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Is every speck of light in this picture a star? | Not every speck of light is **a** star, some of them are *multiple* stars that appear to be stacked on top of each other due to our perspective, and some are *entire galaxies* in the background. And then consider that [almost all of those stars have planets](_URL_3_). Do you feel small yet? I certainly do. |
Why don't spacecraft use nuclear fuel? | Many do; probes and robots such as Curiosity use nuclear decay to provide electrical energy. However it really isn't suitable for propulsion in anything but the most long term, low thrust applications such as with ion drives. Manned vehicles of course would require shielding from the nuclear material and that is heavy. Generally the weight limits make it more attractive to use solar and chemical power sources for manned missions. |
Why don't spacecrafts use nuclear fuel? | Some do. Some spacecraft use radioactive decay as a power source. The craft is equipped with a radioactive material, often plutonium, but some others work as well. This material slowly decays and the energy that is released in the decay is collected and used for the spacecraft. The power output of such a system is quite low, but it lasts for a long time. It's therefore primarily useful for long duration missions, such as probes that are sent to distant planets. Actual nuclear (fission) reactors have been used as well, primarily by the Soviet Union in satellites. The problem with nuclear reactors in spacecraft is that they can be quite complex to design and build and there is the ongoing public concern of potential fallout should a spacecraft explode shortly after launch. |
The truth about Alcohol and Antibiotics: Is it ok to mix them or not? | It really depends on the antibiotic, there is a very small percentage of antibiotics that when mixed with alcohol are/can be lethal. I'm not an expert on the subject but have done some research in past about amoxicillin, and found out that most antibiotics are ok with alcohol. Just need to take them 1h or so before drinking the alcohol, so they can be fully absorbed. Anyway, a medical / pharmacology expert point of view would be good to see here. |
Is the universe expanding at an increasing rate or decreasing rate? | [Recent nobel prize](_URL_0_) Learned about this a few weeks ago in a lecture. |
Is terraforming Mars possible, in theory? | Not really. You need a strong magnetic field to stop the sun from blowing the atmosphere away, currently mars does not have a molten core and a very weak magnetic field.. So while it may theoretically be possible to reheat the core of mars and make that iron spin, i do not see how. |
Is terraforming Mars possible? | It's certainly possible. That is quite different from feasible. |
Why don't objects in orbit accelerate towards Earth? | It doesn't increase in speed because the force is perpendicular to the velocity vector. However it does accelerate. The fact that it's rotating implies that the velocity vector is changing direction constantly. That change of velocity divided by time (or its derivative, it's the same if it's constant) gives the acceleration. The above is true for perfectly circular orbits. If you have an elliptical orbit, then it does increase its speed as it approaches the perigee. This is because the force is not perfectly perpendicular to the speed in this path of the orbit. The same way it will decrease in speed when approaching the apogee. |
How are orbiting objects not accelerating due to gravity? | Acceleration is a change in velocity, not speed. Velocity is a vector quantity (i.e. it has both a direction and a magnitude) and so the change can either be in the magnitude (a change in speed) or the direction. Unfortunately, we don't have a separate word for the vector acceleration, so that fact that you associate acceleration with a changing speed (scalar 'acceleration') makes this less intuitive. Only force in the same direction as the movement will change the speed; however, in the case of the orbiting satellite, the force and velocity are always at right angles, so only the direction changes. |
Where does tire tread go as car tires wear? | The reason you don't see roads get darker is because of the nature of asphalt. It contains a bunch of light colored rocks bound together with black tar. When it is new, it is very dark, as all rocks are covered with tar. As the road is used, the tar is worn off from above the rocks, and the light color of the rocks becomes visible. The rubber is worn off during usage, but it's happening so slow that you don't notice it. For a regular tire, you are only losing a couple millimeters of rubber over the life of the tire, which could be 60,000 miles. It's more like a dust than like skidmarks. |
Where does all of the tread rubber go from tires on the road? | It basically turns to dust, which as you would imagine, goes everywhere near the road. It also washes into the storm water drains when it rains, ending up in our waterways, along with all of the oil and other junk that comes from cars. |
How did the Ozone layer originally form if the oxygen had to come from organisms exposed to harmful UV light? | Because they existed in water that protected them! |
Are no two fingerprints alike because of the sheer number of possibilities or does something in our DNA create unique fingerprints? | Finger prints are random. They form before birth based on the middle layer of skin. If they were represented by a number (folds/directions, etc), the number would be so big that, if each human were randomly assigned a number, no two humans would have the same one. Is it *possible*? Sure. Will it happen? No. |
Given that two thirds of the planet is covered with Water why didn't more intelligent life forms evolve in the water? | It turns out that the ability to finely manipulate objects is pretty well correlated with intelligence. For instance simians and humans have opposable thumbs, elephants have their trunk, and octopuses have their tentacles. It makes sense that having this manipulative ability would spur the development for a more abstract type of thought. It may be that since there are fewer sea creatures with this physical ability, fewer of them developed higher intelligence. Obviously whales and dolphins are the exception here, and I look forward to someone else explaining why they _do_ have such intelligence. |
How far have the continents drifted in the last 3-4 thousand years? | [This map](_URL_0_) shows drift rates and directions with respect to Africa in mm/yr. South America is drifting 30+ mm/yr, or 3+ m every thousand years. So ~10 m. |
