Datasets:
sentence-transformers
/
eli5

Dataset card Data Studio Files
xet
Community
question
stringlengths
19
300
answer
stringlengths
28
1.02k
Could Martian soil grow plants?
The main problem I can foresee is the lack of nitrogen in martian substrate. There are many various plant species that can prosper with a lack of certain nutrients that others demand.
If the atmosphere absorbs the blue light from the sun, why do we still see blue on the surface?
The atmosphere does not absorb blue light...it scatters it. Long wavelength light (red) passes right through the atmosphere while the blue light (shorter wavelength) is scattered so more reaches your eyes. At sunset, when the sun is low in the sky, it shines through even more air. In this case the blue light is scattered before it gets to you but the red light passes straight through to you so you see a red sunset.
Why does there appear to be a higher concentration of craters on the poles of the Moon?
You're kind of right. There are more craters in general on the dark side of the moon. The near side features *mare* or seas. Essentially these are lava flows. The story of why one side is different is intimately connected with the formation of the Earth-Moon system. This is an active area of research. But basically imagine one side having a thinner crust. Would highly recommend [this talk](_URL_0_) given at the SETI Institute in January.
Is the Earth brighter in the Moon's sky than the Moon is in our sky?
The Earth is much brighter in the Moon's sky than the Moon in Earth's sky. Not only is Earth ~~3.6 times~~ 13 times larger by angular area, but its average [albedo of 0.37](_URL_0_) (meaning Earth reflects 37% of the Sun's light on average) is more than three times higher than the Moon's (0.11). However, your original assumption about the reflectance of water is wrong. The albedo of deep water is [between 0.07 and 0.10](_URL_1_), meaning if the Earth was purely an ocean planet, it would be slightly less reflective than the Moon. The major contributors to Earth's high albedo are snow and ice (which have albedos of greater than 0.9) clouds (which have an average albedo of 0.5 but can be quite variable) and deserts (an albedo of ~0.4)
Why are most drones quadcopters while full scale helicopters tend to be monocopters?
Electronic motors are very light compared to a same powered combustion motor. So you can easily put 4 Or more in a drone. But when it comes to fuel, the combustion Engine wins this competition. Batteries are very heavy if you want to fly 3 hours. Combustion engines also tend to be difficult to maintain compared to electric so you don't want 4 of them in your aircraft.
Why is it apparently accepted that different breeds of cats and dogs have certain personalities, abilities, and levels of aggressiveness, but not different races of humans?
This is really a snakepit of a question and I don't know how to answer it completely. It's important to note, though, that dog and cat breeds are extensively inbred compared to human races, and are much less genetically diverse. This makes it a lot easier to predict how a puppy will turn out than how a child will turn out, and even then everyone know there's a lot of personality and morphological differences even within breeds. It's not a very accurate comparison.
What is acne? Why does our body produce it?
Your body doesn't "produce" acne per se. Pimples come about as a result of pores or hair follicles becoming clogged and in some cases, infected. While not exclusively due to bacterial infection, some acne is caused by the bacterium Propionobacterium acnes, whereas other forms can be due to normal backup of oils or dirt in the pores. Your skin produces a waxy substance called sebum that serves to lubricate hair and skin, and may well have some antimicrobial activity. However, overproduction of sebum can lead to clogged pores and thus acne. _URL_0_
Would bee hives grow larger if we didn't harvest their honey?
Found the guy who made a reddit topic after reading about the [70,000 bees](_URL_1_) that were dislodged from a rotted out tree after a Virginia tornado. I'm guessing you were wondering if this nest got so big because it wasn't getting harvested? From the other answers, it sounds like this hive must've been special in some way. Although now I wonder how possible it would be for a second hive to be established within the same (huge hollow) tree, and then after that the second queen dies and the first hive just adopts the second hive. I would love to hear how possible this would be
What determines the size of a hard drive or flash drive?
The amount of storage space is going to be determined by the number of storage elements, and the storage density of those elements. For a hard disk drive, it's the platters. Here's a pic of a [drive with three platters.](_URL_0_) Smaller drives might have only one platter. Then you need to consider the read/write heads. Depending on how precisely they can move, and how close they can place data on the disk, you'll get the storage amount for a given platter. As time has gone on we've gotten better and better and making platters and read/write heads, which is why you can have a drive the same size with thousands of times more data on it. Same goes for flash drives, but instead of platters, it's flash memory chips. Different, more precision made, chips have higher capacity, and a high-capacity drive might have multiple chips inside.
When we microwave food, why isn't the air in the microwave heated?
It's not just water molecules, it's polar molecules that rotate in response to the alternating magnetic fields. This constant rotation is more akin to a vibration, and when molecules hit each other, they create heat. The majority of molecules in the air aren't polar (80% n2 19% o2, trace amounts of others). Since they aren't polar, they don't rotate to align with the magnetic field and thereby generate heat. However, the air does heat as a result of convection/conduction from the material that is polar.
Do we see any stars from out of the milky way, or maybe whole galaxies, with the bare eye?
You can just about make out the [Andromeda galaxy](_URL_0_) with your naked eye (if you live in the northern hemisphere). You will probably need to travel to a very dark area to do so but it is relatively easy to find, have a google for a guide if you are interested, it is near the constellation Cassiopeia (the big W on the opposite side of the north star from the plough). It will sadly only look like a very faint, grey, fuzzy blob. The Andromeda galaxy is about 2 million lightyears away which compares to about 10,000 lightyears for the most distant visible stars in our galaxy. This makes it by far the most distant object observable with the naked eye. If you live in the south, you can see the large Magellanic cloud. This is also extragalactic and it (along with it's small friend) is known as a satellite galaxy. Satellite galaxies are basically small clusters of stars which orbit their host galaxy (the milky way in the case of the LMG and SMG).
