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[
"Does the moon experience \"Earth Eclipses\" ?"
] |
[
false
] |
[deleted]
|
[
"You just flip your perspective. What we on Earth call a lunar eclipse is when our (the Earth's) shadow covers something else (the moon). And a solar eclipse is when some other shadow (the moon's) covers (part of) us.",
"So every time Earth sees a lunar eclipse, on the moon some other shadow (the Earth's) is covering us (the moon): this would be a solar eclipse. And every time the Earth sees a solar eclipse, on the moon our shadow (the moon's) is covering something else (a part of the Earth): this is a 'lunar' eclipse.",
"The eclipses happen at the same time, you would just call them the opposite because they have opposite geometries.",
"The only difference (because of the difference in sizes of the two objects) is that on the Earth a lunar eclipse is visible to half the planet, and a solar eclipse is visible to a narrow band of the planet. While on the moon both types of eclipses would be visible to half the moon."
] |
[
"There was one early this morning, it's called a ",
"lunar eclipse"
] |
[
"Almost. During a solar eclipse on Earth an observer on the Moon would in fact see the Moon's shadow on Earth, but it isn't big enough to cover a meaningful fraction of the planet.",
"Looks like this: ",
"http://apod.nasa.gov/apod/ap990830.html"
] |
[
"If a nuclear payload was inbound via ICBM, would a ground observer be able to see it coming before the explosion?"
] |
[
false
] | null |
[
"Yes",
"."
] |
[
"In the terminal stage, the reentry vehicle (RV) has little to no propulsion, and is just falling on a ballistic trajectory. So no rocket exhaust.",
"However, reentering the atmosphere from space generally means traveling at very high Mach numbers, so the flow around the RV is strongly hypersonic. The air is strongly shocked, which increases its temperature, and heating of the air and the RV causes a visible glow."
] |
[
"Yup. RV's move at hypersonic velocities but they would be white hot and at a distance they would appear to be moving rather slowly.",
"If you kept watching, it would be the last thing you see as the explosion would likely blind you even if you were outside the blast radius"
] |
[
"Why do we use speed *bumps* rather than furrows?"
] |
[
false
] |
Furrows as in digging out the road like an . Is this more dangerous and if so how?
|
[
"A furrow or trench would likely collect all sorts of crap. Leaves, trash, dirt. In rain it would be more likely to flood, making it harder to see. In snow, it would fill up and become useless (or a traction hazard). It would be harder to see from a distance, making it more likely that people would miss it and slam across it. ",
"I'd also imagine the edges would get damaged more easily as well, especially the far lip, which would take the brunt of the tires of fast-moving vehicles."
] |
[
"A bump can be added anywhere, even years after the surface was made, with a little extra material. You can bolt them down, form them from a bit of extra asphalt, etc., and it doesn't collect water which can lead to everything from mosquitoes to ice damage. ",
"A furrow would require much more work to install (cutting down into the road), it requires engineering both to ensure it doesn't create a weak point in the roadway but also that it drains properly, etc.."
] |
[
"Water collection would freeze in a trough making its depth moot & dangerous"
] |
[
"Is the color of a plasma due to a jump from only one shell to another, and not any other shells?"
] |
[
false
] |
In other words, can an argon plasma (purplish) show up as different colors if the electrons are excited to a "further away" shell? Everywhere I look says the colors of various gases are one color, but the presence of multiple energy levels in atoms makes me think there should be a variety of colors dependent on how much energy you are sending to the gas.
|
[
"You can have many possible jumps! And the color from each one can be revealed by a spectrometer.",
"Hydrogen plasma will have ",
"three spectral lines in visible light",
". The reddish-pink line produced by a 3>2 transition is the lowest energy and gives low-pressure hot hydrogen ",
"most of its distinctive color",
" but the other lines (aqua-colored 4>2, blue 5>2) are always there to some extent."
] |
[
"Increasing the \"energy\" of a plasma will only make more plasma, the thing with quantum mechanics is that light interacts with \"matter\" in discrete amounts, so when we are looking at a system with only hydrogen, there are only discrete increments of light that can be emitted via electron excitation. The reason increasing energy only produces more plasma is the same reason neon lights might take a minute to \"warm up\". This involves the thermal energy of the system helping with the vibrating reaction, why the potential electric energy applied does a similar thing but to a much stronger effect.",
"As for the relationship of energy and ionizing electrons. Once an electron has managed to escape the potential well of an atom and become ionized it is already involved in another potential well (if we are discussing plasma). This comes back to my earlier explanation about discrete amounts. ",
"If you want to make a plasma ball that's more blue, you would need to use a material that produces a \"blue\" wavelength of light strong enough to be the major player in a plasma state. "
] |
[
"So could increasing the energy make the plasma more aqua or blue? I.e. is there any sort of relationship with the energy of the ionizing electrons?"
] |
[
"Can 2 sperms enter one egg?"
] |
[
false
] | null |
[
"Yes it can, even in humans. However the result is something called a ",
"molar pregnancy.",
"These need to be removed, usually by dilation of the cervix and curettage with suction. Essentially, the contents of the uterus need to be sucked out. Not only is the pregnancy not viable, there is a risk the will become cancerous and metastasize to the woman's liver, lungs, and brain."
] |
[
"Yes. This is called polyspermy. The typical result is an invaible zygote."
] |
[
"In humans, yeah it can, but its rare and does not lead to a viable embryo most of the time. ",
"http://my.clevelandclinic.org/health/diseases_conditions/hic_Partial_Molar_Pregnancy"
] |
[
"Why do cats sit on/in strange objects?"
] |
[
false
] |
Why is it that if you place a box on the ground, or a piece of paper, a cat will inevitably sit in the box or directly on the paper? The best I can assume is that sitting in the box, due to the fact it has four "walls" gives a sense of security, or a feeling of being hidden. Was hoping someone in here may have an animal behaviour background and could clear this up.
|
[
"As far as sitting in boxes go, it is rooted in play and psuedo hunting. A cat in a box can not worry about something bitting at it from behind and simultaneous hide itself from whatever it is \"hunting\". So your right that alot of it is based in feeling secure.",
"Now for the sitting on paper thing, I've actually been searching for this for a long time and i've never heard a good answer. It may be a very important thing to know when we are talking about an exceedingly small box (ex. shoe box lid) that may be closer to a piece of paper than a large box. I've done far more cat behavior learning than my advisor would prefer lately. "
] |
[
"It's an innate survival mechanism. They sit on objects that are already out of the ordinary in an environment. To avoid detection, they seek to avoid disrupting any patterns. If a pattern is already disrupted, it already stands out. By occupying that space, the total disruption to the environment's pattern is minimized. If the floor is all homogeneous except for a piece of paper, they will sit on that as to minimize detection. ",
"I believe someone tried covering the floor in paper with one spot open, and the cat chose the bare floor spot. I'm trying to find that citation."
