you pluck it. If you pick one spot on the plucked string and look at it closely, it is definitely moving from one location in space to another, back and forth repeatedly. By pulling the string, you transferred chemical energy in your arm to elastic energy in the stretched string. When you let go, the elastic energy was converted to motional energy (kinetic energy) as the string snapped back and started vibrating. The total kinetic energy of the entire string averaged over time is zero, since the overall string is not going anywhere with respect to the guitar. But the kinetic energy of any small part of the string at a given moment is not zero. In this way, a plucked guitar string experiences local motion but not overall motion. An electron in an atomic orbital state acts somewhat like a plucked guitar string. It is spread out in a three-dimensional cloud-like wavefunction that vibrates. Whereas a guitar string vibrates up and down, an atomic electron wavefunction simply vibrates strong and weak. The frequency at which the electron wavefunction vibrates is directly proportional to the total energy of the electron. Electrons in higher-energy atomic states vibrate more quickly. Because an electron is a quantum object with wave-like properties, it must always be vibrating at some frequency. In order for an electron to stop vibrating and therefore have a frequency of zero, it must be destroyed. In an atom, this happens when an electron is sucked into the nucleus and takes part in a nuclear reaction known as electron capture. With all of this in mind, an electron in a stable atomic state does not move in the sense of a solid little ball zipping around in circles like how the planets orbit the sun, since the electron is spread out in a wave. Furthermore, an electron in a stable atomic state does not move in the sense of waving through space. The orbital electron does move in the sense of vibrating in time. But the truth is more complicated than this simple picture depicts. There are two things that describe the electron in quantum theory: the electron's quantum wavefunction, and the magnitude squared of the electron's quantum wavefunction. (The "magnitude squared" operation just means that you drop phase factors such as negative signs and then take the square. For instance, the magnitude squared of negative three is nine.) Interestingly, experiments can only directly measure the magnitude squared of the electron wavefunction, and yet we need the original wavefunction in order to predict the outcome of many experiments. For this reason, some people say that the magnitude squared of the wavefunction is the only real entity, whereas the original wavefunction itself is just a mathematical crutch that is needed because our theory is inelegant. Is the magnitude squared of the electron wavefuntion the real physical entity or is the original wavefunction the real physical entity? This question is really a philosophical one and not a physical one, so I will not pursue the question here. To scientists, the question, "What is actually real?" is unimportant. We are more concerned with making the equations match the experiments. So what does all this have to do with an electron in an atom? The point is that an atomic electron's raw wavefunction does vibrate, but the magnitude squared of the wavefunction does not vibrate. In fact, physicists call stable atomic electron states "stationary states" because the magnitude squared of the wavefunction is constant in time. If you consider the raw wavefunction to be the truly physical entity, then you have to say that an electron in an atom experiences motion in the form of a vibration. If you consider the magnitude squared of the wavefunction to be the truly physical entity, then you have to say that an electron in an atom experiences no vibration, and therefore no motion. I consider the first choice to make more sense. You can mathematically show that certain atomic electron states contain angular momentum (i.e. rotational momentum). It's hard to make sense of the claim that an atomic electron contains angular momentum and at the same claim that the electron is completely motionless in every sense of the word. For this reason, I prefer to view the raw wavefunction as the truly physical entity, and therefore an electron in an atom experiences motion in the form of vibrations. But, again, the question, "What is actually real?" is a philosophical one and is unimportant in science. The bottom line is that the raw wavefunction of an electron in a stable atomic state experiences vibrational motion. Whether you consider this motion real or not is up to you.	tag/atom/	context: tag/atom/ question: Does an electron in an atom move at all?	First of all, I assume you meant to ask the question, "Does an electron in a stable (non-transitioning) atomic state experience any movement?" Obviously, an electron that is transitioning between states is moving from one state to the other. But for an electron that is just staying in one stable state in an atom, the question is more interesting. Does it move? The answer could be yes or no depending on how we define motion and what form of the electron we consider to be truly real. The problem is that an electron is not a solid little ball that we can watch zip around. An electron is a quantum object. As such, an electron is partially particle-like and partially wave-like, but is really something more complex that is neither a simple wave nor a simple particle. The electron is described by a probabilistic quantum wavefunction, which spreads out through space and vibrates, but in such a way that it still has certain discrete properties such as mass. When bound in a stable state in an atom, the electron wavefunction spreads out into a certain shape called an "orbital". The orbital does not contain the electron or describe the average location of a little hard electron orbiting around. Rather, the orbital is the electron. When bound in a stable state in an atom, an electron behaves mostly like an oscillating three-dimensional wave, i.e. the orbital vibrates. It's a bit like a vibrating guitar string. When you pluck a guitar string, you get the string shaking, which is what creates the sound. Scientifically, we would say that you have excited a standing wave in the string. The guitar string is not moving in the sense of shooting off to the other side of the room. In this sense, the guitar string is not moving at all, but remains clamped to the guitar. But the guitar string is moving in the sense that it is vibrating when you pluck it. If you pick one spot on the plucked string and look at it closely, it is definitely moving from one location in space to another, back and forth repeatedly. By pulling the string, you transferred chemical energy in your arm to elastic energy in the stretched string. When you let go, the elastic energy was converted to motional energy (kinetic energy) as the string snapped back and started vibrating. The total kinetic energy of the entire string averaged over time is zero, since the overall string is not going anywhere with respect to the guitar. But the kinetic energy of any small part of the string at a given moment is not zero. In this way, a plucked guitar string experiences local motion but not overall motion. An electron in an atomic orbital state acts somewhat like a plucked guitar string. It is spread out in a three-dimensional cloud-like wavefunction that vibrates. Whereas a guitar string vibrates up and down, an atomic electron wavefunction simply vibrates strong and weak. The frequency at which the electron wavefunction vibrates is directly proportional to the total energy of the electron. Electrons in higher-energy atomic states vibrate more quickly. Because an electron is a quantum object with wave-like properties, it must always be vibrating at some frequency. In order for an electron to stop vibrating and therefore have a frequency of zero, it must be destroyed. In an atom, this happens when an electron is sucked into the nucleus and takes part in a nuclear reaction known as electron capture. With all of this in mind, an electron in a stable atomic state does not move in the sense of a solid little ball zipping around in circles like how the planets orbit the sun, since the electron is spread out in a wave. Furthermore, an electron in a stable atomic state does not move in the sense of waving through space. The orbital electron does move in the sense of vibrating in time. But the truth is more complicated than this simple picture depicts. There are two things that describe the electron in quantum theory: the electron's quantum wavefunction, and the magnitude squared of the electron's quantum wavefunction. (The "magnitude squared" operation just means that you drop phase factors such as negative signs and then take the square. For instance, the magnitude squared of negative three is nine.) Interestingly, experiments can only directly measure the magnitude squared of the electron wavefunction, and yet we need the original wavefunction in order to predict the outcome of many experiments. For this reason, some people say that the magnitude squared of the wavefunction is the only real entity, whereas the original wavefunction itself is just a mathematical crutch that is needed because our theory is inelegant. Is the magnitude squared of the electron wavefuntion the real physical entity or is the original wavefunction the real physical entity? This question is really a philosophical one and not a physical one, so I will not pursue the question here. To scientists, the question, "What is actually real?" is unimportant. We are more concerned with making the equations match the experiments. So what does all this have to do with an electron in an atom? The point is that an atomic electron's raw wavefunction does vibrate, but the magnitude squared of the wavefunction does not vibrate. In fact, physicists call stable atomic electron states "stationary states" because the magnitude squared of the wavefunction is constant in time. If you consider the raw wavefunction to be the truly physical entity, then you have to say that an electron in an atom experiences motion in the form of a vibration. If you consider the magnitude squared of the wavefunction to be the truly physical entity, then you have to say that an electron in an atom experiences no vibration, and therefore no motion. I consider the first choice to make more sense. You can mathematically show that certain atomic electron states contain angular momentum (i.e. rotational momentum). It's hard to make sense of the claim that an atomic electron contains angular momentum and at the same claim that the electron is completely motionless in every sense of the word. For this reason, I prefer to view the raw wavefunction as the truly physical entity, and therefore an electron in an atom experiences motion in the form of vibrations. But, again, the question, "What is actually real?" is a philosophical one and is unimportant in science. The bottom line is that the raw wavefunction of an electron in a stable atomic state experiences vibrational motion. Whether you consider this motion real or not is up to you.