As a star begins to die, what are the effects on orbiting planets before the supernova?
All life on Earth will cease to exist when the sun is still clearly on mainastage. Despite the fact that sun will not become a red giant before 4billion more years, the sun is steadily becomming more luminous. After about 1billion years from now, the sun is so hot that all life on earth is compleatly impossible. After that the sun becomes a red giant and possibly destroyes the entire planet. After that the sun goes through some up and downs in power (so severe that life at any distance orbiting the sun is impossible.), and then finally shrinks to a white dwarf. A 1 solar mass star will never explode. Stars that do go supernova go through phase transitions aswell but MUCH faster, at an increasing rate. One a year before explosion, one a week before and a final one 24h before. So no, one would not be well and good before the supernova. A super nova is just the grand finale of a destructive dance the star performs.
If there are more stars in space than we can count, is possible we would get to a point where we can't look any further due to stars in the way?
Nice work, you've discovered Olbers' Paradox :) This was a much-discussed problem in antiquity. _URL_0_ Take a read of the wiki page, it's very good at explaining. And ask away if there is more you want to know.
If there is nothing in space, how do spacecraft not constantly overheat when they have nowhere to dump their heat?
Everything that exists produces radiation caused by its temperature. Radiation is a form of energy, just like temperature, so by producing radiation, which travels away from the thing, it loses energy and therefore the temperature decreases. So long as it loses energy at the same rate as it absorbs energy from stars or produces energy itself, it won't overheat.
How much space is there in between particles in a gas cloud in space that is many light years in size?
The densest regions of molecular clouds reach particle densities of around a million particles per cubic centimeter. Assuming the particles are hydrogen, this gives an order of magnitude density of 10^-18 g/cc. Air is around 10^-3 g/cc, so even the densest regions of nebulae are diffuse enough that they're effectively vacuum compared with being on Earth. While you wouldn't notice the gas in your immediate vicinity, you probably would notice the sky around you looking darker due to the accumulated effect of looking through lightyears worth of dust. It would probably be similar to looking at the nebula from just outside, only you'd see it in every direction.
How is hair curly or straight?
Contrary to what my mum used to tell me, it's not caused by eating the crust on bread. "The shape of the follicle determines the shape of the cortex, and the shape of the fiber is related to how straight or curly the hair is." Source: [_URL_0_](_URL_0_)
Are solar panels in hotter places more efficient than solar panels in other, cooler temperatures?
The technically correct answer is that lower temperatures are more efficient, the thermal coefficient is about -0.4%/⁰K, see PV panel datasheet [example (pdf)](_URL_2_), however, that colder temperature usually means the sun is lower in the sky, losing energy due to [air mass](_URL_0_). Find locations of interest on _URL_1_ and compare the "AC Energy (kWh)" on the last page.
If time was created by the big bang does that mean that the universe has always existed?
You're right this is a philosophical question, and based on the way you phrased it, I am assuming you understand it perfectly. If there was nothing before the universe, then there was no point in time when the universe did not exist, so the universe always existed. This is more of an argument about the definition of words which only make sense if time has no beginning, so I would categorize it as philosophy, and not science.
How is it possible to carbon date something over 50000 years old?
All types of dating have their limitations. That why there is more than one type of radiometric dating. Different types of dating cover different time spans. As for the sample size, they are very small these days, think micro or nano grams. Once again creationist are cherry picking information and using knowledge levels from decades ago. That's one advantage science has, it rarely stands still. More on radiometric dating [here](_URL_0_).
Are the Voyager probes still taking pictures?
The cameras on the voyager probes have been disabled to save power.
Are the pictures on the Voyager Space Probe still recognizable?
The pictures on the Voyager are stored via analog on the Golden Record. These are 12" gold-plated copper discs with protective aluminum jackets. As they aren't photographs in the conventional sense such as was left on the Moon they aren't as subject to the white out effect from unshielded cosmic radiation. Barring some physical disaster, such as being pulled into a distant star or other stellar body then it's likely they will remain viable for an incredibly long time.
Why is wax clear when melted but opaque when cooled?
I found this nice .pdf with optical microscope images of wax _URL_0_ The thing melted was is that it is a homogenous single phase solution, so the properties do not vary with position. This allows light to pass through without scattering. Solid wax partially composed of crystals and partially composed of amorphous/disordered regions. When the light passes between the crystal and non-crystal regions it can scatter from the boundaries. This is because the 2 different materials have different indexes of refraction, like when light bends when it hits water. When you have a lot of these interfaces and small spaces between them the light scatters more randomly and the object looks white. Light can also scatter at the boundary between 2 crystals of the same type if those crystals have an index of refraction that depends on polarization. This is true of paraffin wax crystals, but I think it is probably not the dominant effect.
When something is spinning very fast [e.g: the blades on a windmill] why does it look like they're spinning counter-clockwise if they're actually spinning clockwise?
It's called aliasing. Imagine a windmill being captured by a video camera. Let's say a snapshot is taken and the blade is at 0 degrees. Then between frames, the blade rotates 359 degrees. It will appear to have rotated 1 degree in the opposite direction. This will continue for each frame.
When something (a fan or helicopter blades) is spinning very fast, let's say counter clockwise, then why does it appear to be slowly turning the opposite direction?
It is because the sample rate used for the device/organ doing the detection is too low to properly observe the motion. The result is that you see one spoke, and then by the time the next frame is taken, another spoke is near the area where you saw a different spoke in the first frame. Your brain puts these images together in a way that may not be indicative of the true motion. It is discussed in much more detail [here](_URL_0_).
Since there's no frictional resistance and perpetual motion in the vacuum of space is possible, wouldn't everything with an accelerating force eventually reach light speed until a frictional force is encountered?