How much have continents moved since the dawn of civilization 12,000 years ago? | They actually move more than one might think. There is a nice summary of how we know this, and how we measure it on Observation Deck’s [How Do We Know The Continents Are Moving?](_URL_0_) webpage. NASA uses sensors around the world and you can now look up the movement of these sensors for any plate your interested in, by clicking on the appropriate sensor on JPL’s [GPS Time Series](_URL_1_) website. You can back calculate to 12,000 years ago, from JPL’s mm/year numbers for the plate you are interested in. Maui, in the Pacific plate for instance, is moving 34.7 mm/year North and 62.3 mm/year West, which works out to 71.3 mm/year. So assuming it has been moving at about the same rate, in 12,000 years it has moved 856 meters. Similarly, Chicago is moving at a rate of 15.7 mm/year, so the center of the North American plate has only moved 188 meters. |
Can insects get concussions? | No. A concussion is caused by [trauma to the cranium](_URL_0_) that causes the brain to contact the inside of the skull with enough force to cause an injury. Since insects lack [endoskeletons and dedicated brain cases](_URL_1_), any trauma that may be sufficient to cause a concussion will simply kill the insect outright. In addition, since insects often *don't* have dedicated cerebral ganglia (present in the diagram above), trauma to their nervous systems are not as debilitating since their nervous system isn't centralized. |
Why do we have to fry food in oil? | As a chef the reasons we were told during my apprenticeship are as follows: - provides a barrier to prevent sticking - adds flavour - with steak it encourages the millard effect which provides a nice crust (this is more created by the air flowing around the item being fried) - protects the item from drying out. |
Why can't we fry stuff in substances like water, as opposed to frying them in oil? | Not a very scientific answer, but "frying" in oil is the same as "boiling" in water. Water doesn't boil at near hot enough temperature as oil boils, which causes that nice crunchy texture to food. Frying and boiling mean the same thing in cooking, essentially. |
How is a mirror both silver AND able to reflect everything at the same time? | I believe your question is asking how can a mirror be colored silver, and at the same time show a reflection. The way vision works is that light hits an object, bounces off, and then hits our eyes. When this happens some of the colors of light get absorbed, and what is left gets reflected. A green leaf will absorb every color except for green, which then bounces off for us to see. A mirror is a very very smoothly polished surface, so that light bouncing off does not go in random directions. Instead all of the light rays bounce in the same way, so the light we see is almost exactly the same as what originally bounced off the object. A mirror also does not absorb very much light, so most of it bounces off unchanged. If the silver part of a mirror was roughed up it would start to appear more "silver" because the light would be bouncing around randomly instead of all reflecting the same way. TLDR Mirrors don't absorb colors of light, so their color is whatever hits them. |
From a physics perspective, is there a difference between liquids and gases? | Macroscopically, liquids have surface tension and gasses do not, so a liquid will take a form that minimizes surface area, while a gas will just expand to fill space. Microscopically, the molecular or atomic components of a liquid are touching each other (to the extent that touching can be defined at that scale) and attracting each other (through van der Waals and similar forces). This affects how radiation gets diffracted through it, so liquids and gasses can be distinguished in scattering experiments. |
Is breakfast really the most important meal of the day? Why/Why not? How long after waking is the ideal "breakfast time"? | Some nutritionists suggest that large breakfasts decrease appetite through the rest of the day. However weight loss studies show that if you skip breakfast and still end the day with a calorie deficit, it is just as effective as a tapered meal size from breakfast to dinner. So basically no, it is not the more important meal, but it may help some people eat less. EDIT: As jarebear pointed out, this pertains to weightloss aspect only. There are no studies that demonstrate a causal relationship between breakfast eating and either weight loss or better nutrition - though it is suggested that people who eat breakfast are generally hoopy froods who know where their towels are. |
What's the next term in this series calculating the proportion of prime numbers? | What you are looking for is the [inclusion-exclusion formula](_URL_3_). What it comes down to is: * Fraction of numbers not divisible by 2: 1 - 1/2 * Fraction of numbers not divisible by 3: 1 - 1/3 * Fraction of numbers not divisible by 2 or 3: 1 - 1/2 - 1/3 + 1/2 * 1/3 * Fraction of numbers not divisible by 5: 1 - 1/5 * Fraction of numbers not divisible by 2, 3, or 5: 1 - 1/2 - 1/3 - 1/5 + 1/2 * 1/3 + 1/2 * 1/5 + 1/3 * 1/5 - 1/2 * 1/3 * 1/5 And so on. |
Why does pasteurized and sealed food still have a shelf life? | There are still trace amounts of bacteria. Heating the caviar is not enough since bacteria can get into the container when filling. Now unless they used a hot fill (putting the food product into its container at 180 degrees Fahrenheit, and forming a vacuum to ensure as little oxygen as possible) there is still enough bacteria in there to replicate enough that the food's quality or safety is compromised. |
Do wild animals often die of old age? | Nothing "dies of old age", there is always a specific cause. Animals in general die "early" ie. they dont live well past the age at which they can no longer rear young. In the case of prey they usually fall victim to predators due deteriorating condition. Interestingly, it is only recently that H.sapiens have started to live well past 30-50 years old, and it is a possibility that genes that have an advantageous effect in development but a deleterious effect after 30-50 years old may finally be showing themselves at the phenotypic level in the huge numbers of people with conditions such as diabetes and cancers. |
Could a planet be so close to the star it orbits that it would be torn apart by the slightly higher gravity on the side which faces the star? | Spaghettification is more a black hole thing, I'm not aware of it being used to apply to non-black hole cases. As to the planet being torn apart, the distance one body has to be from a larger one and NOT have this happen is called the Roche limit. For the sun, that body has to be within a couple radii. The distance does depend, a bit, on what sort of object it is. A rocky planet is harder to break up than a gas planet, for example. Wiki's page on Roche limits gives a few sample calculations. Tidal locking occurs at a much further distance, although on a base level I'd consider the two related phenomena since they're both tied to distortions due to gravity being strongest on the closest side. |