Does the human body contain minerals?	For the most part, the human body does not contain minerals. Scientifically speaking, a mineral is a naturally-occurring inorganic crystalline solid with a single chemical formula. Rocks are aggregates of minerals and organic materials. Except for in bones and teeth, the atoms and molecules making up a healthy body are not crystalline and are not solid. In this way, most of the molecules making up a human body fail to meet the definition of a mineral. Confusion often arises because many health professionals, nutritionists, and biologists misuse the word "mineral". When they say "mineral" in the context of human nutrition, they really mean "dietary element". Scientifically, the phrase "trace element" should really be used instead of "trace mineral" when talking about rare atoms required by the human body. The words "element" and "mineral" do not mean the same thing. A chemical "element" is a material containing only one kind of atom. In some cases, elements can form minerals, but they don't have to. For example, hydrogen is an element, but it is not a mineral because it is neither crystalline nor a solid. In contrast, quartz is indeed a mineral, but it is not an element because it contains more than one kind of atom. A gold nugget found in the ground is both an element (because it contains only gold atoms) and a mineral (because it has a natural crystalline solid structure). The small subset of materials in the world that contain only one kind of atom and have the atoms naturally bonded into a solid crystalline lattice are called "native element minerals". 1. Materials that are elements, but not minerals 2. Materials that are minerals, but not elements 3. Materials that are both minerals and elements (native element minerals): For example, table salt contains sodium atoms and chlorine atoms bound into a solid, ionic, cubic crystalline lattice. Naturally occurring salt is therefore a mineral. But as soon as you sprinkle salt on your tongue and begin to eat it, the salt dissolves in the water on your tongue. This means that the sodium and chlorine atoms break apart and float around in the water. You no longer have a mineral. You have elemental ions in solution. Your body then uses the dissolved elemental sodium ions to regulate fluid pressure levels and to send electrical signals along your nerves. In this way, you can eat minerals, but once you eat them, they aren't minerals anymore. Furthermore, you can get dietary elements from non-mineral sources. For example, you can get dietary sodium from milk, which is not a mineral. In fact, we get most of our dietary elements from non-mineral sources. The only mineral we really eat on a regular basis is table salt. The one exception in a healthy human is bone mineral, such as in bones and teeth. Bone mineral is indeed an inorganic, crystalline, solid with a single chemical formula and therefore qualifies as a genuine mineral. The mineral in your bones is called hydroxyapatite and has the chemical formula Ca5(PO4)3(OH). Our bodies build bone mineral on the spot, so we don't have to swallow hydroxyapatite crystals. But we do have to eat food with enough of the right kinds of atoms to build bone mineral. Looking at the chemical formula, we see that our bodies can't build bone mineral unless we supply it with enough calcium, phosphorus, oxygen, and hydrogen. A typical person has almost unlimited access to hydrogen and oxygen atoms through the water he drinks and the air he breaths. In contrast, a person can only get enough calcium and phosphorus to build healthy bones if he eats and drinks foods containing these elements. Minerals can also form in the human body as part of disease states such as in kidney stones.	tag/atom/	context: tag/atom/ question: Does the human body contain minerals?	For the most part, the human body does not contain minerals. Scientifically speaking, a mineral is a naturally-occurring inorganic crystalline solid with a single chemical formula. Rocks are aggregates of minerals and organic materials. Except for in bones and teeth, the atoms and molecules making up a healthy body are not crystalline and are not solid. In this way, most of the molecules making up a human body fail to meet the definition of a mineral. Confusion often arises because many health professionals, nutritionists, and biologists misuse the word "mineral". When they say "mineral" in the context of human nutrition, they really mean "dietary element". Scientifically, the phrase "trace element" should really be used instead of "trace mineral" when talking about rare atoms required by the human body. The words "element" and "mineral" do not mean the same thing. A chemical "element" is a material containing only one kind of atom. In some cases, elements can form minerals, but they don't have to. For example, hydrogen is an element, but it is not a mineral because it is neither crystalline nor a solid. In contrast, quartz is indeed a mineral, but it is not an element because it contains more than one kind of atom. A gold nugget found in the ground is both an element (because it contains only gold atoms) and a mineral (because it has a natural crystalline solid structure). The small subset of materials in the world that contain only one kind of atom and have the atoms naturally bonded into a solid crystalline lattice are called "native element minerals". 1. Materials that are elements, but not minerals 2. Materials that are minerals, but not elements 3. Materials that are both minerals and elements (native element minerals): For example, table salt contains sodium atoms and chlorine atoms bound into a solid, ionic, cubic crystalline lattice. Naturally occurring salt is therefore a mineral. But as soon as you sprinkle salt on your tongue and begin to eat it, the salt dissolves in the water on your tongue. This means that the sodium and chlorine atoms break apart and float around in the water. You no longer have a mineral. You have elemental ions in solution. Your body then uses the dissolved elemental sodium ions to regulate fluid pressure levels and to send electrical signals along your nerves. In this way, you can eat minerals, but once you eat them, they aren't minerals anymore. Furthermore, you can get dietary elements from non-mineral sources. For example, you can get dietary sodium from milk, which is not a mineral. In fact, we get most of our dietary elements from non-mineral sources. The only mineral we really eat on a regular basis is table salt. The one exception in a healthy human is bone mineral, such as in bones and teeth. Bone mineral is indeed an inorganic, crystalline, solid with a single chemical formula and therefore qualifies as a genuine mineral. The mineral in your bones is called hydroxyapatite and has the chemical formula Ca5(PO4)3(OH). Our bodies build bone mineral on the spot, so we don't have to swallow hydroxyapatite crystals. But we do have to eat food with enough of the right kinds of atoms to build bone mineral. Looking at the chemical formula, we see that our bodies can't build bone mineral unless we supply it with enough calcium, phosphorus, oxygen, and hydrogen. A typical person has almost unlimited access to hydrogen and oxygen atoms through the water he drinks and the air he breaths. In contrast, a person can only get enough calcium and phosphorus to build healthy bones if he eats and drinks foods containing these elements. Minerals can also form in the human body as part of disease states such as in kidney stones.