The interesting thing about spacetime is that the closer you get to the speed of light, the stronger the force pushing you has to be to get you to increase your speed one more unit. It would take an infinite force to actually get you from 99.9% the speed of light to exactly the speed of light. Your basic idea is correct, though. Continually applying a force to an object will get it ever closer to the speed of light. For instance, protons in the LHC are accelerated to 99.999999% the speed of light. It takes the amount of electrical energy that is equivalent to that used by small city in order to get a handful of the microscopic particles up this speed. Pumping more energy into these protons will just add more 9's to the end of the decimal part of that number.
Why don't microwave ovens heat up air?
Because water molecules are polar (have positively and negatively charged ends) so the oscillating EM field affects those molecules, but molecules that comprise air (O2, N2, etc) are non-polar, so the oscillating EM field doesn't affect them.
Why do microwaves cook/heat things faster than ovens, when ovens reach higher temperatures?
Microwave ovens work by using a type of high-energy electromagnetic radiation to warm uo your food. Since the microwaves are so low in energy/have such a high wavelength, they pass through whatever is inside the oven and transfer some of ther energy into that item, which heats it up. So the only constraints on how long it'll take are the speed of light in typical air and the amount of waves/exposure time compared with the volume and density of the item placed within. Traditional ovens, on the other hand, rely on thr transmission of infrared radiation, which doesn't as easily pass through solid items. This means that instead of cooking it from the inside, the object in question has to be headed on the outside and have the energy work it's way inside. Here the fact that plays most into how fast the thing will heat up is how easily the material conducts heat.
How and why does touching the opposite end of an auxiliary cable produce a buzzing noise from the speaker it is plugged into?
Most of it is [mains hum](_URL_0_) a 50 or 60 Hz signal created by the mains electricity, which is alternating current. It's annoyingly present in every recording you make unless you use shielded hardware. Your body functions as the antenna, and when you touch the aux cable, you transfer that signal to the speakers, which will happily play it.
Are electric cars actually better for the environment? Wouldn't the increased electricity generation be just as bad or even worse than gasoline?
Electric cars are a net win no matter what the fuel the power plant consumes. On the broadest level, the larger the heat engine, the more efficient it can run. GE manufactures a combined-cycle gas turbine that generates electricity at 60% efficiency. For comparison, a modern, typical gasoline engine in a car is only 20-25% efficient. And keep in mind, that gasoline had to be refined and transported, at great secondary cost. It's much cheaper and cleaner to pipe more current down a high tension line.
Why do planets form in the first place?
A collapsing cloud of gas and material (which will soon form a star) has a small rotation to it. As the material falls in and gets denser, the material spins up, much like a spinning ice skater. Some of the material makes it down to the center and forms the star, but other material is orbiting too fast to fall in. (The moon doesn't crash into the Earth because it has a fast enough orbital speed.) This results in a star at the center, and a disk of debris orbiting comfortably around the star. The debris can attract other debris near by and build up slowly to form the planets.
When I look into space through a telescope, why don't objects appear 'streaky' if we revolve and orbit around the sun? My ceiling fan looks streaky as it spins fast. What is the difference?
We don't move quite fast enough to perceive the ceiling fan visual effect, but if you look through a telescope once, then look again a couple minutes later you will notice everything has shifted. Another option is a [long exposure picture](_URL_0_) of the night sky. Similar concept.
Why aren't reflections in a mirror clear when I'm not wearing glasses?
When you look at an object in a mirror, you're focusing on the virtual image of the object. This means that if an object is 10m away from the mirror and you look at it in the mirror, you're focusing on a spot 10m beyond the mirror.
Fire requires Oxygen: So what would happen if wood or another flammable material slowly drifted towards a star in space?
The wood becomes carbon eg charcoal. see: _URL_0_
Why can't we use antibiotics to cure body odor?
First, the accumulation of commensal bacteria such as *S. epidermidis* is manageable by using mild soap and water, making the use of antibiotics overkill. Second, the irresponsible use of antibiotics is dangerous in that antibiotic resistance can arise. Antibiotic resistant strains of bacteria are much more dangerous than BO.
I just read that space has a near absolute zero temperature but wouldn't a vacuum technically not have a temperature?
Space is not a vacuum. > Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos. Theory suggests that it also contains dark matter and dark energy. In the space between galaxies, matter density can be as low as a few atoms of hydrogen per cubic meter. The baseline temperature, as set by background radiation left over from the Big Bang, is only 3 Kelvin; in contrast, temperatures in the coronae of stars can reach over a million Kelvin.
How did eyes evolve?
* step 1: A patch of light sensitive cells on the skin allows the animal to detect simple changes in a certain direction. * step 2: The light-sensitive patch becomes hollow, enabling rudimentary directional light detection. * step 3: Becoming even more hollow with a small hole in the front, resembling a camera obscura. * step 4: A lens forms at the opening, allowing light to be focused on the light sensitive area. The opening is covered by a protective layer to prevent dust from gathering in it. * step 5: The iris allows the amount of light being regulated. There you have it, your basic eye.
Why or how did we evolve eyes?
> However, if we (talking as if we were still single cell amiba) were blind, no eyeballs to speak of, then we would not know that a seeing world would even exist. What an organism knows has nothing to do with what features evolve. In a world full of organisms that can't sense light, an organism that can sense light a little bit has an advantage. In a world full of organisms that can sense light a little bit, an organism that can sense light a little bit more has an advantage.
So it is possible to die from drinking an excess amount of water, before you die what are the symptoms you experience?
Yes. It's called water intoxication. _URL_0_ Here is a recently documented death. _URL_1_
If you cloned a human, would those two humans have the same fingerprints?