Why are clouds all fluffy on top but flat on the bottom? | Think of it like oil sitting on water. The denser, warmer air is pulled down by gravity and essentially acts like liquid with the colder, less-dense air floats to the top. Different cloud densities are sitting on top of layers of air with greater density. That's why there are the different types of clouds at different altitudes. |
off camera lenses are round, why do they take rectangular pictures? | The sensor that these lenses project their image on is rectangular. It's possible to construct a circular sensor and obtain circular pictures, but people tend to prefer rectangular pictures. On the other hand, producing rectangular lenses is more difficult than producing circular ones, so we end up with circular lenses that project an circular image that is larger than the sensor, while the rectangular sensor registers the central part of the image. You can see the effect of the lenses being circular in the image, to some extent. A phenomenon called vignetting causes the image to darken as you move away from the center. When taking a picture of a uniform background, you can see the corners of the image being slightly darker than the center (the strength of this effect depends on the quality of the lens and the apareture setting used). |
When stars are formed in the universe, why is there a limit to its size? | Because of thermal and radiation pressure. When a gas cloud collapses into a protostar, considerable energy is released-- first from the sheer gravitational energy of all that falling gas, and then once the star turns on from the energy released by fusion. This pressure will push gas away, which limits the rate at which a star can grow. See the [Eddington Limit](_URL_0_) for more-- because it limits luminosity, it therefore limits the rate of gas infall, since a protostar's luminosity is produced by the energy of infalling gas. |
Why does canned food that has been properly sealed still spoil eventually? | What makes you think that canned food spoils? If you're going by an expiry date on the can, this is not there because the food spoils, but due to certain laws on labelling food and beverage products (bottles of water do not spoil either, but they have expiry dates as well). Properly canned food is sterile, so it will not spoil due to bacteria. It may break down physically and chemically over very long periods of time, but AFAIK there is no particular reason that canned food from today will be inedible 100+ years from now if the cans and lining remain intact. Canned food from the 19th century has been found and found to be basically edible. Interesting article that was on _URL_1_ a few years ago: _URL_0_ |
How do people mentally and physically develop in a coma? | There is no reason why body wouldn't age, but it leads to muscle atrophy, so it wouldn't be exactly a body of a normally-developed 18-year old. Can't say anything about mental development, not being an expert, but I do not believe it advances as that person wouldn't be conscious, therefore not experiencing anything leading to such development. |
Is it possible to see Stars in other galaxies with modern telescopes/detection devises? | Yes, we can more or less see individual stars in the Andromeda Galaxy at a few pixels resolution. For other galaxies I don't know of photos existing. Here is hubble's view of he Andromeda galaxy: _URL_0_ And: _URL_1_ We can see individual stars in Andromeda only starting half way away from it's galactic center, as the center is too dense to highlight them. Even with our best resolution we end up with blurry 5 pixel stars, so there is not much to look at, but it's cool in that you can tell apart individual red giants and white dwarfs. The larger stars you see are in our own galaxy. |
Why aren't all the planets in a solar system made of similar mixtures of elements? | The principle control is the temperature gradient present in the protosolar nebula, with high temperatures near the Sun and low ones in the outer regions. The planets formed as [materials condensed](_URL_1_) (solidified) out of the hot gases in the PSN. At about 5 AU from the Sun, temperatures were low enough for frozen water to condense (water was very abundant in the PSN); this is sometimes called the ["frost" line](_URL_0_). This allowed the outer planets to gain mass quickly and become large. Their increased gravity let them retain primordial gases such as H and He. |
Why does my voice get deeper when I have a cold? | The infection from having the cold causes both swelling of the vocal chords, and a coating of mucus. This makes them heavier and thus they move slower than normal, resulting in lower tones. |
Why do our voices become deeper and more coarse when we get a cold with a lot phlegm? | Your vocal cords are located in the larynx of the throat which is just above your trachea, the airway to the lungs, through the bronchi, and smaller bronchioles. When you are sick your airways become inflamed, as well as filled with mucous being coughed up from the lungs due to the infection. I believe your voice gets deeper as the inflammation along your respiratory track would manifest in the larynx, and vocal cords as well, changing how well they perform. When they are inflamed they cannot vibrate as fast as normal, causing your voice to sound deeper. I'm a Health Science student going into my last year, I believe that's what happens but feel free to correct me ! |
Why can't earplugs block out sound completely? Is there a way to plug your ears to entirely block out sound? | Sound consists of pressure waves. So when you used earplugs, they act as intermediary to dissipate pressures that would be potentially harmful to the inner ear. If you want silence, you should invest in noise cancelling headphones, which match incoming noise with destructive interference. |
When classifying a moon, is it based around the relative size to the planet? Or do all moons have to be a certain size or larger? | The word moon clearly describes an object that orbits something other than the main star in a system. Moons are not classified by their mass, size or composition. *Ganymede for example is the biggest one* with a diameter of 5,262 kilometers and we have just found that there are some with only a diameter of 1 kilometers orbiting Jupiter. Moons are classified by their motion around the object they orbit. That motion could be in same direction or contrary. |