How can an electron leap between atomic levels without passing through all the space in between?	An electron that is transitioning between two atomic states does not skip any intervening space. The idea of a quantum leap is highly misleading and commonly misunderstood. First of all, an electron is a quantum object. As such, it acts both as a wave and as a particle at the same time. When bound as part of an atom, an electron mostly acts like a wave. An atomic electron spreads out into cloud-like wave shapes called "orbitals". If you look closely at the various orbitals of an atom (for instance, the hydrogen atom), you see that they all overlap in space. Therefore, when an electron transitions from one atomic energy level to another energy level, it does not really go anywhere. It just changes shape. The orbital shapes with more fluctuations (with more highs, lows, and bends to its shape) contain more energy. In other words, when an electron transitions to a lower atomic energy level, its wave shape changes to have less kinks in it. But the electron does not "leap" anywhere. The wave behavior of an electron in an atom is very similar to the behavior of classical waves on a guitar string. When you pluck a guitar string, you excite standing waves in the string, which are what make the sound. A certain string can only experience certain types of standing waves because the string is clamped down on both ends. The types of waves allowed on a particular string are called its "harmonics". The harmonics of a string depend on the string's length, tension, and mass density. A particular guitar string (of a particular length, tension, and mass) can therefore only play a certain type of sound, which is a combination of its harmonics. If you are very careful about how you pluck the string, you can create a wave on the string which is mostly the lower, fundamental harmonic (which has very few kinks), or you can create a wave on the string which is mostly a higher harmonic (which has many kinks). It takes more energy and is therefore harder to strongly excite the higher harmonic in a guitar string. Furthermore, if you pluck the string properly so as to strongly excite a higher harmonic wave in the string, you can even coax the string to transition down to the lower-energy harmonic. The wave on the guitar string does not go anywhere when the string transitions from a higher-energy state to a lower-energy state. The wave just changes shape. In a similar way, the discrete set of electron orbitals possible in a certain atom are effectively the harmonics of the atom. The electron can transition to a higher harmonic wave shape by absorbing energy and kinking more, or transition to a lower harmonic wave shape by emitting energy and kinking less (relaxing). It should be clear at this point that an electron that transitions in an atom does not make any kind of leap from one location in space to another location in space. But you may still be worried that the electron makes a leap from one energy level to another, and therefore bypasses all the in-between energy states. Although we are talking about a leap on the energy scale, and not a leap in space, such a leap may still strike you as unnatural, as it should. The fact is that an electron transitioning in an atom does not actually discontinuously leap from one energy level to another energy level, but makes a smooth transition. You may wonder, "Doesn't quantum theory tell us that an electron in an atom can only exist at certain, discrete energy levels?" Actually, no. Quantum theory tells us that an electron with a stationary energy can only exist at certain, discrete energy levels. This distinction is very important. By "stationary energy" we mean that the electron's energy stays constant for a fairly long period of time. The orbitals of a particular atom are not the only allowed states that an electron can take on in the atom. They are the only stable states of the atom, meaning that when an electron settles down to a particular state in an atom, it must be in one of the orbital states. When an electron is in the process of transitioning between stable states, it is not itself stable and therefore has less restrictions on its energy. In fact, an electron that transitions does not even have a well-defined energy. Innate quantum uncertainty arises in the electron's energy because of its transition. The quicker an electron transitions, the more uncertain its energy. This "innate quantum uncertainty" is not some metaphysical mystery, but is better understood as the wave spreading out over many values. Just as the electron can spread out into a wave that extends over a region of space, it can also spread out into a wave that extends over a region along the energy scale. If you calculate the average energy (the "expectation value") of this transitioning electron's spread of energies, you find that the electron's average energy does not instantaneously jump from one energy level to another. Rather, it smoothly transitions on average from the one energy level to the other energy level over a period of time. There is really no "instantaneous quantum leap" at all. The electron does not leap in space, and it does not leap up the energy scale. In fact, the term "quantum leap" is almost universally shunned by scientists as it is highly misleading. If you want a better mental image, you can think of the electron as quickly, but smoothly sliding along the energy scale from one stable state to the next. Because a typical atomic electron transition is so fast (often on the order of nanoseconds), it can seem to be nearly instantaneous to the slow human senses, but fundamentally it is not.	tag/atom/	context: tag/atom/ question: How can an electron leap between atomic levels without passing through all the space in between?	An electron that is transitioning between two atomic states does not skip any intervening space. The idea of a quantum leap is highly misleading and commonly misunderstood. First of all, an electron is a quantum object. As such, it acts both as a wave and as a particle at the same time. When bound as part of an atom, an electron mostly acts like a wave. An atomic electron spreads out into cloud-like wave shapes called "orbitals". If you look closely at the various orbitals of an atom (for instance, the hydrogen atom), you see that they all overlap in space. Therefore, when an electron transitions from one atomic energy level to another energy level, it does not really go anywhere. It just changes shape. The orbital shapes with more fluctuations (with more highs, lows, and bends to its shape) contain more energy. In other words, when an electron transitions to a lower atomic energy level, its wave shape changes to have less kinks in it. But the electron does not "leap" anywhere. The wave behavior of an electron in an atom is very similar to the behavior of classical waves on a guitar string. When you pluck a guitar string, you excite standing waves in the string, which are what make the sound. A certain string can only experience certain types of standing waves because the string is clamped down on both ends. The types of waves allowed on a particular string are called its "harmonics". The harmonics of a string depend on the string's length, tension, and mass density. A particular guitar string (of a particular length, tension, and mass) can therefore only play a certain type of sound, which is a combination of its harmonics. If you are very careful about how you pluck the string, you can create a wave on the string which is mostly the lower, fundamental harmonic (which has very few kinks), or you can create a wave on the string which is mostly a higher harmonic (which has many kinks). It takes more energy and is therefore harder to strongly excite the higher harmonic in a guitar string. Furthermore, if you pluck the string properly so as to strongly excite a higher harmonic wave in the string, you can even coax the string to transition down to the lower-energy harmonic. The wave on the guitar string does not go anywhere when the string transitions from a higher-energy state to a lower-energy state. The wave just changes shape. In a similar way, the discrete set of electron orbitals possible in a certain atom are effectively the harmonics of the atom. The electron can transition to a higher harmonic wave shape by absorbing energy and kinking more, or transition to a lower harmonic wave shape by emitting energy and kinking less (relaxing). It should be clear at this point that an electron that transitions in an atom does not make any kind of leap from one location in space to another location in space. But you may still be worried that the electron makes a leap from one energy level to another, and therefore bypasses all the in-between energy states. Although we are talking about a leap on the energy scale, and not a leap in space, such a leap may still strike you as unnatural, as it should. The fact is that an electron transitioning in an atom does not actually discontinuously leap from one energy level to another energy level, but makes a smooth transition. You may wonder, "Doesn't quantum theory tell us that an electron in an atom can only exist at certain, discrete energy levels?" Actually, no. Quantum theory tells us that an electron with a stationary energy can only exist at certain, discrete energy levels. This distinction is very important. By "stationary energy" we mean that the electron's energy stays constant for a fairly long period of time. The orbitals of a particular atom are not the only allowed states that an electron can take on in the atom. They are the only stable states of the atom, meaning that when an electron settles down to a particular state in an atom, it must be in one of the orbital states. When an electron is in the process of transitioning between stable states, it is not itself stable and therefore has less restrictions on its energy. In fact, an electron that transitions does not even have a well-defined energy. Innate quantum uncertainty arises in the electron's energy because of its transition. The quicker an electron transitions, the more uncertain its energy. This "innate quantum uncertainty" is not some metaphysical mystery, but is better understood as the wave spreading out over many values. Just as the electron can spread out into a wave that extends over a region of space, it can also spread out into a wave that extends over a region along the energy scale. If you calculate the average energy (the "expectation value") of this transitioning electron's spread of energies, you find that the electron's average energy does not instantaneously jump from one energy level to another. Rather, it smoothly transitions on average from the one energy level to the other energy level over a period of time. There is really no "instantaneous quantum leap" at all. The electron does not leap in space, and it does not leap up the energy scale. In fact, the term "quantum leap" is almost universally shunned by scientists as it is highly misleading. If you want a better mental image, you can think of the electron as quickly, but smoothly sliding along the energy scale from one stable state to the next. Because a typical atomic electron transition is so fast (often on the order of nanoseconds), it can seem to be nearly instantaneous to the slow human senses, but fundamentally it is not.