[This paper](_URL_0_) assayed only a specific feature of variation in fingerprint pattern, namely whether you have an arch pattern in your fingerprint. They compared sets of identical and non identical twins, and found that most of the time, if one identical twin has an arch pattern, the other does as well, but that it isn't universally true. For basically any trait that you can name, the heritability is less than 100%, meaning there are non-genetic influences which cause differences between individuals, and so "identical" twins, or clones will never ben *exactly* identical.
Why is lead so dense but so soft, aluminium so light but also soft, but then tungsten is very dense but incredibly hard and titanium is so light but also really hard?
So, an important concept here is the lattice structure. You can imagine this as just how the atoms are stacked, so, for example you could have a cubic lattice where every atom is located at the vertex of a cube. You could also have some sort of hexagonal structure (imagine stacking oranges). All sorts of structures are possible. Now, the density is going to depend on how "tight" the packing is in the lattice structure and the atomic weight of the individual atoms. Hardness / softness (I'm thinking malleability) is going to be a function of how strong the atomic bonds are, that is, how much energy do you need to dislocate an atom from the structure? If it's low, then your metal is soft, higher energies would be harder.
Is Tungsten Carbide an alloy?
The second answer is right, tungsten carbide simply refers to a tungsten atom and a carbon atom that are bound together. In bulk, it's 50% carbon and 50% carbon, but it's not just a mixture like brass is a mixture of copper and zinc. Bulk metals and alloys are held together by metallic bonds, where the atoms all share their valence electrons, while the bond between tungsten and carbon is a stronger covalent bond.
how does my body get vitamin d just from being out in the sunlight? or is the vitamin d already present in my body and the sunlight "activates" it in some way?
Vitamin D is produced by the reaction of UVB in sunlight with a chemical called 7-Dehydrocholesterol that is already present in the skin.
How do we know what colors animals can detect?
For lots of animals you can use operant conditioning with colour as a discriminatory stimuli. if you illuminate a cage with red light and train an animal to press a lever for food, it'll get pretty good at doing that. If the next day you illuminate the chamber with green light, the animal will probably still press the lever. However, if the chamber is green you can shock them instead of reinforcing them. Eventually, the animal will get really good at pressing the lever when there's a red light, and avoiding it when there is a green light. Thus, you can say with some degree of confidence that the animal can distinguish red and green.
Why Does Water Make Absorbed Objects Significantly Darker?
Educated guess: I imagine it has to do with the fact that light refracts more through water than solids whereas it tends to reflect off solid objects (obvious exceptions like glass etc aside). This would mean that a portion of the light hitting a wet object likely refracts or at least reflects at a more oblique angle than a dry object thus returning less light to the eye and therein making it appear darker.
Has the average human IQ fluctuated significantly over the time it has been measured?
Mathematically the answer is no because the average IQ is defined to be 100 with a standard deviation of 15. So the measurement system will scale with the population. However, 100 IQ now days is a lot more than 100 IQ 50 years ago. Global intelligence averages are steadily on the rise.
If time and space are of the same fabric and space is expanding, how does time stay the same?
When someone says space expands, it means that two points are further apart *at a later point in time*. It doesn't make sense for time to expand, because what does it expand with respect to? The analog would be if durations of time changed in different places in the universe, but that is not observed to happen. [These](_URL_0_) are some possible diagrams for an expanding universe, where in the image time is the vertical axis and we imagine that space is two-dimensional. In reality space is three dimensional but showing that would require a four-dimensional plot, which we can't really draw.
Supernova trigger for formation of the solar system
There is no doubt that primitive meteorites (like Allende) contain material produced in supernovae very shortly before their formation. Two very well documented isotopic examples are [iron-60](_URL_1_) and [chromium](_URL_0_). Whether formation of the solar system was triggered is more problematic, but the general consensus is that it did. Here's a good popular article discussing [supernovae triggering](_URL_2_).
If glass is a solid, does it have a liquid form?
Absolutely - that's how glassblowing is done. Molten glass is very thick and sticky, somewhat lava-like, but it can definitely be poured. Various types of glass have, of course, different softening points, and as an amorphous solid, none of them have anything like a sharp melting point. (Artists working with glass refer to fusing, which is heating glass objects enough to make them sticky, and slumping, heating a glass object enough to make it partially collapse under its own weight, as well as casting molten glass).
Plastics Melting While Cold?
Off-gassing, probably. To make plastic - take a solution of monomers (think links of chain) dissolved in some appropriate solvent and initiate a reaction to polymerize them (connect the links). Then you dry off the solvent and you're left with long chain molecules (plastic). Sometimes you add other things like softeners or other polymers to the mix to get just the plastic you want. Problem is that all these things (monomers, softeners, residual solvent) can evaporate. You left the plastic in a closed container for a long time, so if there was residual solvent left behind in the picks, then that solvent could evaporate, absorb onto another pick, dissolve some of the surface, then re-evaporate over and over again. If two picks that were touching both were a little dissolved on the surface, they could dissolve into each other and fuse.
Why can we eat raw fish but not raw meat?
people eat raw meat all the time. ever gone to an ethiopian restaurant and had kitfo?
Why can we eat raw fish, but not raw meat?
You can eat raw meat. However, you should understand that both fish and meat is relatively dangerous to eat raw, since it you'll be consuming all the pathogens that the meat contains before handling and the ones that come from handling; so know your source. It is strongly adviced to freeze both fish and meat beforehand, since it kills majority of but not all pathogens. For a complete sterilisation you need to use other techniques like cooking, drying, holding in anti\-septic materials like salt or vinegar. But there is not much difference between raw fish and meat.
Why do so many medications have the side effect of suicidal thoughts?