Are the tectonic plates pretty much where they're going to stay or will the earth look quite different a few million years from now? | The tectonic plates are always in motion. We can see rifts being formed (large valleys), mountains growing, and oceans disappearing. If you take a look at [this gif](_URL_0_) by Colin Reeves, you can see that the plates are certainly moving (keep in mind that the gif goes forwards and backwards, so look at the time (Ma) in the upper left hand corner). The rate of movement on the plates have been quite constant since we had a solidified crust, so for the past few billion years. There is a prediction that in the next 50-200 million years, that another supercontinent (where all of the landmasses are joined together) named Amasia will form. So, in 100 million years, the Earth will look very VERY different. |
Why do humans have to brush their teeth in order to keep it healthy while most (all?) animal naturally have good teeth? | From a human end, we don't have a lot of antibacterial components to our saliva. Also, we eat a lot of processed foods with simple carbohydrates (read sucrose) in them. These case acidogenic bacteria to produce acid and demineralize tooth structure. This demineralization over time causes cavities (a disease called caries). There are different ways to stop this process. Fluoride is the main way. It has a topical effect from drinking water constantly and prevents certain bacterial enzymes from working thus slowing down the acidogenic bacteria. Also, it is incorporated into the hydroxy apetite crystals forming fluoro apetite crystals which are mush less soluble in acid. Pets benefit from the fluoride in the water as well since they drink primarily tap water and no sodas like a lot of people. |
Why can our eyes handle mixed lighting better than cameras? | Your brain does a huge amount of processing of the input it gets from your eyes. Basically, the same image is coming through to your eyes/retina, but your brain has seen that kind of lighting and scene many many times before and "corrects" your perception for consistency. Similar to how you have a blind spot in each eye, but your brain simply fills it in based on what's around it & input from the other eye. |
Why is my plate (and food) hot when I open my microwave, but not the air inside like it would be in an oven? | Microwaves heat the water molecules (and other dipoles) in the food. The plate is better at conducting heat than the air is, so it will heat up relatively quickly by touching the food. Ovens, on the other hand, heat the air, which will indirectly heat the food. Edit: typo |
If an asteroid was to collide with a gas planet, what would happen? | In 1994, the comet Shoemaker-Levy 9 actually impacted on Jupiter. This impact was visible from Earth. Hence, a lot of research was done. I don't know the details but you can find all about it here: _URL_1_ Cheers Edit: The wiki page is probably easier to read: _URL_0_ |
Follow up question to the photon mass/energy question, Do photons have gravity associated with them? | Yes, photons exert a very small gravitational influence. [Here](_URL_0_) is a paper on the topic, which I don't think anyone has ever bothered simplifying. |
will a room completely made up of mirrors stay lit longer if the lights are turned off vs a room without mirrors. | Yes, but for an imperceptible amount of time. The light would bounce off the mirrors until it is fully absorbed (mirrors do not reflect perfectly). This would happen instantaneously to the human eye. |
Can a tree "die" of old age? | No living creature ever dies of old age. There is always something that causes death. Natural causes is the term used when attributing death from cardiac arrest or aneurysm in humans. Simply age can't kill you. What keeps trees living is their resiliency against drought and freeze which can cause embolisms, their wound repair mechanisms, and their ability to fight parasitism by bacteria, fungi, or animals. |
Putting pressure under my nose stops me from sneezing. Is there something similar for vomiting? | I work with medical personnel and they offered me [this.](_URL_0_) |
Why does fire look like fire?? | > Does it have to do with it thermal radiation of different wavelengths or something else? That would be it. Everything gives off radiation based on its temperature, the hotter you get, the shorter the wavelengths. For most normal earth temperatures, this radiation is infrared and invisible, but at around 1000K, it starts to reach the visible range. So when you see a flame, you are seeing envelopes of hot gas emitting light, blue in the hottest regions, then yellow and red as the regions get cooler. |
Why is fire the color it is? | So, as you expect, the variety of fuel-specific colours such as the blue from butane or green from copper and the standard flame orange are formed by different processes. In one hand you have excitation of bound electrons in ions and atoms and molecules that produce spectral lines. The other process that produces the orange/yellow colours is black body radiation. What happens is little particles of soot in the flame get heated to 1000+C and emit the black body colour appropriate for their temperature. There are some easy tests that provide evidence in support of this. A standard bunsen burner will have a blue flame with the oxygen valve open. However, if you shut the valve, the combustion is no longer complete meaning that more soot is left unburned and you get the standard yellow. If you hold something (non-flammable) in the yellow flame from a bunsen burner you will find yourself collecting a layer of soot. If you repeat this with the blue flame you won't find the same soot. |
How fast do galaxies move relative to each other? | The [Antennae Galaxies](_URL_0_) are moving towards each other at hundreds of kilometers per second ([source](_URL_2_)). Andromeda, our closest large neighbor galaxy, is moving towards us at around 300 km/s ([source](_URL_1_)). Our galaxy is about 100,000 lightyears across, which means it takes light 100,000 years to cross it, so nothing will cross that distance in less time. For reference, the speed of light is about c=300,000 km/s, so at 300 km/s, Andromeda is traveling at 0.001c, so the crossing time will be about 100 million years. |
Helium - How did it get here, where do we get it from today, and why hasn't it all settled to the top of our atmosphere in the billions of years that it has had to do so? | Helium that we produce comes mostly from the decomposition of Uranium-238 in the earth's crust. It accumulates in natural gas deposits and is extracted from the natural gas by freezing out everything else. All the helium that leaks into the atmosphere eventually escapes into space, since it is too light to be held by the Earth's gravity. |