How can radioactive decay just happen with nothing triggering it?	Although a radioactive decay event seems spontaneous and is unpredictable, it is indeed triggered by a physical agent. That physical agent is a vacuum fluctuation. Due to the quantum nature of the universe, a vacuum always contains vacuum fluctuations. Vacuum fluctuations are also called vacuum energy and zero-point energy. You can think of vacuum fluctuations as a sea of particles and antiparticles briefly popping into and out of existence. These particles originate from the vacuum itself due to intrinsic quantum uncertainty. Vacuum fluctuations are very short-lived (short-lived enough that they do not violate any conservation laws, within the level of quantum uncertainty). However, vacuum fluctuations are physically real and cause real effects. For instance, vacuum fluctuations tend to weaken, or screen, electromagnetic fields. Vacuum fluctuations also give rise to the Casimir effect as well as the Lamb shift in hydrogen energy levels. Every spontaneous quantum transition is actually triggered by a vacuum fluctuation. Lasers crucially depend on vacuum fluctuations. The light emitted from a laser is generated by a chain reaction of coherent photon emissions. This chain reaction is triggered at the beginning by a vacuum fluctuation. When an electron is put in an excited atomic state and left alone, it will eventually, naturally transition back down to its original state. When exactly this happens seems spontaneous, but it is actually triggered by a vacuum fluctuation. Similarly, vacuum fluctuations are what trigger a radioactive decay event. As part of the background quantum fluctuations that are intrinsic to the vacuum, a particle pops into existence just long enough to collide with the nucleus and trigger radioactive decay. The exact moment that radioactive decay happens is random and unpredictable because vacuum fluctuations are random and unpredictable. All of this just leads to the question, what triggers vacuum fluctuations? The answer is that nothing triggers vacuum fluctuations. They are constantly happening due to the quantum nature of the universe. Vacuum fluctuations are a well-established principle of mainstream physics. Note that there are a lot of incorrect, unscientific notions online about vacuum energy. Even though vacuum energy is real, it cannot be harnessed as a free source of energy. Quantum physics is strange, but it still must obey the physical conservation laws of the universe, including the law of conservation of energy. A vacuum fluctuation cannot permanently give its energy to another object. That would violate the law of conservation of energy. In fact, conservation of energy is what prevents a vacuum fluctuation from continuing to exist beyond its short life. However, if conditions are right, a vacuum fluctuation can be given enough energy from another object for it to be promoted to a stable particle that continues to exist. For instance, in an effect called spontaneous emission, an electron transitions spontaneously from an excited quantum state to a lower quantum state and emits a bit of light called a photon in the process. It looks like the photon is just created out of nowhere. However, the more accurate description is that a photon vacuum fluctuation collides with the electron, triggering the electron to transition. In the process, the electron gives some of its energy to the vacuum fluctuation, thereby promoting it to a regular photon that can continue to exist forever.	tag/atom/	context: tag/atom/ question: How can radioactive decay just happen with nothing triggering it?	Although a radioactive decay event seems spontaneous and is unpredictable, it is indeed triggered by a physical agent. That physical agent is a vacuum fluctuation. Due to the quantum nature of the universe, a vacuum always contains vacuum fluctuations. Vacuum fluctuations are also called vacuum energy and zero-point energy. You can think of vacuum fluctuations as a sea of particles and antiparticles briefly popping into and out of existence. These particles originate from the vacuum itself due to intrinsic quantum uncertainty. Vacuum fluctuations are very short-lived (short-lived enough that they do not violate any conservation laws, within the level of quantum uncertainty). However, vacuum fluctuations are physically real and cause real effects. For instance, vacuum fluctuations tend to weaken, or screen, electromagnetic fields. Vacuum fluctuations also give rise to the Casimir effect as well as the Lamb shift in hydrogen energy levels. Every spontaneous quantum transition is actually triggered by a vacuum fluctuation. Lasers crucially depend on vacuum fluctuations. The light emitted from a laser is generated by a chain reaction of coherent photon emissions. This chain reaction is triggered at the beginning by a vacuum fluctuation. When an electron is put in an excited atomic state and left alone, it will eventually, naturally transition back down to its original state. When exactly this happens seems spontaneous, but it is actually triggered by a vacuum fluctuation. Similarly, vacuum fluctuations are what trigger a radioactive decay event. As part of the background quantum fluctuations that are intrinsic to the vacuum, a particle pops into existence just long enough to collide with the nucleus and trigger radioactive decay. The exact moment that radioactive decay happens is random and unpredictable because vacuum fluctuations are random and unpredictable. All of this just leads to the question, what triggers vacuum fluctuations? The answer is that nothing triggers vacuum fluctuations. They are constantly happening due to the quantum nature of the universe. Vacuum fluctuations are a well-established principle of mainstream physics. Note that there are a lot of incorrect, unscientific notions online about vacuum energy. Even though vacuum energy is real, it cannot be harnessed as a free source of energy. Quantum physics is strange, but it still must obey the physical conservation laws of the universe, including the law of conservation of energy. A vacuum fluctuation cannot permanently give its energy to another object. That would violate the law of conservation of energy. In fact, conservation of energy is what prevents a vacuum fluctuation from continuing to exist beyond its short life. However, if conditions are right, a vacuum fluctuation can be given enough energy from another object for it to be promoted to a stable particle that continues to exist. For instance, in an effect called spontaneous emission, an electron transitions spontaneously from an excited quantum state to a lower quantum state and emits a bit of light called a photon in the process. It looks like the photon is just created out of nowhere. However, the more accurate description is that a photon vacuum fluctuation collides with the electron, triggering the electron to transition. In the process, the electron gives some of its energy to the vacuum fluctuation, thereby promoting it to a regular photon that can continue to exist forever.
How does dissolving a salt molecule in water make its atoms ionize?	Dissolving a salt molecule in water does not make its atoms ionize. The atoms in solid salts are already ionized long before touching water. Electrons in an atom can only take on specific wave states, and only one electron can occupy one wave state at a time. As a result, electrons in an atom take different states, starting from the lowest energy state and going upwards in energy until the electrons have all found distinct states. For various reasons that are not worth mentioning here, electron states in atoms tend to form various groups, with the states in the same group having very similar energies and states. Chemists call these groups of electron states "shells", even though they have nothing to do with literal shells. The interesting thing is that an atom with completely filled shells is very stable (all the available states in each group are occupied by electrons). On the other hand, an atom with its outermost shell only partially filled has a strong tendency to steal, lose, or share electrons from other atoms in order to fill its outermost shell and become stable. Such atoms are therefore chemically reactive. A well-known salt is sodium chloride (table salt), so let's use it as an example. A single neutral sodium atom has eleven electrons. Ten of these electrons fill states such that they form complete shells. The eleventh electron of sodium, however, is alone in the outermost, partially filled shell. Electrons are bound in atoms because their negative electric charge experiences electric attraction to the positive charge of the atom's nucleus. But for sodium, the negatively-charged electrons in the inner, completed shells do a good job of blocking, or screening, the attractive force of the nucleus on the eleventh electron. As a result, the eleventh electron of sodium is loosely bound to the atom and is ripe for being stolen by a more powerful atom. In contrast, chlorine (17 electrons) has all of its shells filled with electrons except for its outermost shell which is one electron short of being complete. There is a very strong attraction by the chlorine atom on an outside electron which is needed to complete its shell. Sodium and chlorine are therefore a perfect match. Sodium has one electron it is not holding onto very strongly, and chlorine is looking for one more electron to steal to fill its shell. As a result, a pure sample of sodium reacts strongly with a pure sample of chlorine and the end product is table salt. Each chlorine atom steals an electron from the sodium atom. Each sodium atom now has 11 positive protons and 10 negative electrons, for a net charge of +1. Each chlorine atom now has 17 positive protons and 18 negative electrons for a net charge of -1. The atoms have therefore been ionized by the reaction that forms solid table salt, all without the presence of water. Both the sodium and the chlorine ions now have completely filled shells and are therefore stable. This is a good example of an atom that naturally has an unequal number of electron and protons. The net positive sodium ion is now attracted to the net negative chlorine ion and this attraction forms what we call an "ionic bond". But, in reality, we don't have just one sodium ion sticking to ion chlorine ion. Instead, a lattice of many sodium ions ionically bonds to a lattice of chlorine ions, and we end up with a crystalline solid. Each sodium ion in the crystalline lattice of table salt is bound to the 6 nearest chlorine ions, and the same goes for each chlorine ion. The atoms in table salt are therefore already in the ionized state. Adding water does not ionize the atoms in salt, because they are already ionized. Instead, the water molecules stick to the already formed ions in the salt. The textbook titled Cell and Molecular Biology: Concepts and Experiments by Gerald Karp states, "A crystal of table salt is held together by an electrostatic attraction between positively charged Na+ and negatively charged Cl– ions. This type of attraction between fully charged components is called an ionic bond (or a salt bridge). Ionic bonds within a salt crystal may be quite strong. However, if a crystal of salt is dissolved in water, each of the individual ions becomes surrounded by water molecules, which inhibit oppositely charged ions from approaching one another closely enough to form ionic bonds." Each water molecule has a permanent dipole, meaning that one end is always slightly positively charged and the other end is always slightly negatively charged. The charged ends of the water molecules are so strongly attracted to the charged ions in the salt crystal that the water destroys the solid lattice structure of the salt and each sodium and chlorine ion becomes surrounded by a layer of sticky water molecules. In chemistry, we say the salt has been dissolved by the water. It's like a rock band exiting the limousine into a crowd of fans and becoming separated as each band member gets surrounded by his own circle of fans. If the atoms in solid salt were not ionized to begin with, the water would not do such a good job dissolving the salt.	tag/atom/	context: tag/atom/ question: How does dissolving a salt molecule in water make its atoms ionize?	