One reason is because seratonin and dopamine are involved in both psychiatric pathways and many non-psychiatric pathways from nausea and diarrhea to milk production. Therefore the drugs for many non-psychiatric diseases alter seratonin or dopamine, putting you at risk for psychiatric disturbances. Another reason is because drug companies try to list all the problems that were reported when they did drug trials, even if there is no clear link (statistically or physiologically) between a problem and the drug. Lots of people have suicidal thoughts, especially people who are sick, so that often shows up by chance and is listed. In the end though, there are numerous drugs that aren't related to the dopamine or seratonin pathways and do cause a statistically significant increase in suicidal thoughts. The reason is simply not known.
Why/How does a person's natural color of facial hair not always match that of the natural color on their head? Why does hair color change over time?
I would like to know this too. I know blonde often darkens, but does everything darken? And OP seems to have significantly changed. I used to have very light brown hair, and now it's basically black. Changed from around ages 15-20.
What will the Earth look like after all of the tectonic plates settled?
We really have no way of knowing what it will look like that far ahead. [250 million years into the future projection](_URL_2_) (left click and hold/drag the small java applet) It is guaranteed that the internal heat of the Earth will diminish and tectonic activity will cease but we have another 4 or so billion years before that happens. (around that time the sun will be going nova and roasting the earth anyway) _URL_1_ _URL_0_
Why does silver have antimicrobial properties?
It isn't just silver. All of the coinage metals have antimicrobial properties. I've read some hospitals are installing copper alloy surfaces on things such as hand rails to help reduce the spread of antibiotic resistant bacteria. The metals can interfere with proteins making them non-functional. Also can create an oxidative environment which kills cells. There is a lot more going on but in short it disrupts many aspects of cell chemistry.
Why do storms seem to be worse at night?
Prepare for the knowledge of an interested amateur... Severe thunderstorms do tend to be at their worst between noon and midnight. During the afternoon, intense surface heating destabilizes the atmosphere, and assists convective processes. After sunset, storms are slow to wane for kinetic as opposed to thermodynamic reasons (low level jet streaks tend to intensify at night). Of course, if they ingredients are there, they can occur at any time of the day. Infant tropical waves are prone to diurnal intensity fluctuations, but by the time they're at hurricane strength other factors play far more important roles. For snow, I think your experience is a combination of coincidence and the fact that night is significantly longer in the middle of winter -- there's more time that one may consider "overnight"!
If TV remote controls use infrared light, why does my TV respond to my remote control when the path between the RC and the TV is completely blocked or when the remote control isn't even pointed at the TV?
If you have a flashlight, turn it on and off at some interval to convey a message, and put some object in the path of the light, would you be able to tell what the light pattern is by observing the room in general? You'll see reflections off surfaces in your room - walls, ceilings, floors, etc.
Why does the TV remote control still work even if you don't point at the TV with it (at least at the newer TV's) ?
Shine a torch in a dark room. How come you don't just see a disk of light on the wall you are pointing it at, surrounding by total darkness everywhere else? Obviously because of reflections, scattering etc. You have a bright disk, and then a dimmer shedding of light all around the scene. Now mentally switch the white torch bulb for an infrared bulb, and flick the torch on and off rapidly in coded patterns: you've just built a tv remote, and the infrared light is bouncing around the room off of surfaces just the way the torchlight did.
Why do people get runny noses? Why does it continue to flow even though you blow your nose many times? Finally, is there a limit to how much mucus you can produce?
Mucus is formed to excrete unwanted microbes. [Mucuous membranes](_URL_0_) secrete mucous. It continues to flow because it continues to be produced by said membranes. The reason you can produce so much of it is because of how much of it is simply water. > 90%. [Here](/r/askscience/comments/n71ly/while_you_are_sick_where_does_the_mucus_in_my) is a thread asking pretty much the exact same question with good information in it. Consider the search function for future questions. :)
At what temperature do bacteria die?
Depends on the bacteria. Members of the Clostridium and Bacillus genera can form spores and survive boiling water. B. cereus can cause food poisoning on leftover rice after boiling/cooking it; that’s why it’s important to refrigerate it as soon as possible after eating.
why do we breath Oxygen and not Nitrogen?
Marsdreams does a great job of answering the Why Oxygen question. You also asked Why Not Nitrogen: the answer is because most nitrogenases (enzymes that break down N2) are inhibited by oxygen; if there's any oxygen around, they won't work. If you're a bacterium or a plant with roots in the soil, you have areas where you can use those enzymes, but if you're an animal living in the air, there's no way to avoid oxygen, so nitrogenases aren't going to be useful for you.
Why does a helium baloon goes foward in an accelerating car?
For the same reason it goes up in still air: its lighter/less dense than regular air. When the car accelerates, the heavier/denser regular air moves towards the back of the car by inertia, just the same way you feel pressed into your seat. The helium balloon wants to do that also, but the heavier air rushes past it and pushes the helium balloon forwards. Think of the back of the accelerating car as "down" and it should make more sense.
Why are some grapes sweet and some sour/bitter on the same cluster?
Varying levels of ripeness. While grape vines' flowers all open up around the same time, there's a bit of staggering to ensure extended opportunities for pollination. This continues on through the fruit's development, also encouraging multiple opportunities for different dispersal agents (birds).
Is a Mach 3 sonic boom louder than a Mach 1.5 sonic boom? Would travelling super sonic for longer periods of time increase the loudness or intensity of the boom?
Can I sidebar off of this? How high up in the sky would you have to fly at speeds above mach 1, to negate the heard and felt pressure wave on the ground? The SR-71 was considered "stealth" was that just because of it's sheer speed or was it undetectable on the ground as far as the sonic boom goes?
If copper and its alloys are naturally antimicrobial, why aren't they used for cutlery?