] |
[
"Sadly, yes. I work with fertility control on feral cat populations. "
] |
[
"How were forest fires contained 150 years ago, especially in remote areas like the west?"
] |
[
false
] |
It seems like if there was a fire back then in say, what is now Idaho, it would burn down the entire western US and there would be no way to stop it.
|
[
"Well, in short they weren't contained. Only natural obstacles like cliffs, rivers, sparse vegetation, wetlands, rain, and the fact that the wind doesn't blow in all four directions at once, limited the forest fires. ",
"That would be the case today as well, but we have put suburbs and towns everywhere so we simply can't let fires go the way the wind blows them anymore. Fires weren't a big problem back then because there simply wasn't that much human property in the way of the fires. In 1850 there was only about 23 million people in the US. If you took a thousand long steps in one direction, and then turned right 90 degrees and went a thousand more steps, and then did it twice more, the square area you would have walked around would be shared by you and just one more person in 1850. Today you will share it with 30 people. So any random area there's a fire, its 1600% more property that the fire will destroy, that is why fires are a problem now, not then. ",
"PS: Though it should be noted that towns did burn to the ground back then because of forest fires. It was just far less likely to happen because towns were smaller, fewer and farther apart. ",
"PPS: Oh, and people tended to use the trees near a town to build the town, so there was usually open barren area around towns to protect against forest fires. At worst some crops around the town, that they could burn away before the forest fire arrived. The forest fire brings extra wind because of the movement of the hot air upwards, so if you do a small burning of some fields of crops there's little of that and the wind doesn't make the fires jump across the road to your buildings. Whereas when the forest fire arrives the wind gusts will make the fire skip from the crops to the buildings across the road. They did not normally keep trees as pets close by their suburb for it to look nice and be a huge forest-fire hazard. But we do today. "
] |
[
"There's also the fact that because fires occurred more frequently there was less accumulated fuel for them to burn. Essentially more frequent fires = smaller fires (with the caveat that there were always exceptions).",
"Then we decided we didn't like stuff burning so we got a lot better at putting out forest fires before they did much damage. Unfortunately this meant the gradual buildup of dead plant matter which can turn a minor fire into a raging inferno.",
"I don't know if the USA practices controlled burns like we have in Australia but controlled burns can help (although there is always an element of risk)."
] |
[
"We do them, but not enough of them to prevent buildup/we waited too long in some areas so we can't do them there. "
] |
[
"Question about electromagnetic field."
] |
[
false
] |
I'm taking classical physics and we are studying electric fields. We obviously didn't go into that much detail about how the fields actually work. From what I've read, the electromagnetic force is caused by particle interaction of emitted photons, which carry the force. I've read tons of wiki articles that are obviously above my level, but I'm still really confused on the difference between these photons that carry the electromagnetic force and the photons that are emitted by say, a candle. Also any explanation of force carrier particle transfer in general would be much appreciated. Thanks in advance.
|
[
"My specialty is spectroscopy in a chemical sense, so I have a bit of comfort with virtual states and photons, but I'll defer once an expert arrives.",
"Generally, from the ",
" point of view, the candle interacting with your eye and the nucleus interacting with the electron emit the same photons. Remember that photons don't time-evolve (though once you start putting them into wavepackets and the like, ",
" can.) ",
"The photon from a candle is emit as a result of blackbody radiation, and is in fact really some streams of photons all being emit with a particular energy profile as defined by the property of blackbodies. It carries force (energy) from the candle to your eye, where it excites a transition in one of your photoreceptors and you interpret as light.",
"The photon traveling from the nucleus to the electron of an atom is also carrying energy with it (and in fact, the two are constantly exchanging photons.) The main difference is in lifetime. The carrier photon in this case is much, much shorter-lived--so short-lived, in fact, that it's called a \"virtual particle.\" Basically, we have no way to directly observe a virtual particle (typically) because of its extremely short lifetime, but we ",
" do the math that shows the sort of behavior that exchange of these particles would result in, and say, \"oh, so the nucleus and the electrons behave as though they are exchanging virtual particles.\" The big take-home difference comes from the uncertainty principle. We can know the energy of the candle's photons pretty well, but the virtual photons in this case exist for such a short amount of time that we can't say much of anything at all about the energy being carried. This has the additional result that, because of their short lifetimes, these carrier photons can be thought of as having ",
". I still have fun wrapping my head around that one.",
"TL;DR - The significant difference in the lifetime of real and virtual photons results in cool implications for the energy and mass of the photon."
] |
[
"What you're reading about is a theoretical model known as ",
". See in the early 20th century, we had two theories. Classical electromagnetism described electromagnetic interactions as the effects of fields created around charged particles. This theory predicted propagating waves in electromagnetic fields (ie. light and other EM radiation) that travel at a constant speed, c, which then led to the discovery of special relativity. SR predicts that information cannot be transmitted faster than the speed of light. Thus we have the first sign that there's a problem here. How can charged particles affect other charged particles over a long distance if information must propagate at a finite speed?",
"The other major theory we had was \"classical\" quantum mechanics (what we now call nonrelativistic quantum mechanics). This described how single particles, ie. wavefunctions, interact with fixed potentials, but it didn't explain how these potentials (that is, electromagnetic fields) were generated, it couldn't describe creation and annihilation of particles, and it wasn't ",
", that is, it didn't fit with special relativity.",
"Second quantization was the solution. The idea is to suppose that there's a simple harmonic oscillator (think masses on springs) at every point in space. This field of SHOs can be excited to produce waves which propagate at the speed of light. These are photons. However, small perturbations, such as an accelerating charge, have effects that may not look like freely propagating waves, but still transfer momentum over a distance to other charged particles. Thus, we see the effects of electromagnetic forces. These effects are called ",
" because mathematically they are similar to free particles, but they have a property called being \"off mass-shell,\" meaning their energy isn't exactly E",
" = m",
" c",
" + p",
" c",
" . ",
"We also refer to them as virtual particles because of the way we work out the interaction of two charged particles. We work out the solution for two particles, say electrons, transferring momentum by exchanging one photon with momentum equal to the amount transferred. Then we add all the ways that this can be done by exchanging exactly two photons (for the nitpickers, I know there are other types of 1-loop diagrams). Then we add in the effects of exchanging exactly three photons and so on. Each step contributes a little less than the last. The actual effect is the infinite sum of all these possible interactions. By the way, in practice we work out the first few steps until we have high enough precision to be satisfied.",
"Edit: I hope that made some sort of sense. It's quite tricky to try to describe the basic ideas of quantum field theory without using any math."