Dissolving a salt molecule in water does not make its atoms ionize. The atoms in solid salts are already ionized long before touching water. Electrons in an atom can only take on specific wave states, and only one electron can occupy one wave state at a time. As a result, electrons in an atom take different states, starting from the lowest energy state and going upwards in energy until the electrons have all found distinct states. For various reasons that are not worth mentioning here, electron states in atoms tend to form various groups, with the states in the same group having very similar energies and states. Chemists call these groups of electron states "shells", even though they have nothing to do with literal shells. The interesting thing is that an atom with completely filled shells is very stable (all the available states in each group are occupied by electrons). On the other hand, an atom with its outermost shell only partially filled has a strong tendency to steal, lose, or share electrons from other atoms in order to fill its outermost shell and become stable. Such atoms are therefore chemically reactive. A well-known salt is sodium chloride (table salt), so let's use it as an example. A single neutral sodium atom has eleven electrons. Ten of these electrons fill states such that they form complete shells. The eleventh electron of sodium, however, is alone in the outermost, partially filled shell. Electrons are bound in atoms because their negative electric charge experiences electric attraction to the positive charge of the atom's nucleus. But for sodium, the negatively-charged electrons in the inner, completed shells do a good job of blocking, or screening, the attractive force of the nucleus on the eleventh electron. As a result, the eleventh electron of sodium is loosely bound to the atom and is ripe for being stolen by a more powerful atom. In contrast, chlorine (17 electrons) has all of its shells filled with electrons except for its outermost shell which is one electron short of being complete. There is a very strong attraction by the chlorine atom on an outside electron which is needed to complete its shell. Sodium and chlorine are therefore a perfect match. Sodium has one electron it is not holding onto very strongly, and chlorine is looking for one more electron to steal to fill its shell. As a result, a pure sample of sodium reacts strongly with a pure sample of chlorine and the end product is table salt. Each chlorine atom steals an electron from the sodium atom. Each sodium atom now has 11 positive protons and 10 negative electrons, for a net charge of +1. Each chlorine atom now has 17 positive protons and 18 negative electrons for a net charge of -1. The atoms have therefore been ionized by the reaction that forms solid table salt, all without the presence of water. Both the sodium and the chlorine ions now have completely filled shells and are therefore stable. This is a good example of an atom that naturally has an unequal number of electron and protons. The net positive sodium ion is now attracted to the net negative chlorine ion and this attraction forms what we call an "ionic bond". But, in reality, we don't have just one sodium ion sticking to ion chlorine ion. Instead, a lattice of many sodium ions ionically bonds to a lattice of chlorine ions, and we end up with a crystalline solid. Each sodium ion in the crystalline lattice of table salt is bound to the 6 nearest chlorine ions, and the same goes for each chlorine ion. The atoms in table salt are therefore already in the ionized state. Adding water does not ionize the atoms in salt, because they are already ionized. Instead, the water molecules stick to the already formed ions in the salt. The textbook titled Cell and Molecular Biology: Concepts and Experiments by Gerald Karp states, "A crystal of table salt is held together by an electrostatic attraction between positively charged Na+ and negatively charged Cl– ions. This type of attraction between fully charged components is called an ionic bond (or a salt bridge). Ionic bonds within a salt crystal may be quite strong. However, if a crystal of salt is dissolved in water, each of the individual ions becomes surrounded by water molecules, which inhibit oppositely charged ions from approaching one another closely enough to form ionic bonds." Each water molecule has a permanent dipole, meaning that one end is always slightly positively charged and the other end is always slightly negatively charged. The charged ends of the water molecules are so strongly attracted to the charged ions in the salt crystal that the water destroys the solid lattice structure of the salt and each sodium and chlorine ion becomes surrounded by a layer of sticky water molecules. In chemistry, we say the salt has been dissolved by the water. It's like a rock band exiting the limousine into a crowd of fans and becoming separated as each band member gets surrounded by his own circle of fans. If the atoms in solid salt were not ionized to begin with, the water would not do such a good job dissolving the salt.
If I hammered and flattened a penny enough, could I cover the entire earth with it?	No. If you spread out the atoms from a single penny over the entire surface of the earth, you would no longer have a single piece of solid material since the atoms would be too far apart to bond to each other. Let's do some careful calculations to show this result. A modern United States penny has a mass of 2.500 grams according to the US Mint. Since a penny is composed of 97.50% zinc and 2.50% copper, it therefore contains 2.4375 grams of zinc and 0.0625 grams of copper. At a molar mass of 65.380 grams per mole for zinc and 63.546 grams per mole for copper, a penny therefore contains 0.037282 moles of zinc and 0.00098354 moles of copper. Since a mole of atoms contains 6.0221 x 1023 atoms, there are 2.2452 x 1022 zinc atoms and 5.9230 x 1020 copper atoms in a penny, for a total of 2.3044 x 1022 atoms in a penny. The earth has a surface area of 510,072,000 square kilometers, or 5.10072 x 1032 square nanometers. The surface area of the earth really depends on what you include in your definition of surface. For instance, if we wish to cover the area of every leaf on every tree and shrub with atoms from the penny, then this will change our answer. Surprisingly, it will not change our answer very much. Most of the earth is covered in relativity flat oceans, sandy deserts, snow fields, barren rocks, and meadows. Trees, shrubs, buildings, and other irregularly-shaped objects only cover a very small percentage of the earth (trees and buildings seem common to most of us humans because most of us live near crowded concentrations of trees and/or buildings). At any rate, we must pick some definition of earth's surface area to make any calculations. The number cited above does not include the surface area of tree leaves and other small irregularities. In the context of trying to cover the earth with a flattened penny, you can think of this definition of surface area as us lowering a sheet of zinc so that it drapes along the tops of the trees, but does not wrap around any of the leaves or branches of the trees. The thinnest we could ever hammer a sheet of material is one atom thick. We therefore assume that we are creating a one-atom-thick planar sheet of material. Using the above value for earth's surface area, we divide it by the number of atoms in a penny to find how much area each atom will occupy when the atoms are spread evenly across earth's surface. We get the value of 2.21347 x 1010 square nanometers per atom, or 0.0000343 square inches per atom. This may seem like a small area, but it is huge compared to the types of areas spanned by simple molecules. From here on out we will assume that all of the atoms in the penny are zinc atoms. This is a good assumption because almost all of the atoms in the penny are zinc atoms (97.5%). Also, in terms of atomic size and bonding distance, zinc and copper are nearly identical. When allowed to bond into a solid piece of material, zinc atoms arrange themselves into stacks of planar hexagonal grids. Therefore, in creating our one-atom thick sheet of zinc, we will arrange our zinc atoms along a planar hexagonal grid. If the penny's atoms are spread out uniformly on a hexagonal grid covering earth's surface, then each atom will have to be 159,870 nanometers away from its next nearest atoms in order to cover the entire earth (for a hexagonal grid of objects, the distance between nearest-neighbor objects is 1.0746 times the square root of the area that each object has to itself). In other words, taking the atoms of a single penny and spreading them out over the entire earth in a hexagonal arrangement will cause each atom to be about 0.16 millimeters away from its neighboring atoms. In order to form a solid chunk of material, atoms have to be close enough to form stable bonds. In regular pieces of zinc metal, stable chemical bonds are formed when each zinc atom is a distance of 0.26649 nanometers away from its next nearest zinc atoms. Therefore, the atoms of our smashed penny will be almost exactly 600,000 times too far apart to maintain stable bonds and constitute a solid piece of metal. With this kind of separation, we don't have a solid penny at all. We have a very dilute zinc gas spread over the earth. These widely separated atoms would blow around, dissolve into the ocean, mix with the clouds, and react with other atoms, so that we no longer have any type of distinct object that we would say is covering the earth. For this reason, you cannot hammer and flatten a penny until it covers the entire. The earth is simply too big and a penny has simply too few atoms to accomplish this task. Even if we break each zinc atom into 30 hydrogen atoms (ignoring all the messy details of the nuclear reactions involved), the atoms are still about a hundred thousand times too far apart to form stable chemical bonds. Besides, hydrogen atoms don't bond to form a solid chunk of material under normal conditions. These thoughts lead to another question: How much area can a smashed penny cover and still remain a solid chunk of material? To calculate this, we again realize that the thinnest a material can get is one atom thick. Also, the distance that zinc atoms need to be from each other and still stay bonded as a solid is 0.26649 nanometers, as already mentioned. This means that as part of a hexagonal planar arrangement of atoms, each zinc atom needs to occupy 0.0615 square nanometers of area. Multiply this number by the 2.3044 x 1022 atoms in a penny and we get a total area of 1417 square meters, which is about a quarter of the size of an American football field. In other words, if you had a special machine that carefully hammered a penny until it was everywhere just an atom thick, it would only cover a quarter of a football field. Keep in mind that at this thickness, you would be hard pressed to even see the penny and you would rip the penny when walking on it without feeling any resistance (think of walking on aluminum foil, but much, much thinner). To cover the entire earth's surface with one-atom-thick smashed pennies, you would need at least 360 billion pennies.	tag/atom/	context: tag/atom/ question: If I hammered and flattened a penny enough, could I cover the entire earth with it?	