Copper is a very soft metal, so any knife would dull very quickly. Also copper is very reactive and will tarnish to a green patina. Not exactly something that looks great when you are trying to cut food. If you look at copper pots, the copper is on the outside, not in contact with food. The copper is there for heat conductivity. If it made contact with the food (especially acidic foods) it would leach in and give the food an off taste.
Since copper has antimicrobial properties, why aren't most medical tools made with it?
Copper is very soft, expensive, and has a tendency to corrode. Compare to stainless steel, which is strong, a lot cheaper, and doesn't corrode. Copper salts are also toxic inside the body, but the main reasons are the other things.
Can spitting water be flammable?
What likely happened is that he in fact jetted the water at the pool of molten wax below the wick. The heat within the wax may have flash-boiled the water, causing rapid expansion, and generating a cloud of very fine particulate hot wax, carried in a cloud of steam. That mixes with the surrounding air to produce a fuel-air mixture, which the flame can then ignite. Like this: _URL_0_
Why do new fridges not get hot on the outside?
Energy efficiency is to thank. Old fridges used something like 1400 kWh a year. Modern ones of the same size use 350 kWh. That’s far less heat it needs to dissipate into the room, hence the coils on the back only get mildly warmer than room air. As to what made them so much more efficient, a lot of things. From insulation in the unit themselves, to advanced in the types of refrigerant, to more efficient motors. To better controls that monitor things like sweat and humidity, and use logic on when to run the defrost cycle instead of just a timer.
Extra sugar-free gum claims to have 5 calories, but is that taking into account how many calories you burn by chewing it, or is that before chewing?
Calories listed on food products never take into account the energy required to digest them. They also don’t take into account bioavailability; how much of what you eat actually gets absorbed by your digestive system. Usually the values are empirically calculated based on known caloric values of the ingredients, or maybe it is directly measured by calorimetry
Is there actually lightning in space nebulas?
Actual nebulas are nothing like their portrayal in movies and tv. The density of matter in a real nebula is so low that if we put it in a box and brought it back to Earth it would be considered a vacuum. Traveling within a nebula would bear little resemblance to being in an atmosphere, it would be very much like traveling through empty space with either a dim, diffuse glow in the distant sky if you were within an emission nebula or reduced visibility of distant stars otherwise.
How come we never witness lightning in open space? Can't there be charge differentials in large nebulas, etc.?
Even if there was long range charge transfer, we wouldn't see it because there is no atmosphere to be ionized like there is for lightning. We do see the effects of rapidly accelerating charge in space though, for example, in x-rays produced in accretion disks.
How do mathematicians calculate an nth digit of pi?
There are formulas that give better and better approximations of pi as you keep more and more terms. For example, take a look at [this](_URL_1_). There is also a formula that will directly give the n^(th) digit of pi in base 16 without calculating all the preceding digits; that formula is presented [here](_URL_0_).
Why can we still hear the cosmic microwave background? How much longer will we be able to hear it? The big bang was almost 14 billion years ago, how can we possibly see something from that long ago given that it no longer exists?
We don't hear it, we see it. It's photons. It's still around because the universe has a non zero temperature. The temperature has decreased as the universe has expanded and will further decrease in the future, and the thermal radiation of the universe (CMB) will shift further to longer wavelengths, which at some point in the future may become difficult to detect.
Why do the storms on Jupiter and Saturn last much longer than storms on Earth?
Because they have a lot more energy to work with. Also there’s nothing in the way to stop them (like mountains). Also they draw energy from different places. Storms generally form from evaporation of water (I know I’m over simplifying). Storms in those planets form from the energy and disturbances in their atmospheres. Since they’re all atmosphere, they have no shortage of energy
Since things like neutron stars and black holes can bend light, can light orbit around them? What would we see if we looked at the orbiting light?
First of all; we look by having light hit our eyes. We can't see light that doesn't hit our eyes. That being said, light absolutely can orbit black holes. This region is called the [Photon Sphere](_URL_0_). The photon sphere is at a radius of 1.5 times the Schwarzschild radius, which is the radius at which no light can escape; the event horizon, in other words. Within the photon sphere, it is impossible for anything to orbit the black hole. Things can still escape from it, but they have to be moving away from the black hole.
How did the mountains on Mars in the newly released panoramic picture form? Does Mars have tectonic plates like Earth?
Mars lithosphere and crust is much thicker and stronger than Earth's (in relation to the size of the planet). It's the thicker lithosphere and crust that allows it to support large geological structures such as the volcano Olympus Mons (which is over 3 times the height of Mount Everest). Although Mars is no longer geologically active, there are two distinct types of crust which appear similar to Earth's continental and oceanic crust. There are theories that Valles Marineris (similar to but much larger than the Grand Canyon) and other ridge formations could be formed by continental spreading, but they could also have formed from fracturing caused by uplift of an area called the Tharsis region.
Shouldn't the Earth's core be made up of different heavy elements and not just iron?
Well, the Earth's core is mainly iron, but there is also nickel and a few other possible light elements. The reason that is is mainly iron though is that early in earth's formation, the dense elements sunk to the core while the less-dense ones would "float" upwards to the earth's crust. Other dense elements besides iron don't appear because they are either too rare (like uranium; see solar abundances) or they bind together with other elements in the crust easily. The composition of Earth's core is still an ongoing subject of research in modern science.
Why is the Earth's core iron, and not a heavier element?
Short answer: iron (and nickel) are extremely common byproducts of the supernova explosions that supplied the building blocks of the Earth, and are both denser than most other common elements: hydrogen, carbon, oxygen, etc. Longer answer, see _URL_0_
Stoner friend keeps trying to convince me that smoking pot doesn't cause cancer. How can this be true? Is marijuana smoke really that different from cigarette smoke?