] |
[
"The other responses are not bad, but here's my try:",
"In quantum field theory, all objects in the universe are part of a field of some sort or another. The 'excitations', or localized wiggly pieces, of these fields are manifested as little subatomic particles. When the pieces are interacting, the interactions take place by way of fields and so can also be represented using particles.",
"In classical electromagnetism, you learn about one set of these fundamental fields - the electric and magnetic fields. The particle that represents these fields in QFT is the photon; Photons are little 'ripples' of electric and magnetic fields. Whenever you see a photon in a QFT diagram it represents a piece of the electromagnetic field.",
"So, even classically speaking, the charges and the electromagnetic field interact directly. Two charges interact ",
" this field- they don't directly exert forces on each other. This is what gives rise to the verbiage \"charges exert force on each other mediated by the electromagnetic field.\" The point of this is simply that mediation has nothing to do with quantization.",
"As far the photons and the like, it so happens that every interaction in electromagnetism can be represented using feynman diagrams, which break down the interaction into discrete classes particle exchange scenarios. So, the classical force between electrons can be calculated using a diagram where the first electron emits a photon which gets absorbed by the second electron. The photon has momentum, so both of the electrons change momentum; there's a force between them.",
"The point of what I'm trying to say is that the electromagnetic field is a mediator between charges even in classical electromagnetism- and there's no need for an explanation for it; it's right there in the theory. The quantum mechanical version does not actually add other sub-objects which explain how the classical picture works; the photon is just another name for the electromagnetic field."
] |
[
"Why can't camera manufactures make a camera with the equivalent dynamic range of the human eye?"
] |
[
false
] |
There's HDR photography and graduated filters to help deal with this problem but it would be easier if it just worked.
|
[
"As others have said, there is a lot of awesome things our visual processing system does beyond our eyes, and processing algorithms have a long way to go. In fact, the image quality from just our eyes is relatively low compared to our larger sensor camera systems, limited in resolution by around 1 arcminute or ",
"2800 LW/PH",
" in a standard test. This drops off rapidly from the center of our field of view. ",
"With respect to dynamic range, the eyes can chemically adjust the gain of the rods and cones. The cones can change their sensitivity chemically within seconds, though rods can take 20 minutes. This part is more like dynamic contrast and changes the entire scene's intensity, like adapting to a dark cave then walking outside into bright sunlight.",
"If we're talking about one scene, the eye and brain processes, integrates, and infers information very fast using ",
"saccades",
". As it rapidly darts around the field of view, it intelligently and quickly changes gain, aperture, and integration time/shutter speed forming a ",
"HDR",
" ",
"tone-mapped",
" ",
"panoramic",
" ",
"super resolution",
" ",
"focused stacked",
" result. In addition, our brains perceive light logarithmically and our devices display everything in a smaller linear range, but tone mapping done right can easily combat that.",
"But to question on dynamic range: it is limited by signal to noise ratio. There are ",
"several sources of noise",
". There is physics limits like shot noise. There is ",
"quantum efficiency",
", pixel-to-pixel unformity, ",
"fill factor",
", dark current read noise, amplifier noise, quantization noise(bit depth), etc. Sampling a larger area with a larger sensor is also one way to increase the signal.",
"Large strides continue to be made in improving dynamic range",
". Recently, a lot of it has been read noise. CMOS sensors lowered noise significantly by putting amplifiers closer to the sensels, drastically reducing noise gained when the charge was traveling off to the amplifier. But there has been a lot of other work.",
"At 14.4 stops and reports that our eyes see up to 14 stops, it might seem like we're there, but the way it is measured is different and I don't have a good real comparison.",
"But the fact remains that we can't just directly use all that information without a high dynamic range display medium. Algorithms are getting better for tone mapping it to our mediums, but is very easy to ",
"overdo",
" with some of them, so ",
"other people",
" do it ",
"manually",
". If it is done right, it looks real, and you can't easily tell it's HDR."
] |
[
"Time is a factor here. Videocameras change aperture over time. Human eye does this too. So when you look at something bright, you're not necessarily even seeing the not-bright stuff in your field of view that you're not looking at.\nEven the sensors in our eyes change how much light they need to produce a signal (to the brain). E.g. nightvision. Again though, this is over time."
] |
[
"Your eye is only able to see a very small area clearly. Thus only this area needs to be perfectly adapted to the brightness. But more importantly, we see light in a logarithmic way, that means that light which is 10x brighter, seems about twice as bright to us. Therefore our devices would need to show much finer differences of color in dark areas than in bright areas. But they don't, which is why it's so hard to make convincing night scenes in movies. Our devices display light in a linear matter..."
] |
[
"NASA's JTrack 3D satellite viewer is down/gone/toast! Does anyone know of any mirrors or how I can download everything and run it independently of NASA."
] |
[
false
] | null |
[
"I need this for teaching about space. ASAP."
] |
[
"Could you install Stellarium and use its search function to display satellites in real time? I've tracked the ISS a couple of times with it."
] |
[
"Going to this website (",
"http://science.msfc.nasa.gov/realtime/",
") which looks promising results in this.",
"Error 503 Service Unavailable\nService Unavailable\nGuru Meditation:\nXID: 898967947\nVarnish cache server \n"
] |
[
"Is there any limit to how large a Bose–Einstein condensate could get?"
] |
[
false
] |
[deleted]
|
[
"This paper is talking about experimental difficulties with creating large condensates, not a theoretical limit on how many atoms you can have. Also, when you quote them you should use",
"qouted text.",
"Please provide sources for your first sentence as it seems to have limited information content."
] |
[
"A bose-einstein condensate depends on there being particular elements and relies on special conditions, such as a dilute gas. They are also extremely fragile to outside conditions.",
"http://massey.dur.ac.uk/resources/mlharris/Chapter2.pdf",
"Interactions between superfluid helium atoms, for example, prevent\nmore than $10% of atoms from being the ground state even at temperatures\nvery close to absolute zero [93]. The liquid nature of the helium system\nmeans that multi-body interactions and non-condensed fractions cannot be\nignored or treated as perturbations, making helium condensates very difficult\nto describe theoretically",
"There are many more such quotes in the nature of condensates on there- long story short, any sort of interaction, such as those in a liquid or a solid, makes it hard to form a condensate. ",
"The earth is solid, so it wouldn't form a BEC and even if it did a whole planet would likely not be stable enough to form a condensate.",
"http://rsi.aip.org/resource/1/rsinak/v78/i1/p013102_s1?isAuthorized=no",
"We describe the setup to create a large Bose-Einstein condensate containing more than 120×106 atoms. In the experiment a thermal beam is slowed by a Zeeman slower and captured in a dark-spot magneto-optical trap (MOT). A typical dark-spot MOT in our experiments contains 2.0×1010 atoms with a temperature of 320 μK and a density of about 1.0×1011 atoms/cm3. The sample is spin polarized in a high magnetic field before the atoms are loaded in the magnetic trap. Spin polarizing in a high magnetic field results in an increase in the transfer efficiency by a factor of 2 compared to experiments without spin polarizing. In the magnetic trap the cloud is cooled to degeneracy in 50 s by evaporative cooling. To suppress the three-body losses at the end of the evaporation, the magnetic trap is decompressed in the axial direction.",
"You can see they're doing all sorts of weird physics things to make it work and that even so they can only trap a small number of atoms. And it would be rather hard to put the entire earth in a magnetic trap."