No. If you spread out the atoms from a single penny over the entire surface of the earth, you would no longer have a single piece of solid material since the atoms would be too far apart to bond to each other. Let's do some careful calculations to show this result. A modern United States penny has a mass of 2.500 grams according to the US Mint. Since a penny is composed of 97.50% zinc and 2.50% copper, it therefore contains 2.4375 grams of zinc and 0.0625 grams of copper. At a molar mass of 65.380 grams per mole for zinc and 63.546 grams per mole for copper, a penny therefore contains 0.037282 moles of zinc and 0.00098354 moles of copper. Since a mole of atoms contains 6.0221 x 1023 atoms, there are 2.2452 x 1022 zinc atoms and 5.9230 x 1020 copper atoms in a penny, for a total of 2.3044 x 1022 atoms in a penny. The earth has a surface area of 510,072,000 square kilometers, or 5.10072 x 1032 square nanometers. The surface area of the earth really depends on what you include in your definition of surface. For instance, if we wish to cover the area of every leaf on every tree and shrub with atoms from the penny, then this will change our answer. Surprisingly, it will not change our answer very much. Most of the earth is covered in relativity flat oceans, sandy deserts, snow fields, barren rocks, and meadows. Trees, shrubs, buildings, and other irregularly-shaped objects only cover a very small percentage of the earth (trees and buildings seem common to most of us humans because most of us live near crowded concentrations of trees and/or buildings). At any rate, we must pick some definition of earth's surface area to make any calculations. The number cited above does not include the surface area of tree leaves and other small irregularities. In the context of trying to cover the earth with a flattened penny, you can think of this definition of surface area as us lowering a sheet of zinc so that it drapes along the tops of the trees, but does not wrap around any of the leaves or branches of the trees. The thinnest we could ever hammer a sheet of material is one atom thick. We therefore assume that we are creating a one-atom-thick planar sheet of material. Using the above value for earth's surface area, we divide it by the number of atoms in a penny to find how much area each atom will occupy when the atoms are spread evenly across earth's surface. We get the value of 2.21347 x 1010 square nanometers per atom, or 0.0000343 square inches per atom. This may seem like a small area, but it is huge compared to the types of areas spanned by simple molecules. From here on out we will assume that all of the atoms in the penny are zinc atoms. This is a good assumption because almost all of the atoms in the penny are zinc atoms (97.5%). Also, in terms of atomic size and bonding distance, zinc and copper are nearly identical. When allowed to bond into a solid piece of material, zinc atoms arrange themselves into stacks of planar hexagonal grids. Therefore, in creating our one-atom thick sheet of zinc, we will arrange our zinc atoms along a planar hexagonal grid. If the penny's atoms are spread out uniformly on a hexagonal grid covering earth's surface, then each atom will have to be 159,870 nanometers away from its next nearest atoms in order to cover the entire earth (for a hexagonal grid of objects, the distance between nearest-neighbor objects is 1.0746 times the square root of the area that each object has to itself). In other words, taking the atoms of a single penny and spreading them out over the entire earth in a hexagonal arrangement will cause each atom to be about 0.16 millimeters away from its neighboring atoms. In order to form a solid chunk of material, atoms have to be close enough to form stable bonds. In regular pieces of zinc metal, stable chemical bonds are formed when each zinc atom is a distance of 0.26649 nanometers away from its next nearest zinc atoms. Therefore, the atoms of our smashed penny will be almost exactly 600,000 times too far apart to maintain stable bonds and constitute a solid piece of metal. With this kind of separation, we don't have a solid penny at all. We have a very dilute zinc gas spread over the earth. These widely separated atoms would blow around, dissolve into the ocean, mix with the clouds, and react with other atoms, so that we no longer have any type of distinct object that we would say is covering the earth. For this reason, you cannot hammer and flatten a penny until it covers the entire. The earth is simply too big and a penny has simply too few atoms to accomplish this task. Even if we break each zinc atom into 30 hydrogen atoms (ignoring all the messy details of the nuclear reactions involved), the atoms are still about a hundred thousand times too far apart to form stable chemical bonds. Besides, hydrogen atoms don't bond to form a solid chunk of material under normal conditions. These thoughts lead to another question: How much area can a smashed penny cover and still remain a solid chunk of material? To calculate this, we again realize that the thinnest a material can get is one atom thick. Also, the distance that zinc atoms need to be from each other and still stay bonded as a solid is 0.26649 nanometers, as already mentioned. This means that as part of a hexagonal planar arrangement of atoms, each zinc atom needs to occupy 0.0615 square nanometers of area. Multiply this number by the 2.3044 x 1022 atoms in a penny and we get a total area of 1417 square meters, which is about a quarter of the size of an American football field. In other words, if you had a special machine that carefully hammered a penny until it was everywhere just an atom thick, it would only cover a quarter of a football field. Keep in mind that at this thickness, you would be hard pressed to even see the penny and you would rip the penny when walking on it without feeling any resistance (think of walking on aluminum foil, but much, much thinner). To cover the entire earth's surface with one-atom-thick smashed pennies, you would need at least 360 billion pennies.
What is the shape of an electron?	Depending on how you define "shape", an electron either has no shape, or an electron can take on various wave shapes. The shape of an electron is never statically round like an orange. The reason for this is that an electron is not a solid little ball, despite being so often portrayed this way in the popular media and in elementary-level science texts. Rather, electrons are quantum objects. Along with all other quantum objects, an electron is partly a wave and partly a particle. To be more accurate, an electron is neither literally a traditional wave nor a traditional particle, but is instead a quantized fluctuating probability wavefunction. This wavefunction looks in certain ways like a wave and in other ways like a particle. An electron looks like a particle when it interacts with other objects in certain ways (such as in high-speed collisions). When an electron looks more like a particle it has no shape, according to the Standard Model. In this context, physicists call an electron a "point particle," meaning that it interacts as if it is entirely located at a single point in space and does not spread out to fill a three-dimensional volume. If you find the concept of a fixed amount of mass being contained in the infinitely small volume of a single point illogical, then you should. But you have to realize that the electron is not literally a solid ball. This means that the electron's mass is not literally squeezed into an infinitely small volume. Rather, in certain cases where the electron looks somewhat like a particle, it interacts as if it were completely located at a single point. Therefore, in the sense of particle-like interactions, an electron has no shape. Note that an electron is a fundamental particle; it is not made out of anything else (according to our current experiments and theories). All fundamental particles interact as shapeless points when acting like particles. But not all quantum objects are fundamental, and therefore not all quantum objects are point particles. The proton, for instance, is not fundamental, but is instead composed of three quarks. The existence of particles inside a proton means that a proton must spread out to fill a certain space and have a certain shape. A proton is not a point particle, but is in fact a sphere with a radius of 8.8 × 10-16 meters. (Note that as a quantum object, a proton is not a solid sphere with a hard surface, but is really a quantized wave function that interacts in particle-like collisions as if it were a cloud-like sphere.) If the electron was composed of other particles, it could indeed have a shape when interacting like a particle. But it doesn't. The electron is a point particle. When an electron is behaving more like a wave, it can have all sorts of shapes, as long as its shape obeys the electron wave equation. An electron's wave equation, and therefore its shape, is a function of its energy and the shape of the potential well trapping it. For instance, when an electron is bound in a simple hydrogen atom, an electron can take on the familiar orbitals taught in elementary physics and chemistry classes, such as the shape shown on the right. In fact, the word "orbital" in this context really just means "the shape of an electron when acting as a wave bound in an atom". Each atomic orbital is not some mathematical average of where the electron has been, or some average forecast of where the electron may be. Each orbital is the electron, spread out in the quantum wavefunction state. In the sense of its wave-like state, an electron in a hydrogen atom can have the shape of layered spheres (the "s" states), layered dumbbells (the "p" states), layered four-leaf clovers (the "d" states), and other shapes at higher energies. In other atoms and molecules, an electron can take on even more complex shapes. An electron can also be trapped by other objects besides atoms. For instance, electrons trapped in the potential wells of a quantum cascade laser take on shapes that look more like traditional waves. An example of electron wavefunction shapes in a quantum cascade laser is shown on the right. Note that when scientists or journalists say "the shape of an electron is round," they are not talking about the literal shape. They are talking about the electric field distribution created by a free electron, which is entirely different from the actual shape.	tag/atom/	context: tag/atom/ question: What is the shape of an electron?	