Can single celled bacteria get cancer? | No, because cancer is defines as abnormal growth of cells inside of a multicellular organism. A 'cancerous' single cell organism just.. doesn't make sense. Maybe in a colonial organism, but that's not a truly independent cell. A cancer is just a single cell mutation where in a single cell line tries to grow and multiply uncontrollably. This is only important in a larger organism, for a single celled creature this is normal life. |
When I stub my toe, why does it take 1-2 seconds to feel pain, when I feel the hit itself instantly? | Pain gets transmitted by different fibers than general tactile sensation. The former uses smaller Ad or c fibers, while the latter uses larger Ab fibers. In terms of nerve conduction, larger myelinated fibers have much faster conduction than smaller unmyelinated fibers. Applying pressure to an injured area may also decrease (low levels of) pain. This is explained by the 'gate control theory' of pain sensation. When you stimulate the touch fibers, they actually inhibit the pain neuron in the spinal cord (that is receiving signal from peripheral sensory afferent fibers). Thus, adding a sensation of pressure can help reduce pain sensation. This gets a bit more complex at higher levels of pain, because then the C fibers will inhibit the inhibitory action of the A-beta fibers, thus resulting in override and transmission of pain signals. edit with numbers: Ad fibers: 2-30m/s (the fast pain/first pain neuroPSYK refers to below); C fibers 2m/s (slow pain/second pain); Ab fibers: 35-75m/s (touch sensation) |
If the universe is expanding and everything is moving away from eachother how do galaxies collide? | I don't know if I'm the best person to answer this but... It's really just the same concept of smaller stars colliding because of gravitational forces, just applied to a galaxy of stars as a whole. That's what they mean when galaxies collide. The two concepts are one in the same, just imagine a plethora of stars from two galaxies interacting with each other when they get near. As a side note, the space between stars is so enormous that when two galaxies "collide", many stars may not even interact with each other at all. As for everything moving away from each other, I believe that's a general trend, but when you factor in gravity, bodies tend to come together faster than the expansion away. But that part I'm not so certain about. Correct me if I'm wrong! This information I heard very long ago! EDIT: Here is some wiki information that will back it up... _URL_0_ |
If you have ten tickets to put into various raffles, do your odds change if you put one ticket in ten different raffle drawings that are capped at 100 entries each, versus putting all ten tickets into one raffle also capped at 100 entries (resulting in a 1/10 chance of winning)? | The important point here is the difference between chance of winning and expectation value of number of wins. It's not explicitly stated, but I'm assuming that all raffles fill up to 100 tickets and each raffle has a single winning ticket. If you're interested in maximizing the chance of winning (at least) 1 raffle, then it's better to participate in just 1 raffle with all 10 tickets. That way, you have a 1/10 chance of winning. If you spread them out, the chance to win at least 1 raffle is 1 minus the chance that you lose all 10, so 1 - (99/100)^(10) = 0.0956. So slightly less than if you'd stack them all in one raffle. However, if you're interested in the expectation value of the number of wins, then in both cases you can expect an average of 1/10 win per game (= a set of raffles in which you spend 10 tickets). In the case of the spreading out of the tickets, you have a small chance to win more than 1 raffle, but the chance of winning at least something is lower than if you stack. |
How were polymerases created from DNA, if polymerases are required to make a polymerase molecule? | This may not be **truly** answerable by current science. The speculation to this is that life and its biology/biochemistry wasn't nearly as complex as it is now. If you go back far enough, you'll end up with life, or at least something that looks like life that was able to replicate DNA/RNA without today's complex polymerase enzymes. This very early development is covered by the idea of [abiogenesis] (_URL_1_). Something like the [RNA world](_URL_0_) hypothesis conceives of RNA molecules which catalyze their own replication, thus kickstarting evolution. |
Why are lithium, beryllium and boron so rare? | Elements are forged in stars. Moderately massive stars make C/N/O easily and for a decent chunk of their lifetimes in [a cycle named after those elements](_URL_2_), but they don't spend much time making beryllium, boron or lithium. To paraphrase [Neil DeGrasse Tyson](_URL_0_), when stars die, they unleash their guts on the universe, and so their CNO rich guts wind up everywhere, including your backyard and your lab bench. And you. Read up on [stellar nucleosynthesis](_URL_1_). |
Why do snowflakes exhibit a 6 fold symmetry? | Water crystallizes in a hexagonal unit cell (the smallest repeating pattern in a crystal), and crystals tend to take the shape of their unit cells, much like sodium chloride makes cubic crystals that match their cubic unit cells. |
How are my eyes changing to a completely different colour as I grow older? | [This image](_URL_0_) has best explanation that I've found I don't work on the anatomical or genetic side of vision, but my ~~rudamentary~~ rudimentary understanding is that the amount of melanin can change with age. * Your iris seems to have started with a lot of melanin (dark brown). * Then it reduced (lighter brown). * Then it reduced more (yellow + blue stroma = green) * If it reduces even more, your eyes may become blue Your father probably has a differently structured stroma, so his eyes became gray. Maybe an anatomist can explain whether the stroma can change over time too. |
What causes eye color to change after birth? | Melanin in the eye is what causes eye color - babies are born without any melanin and over time it slowly gets produced. more info here : _URL_0_ |
How does soap kill germs? | Soap is made up of micelles, which have hydrophilic interiors and hydrophobic exteriors. They interact with lipids on your hands or body and break them into smaller aggregates that can be easily washed away. Bacteria are protected from water by this lipid layer on your skin that your body naturally produces. Removing the lipid allows the bacteria to be exposed, washed away, and some killed. Antibacterial soaps have specific compounds that target common pathogens. To have a real effect, the soap must be thoroughly rubbed on your hands for at least 20 seconds and then washed under water for 6-10 seconds. When at a public restroom, I bring the paper towel dispenser handle down with my elbow, therefore keeping my hands clean. After drying my hands, I turn off the faucet with the paper towel, because the faucet is a fomite that will re-contaminate my hands. I will often use the paper towel to open the swing door to leave. Stupid design to have the PULL side be the exit of the bathroom. |