] |
[
"BEC's themselves are still under a lot of investigation as a general universality class of materials. I don't think the answer to this is known - experimentally speaking.",
"Interestingly, my work tries to answer the compliment to this question - how small can we make BEC's? "
] |
[
"In a microwave, why doesn't the rotating glass/plastic table get hot or melt?"
] |
[
false
] | null |
[
"The short answer is that the plate doesn't get hot because that the material it is made of is very bad at absorbing electromagnetic radiation at the frequency used by the microwave oven (~2GHz). ",
"Microwave ovens work on a principle called ",
"dielectric heating",
". Within the oven there is a microwave generator that spits out EM radiation which then bounces around, ",
"roughly as shown in this diagram",
". As this radiation sloshes around, part of it is absorbed by the stuff inside of the oven, as a result of which you get local heating. How well a material can absorb this radiation is quantified by the imaginary part of its ",
"permittivity",
". This value in turn is related to the kinds of transitions (rotations, vibrations, changes in the electronic state) in the material can couple to the EM radiation, ",
"as shown in this graph",
". ",
"Because materials have different chemical compositions and structures, their value of the imaginary permittivity in the GHz frequency range will vary drastically. As a result, some substances will rapidly heat up in a microwave oven (e.g. water), while others (e.g. glass or certain ceramics) will only absorb far less energy and will be much cooler. The same effect explains why sometimes part of a dish that you quickly heat up in a microwave can feel scorching hot, while others seem as cold as it was before you microwaved it."
] |
[
"Bowls and plates that are \"microwave safe\" should be transparent to microwaves, and they should not get hot by themselves. When you have a mug that gets much hotter than the liquid inside, it's not microwave safe."
] |
[
"Maybe they got hot from the food being hot and not from the microwave itself? "
] |
[
"If the moon's gravity affects the tides, how come there isn't a visible effect on people, land etc.?"
] |
[
false
] |
I've searched on google, but I haven't been able to find a clear and concise answer to this. Thanks! :D EDIT: Thank you all for the responses! I think I understand this a bit better now! :D
|
[
"Although it's not clear this is what you're asking, the moon's gravity does create a \"tidal effect\" on both the oceans and the land mass. That is, there is a \"tidal bulge\" in the earth's surface of about 1 meter due to the moon's gravitational effect (I've read conflicting numbers but this is the order of magnitude.)",
"In terms of the moon's effect on people, if you mean why don't we stretch or something due to the moon's gravitational effect then, well, in fact we do but it is a matter of scale. The moon creates tidal effects on the earth because of a difference in the gravitational pull between the closer and further sides of the earth. This difference in gravitational pull is a function of the difference in distance to the moon between the closer and further sides of the earth, which is non-negligible (in fact it is proportional to r/R",
" where r is the diameter of the Earth and R is the distance between the Earth and Moon.)",
"In the case of something the size of a person, the difference in gravitational pull due to the moon between the top of your head and your feet is negligible, so the effect is so small as to be not measurable."
] |
[
"The thing to realise is what a 'tidal force' actually is. It's not just being affected by gravity - a tidal force is what you get when you get a gravitational force that ",
" along a body.",
"So, the reason for tides is that the Moon's gravity is stronger on the near side of the Earth than the far side (because it's closer!), which raises a tide. People are very small in comparison, so there is almost no tidal force on the scale of a human. The gravitational difference between your head and your feet is insignificant. ",
"To get a tidal force on the scale of a human, gravity would have to be really strong. As you fall into a black hole, for example, you get 'spaghettified', stretched out, by the extreme gravity - this is due to a tidal force. "
] |
[
"You are a fraction of a gram lighter when the moon is overhead than when it is not visible. It's not enough to notice.",
"Tides are a lot more complicated than they look. It's not as if the Earth is anchored in space and the moon is just pulling the oceans in different directions. The whole Earth is pulled toward the moon, but the side of it near the moon is pulled a little harder. Tides are the Earth deforming itself in response to these varying forces."
] |
[
"How long will it take before someome makes an subreddit called /r/simpleaskscience?"
] |
[
false
] | null |
[
"/r/explainlikeimfive",
" "
] |
[
"This is probably isn't the best place to ask this question, because its not actually science, but I'll answer anyway. There aren't a whole lot of meta posts in askscience. ",
"You can always post in ",
"/r/explainlikeimfive",
" with a link to the post in ",
"/r/askscience",
", or you could ask for clarification from the poster. ",
"I, for one, am always happy to simplify my answers. It's easy for someone to forget the person reading doesn't have the same background they do, that it may not just be an issue of exposure to information, but the basics of it as well. It's valuable feedback for the posters, if their answer is going over your head, for you to tell them. It doesn't necessarily mean they ",
" simplify it, but they or someone else might. ",
"So, in short - if you don't understand, ask. If you don't want to, post in eli5. If none of those options suit you, you can always create a subreddit. "
] |
[
"Thank you."
] |
[
"Why does the winter cause so many potholes?"
] |
[
false
] |
[deleted]
|
[
"Two major effects cause this. One is simply thermal expansion and contraction. The other is called \"frost heaving\". This is what happens when water is allowed to get below the road surface, freeze, and expand. It tends to occur on low cost or poorly engineered surfaces. "
] |
[
"The water that gets in the cracks in the pavement freezes and expands, which causes it to fracture, resulting in potholes. This doesn't happen in spring and summer, obviously."
] |
[
"In the UK at least, grit and salt are spread onto the roads prior to, or during spells of freezing weather. Would either of these contribute to the degradation of the road surface?"
] |
[
"If aluminium has no fatigue limit, why are flexible shaft couplings often made from it?"