From a recent review: "Cannabis smoke is carcinogenic in rodents and mutagenic in the Ames test. Cannabis smoke contains several of the same carcinogens as tobacco smoke at up to 50% higher concentrations and with three times the tar per cigarette." However, "it has been difficult to strongly correlate cannabis use and the development of human cancers." The studies that the review looked at gave mixed results, with some studies showing correlation between marijuana use and cancer rates, and other studies showing no effect of marijuana on cancer rates. So, currently there is no strong consensus one way or another in terms of the carcinogenic effects of marijuana smoking. The review can be found here: _URL_0_
Is there a finite limit to how large/massive a star can be?
Size can have different meanings when it comes to celestial bodies. As far as diameter, Eta Carinae is so large it's actually difficult to determine how large it really is. Eta Carinae throws off so much coronal mass that its solar wind obscures measurements of its radius. As far as mass, R136a1 is estimated to be 265 times the mass of our sun. The theoretical limit is between 150 and 200 solar masses. The idea is that more mass would tip the balance between gravity and the expanding force of the core.
Can radio/infrared/UV waves (etc.) heat up food too or is the microwave portion of the spectrum special?
They most certainly can, and they do! But hey all are differently absorbed by food. A typical electrical grill or toaster will heat up a wire through electricity untill it reaches a temperature, when it radiates mostly in infrared. It's a temperature lower than incandescent lightbulbs, that radiate a nice mix of visible light, the grill only glows red, but also emits a lot of IR. It's that radiation that cooks the food. However, those waves don't penetrate food very well, so only the "skin" is heated by them. The rest of the food is cooked by heat conduction from said skin. Therefore, the cooking result is different then a microwave oven.
Is there anything truly random in the Universe?
*Subjectively* it appears as if the universe is non-deterministic. According to quantum mechanics the outcome of a measurement can only be described in terms of probability distributions over multiple outcomes. However, there are interpretations of quantum mechanics (such as the [many worlds interpretation](_URL_0_)) that allow for an objectively deterministic universe. In this sense you could know all future and all past by simply knowing the present. This concept is also known as [Laplace's demon](_URL_1_). At the end of the day it seems like the jury is still out.
Why do we get "goosebumps" when it's cold out?
The goosebumps cause you hair to stand up..let me explain. Erector pilli muscles attached to body hair just under the skin contract when certain stimuli are present, this causes the hair to stand up. The goosebumps you see are like the bulge you get on your arm when you contract your biceps. The muscle fibers are shortening, causing the middle of the muscle to get thicker and protrude. Here's a [reference picture](_URL_0_) to help you understand. We get goosebumps when it's cold to try to trap the warm air rising off of our skin to help keep us warm. Of course this doesn't work very well since our body hair is so fine and short, so scientists think this is mostly a leftover response from when our ancestors still had hair like chimps.
Are galaxies moving and if yes, is there one "center" of the universe they orbit around?
Yes and no, respectively. Galaxies don't just sit there stationary - for the most part they're moving away from one another as the Universe expands, and then on top of that they have some additional motion as well. But they don't orbit around any common center. As far as we know there is no center of the Universe.
Since the earth orbits in an ellipse, and sometimes the distance between it and the sun can differ by thousands of miles, why does a slight tilt affect climate and seasons so much?
Axial tilt affects the season because it affects the duration of a day and the "altitude" of the sun in the sky. It's not simply because some parts of the earth are closer to the sun. Longer day means more exposure to the sun. When the sun is "higher" in the sky, its heat and radiation have less atmosphere to travel through, thus more heat and radiation reaches the surface of the earth.
If Earth's orbit around the sun is elliptical, which causes Earth to be well over a million miles closer to the sun at some points than others, why is that unnoticeable while a slight tilt of the earth's axis one way or the other causes drastic climate change (seasons) to occur?
The answer gets into a lot of math, but you have to realize a million miles sounds like a lot until you realize the Earth's orbit is 93 million miles, so really it's a little more than 1% change. Now just think about the length of daylight during the summer and during the winter. That is way more than 1% change. Also the sun is higher in the sky. Take a flashlight. Hold is at a low angle relative to the floor. See how the light is spread out. Now hold it at a high angle. The light is more concentrated. The energy is over a smaller area, allowing us to heat up. _URL_0_ The variation in the Earth's orbit and tilt are responsible for the Milankovitch cycles. _URL_1_
What happens inside a landfill?
Microbes! Microorganisms will eat up a lot of the organic waste and often will produce methane and CO2 as products. Some can use metals as reducing equivalents to get energy and slowly degrade it. All of this metabolic activity can have a build up of heat which helps the decomposition of things that microbes can't eat such as some plastics. As organic molecules start to leach out of the plastic, they can get metabolized (quite slowly) and the plastic will begin to lose some shape. Basically, it's all thousands of different microbe species going about their lives.
Why is carbon so rare compared to oxygen in the inner solar system? Why don't we have tons of carbide minerals on earth?
Largely because of the quantities of the elements in the universe. The Milky Way, which seems to be a generally good indicator of the broader universe, has much more oxygen than carbon. 10,400 PPM are oxygen, while only 4,600 are carbon. Source: Croswell, Ken (February 1996). Alchemy of the Heavens. Anchor. ISBN 0-385-47214-5.
If you were to make a tire hydrophobic, would it increase or decrease traction on a wet road?
Styrene-butadiene has a contact angle of 106-114 degrees, so it's already hydrophobic. The performance of superhydrophobic materials is heavily dependent upon the microscopic/nanoscopic surface geometry. You could apply a coating to a tire which would last for a little while, but tires wear down. It would be very difficult, and cost prohibitive, to engineer a tire, such that as it wore, the removal of microscopic layers reliably resulted in a renewed surface microstructure.