Can galaxies orbit each other? | Yes, and they do. To be exact, they don't actually orbit one around the other, one being in the middle and the other going around, but they orbit their shared center of gravity. In the case where one is a lot more massive than the other one, it does look like the smaller one orbits the bigger one. If you look at high quality pictures of the Andromeda Galaxy ([M31](_URL_0_)), you may be able to spot M32 and M110, the 2 biggest of the 14 known dwarf satellite galaxies Andromeda has. |
Can galaxies orbit other galaxies? | The Milky Way itself has two naked eye visible satellite galaxies, the Magellanic Clouds, and a number of lesser galaxies orbiting it. Andromeda has two well know satellites galaxies (M32 and M110) as well as many other smaller ones. Having smaller satellite galaxies is a normal feature of large galaxies. The structures influenced by gravity extend even further into galactic clusters. The Milky Way and Andromeda are part of the Local Group, which orbits a point between our two galaxies. The Local Group is part of the larger Virgo Supercluster, which itself is part of the larger Laniakea. The Laniakea Supercluster has some 100,000 galaxies and spans 520 million light years. The structure of all this is maintained by gravity. Laniakea may be part of a larger structure with other superclusters likes the Shapely supercluster. |
[Medicine/Biology] Do wounds and illnesses heal faster with less sleep? | It's unlikely, though I'm not sure if it's been studied in such a direct manner. Decreases in sleep have been shown to [increase circulating catecholamines](_URL_2_), the so-called "stress hormones", which impair the immune system and [impair wound healing](_URL_0_). Sleep deprivation has been linked to an [increase in susceptibility to infection](_URL_1_). The immune system is critical in repairing damaged tissue as well as preventing and fighting illness, so get a good night's sleep! |
Why do some people sweat when they sleep? | [Searched](_URL_1_) Relevant [discussion](_URL_0_) Original text by [fuckinlovecats](_URL_2_) > If your body temperature drops while you sleep, why do you often wake up in sweat? Top comment courtesy [Duhaay](_URL_3_) > The exactly same (opposite) thing happens when you have a fever- Your body raises its temperature to kill bugs that are infecting you, and the sensation is that you have chills. It might be related to temperature relativity, in that since your body temp becomes a bit lower, the ambient temperature of the room is perceived as a bit warmer than usual. The two main reasons for sweating are from either your hypothalamus trying to lower body temperature, or a sympathetic response on sweat gland acetylcholine receptors. |
Why are night sweats often a sign of a serious illness? What causes the body to sweat to such an extent that your bedsheets are soaked, and why does it happen while we sleep? | I think the first question that needs answering is: Are night sweats a known symptom of certain illnesses? |
How does changing the tire pressure affect the car's traction? | More lateral force can be applied through a larger contact patch given the same downforce because the contact pressure will be lower. Therefore the shear stress between the tire and the road can be greater before losing traction. |
Is a star the largest possible (single body?) structure in the universe (aside from structures like the universe or galaxies)? | Not that well versed with the scientific aspects but if you count nebulae then they are bigger than stars. If you mean something with a "symetrical" shape then AFAIK stars are the biggest thing you get. [This here](_URL_0_) is actually pretty interesting to look at the scales of things in the universe. To your second question about the iron becoming a star. IIRC it wouldn't be able to keep up the fusion process. Stars already fuse their atoms (Hydrogen) to other elements (Helium). When they used up most of the hydrogen they start fusing helium to even heavier elements (and so on). But at a certain point (when trying to fuse much heavier elements) the fusion generates less energy than it needs to do the fusion. That is the point where a star begins to die. Now IIRC iron is one of the heavier elements that cannot be used for a "net gain" fusion (i.e. producing more energy than it takes to fuse). |
Why are some greenhouse gases more effective than others? | A greenhouse gas is just any (atmospheric) gas that primarily absorbs and emits radiation in the infrared region of the spectrum - and some are much better at doing this than others (i.e. they absorb/emit a greater range of infrared wavelengths). It also depends on the lifetime of the gas in the atmosphere, as well as the proportion of each; CO2, for example, is the primary greenhouse gas on Earth due to it being more abundant than methane and nitrous oxide, despite the latter two having much higher global-warming potentials. For more information: _URL_0_ |
How small can a star be? | Stars start to fuse hydrogen at about 80 times the mass of Jupiter. Below this, they are brown dwarves. Above about 12 times the mass of Jupiter they also fuse deuterium, and this is a grey area as to whether you want to call these stars or not. |
How small can a star be? | In terms of mass, objects below 80 times the mass of Jupiter are not big enough to ignite hydrogen fusion and are classified as brown dwarves. Objects below about 12 times the mass of Jupiter are not hot enough to fuse deuterium. In terms of radius, neutron stars are extremely dense and can be below 10 km in radius despite being similar to the sun in mass. White dwarves are in between, about as massive as the sun but about as wide as the Earth. |
At what point will the expansion of the universe cause the "heat death" to reach the point where, the density of energy is so low that it is effectively zero? | [This page gives you a timeline of the events we predict for the universe over the long term, including heat death](_URL_0_) |
How much more efficient is riding a bike (on flat ground) than walking? | Not a physics guy, but this link may help: _URL_0_ |
Why are we "carbon" based life, not Hydrogen? | It's all about organic chemistry. Carbon makes four bonds, which gives rise to an amazing versatility in organic chemistry. In fact, if you wanted a non-carbon based life form, you'd have a better shot at guessing something just directly below carbon on the periodic table, because it's more about carbon's specific behavior than the abundance of say....hydrogen. However, hydrogen does play a big role in our physiology. I'm sure there is a better, more in-depth way to explain this. |