Depending on how you define "shape", an electron either has no shape, or an electron can take on various wave shapes. The shape of an electron is never statically round like an orange. The reason for this is that an electron is not a solid little ball, despite being so often portrayed this way in the popular media and in elementary-level science texts. Rather, electrons are quantum objects. Along with all other quantum objects, an electron is partly a wave and partly a particle. To be more accurate, an electron is neither literally a traditional wave nor a traditional particle, but is instead a quantized fluctuating probability wavefunction. This wavefunction looks in certain ways like a wave and in other ways like a particle. An electron looks like a particle when it interacts with other objects in certain ways (such as in high-speed collisions). When an electron looks more like a particle it has no shape, according to the Standard Model. In this context, physicists call an electron a "point particle," meaning that it interacts as if it is entirely located at a single point in space and does not spread out to fill a three-dimensional volume. If you find the concept of a fixed amount of mass being contained in the infinitely small volume of a single point illogical, then you should. But you have to realize that the electron is not literally a solid ball. This means that the electron's mass is not literally squeezed into an infinitely small volume. Rather, in certain cases where the electron looks somewhat like a particle, it interacts as if it were completely located at a single point. Therefore, in the sense of particle-like interactions, an electron has no shape. Note that an electron is a fundamental particle; it is not made out of anything else (according to our current experiments and theories). All fundamental particles interact as shapeless points when acting like particles. But not all quantum objects are fundamental, and therefore not all quantum objects are point particles. The proton, for instance, is not fundamental, but is instead composed of three quarks. The existence of particles inside a proton means that a proton must spread out to fill a certain space and have a certain shape. A proton is not a point particle, but is in fact a sphere with a radius of 8.8 × 10-16 meters. (Note that as a quantum object, a proton is not a solid sphere with a hard surface, but is really a quantized wave function that interacts in particle-like collisions as if it were a cloud-like sphere.) If the electron was composed of other particles, it could indeed have a shape when interacting like a particle. But it doesn't. The electron is a point particle. When an electron is behaving more like a wave, it can have all sorts of shapes, as long as its shape obeys the electron wave equation. An electron's wave equation, and therefore its shape, is a function of its energy and the shape of the potential well trapping it. For instance, when an electron is bound in a simple hydrogen atom, an electron can take on the familiar orbitals taught in elementary physics and chemistry classes, such as the shape shown on the right. In fact, the word "orbital" in this context really just means "the shape of an electron when acting as a wave bound in an atom". Each atomic orbital is not some mathematical average of where the electron has been, or some average forecast of where the electron may be. Each orbital is the electron, spread out in the quantum wavefunction state. In the sense of its wave-like state, an electron in a hydrogen atom can have the shape of layered spheres (the "s" states), layered dumbbells (the "p" states), layered four-leaf clovers (the "d" states), and other shapes at higher energies. In other atoms and molecules, an electron can take on even more complex shapes. An electron can also be trapped by other objects besides atoms. For instance, electrons trapped in the potential wells of a quantum cascade laser take on shapes that look more like traditional waves. An example of electron wavefunction shapes in a quantum cascade laser is shown on the right. Note that when scientists or journalists say "the shape of an electron is round," they are not talking about the literal shape. They are talking about the electric field distribution created by a free electron, which is entirely different from the actual shape.
What is the strongest magnetic field possible? Is there a limit?	There is no firmly-established fundamental limit on magnetic field strength, although exotic things start to happen at very high magnetic field strengths. A magnetic field exerts a sideways force on a moving electric charge, causing it to turn sideways. As long as the magnetic field is on, this turning continues, causing the electric charge to travel in spirals. Once traveling in spirals, an electric charge acts like a small, oriented, permanent magnet and is therefore repelled from regions of high magnetic field gradient. Therefore, electric charges tend to spiral around magnetic field lines and be pushed away from regions where magnetic field lines bunch up. These two effects cause electric charges to get trapped along magnetic field lines that are strong enough. Examples of this effect include ions trapped in earth's ionosphere, radiation trapped in earth's radiation belts, hot plasma looping over the sun's surface in solar prominences, and plasmas contained in the laboratory using magnetic traps. The stronger the magnetic field gets, the more violently an electric charge is pushed sideways by the magnetic field, the faster and tighter it therefore spirals around in circles, and the stronger it gets pushed away from regions of high magnetic field gradient. Interestingly, all normal objects are made out of atoms, and all atoms are made out of electric charges: electrons and protons. Therefore, strong enough magnetic fields have the ability to deform and even break objects. When a magnetic field gets stronger than about 500,000 Gauss, objects get ripped to pieces by the intense forces. For this reason, scientists cannot build a machine that creates a magnetic field stronger than 500,000 Gauss and survives longer than a fraction of a second. Strong enough magnetic fields therefore destroy objects as we know them. Note that the magnetic fields used in medical MRI scanners are much weaker than 500,000 Gauss and are perfectly safe when used properly. While the destructive nature of strong magnetic fields places a practical limit on how strong of a field earthlings can create, it does not place a fundamental limit. Magnetic fields that surpass about a billion Gauss are so strong that they compress atoms to tiny needles, destroying the ordinary chemical bonds that bind atoms into molecules, and making chemistry as we know it impossible. Each atom is compressed into a needle shape because the electrons that fill most of the atom are forced by the magnetic field to spin in tiny circles. While such extremely strong magnetic fields are not possible on earth, they do exist in highly-magnetized stars called magnetars. A magnetar is a type of neutron star left over from a supernova. The intense magnetic field of a magnetar is created by superconducting currents of protons inside the neutron star, which were established by the manner in which the matter collapsed to form a neutron star. In a review paper presented at the Fifth Huntsville Gamma-Ray Burst Symposium, Robert C. Duncan summarized many of the theoretically-predicted exotic effects of magnetic fields that are even stronger: "In particular, I describe how ultra-strong fields At the most extreme end, a magnetic field that is strong enough could form a black hole. General Relativity tells us that both energy and mass bend spacetime. Therefore, if you get enough energy in one region, then you bend spacetime enough to form a black hole. The black hole does not destroy the magnetic field, it just confines it. Even stronger magnetic fields create larger black holes. It is currently not known whether this is actually possible, as there may be unknown mechanisms that limit a magnetic field from ever getting this strong. Certain unconfirmed extensions of current theories state that there is a fundamental limit to the strength of a magnetic field. For instance, if a magnetic field gets too strong, it may create magnetic monopoles out of the vacuum, which would weaken the magnetic field and prevent it from getting any stronger. However, since there is currently no evidence that magnetic monopoles actually exist, this purported limit is likely not real. We may someday discover a fundamental limit to the magnetic field strength, but there is currently no experimental evidence or well-established theoretical prediction that a limit exists.	tag/atom/	context: tag/atom/ question: What is the strongest magnetic field possible? Is there a limit?	There is no firmly-established fundamental limit on magnetic field strength, although exotic things start to happen at very high magnetic field strengths. A magnetic field exerts a sideways force on a moving electric charge, causing it to turn sideways. As long as the magnetic field is on, this turning continues, causing the electric charge to travel in spirals. Once traveling in spirals, an electric charge acts like a small, oriented, permanent magnet and is therefore repelled from regions of high magnetic field gradient. Therefore, electric charges tend to spiral around magnetic field lines and be pushed away from regions where magnetic field lines bunch up. These two effects cause electric charges to get trapped along magnetic field lines that are strong enough. Examples of this effect include ions trapped in earth's ionosphere, radiation trapped in earth's radiation belts, hot plasma looping over the sun's surface in solar prominences, and plasmas contained in the laboratory using magnetic traps. The stronger the magnetic field gets, the more violently an electric charge is pushed sideways by the magnetic field, the faster and tighter it therefore spirals around in circles, and the stronger it gets pushed away from regions of high magnetic field gradient. Interestingly, all normal objects are made out of atoms, and all atoms are made out of electric charges: electrons and protons. Therefore, strong enough magnetic fields have the ability to deform and even break objects. When a magnetic field gets stronger than about 500,000 Gauss, objects get ripped to pieces by the intense forces. For this reason, scientists cannot build a machine that creates a magnetic field stronger than 500,000 Gauss and survives longer than a fraction of a second. Strong enough magnetic fields therefore destroy objects as we know them. Note that the magnetic fields used in medical MRI scanners are much weaker than 500,000 Gauss and are perfectly safe when used properly. While the destructive nature of strong magnetic fields places a practical limit on how strong of a field earthlings can create, it does not place a fundamental limit. Magnetic fields that surpass about a billion Gauss are so strong that they compress atoms to tiny needles, destroying the ordinary chemical bonds that bind atoms into molecules, and making chemistry as we know it impossible. Each atom is compressed into a needle shape because the electrons that fill most of the atom are forced by the magnetic field to spin in tiny circles. While such extremely strong magnetic fields are not possible on earth, they do exist in highly-magnetized stars called magnetars. A magnetar is a type of neutron star left over from a supernova. The intense magnetic field of a magnetar is created by superconducting currents of protons inside the neutron star, which were established by the manner in which the matter collapsed to form a neutron star. In a review paper presented at the Fifth Huntsville Gamma-Ray Burst Symposium, Robert C. Duncan summarized many of the theoretically-predicted exotic effects of magnetic fields that are even stronger: "In particular, I describe how ultra-strong fields At the most extreme end, a magnetic field that is strong enough could form a black hole. General Relativity tells us that both energy and mass bend spacetime. Therefore, if you get enough energy in one region, then you bend spacetime enough to form a black hole. The black hole does not destroy the magnetic field, it just confines it. Even stronger magnetic fields create larger black holes. It is currently not known whether this is actually possible, as there may be unknown mechanisms that limit a magnetic field from ever getting this strong. Certain unconfirmed extensions of current theories state that there is a fundamental limit to the strength of a magnetic field. For instance, if a magnetic field gets too strong, it may create magnetic monopoles out of the vacuum, which would weaken the magnetic field and prevent it from getting any stronger. However, since there is currently no evidence that magnetic monopoles actually exist, this purported limit is likely not real. We may someday discover a fundamental limit to the magnetic field strength, but there is currently no experimental evidence or well-established theoretical prediction that a limit exists.