] |
[
false
] |
If I understood correctly, aluminium is bound to fail after a high enough number of cycles, unlike for instance steel, which can take small loads indefinitely. Then why is it that a huge amount of flexible shaft couplings seems to be made from aluminium, which would seem to be a horrible material for this application?
|
[
"It also could be a sacrificial piece, where they plan for the aluminum piece to fail in the event of an overload, rather than the more costly or important steel parts. Similar to a shear key used in shafts couplings. Rather than have the whole thing be ruined if there was a problem, a cheap Al piece takes the load and predictably fails"
] |
[
"Because those couplings are not meant to last for a long time. ",
"Depending on the manufacturer, it could be a planned obsolescence, material cost, machining/manufacturing cost decision. ",
"They could predict that said coupling will only take 30-40 loads and aluminum could withstand that, so there was no need to upgrade. ",
"Aluminum is much cheaper, and much easier to work with than most any other metal, so you'll see it in a lot of applications where it's not the ideal material, but it works. "
] |
[
"Couplings are generally the easiest to access to repair as well as cheaper to produce/replace/repair then say a gearbox, motor, or other more expensive part. I don't see many aluminum Couplings where I work. Plastic, rubber, softer metal alloys, as well as disc-flex Couplings are pretty common, but part of their design is to be the weak point in the system. The best way to get the longest life of any coupling is proper alignment. "
] |
[
"Do the asymmetries in size and structure between the left and right lungs cause any differences in gas exchange rates? In other words, does the right lung \"breathe more\" than the left lung due to it being bigger?"
] |
[
false
] |
I didn't even know they were different sizes till today, and now I'm really curious about it
|
[
"Yes. Pulmonologist here. More breathing is done by the right lung. More blood flow goes there too, and in normal physiology ventilation is mostly matched to perfusion. ",
"If we are calculating post operative lung function for a resection, we typically calculate using 10 functional segments in the right and 8 or 9 in the left. ",
"https://en.m.wikipedia.org/wiki/Bronchopulmonary_segment",
"There is some anatomical variability which we can define using arteriography or more typically a CT scan. With functional disease of the lung, for instance COPD which typically affects the upper lobes more, we may also need a ventilation/perfusion scan (VQ scan) or cardiopulmonary exercise test to fully evaluate the lung physiology and anatomy to understand what we can safely resect."
] |
[
"Yes lung cancer is more common in the right. While the lower lobes are biggest, the upper lobes are most susceptible to smoking related damage and so we often see cancers in the upper lobes in those who have smoked."
] |
[
"Is this reflected in survival rates for lung cancer in left vs right lungs?",
"Come to think of it does this also affect the incidence rates? Is right lung cancer more prevalent because there's more going on, therefore more chance for a cancer to develop?"
] |
[
"Dark Matter - Dark Matter Interactions"
] |
[
false
] |
[deleted]
|
[
"In addition to what ",
"/u/fishify",
" said, you could also have a \"dark\" or \"hidden\" gauge sector that is completely decoupled from the SM and contains your dark matter. But then there is no hope for discovering it, since it won't interact with our detectors except gravitationally, and no hope for understanding why its density is what it is, so I don't think there's any research focused on it.",
"Much more common in the literature are models where the dark mater hidden sector is weakly coupled to the SM via messenger particles. I can't really say much more, since it's not my area of research, but there are lots and lots of papers/models on this sort of thing, under lots and lots of different names. ",
"1",
" ",
"2",
" ",
"3",
" etc."
] |
[
"No, we can't rule it out, and that notion has been explored. Such a proposal is made in ",
"this paper",
"; you can read about the paper ",
"here",
" in a piece at ",
"."
] |
[
"But then there is no hope for discovering it, since it won't interact with our detectors except gravitationally, and no hope for understanding why its density is what it is, so I don't think there's any research focused on it.",
"A few months ago there was a huge fuss in the community since it appears that there is a gamma-ray line in the Fermi data, meaning that there is some heavy particle annihilating into photons in the galaxy. Now, they cannot really be charged, otherwise we would have seen them, and the mediation cannot be gravitational for obvious reasons. So there are now hundreds of papers exploring the phenomenology of dark sectors communicating with the SM through a variety of ways. ",
"These were some of the ideas that I remember reading back then, ",
"http://resonaances.blogspot.co.uk/2012/05/how-to-make-line.html",
"(also, the discovery was made by a lone postdoc in the Munich MPI who went through the data. I suppose genuine German kebab had something to do with it)"
] |
[
"What is the role of a pre-combustion chamber in a rocket?"
] |
[
false
] | null |
[
"Most liquid rocket engines use ",
", pumps driven by gas turbines, to pump the fuel and oxidizer into the main combustion chamber. The various ways to do this are known as \"cycles\", and the ",
" drives the turbopumps by burning a small portion of the fuel in a preburner, the exhaust from which spins the turbine then goes into the main combustion chamber. The ",
" also burns a portion of the fuel in a seperate combustion chamber, but the exhaust is vented after exiting the turbine.",
"Turbopumps are used because large rocket engines drink fuel (and oxidizer) like crazy. The fuel pump - not the whole rocket engine, just the pump! - on a Space Shuttle Main Engine produces around 70,000 horsepower, in something about the size of a washing machine. The turbopumps are one of the most highly-engineered parts of the rocket engine and part of the reason the whole engine can have such a high power-to-weight ratios."
] |
[
"Here's a really good video on the internal workings of rocket engines by Scott Manley: ",
"https://www.youtube.com/watch?v=4QXZ2RzN_Oo",
"Basically, if you want to build a big engine, you need to get fuel into it ",
" and under ",
". To do this, most engines use pumps driven by a ",
", which in one way or the other produces high-pressure gas from the liquid fuel which then spins the pump. There are multiple approaches to this, the most common ones are:",
"Here's a vid of a Merlin 1D test",
"There are also some types that don't use pre-combustion:"
] |
[
"A hybrid rocket motor is provided with a precombustion chamber supplied with propellant from separate fuel and oxidizer sources. The propellant can be in the form of gas or liquid and injected substantially tangentially into the head end of the hybrid motor adjacent the oxidizer injector to form a propellant swirl. As the hybrid motor oxidizer is injected into the swirl, it is heated and gasified, and assumes a swirling motion which increases the oxidizer path length and thereby increases the dwell time of the oxidizer. The increased dwell time increases combustion efficiency and permits multiple restarts of the hybrid motor. The propellant may also be a combination of solid and fluid reactants. In one embodiment, the oxidizer injector is extended into the combustion chamber to form a toroidal precombustion chamber which has an annular nozzle adjacent a face of the oxidizer injector.",
"",
"https://patents.google.com/patent/US6807804B2/en"
] |
[
"A conductive cable over a light-year long is connected to a positive & negative pole, how long until current flows?"