Why do we still have wisdom teeth? | Evolution is far from perfect. Wisdom teeth can cause many issues, but they are not detrimental as to prevent someone from reproducing or causing early mortality. Along with a shift in diet that facilitated consumption with such a mouth, we retained wisdom teeth in our species. But for us to lose them, there would have to be variation in our species with people that lack wisdom teeth. I'm not aware of any, but some people in the dental field may have some knowledge about this that I lack. |
Why do we have wisdom teeth? | Shameless repost of what I said to this question a few years ago (and the information hasn't changed): Dentists aren't entirely sure, but one of the popular theories (_URL_1_) is that, in primitive diets, the teeth would be worn down quickly (even in between the teeth) and the spaces would be filled in by erupting teeth. Since we have processed/soft diets, there is less size reduction of the teeth and they crowd more easily. Another theory is that jaw development has decreased as the amount of energy necessary to develop the brain increases. Yet another is that different diets [stimulate the masticatory muscles differently](_URL_0_), which alters bone growth, which changes the amount of space for the teeth. TL;DR - we have no idea. |
Will mosquito bites heal faster if they are not scratched? | The more you scratch, the more inflamed and irritated the area will become. Bite or no bite, it is an open injury and will heal as such. Baking soda mixed with water will help lessen the itchiness. And rub it *on* the bite, don't drink it. |
How can there be lottery winners? | During the last billion dollae draw the number of lottery tickets played actually far exceeded the number of combinations. Assuming most people played a random number rather than their own a priori the chances of at least one winner was approximately 100%. The chances of any particular individual winning is exceedingly small, but the number of people who play the lottery on a regular basis is quite large. |
What are the advantages and disadvantages of substituting sugar with agave syrup/nectar? | Agave nectar can be almost pure fructose, so substituting it for sugar in large quantities is not a good idea. |
Why does wetting a suction cup make it stick better? | Someone will undoubtedly bring a much richer explanation to the table, but the really simple answer is that when you look REALLY closely at the surface being adhered to and the suction cup, you will find that microscopic imperfections and textures in both items do not allow for a perfect seal. A thin film of water can fill those tiny gaps and improve the seal significantly. |
If the earths atmosphere is mostly made out of nitrogen then why haven't we evovled to breath it? | because nitrogen is a largely inert gas which can't be used in nearly as many chemical reactions to shuffle around energy. Oxygen is highly reactive and interacts nicely with other elements which lets us use energy quickly. |
Would there be enough light to see at night if the moon did not exist? | Are you aware there are nights where the moon is not visible...? You can just go out and check for yourself how dark it is. It's pretty dark. |
Dental practices with Fluoride? | There are two key minerals in tooth enamel; hydroxlapatite and fluoroapetite. Fluoride treatment helps "remineralize" fluoroapatite which slows down cavity formation. |
If salt (NaCl) dissolves into Na+(aq) + Cl-(aq) then why does salt water still taste like salt? | Because your tongue is wet; you always taste Na+ & CL-. |
Are there any viruses that affect plants? | Yes, there's a large variety of viruses that can attack plants. The [tobacco mosaic virus](_URL_0_) can be a particular problem since it can attack a wide range of plants. _URL_1_ |
Why isn't the universe bright everywhere all the time? | You've actually stumbled on a classic argument. Essentially, if the universe were infinite in size, infinite in age, and isotropic, then any point in the sky would be in line with the surface of the star and (interstellar dust not withstanding) the entire sky would be as bright as the surface of a star. Since this isn't the case, one of those preconditions must be false, and the one with (by far) the most evidence against it is the infinite age of the universe. The finite age of the universe (i.e. the idea that it began at the big bang), and subsequent inflation, allows that there are parts of the universe that we have not yet received light from and thus, that the sky need not be uniformly bright. Edit: I forgot to link it, but it's formally known as [Olber's Paradox](_URL_0_) |
How do rockets propel in space? | A common misconception about thrust is that the thrust pushes against the ground, and that's what pushes the rocket up. But imagine you tape a balloon to a straw, and thread a string through the straw, and tie that string up horizontally. Inflate the balloon and let it go, and you'll see it rocket horizontally without "pushing" off the ground at all. See what matters is that the thrust is ejected in the opposite direction that you want the rocket to go. It's a matter of conservation of momentum. The thrust leaves with a lot of momentum right (in our balloon rocket above) or down (in a regular rocket) and thus the rocket, to conserve momentum, must travel the opposite way, with the balloon rocket going left, and the regular rocket going up. |
How does a rocket propel in space? | When you suck on a straw, it isn't the suction pulling the milk shake up. It's the weight of the column of air above the milkshake, extending into space pushing down on top of the milk shake as air pressure. All you did by sucking was remove the weight of air on top of the milkshake straw that was holding it down. Rockets use a concept called momentum conservation. The best way to explain it is to get in something that can roll very easily, like a chair on coasters or a skateboard or on ice skates, and throw something heavy in one direction. You should move in the opposite direction. Usually we don't notice this while throwing because our feet have enough traction with the ground to push the other way. Since momentum is conserved, if you push mass in one direction, your body should move in the opposite direction. So all Rockets are doing is taking fuel and oxidizer, burning it, and using that energy to push it out the bottom as fast as possible, which makes the rocket go in the other direction. |
Can there be multiple dimensions of time? | There is a succint description here -- _URL_0_ |