What makes radioactive atoms get old so quickly and decay?	Atoms don't age. Atoms radioactively decay when a lower-energy nuclear configuration exists to which they can transition. The actual decay event of an individual atom happens randomly and is not the result of the atom getting old or changing through time. The phrases "getting old" or "aging" are rather vague and could refer to a lot of things. For biological organisms and mechanical devices, "aging" usually refers to the progression of complex internal processes. A single atom does not have any internal biological or mechanical systems, and therefore does not age in this way. There is no clock inside an atom telling it that it is now a minute older. For other objects, "aging" refers to the wearing down or corrosion of the object because of repeated use or exposure to the environment. Atoms are too simple to wear down, corrode, or steadily change. No matter what reasonable definition we use for the word "aging", individual atoms don't do it. Note that aging is different from experiencing time. Everything, including atoms, experiences time. An atom can sit at on my desk on Tuesday and then fall off and sit on the carpet on Wednesday, because it experiences time. However, an isolated atom does not deterministically change from one day to the next. (An atom's electrons and nucleons can be excited, but these excited particles quickly relax back down to the ground state. Therefore, excitations do not fundamentally change the atom. Also, an atom's nucleus can change via nuclear reactions, but these changes are random rather than the result of aging.) If atoms don't age, how do radioactive atoms know when to decay? How can we possibly say that a radioactive isotope has a lifetime if it does not age? The answer is that radioactive atoms don't know when to decay. In fact, an individual radioactive atom does not decay at a particular, predictable time. It's not like an atom has an internal clock ticking away telling it when it's time to fall apart. Rather, an atom decays at a random time, completely independent of how long it has been in existence. Radioactive decay is governed by random, statistical effects and not by internal deterministic machinery. A particular radioactive atom can and will decay at any time. The "lifetime" of a radioactive isotope is not a description of how long a single atom will survive before decaying. Rather, it is a description of the average amount of time it takes for a significant portion of a group of radioactive atoms to decay. A characteristic lifetime does not come about by the progression of internal machinery, but by the statistical behavior of a large group of atoms governed by probability. An analogy may be helpful. A standard six-sided die will show a single number between "1" and "6" when rolled. Let us agree that when we roll a "6", we smash the die to pieces and the game is over for that particular die. We begin rolling the die and get a "3", and then a "1" and then a "5". Next we roll a "6" and destroy the die as agreed upon. Since the die was destroyed after four rolls, we say that this particular die had an individual lifetime of four rolls. Now we get a new die and repeat the game. For this die, we roll a "2", then a "1", then "4", "3", "1", "5", and then finally a "6". This die therefore had an individual lifetime of seven rolls. When we repeat this game for many dice, we discover that the individual lifetime of a particular die can be anything from one roll to hundreds of rolls. However, if we average over thousands of individual lifetimes, we find that the dice consistently have an average lifetime of about six rolls. Since an individual die has no internal machinery telling it to show a "6" after a certain number of rolls, the individual lifetime of a die is completely random. However, since the random events are governed by probabilities, we can experimentally find a fixed characteristic average lifetime of a group of dice by averaging over a large ensemble of dice. We can also mathematically find the average lifetime by calculating probabilities. For the die, there are six possible outcomes to a single roll, each with equal probability of occurring. Therefore, the probability of rolling a "6" and destroying the die is 1 out of 6 for every roll. For this reason, we expect it to take six rolls on average to roll a 6 and destroy the die, which is just what we found experimentally. The dice do not have a predictable average lifetime because they age, but because they experience probabilistic events. In the same way, atoms do not age and yet we can identify a meaningful decay lifetime because of the probabilities.	tag/atom/	context: tag/atom/ question: What makes radioactive atoms get old so quickly and decay?	Atoms don't age. Atoms radioactively decay when a lower-energy nuclear configuration exists to which they can transition. The actual decay event of an individual atom happens randomly and is not the result of the atom getting old or changing through time. The phrases "getting old" or "aging" are rather vague and could refer to a lot of things. For biological organisms and mechanical devices, "aging" usually refers to the progression of complex internal processes. A single atom does not have any internal biological or mechanical systems, and therefore does not age in this way. There is no clock inside an atom telling it that it is now a minute older. For other objects, "aging" refers to the wearing down or corrosion of the object because of repeated use or exposure to the environment. Atoms are too simple to wear down, corrode, or steadily change. No matter what reasonable definition we use for the word "aging", individual atoms don't do it. Note that aging is different from experiencing time. Everything, including atoms, experiences time. An atom can sit at on my desk on Tuesday and then fall off and sit on the carpet on Wednesday, because it experiences time. However, an isolated atom does not deterministically change from one day to the next. (An atom's electrons and nucleons can be excited, but these excited particles quickly relax back down to the ground state. Therefore, excitations do not fundamentally change the atom. Also, an atom's nucleus can change via nuclear reactions, but these changes are random rather than the result of aging.) If atoms don't age, how do radioactive atoms know when to decay? How can we possibly say that a radioactive isotope has a lifetime if it does not age? The answer is that radioactive atoms don't know when to decay. In fact, an individual radioactive atom does not decay at a particular, predictable time. It's not like an atom has an internal clock ticking away telling it when it's time to fall apart. Rather, an atom decays at a random time, completely independent of how long it has been in existence. Radioactive decay is governed by random, statistical effects and not by internal deterministic machinery. A particular radioactive atom can and will decay at any time. The "lifetime" of a radioactive isotope is not a description of how long a single atom will survive before decaying. Rather, it is a description of the average amount of time it takes for a significant portion of a group of radioactive atoms to decay. A characteristic lifetime does not come about by the progression of internal machinery, but by the statistical behavior of a large group of atoms governed by probability. An analogy may be helpful. A standard six-sided die will show a single number between "1" and "6" when rolled. Let us agree that when we roll a "6", we smash the die to pieces and the game is over for that particular die. We begin rolling the die and get a "3", and then a "1" and then a "5". Next we roll a "6" and destroy the die as agreed upon. Since the die was destroyed after four rolls, we say that this particular die had an individual lifetime of four rolls. Now we get a new die and repeat the game. For this die, we roll a "2", then a "1", then "4", "3", "1", "5", and then finally a "6". This die therefore had an individual lifetime of seven rolls. When we repeat this game for many dice, we discover that the individual lifetime of a particular die can be anything from one roll to hundreds of rolls. However, if we average over thousands of individual lifetimes, we find that the dice consistently have an average lifetime of about six rolls. Since an individual die has no internal machinery telling it to show a "6" after a certain number of rolls, the individual lifetime of a die is completely random. However, since the random events are governed by probabilities, we can experimentally find a fixed characteristic average lifetime of a group of dice by averaging over a large ensemble of dice. We can also mathematically find the average lifetime by calculating probabilities. For the die, there are six possible outcomes to a single roll, each with equal probability of occurring. Therefore, the probability of rolling a "6" and destroying the die is 1 out of 6 for every roll. For this reason, we expect it to take six rolls on average to roll a 6 and destroy the die, which is just what we found experimentally. The dice do not have a predictable average lifetime because they age, but because they experience probabilistic events. In the same way, atoms do not age and yet we can identify a meaningful decay lifetime because of the probabilities.