] |
[
false
] |
Assuming an infinitely large power source for the current. What would the electrical dynamics be if a cable capable of carrying the current from the (-) end to the (+) end starting the second of creating the complete circuit? Do these electrical dynamics breakdown at some point of scale? At this scale could we watch the 'flow' of electricity?
|
[
"The current would start to flow as soon as the circuit is completed, but it would travel at a finite propagation speed.",
"Electrodynamics doesn't break down, but basic circuit theory does. Circuit theory is just a simplified way to look at electrical circuits without solving Maxwell's equations every time. You make certain assumptions, for example in small circuits you neglect the propagation time of electrical signals.",
"In larger circuits, and definitely in this hypothetical situation you've proposed, you need to consider the finite propagation speed of electrical signals. You have to really solve Maxwell's equations to see how this system will behave. What you'll find is that the electrical signal (voltage or current) obeys some kind of wave equation, where the wave speed is related to the capacitance and inductance of the cable. The signal will propagate like a wave down the cable with some speed v, and it will reach the other end after a time delay of L/v, where L is the length of the cable."
] |
[
"As RobusEtCeleritas says it will start flowing immediately. But the very long cable would not appear to the power source as a 'wire' from the plus to the negative side. It will just appear as a sort of 'vat' in which it can release and dump its charge. Normally, if you connect a meter long wire a similar thing would happen as well. HOWEVER, as charge accumulates in the 1m long wire if it is not connected, a charge accumulation will build up an electric potential in the cable which will oppose the terminal potential and the flow will stop. As charges spread through the light year long cable, the charge buildup in the cable will make it harder and harder for the electrons to leave the source. An electron, trying to leave the current source, sees more and more charge ahead of himself which will make it harder and harder for it to leave the source. So the current at first will be very large and it will start decaying. After a certain while, when the charges reach the end of the cable (after a couple of years) only a tiny tiny tiny current will be left as the potential is distributed evenly throughout the cable which makes the local electric field in the cable, driving the charges, almost negligible.",
"This is a very expensive way of saying: a light year long cable has an incredible resistance and the steady state current is almost 0. Only in the beginning a surge current will flow which will settle in the the cable to its steady state value. "
] |
[
"At this scale could we watch the 'flow' of electricity?",
"Yes. Really all we're getting at is the much more mundane situation of transient response. Take for example a transistor, billions of which are the basis of the computer you're using right now, your CPU has a clock rate, say 2 GHz, the higher the clock rate, the faster the computer. The clock rate, amongst other issues, is bottlenecked at the actual physical time it takes to push and pull electrons into and out of a MOSFET transistor. At a GHz clock rate, you have to be able to do it in a fraction of a billionth of a second. ",
"Electricity and circuits have a time scale to them that is a part of everyday electrical engineering. Transient analysis of circuits is an entire field of electrical engineering. Current does not flow instantaneously and it's not something that only matters in heady thought experiments on light-year long poles. "
] |
[
"Can over-using a hot tub be hazardous to your health?"
] |
[
false
] |
I have a hot tub. I sit in it for approximately 1-2 hours almost every night. I keep the temp at about 100-102 degrees Fahrenheit. Are there any health concerns with this amount of use? Either due to chemicals or heat?
|
[
"This question is not allowed to be answered because of the ban on asking for medical advice. From the guidelines: \"If your question includes the words “Me, I, or My”, and asks about the human body, then you are asking for medical advice.\". This is for liability reasons. You need to rephrase your question to something like \"Would using a hot-tub 1-2 hours every day have health effects for someone?\", and remove all references to yourself. Then, there's no liability issues if we answer it."
] |
[
"Thank you for pointing that out. No sidebars on mobile. >.<"
] |
[
"Good to know..if I grow testicles in the future. "
] |
[
"Question about scientific testing of \"psychics\" and the like."
] |
[
false
] |
I have always wondered about this, and never got around to putting my thoughts about it in text, so here goes, and I hope someone has a good answer for me. So here goes. I know that there is currently a "reward" of 1 million dollars put out to anyone who can prove any kind of psychic ability. Proof would obviously involve a scientific approach to testing. But my question is....does the strictly scientific approach actually inhibit any such abilities if they did exist? I say this with an anecdote of mine in mind, which blew my mind for a little while, but makes sense. Try not to laugh at my anecdote. It involves.....crackers and cheese lol. I love eating crackers and cheese, and will grab large stacks of crackers, and cut slices of cheese. I need half as many slices of cheese as crackers. I would grab somewhere between 10-20 crackers at a time, maybe more sometimes, I would never actually count. Then I would cut the cheese, never counting that either. Many times, I will cut a stack of cheese slices, but I feel compelled to cut, say two more. Almost every time I would do this, it would end up being the exact amount I need to have the correct ratio. I'm not saying I was being psychic, but after some thought and freaking myself out a little, I came to the conclusion that my brain can estimate decent sized numbers of similarly sized objects with really amazing accuracy. I have noticed this with other objects as well since then. But the thing is, after I realized this, I start thinking about it when I do it, and now I can't do it to save my life. If I'm not actually thinking about it, I can do it very consistently, but as I start trying to, I fail. So my question is.......if a "psychic ability" is basically just your brain being somehow amazingly tuned in to, say, people's facial expressions and mannerisms, and they can really accurately predict what they are thinking about or predict how they will react/turn out/etc, would actually scientifically testing this, or, basically FORCING this to happen, actually prevent any such abilities from being known? I know if I was scientifically put to the "cheese and cracker test", I would fail, because I would be actively thinking about it, aka, it wouldn't be my sub-conscious brain calculating and making a decision, it would be my active brain and thoughts trying to make those calculations and estimates, and I would second guess myself, just outright guess, etc. So, reddit, is this a thing?
|
[
"Its a very common phenomenon for psychics who have failed rigorous scientific testing to claim that their powers have been effected by the \"negative sceptic energy\" or something similar. There are several problems with this explanation.\nFirstly, its always \"post hoc\" - that is, the psychic takes the test, often claims that they feel good about it, everything went well, but when the results are negative, only then do they pull out the - \"oh its the bad vibes in this laboratory\" excuse. If this was a real phenomenon, and the psychics had real powers, one might expect them to notice during the test that things were going awry.\nSecondly, its an example of \"special pleading\". There is no reason to think that psychic powers if they existed would be affected by scientific observation. After all these people perform in front of crowds, television cameras and paying customers without apparent difficulty. The only reason that this excuse is invoked, is that when the powers are actually properly looked for, they are not there."
] |
[
"Source for any of that?"
] |
[
"Source for any of that?"
] |
[
"Do birds reuse existing nests that have been abandoned previously?"
] |
[
false
] |
If not, do birds avoid areas with old nests?
|
[
"Depends on the birds. Some will reuse old nests, fixing them up each year, while others will push the old nest and start again from scratch, while still others will wait until another bird has made a nest and then come in and eat their eggs and take over the nest.",
"And then cowbirds and cuckoos will just lay their eggs in another bird’s nest and fly away."