If the observable universe is just a tiny fraction of the entire universe, why do we keep saying it's just 13.7 billion years old? | We have to assume that the universe doesn't drastically change beyond what we can see (which due to the expansion of the universe, is a few times larger than 13.7 billion light years). We look at our patch of universe, and see from its rate of expansion that it's 13.7 billion years old, and so we must assume it's about the same everywhere. We make this assumption because it's the only assumption that gives us meaningful results. If we assume the universe *does* drastically change beyond what we can see, then there's no more science to do - any ideas about the universe on a very large scale are just guesses. But by making this one simple and sensible guess, we can work out all sorts of things about the universe. |
Riding a bicycle is a more efficient method of transportation than walking/running. Is there an angle of incline where walking/running becomes more efficient than riding a bike? | My answer is yes, but I don't know the angle. Road bikes weigh somewhere between 15-25 pounds, so you're pushing weight up the hill. This will eventually become less efficient at steeper angles. On the other hand, you get to coast on the bike and like you said, it's generally more efficient. But from personal experience, practically speaking, with a light road bike I've never found a slope that was so steep that it made cycling slower than running. I've gone up slopes of 20% and more, and I've tried to run up the same slopes, and biking is always much faster. Things are different on technical dirt trails, of course, where running allows you to avoid obstacles more easily (for instance in cyclocross races they regularly get off their bike and carry it over mud and obstacles). |
If the symptoms of an illness are typically the body creating a hostile environment to get rid of the infection (runny nose, fever, etc.), what do viruses/bacteria actually do? | Bacteria actually "just wanna live". Since they are living cells hey also have a metabolism like any other living cell, plant, animal, human. What makes them infectious is the materials they secrete - these are poisonous to your body. Of course not all bacteria do this or secrete other stuff that is no danger to your body. So it depends what bacteria you have. Virii in turn don't actually "live". They are more like dead things like a stone. However, they possess detectors on the outside and blueprints of themselves inside. Once their detector docks with the right counterpart (here a certain cell) they inject their blueprint (virus DNA or RNA) that reprograms the cell to just build more virus shells and blueprints and assembles them into new virii. Then the cell collapses and unleashes the virii into the world. |
How does lactose (milk sugar) metabolize compared to sucrose (table sugar), and do they affect health differently? | To my knowledge, there is little evidence that galactose is any more dangerous than glucose to normal, healthy people. Galactose is metabolized to glucose efficiently, so lactose ultimately becomes two glucose molecules anyway. Glucose tends to trigger the insulin response better than fructose. This inhibits appetite, but can be worse for diabetics, natch. However, lactose is substantially less sweet in taste than sucrose... so it wouldn't work as some sort of alternative to table sugar. |
Why are some planets / moons in our solar system so uniformly colored? | I might not be the best person to answer this question, but I'll take a stab at it. Disregarding life, vegetation, atmosphere, and the ocean (none of which are present in the moon), the Earth would actually look quite a bit more homogeneous than it does now. Much of the variation that would be present would be sure to the fact that the earth is geologically active. The Grand Canyon is red because it is made of sandstone, Mauna Kea is black because it is made of basalt, etc. By contrast, the moon is largely geologically inactive. It has neither liquid water nor atmosphere, so there are no sedimentary rocks. It is not as massive as earth, so there wouldn't be much metamorphization (if that's a word). Those metamorphic rocks that did form would never be brought to the surface because the moon doesn't have tectonic activity. In short, the moon looks homogeneous because there are not any processes that would make it heterogeneous. |
do we actually get vitamin D from the sun, or does sunlight just make it easier for our bodies to absorb the vit. D we get from food? | Vitamin D is actually produced by the body when exposed to sunlight. You can read about the process on [this page](_URL_0_) from the US National Institutes of Health; see the subheading *Sun exposure*. |
So if the universe is expanding what exactly is it gaining? | The universe is increasing its volume. It is not growing into an otherwise empty space around it (if this existed, it would be part of the universe!). |
The sun as a perfectly round object | Relatedly, a neutron star is thought to have surface features only a few millimeters high, so it's certainly much *smoother* than the Sun: _URL_0_ |
Most objects outside of our galaxy are too dim to see without the assistance of powerful optics. Are there any exceptions to this? | A few, Andromeda is a notable example. _URL_0_ |
From a genetic perspective are human races comparative with ‘breeds’ of dog? | When asking questions about race and genetics, its important to remember that most of societies notions about race are not rooted in genetics. That is to say that perception of race often has much more to do with cultural or historical notions rather than on shared heritage. Dogs breeds came about following decades and even centuries of selective breeding for specific traits. Humans on the other hand, have no such restrictions on reproduction, and as such distinct genetic subgroups are much less common, and *much* less distinct. Furthermore, your speculation about the greater genetic differences between dog breeds is right on the money; humans are not a particularly diverse species, genetically speaking. |
If different races aren't like different dog breeds, what are they and is "race" even real? | There are certain health conditions that are more prevalent in black people than white, such as certain blood conditions IIRC. I believe there are other examples of this, but outside of that the difference is just skin color, no different than extremely pale people from certain parts of europe. |
Since the universe is expanding, are dark matter particles expanding or are they growing in number? | The amount of [dark matter](_URL_0_) has AFAIK been constant, but *[dark energy](_URL_2_)* seems to be an intrinsic energy of space itself and thus increases as the universe expands. An alternative explanation to dark energy as an intrinsic energy of space is [quintessence](_URL_1_). I don't know if you can meaningfully describe dark energy as particles though. |
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