How far can an optical telescope see?
Yes and no. It depends on the mean free path. Mean free path tells you how far a photon on average will travel before it hits something. For example, we can't see stars on the direct opposite side of the galaxy (looking through the center) because the mean free path is shorter than the distance between us and the star. I don't know what the mean free path of space is, but it is way way way less than the size of the universe. Edit: l=1/(sigma*n) where l is the mean free path, sigma is the cross sectional area of the collision, and n is the number of particles per unit volume.
Since symptoms like coughing are methods for expelling disease from the body, do medicines like cough suppressants extend our exposure to illness?
Coughing is a method of expelling the disease that infects others. It's a way that airborne diseases spread, through things like droplets of mucus. However, that's not how we eliminate the disease. Diseases are eliminated from our body by our immune system. Coughing is the result of bronchial irritation, not the method by which we eliminate disease.
Gold is often found as pure gold nuggets. What other elements can be mined in non-compound, pure elemental form?
Metals found in their pure state are referred to as Native Metals and the [wiki page](_URL_1_) lists the different elements which can be discovered in native form. In addition to gold, it appears that copper, silver and platinum are the other elements which have been commercially mined in native form. In the case of copper, the [upper penninsula of Michigan](_URL_0_) is particularly rich in copper but the last native copper mine ceased operation in 1969.
How did bees evolve stingers if they die after using them?
PocketBuckle is correct, though it is worth adding that bees (not wasps) die after stinging, only worker bees sting and they cannot reproduce anyway. The advantage of the 'suicidal' sting is that far more venom is injected, making it a more effective defense of the hive.
How did bees evolve to have stingers?
Stingers are present in large groups within the suborder Apocrita, including many social and solitary wasps, and also many ants. Basically the stinger is a modified form of the ovipositor (egg laying organ, which also means that only females have stingers) and may or may not have venom. Stingers are used for both offense and defense in predatory wasps and ants (such as paralyzing the prey). So basically you could say that the ancestor of bees already had a stinger. Bees also have much use for a stinger in their defense against predators such as wasps and hornets. Their [barbed stingers](_URL_0_) are especially useful for that as it is easier to penetrate the exoskeleton that way. The stinger also does not break off and kill the bee, this only happens when the skin of the victim is very thick, such as in mammals.
Do antidepressants cause any permanent changes in the brain that persist even after stopping them?
This is a very interesting topic that is extremely complex not well understood. [A 2016 study](_URL_1_) of nearly 2000 individuals found that expression of 129 genes was significantly different between individuals with and without depression. People that had recovered from depression displayed a shift in gene expression towards the control (never depressed) group. Another [study](_URL_0_) found that genes associated with synaptic function were also affected by depression. Research is now indicating that antidepressants are effective partly through indirectly impacting gene expression which should have lasting effects even after someone has stopped taking them.
Why do our limbs tingle or get numb when they "Fall asleep"? Also why does it hurt? And what happens inside the body when this happens ?
Unrelated, but can someone please explain to me rain pain. It doesn't happen everytime it rains , but the type of discomfort I get in my elbows or knees happens only when it rains. Someone told me that it had to do with barometric pressure.
Why do air bubbles in bottles sometimes split ?
It's more energetically favorable to have less water-air interface area, just like it's more energetically favorable to have the air on top of the water. In this case, the split bubbles reduce the surface area by making rounder shapes, which offsets the energy required to lift the water in between up that little extra amount.
Why is time 1-dimensional? Is 2,3,n-dimensional time possible in any 'other' universe, just like we have multiple dimensions of space?
Just like we tend to assume, from experience, that space is 3 dimensional, we naturally assume that time is one dimensional. What is a dimension? Operationally, you can think of something being n-dimensional if you need n numbers to specify a point on that something. How many numbers do you think is required to tell the time? In my experience, just one. However this is something put in by hand, a guess if you will, it's not derived from any more fundamental principles. However people are out there who play around with 2-time physics. I met a guy in Italy, Itzhak Bars, Turkish guy, who does that kind of stuff. His talk, which supposed to last 1 hour, ended up taking 2 hours due to the curiosity of the audience (the irony). Anyways it kind of went over my head, but you're free to dig into it if you want.
Have any bacteria developed alcohol resistance in the same way as antibiotic resistance?
Bacteria are definitely capable of becoming less sensitive to alcohol disinfectants, and has been observed for a long time. Resistance has been seen to occur by changing the fatty acid composition of the membrane, and I'd imagine it's also possible by reducing surface permeability. An area of current interest in the production of alcohol biofuels is generating fermenting organisms that can tolerate higher levels of ethanol. It's also interesting to note that bacterial spores are typically very insensitive to killing by ethanol. Spores are incredibly tough to a wide range of things that would kill an active bacterium very quickly. The main way to kill C. difficile spores is bleach, because they're just so insensitive to everything else. _URL_2_ _URL_1_ _URL_0_
Why does bread get moldy relatively quickly, while other carb-based foods (sugar, dry pasta, crackers, etc.) don't?
Bread is about 50% carbohydrate (sugars, starches, and fiber), 10% protein, and I have to assume that most of the rest is water weight. That's fairly low in water and protein, so bacteria don't grow well on it, but better water scavengers like molds can grow here. Bread also has trace elements that are needed for life (like Iron, for example) that come from being made of other living things (wheat, eggs, yeast). Sugar has no protein content, so it is extremely nitrogen poor. It is a relatively pure chemical sample (sucrose). You need nitrogen for earthling life, and probably all life. Dry pasta has a very low water content, and this discourages all growth. Same with crackers. When you add water to these items... I dare you to leave it on a counter for a week and then eat it (please don't).