] |
[
"Adding to this... some species (eg Kestrels) will use stick nests built by other birds (eg Ravens) after they've finished nesting themselves. Tree hollow nesters (eg Cockatoos) will use a hollow after another species (eg Owl) has finished nesting in the hollow."
] |
[
"Yes, had some smaller birds build a nest on the porch of my rental house - wasn't bothering anyone, so I let them stay rent free. They took nearly the whole summer to raise a bunch of chicks to the point they coukd fly off.",
"The next summer a larger bird used the nest - but built it up in size and had a bunch of chick's that flew off in a matter of weeks.",
"I have no idea what kind of birds they were, but the larger did use the smaller birds nest - albeit as a base to build from, not as a complete home."
] |
[
"Introducing: The official AskScience chatroom on Freenode!"
] |
[
false
] |
Hello science enthusiasts and enthusiastic scientists! Also hello to non-enthusiastic scientists and non-scientific people who might or might not be enthusiastic. We are proud to announce the official AskScience IRC channel. In it, you can talk to scientists from around the world, who have expertise in a multitude of scientific disciplines. Ask them your burning scientific questions, discuss a recent interesting AskScience thread, or inquire about what they had for lunch. Everyone is welcome, as long as the conversation remains civil and respectful. So please join us on in channel ##askscience (double hash!). or here is a For those who use an IRC client, connect to server irc.freenode.net. We hope to see you soon!
|
[
"A quick way to access the channel is by using this link:",
"http://webchat.freenode.net/?channels=#reddit-askscience",
"Corrected thanks to MwM"
] |
[
"You can setup a forward from one to the other.",
"/mode ##askscience +if #reddit-askscience"
] |
[
"We had some discussions with a staffer and the double hash is because we wanted to keep the name simple, but then it isn't an official channel. This is alright for us though, it was done on purpose :) "
] |
[
"My french is rudimentary. If I were to read french books, would I eventually learn the language?"
] |
[
false
] |
My French is very limited. Would I learn the language if I were to read books in french (or set my computer to french)? Or would this take impossibly long to achieve?
|
[
"I would disagree with that, based on my own experience of learning to read as a child. I only became a fluent reader after I started skipping over unfarmiliar words. Prior to that I would halt and try to puzzle out the words phonetically. After that I learned the language through association. True, there were many errors and misunderstandings in my knowledge."
] |
[
"It depends upon how far along you are. Also, what sort of books you're reading. stjep assumed you were reading adult books. But you could start with baby books and learn referents (the objects that pair with words) that way, and then advance. If you did that, I see no reason why you couldn't learn a lot more about the language, though of course, you'd need more than just written exposure to obtain fluency. Speaking in conversations forces you to think and act faster than reading, which you can do at your own pace, and forces improvement."
] |
[
"No, you won't be able to learn the language that way. You won't be able to improve your vocabulary if you're not able to understand the words you're reading, which would prevent you from expanding your understanding of the language. If you have a sufficiently good understanding of French to be able to communicate then reading French books would help expand your understanding, but you'd need to be in a position where you can understand enough of the words, syntax and grammar to be able to decode the meaning of novel words."
] |
[
"If someone has been muscular in the past, does he gain muscle mass more easily as someone who has not gained muscle before?"
] |
[
false
] |
Lets say there are identical twins, one of them gains a lot of muscle while the other doesn't. Now the muscular one stops working out for two years and both twins have the same body's again. Now both start training and doing exactly the same, same workout plan, same diet. Will the person who has been muscular before gain muscle mass more easily than the other one? I'm asking this because I hear and read about this phenomenon and people calling it 'muscle memory'. I think muscle memory means something else but I am still wondering if this phenomenon exists.
|
[
"Yes. The \"muscle memory\" people are referring to is due to, in part, more myonuclie that migrate into the muscle fiber. These satellite cells sit on the outside of the muscle, but during Hypertrophy training, migrate in to the muscle fibers. They essentially \"control\" or produce proteins for a specific area of the muscle. As you get more Hypertrophy, more of these muscle cells migrate in. When you detrain, the muscle fiber proteins (actin, myosin etc.) Get degraded, but the myonuclie stay in the muscle fiber. Essentially giving you a higher number of protein transcripting devices (that's not exactly how it works but it gets the point across). So you gain muscle faster the next time due to the muscle cells retaining these myonuclie. That's why steroid use is a big topic in sport. You gain a lifelong advantage in many sports by using anabolic steroids. ",
"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5086326/#:~:text=Satellite%20cells%20(SCs)%20are%20the,during%20the%20human%20life%20span",
".\nEdit: spelling (on my phone)"
] |
[
"It sounds like sci fi, but when your muscles hypertrophy from working out they make more nuclei in each muscle fiber (cell). The more nuclei, the faster you build muscle.",
"Once you stop working out, your body breaks down the unnecessary actin/myosin proteins in the muscles but the extra nuclei are still intact which allows for creation of more actin and myosin faster.",
"\"Muscle memory\" is a term that means something very different. Call it whatever you like. ",
"https://www.frontiersin.org/articles/10.3389/fphys.2018.01887/full",
"Edit: removed reference to \"meatheads\""
] |
[
"You can definitely return to a highly trained state after time off far easier than it was to get there initially. Some of it will be pyschological, if you know you have lifted a heavy weight before then you are less concerned about your ability to lift it now. Letting you push yourself harder at all weights below that than coming at it all the first time around. ",
"You also have the experience and yes 'muscle memory' (which is really the combination of proprioception ie bodily awareness and neurological adaption ie how effectively your body can use its muscles) of how to use your body to perform lifts properly, which a newbie doesn't have, allowing you to get more out of your training immediately without the learning curve.",
"For example, it's fairly common for Olympic weightlifters to take months or even a year off from training after the Olympics. They lose so much muscle mass they no longer even look slightly athletic. And initially they struggle with weights that used to be a casual warmup. But in a few short months they are close to their peak again. Something that took about a decade of dedicated training the first time around."
] |
[
"Do non-human animals need glasses?"
] |
[
false
] |
Do all dogs and cats and birds of prey have 20/20 vision (or their species' equivalent)? Is visual acuity something that is naturally selected? (You're a nearsighted deer and you can't see the wolf off in the distance, and so you won't survive long enough to reproduce).
|
[
"Wild animals don't ",
" glasses, typically. Almost by definition, your typical animal is capable of surviving without any sort of technological fix like that...after all, all their ancestors did so. ",
"That said, many animal don't have 20/20 vision (and 20/20 isn't actually perfect, it's just normal good vision in humans-even some people exceed it). For instance, rats and beavers have poor, blurry vision. Animals like these make up for their vision with other senses, like smell and hearing, which are often quite a bit better than those of humans. So how selected vision is depends on how much it's used by the species involved. For some species like humans, it's under heavy selection. For something like rats, not so much.",
"It's worth noting that even in humans, nearsightedness is rare in premodern societies. And based on some cursory reading, it appears that nearsightedness is more common in domestic animals than in wild or feral animals of the same species. There's probably an environmental component to nearsightedness in these cases. "
] |
[
"For instance, rats and beavers have poor, blurry vision. ",
"Would it be possible to craft lenses that would make a rat or beaver's vision better?"
] |
[
"My understanding is no, because rats have a much greater depth of focus you'd need much, much thicker lenses to make a difference with their vision.",
"Relevant bit about diopter at the end of this.\n",
"http://www.ratbehavior.org/Eyes.htm"
] |
[
"How exactly is the electron-to-proton mass ratio important and what would be different if this ratio changed with time?"
] |
[
false
] |
I am assuming that this ratio of mass between electrons and protons depends on many other fundamental constants in the universe, and if the ratio was known to be different or changing, some fundamental ideas would have to change. Could somebody please elaborate (in a very very detailed manner), exactly what is affected by the electron-proton mass ratio and what is affected by it's being variable or constant?
|
[
"I am assuming that this ratio of mass between electrons and protons depends on many other fundamental constants in the universe",
"Not particularly. The electron mass is it's own constant, and the proton mass can be calculated from quantum chromodynamics. We often consider the mass ratio to be a fundamental constant, for a variety of reasons.",
"If the mass ratio was changing, we'd point to the proton mass as the culprit. This would mean that the strong nuclear force is changing in strength as a function of time. Fortunately for quantum chromodynamics, there's no experimental reason to think that the strong force has changed strength."
] |
[
"When I said, emergent constant, I meant: \"Emerging as a resultant constant from some mathematical model\" as opposed to a \"Constant that is hardcoded into the universe\""
] |
[
"Yeah, a lot. The thing is most are phased out and not taken seriously because where ever we look, and all the experiments we do converge on a constant, not a variable constant.",
"Oddly enough we don't know what the electron mass is, we ran many many many tests and averaged it."
] |
[
"Can a water allergy actually exist?"
] |
[
false
] |
I read this article today about a and it seems incredibly implausible that we, as humans, would be allergic to water. One of the biggest facts you learn is that all cells are more water than anything else. It seems that the people who have this allergy are allergic to extreme temperatures, not the water itself or potential chemicals in the water. Would this be an accurate assumption or is there something that I'm missing? I'd love clarification!
|
[
"No, you can only be allergic to an organic compound, and being allergic to something that makes up a large portion of your body mass would be deadly. There is something called ",
"Aquagenic Urticaria",
" but due to the nature of the wiki article and the article you linked i'm pretty skeptical. ",
"Cold Urticaria",
" and ",
"Cholinergic Urticaria",
" may be the culprit, because they are both well documented and could easily follow exposure to cold/hot water, since water really isn't body temperature that often."
] |
[
"I completely agree, which is why I thought to ask. I did read the wikipedia article and was not impressed. I feel the disease is documented more by anecdotes than actual data."
] |
[
"I should also mention that I believe the cold urticaria is plausible, if only due to the prevalence of cold or humidity induced asthmatic episodes, which are much more widely documented."
] |
[
"How to flies survive winter in the northern hemisphere?"
] |
[
false
] |
We had the first nice day out that was above 50F in Canada and there were already flies buzzing about. I didn't think they could survive the deep freeze of the winter and didn't think there was time for them to grow from eggs or maggots this early in the season. Did they just hide out all winter or do they freeze and thaw like amphibians and reptiles do in the colder climates?
|
[
"Insects have many strategies for surviving the winter period. As insects are ectotherms, this often is depent on using the external environment to their advantage (i.e. finding a warm or insulated spot). Many enter a phase of either diapause or hibernation, and remain in little crevices or other shelter somewhere until the cold weather is gone.",
"Flies specifically are one of the more 'cold tolerant' species of insects, meaning they have physiological traits that mean they are able to deal with cold temperatures and less reliant on \"escaping\" the cold conditions. 'Cold tolerant' insects can produce certain proteins which reduce the possibility of ice crystals forming within their bodies. Another mechanism is the ability to produce high levels of glycerol which is a sort of antifreeze. I assume that in a \"deep freeze\" situation, a cold tolerant species such as flies will have to take advantage of both their physiological traits, as well as the simple act of finding insulated or warmer spots to take shelter in."
] |
[
"Good answer. To elaborate, there are insects which tolerate freezing, and these are more rare. Most temperate insects are not freeze tolerant, but have a super cooling point as low as -40 C, and there are comparisons of different climatic conditions and the supercooling points of the dozens of species that have been studied. Insects in Temperate Continental (think Midwest America) in 3 habitats, sheltered, partially exposed, and exposed have supercooling points of -19, -27, and -34 C; note that climate change is predicted to push a warmer but drier climate, and in that zone insects have lower average supercooling points, which indicates a harsher winter. Much of that is because a drier climate has less subnivian, the area between snow and ground, which insulates and maintains temperatures around -10 C or above, even when the air temp is very cold.",
"As an insect reaches lower and lower temps, they suffer from dehydration as the intercellular water freezes This leads to higher concentrations of the chemicals, including calcium and potassium as well as proteins, and as you may know higher concentrations of these chemicals usually lowers the freezing point. Glycerol and other chemicals are produced to further reduce the freezing point. The insects I study have a supercooling point of -28 C, however they start to experience mortality at -10 C, so even though they are adapted to harsh winters, they rely on shelter like leaf litter and snow.",
"Insects which tolerate freezing are known to have proteins that are ice nucleators, and to reduce the stress of freezing these insects often freeze at relatively high temperatures, some as high as -2 C.",
"Most insects overwinter protected, either as a pupa or an egg. The flies which wake from winter slumber are the lucky few who found refuge either in the subnivian, or possibly around human disturbance. Note there is a common butterfly in North America, the mourning cloak which often overwinters as an adult. I think they probably also overwinter as eggs, but they are often the first butterfly seen in spring. They are quite large and beautiful, and it is amazing that they overwinter as adults."
] |
[
"One related factoid is that the German Cockroaches found in northern latitudes in the US started to change their taste in food compared to their southern counterparts despite being the same species, precisely because the ones in the north can only survive indoors unlike the ones in the south. A common form of roach control product is a sweet-tasting glucose bait laced with a slow-acting poison. In the south when this product is used and kills off lots of indoor roach hives, the next generation of roaches come mostly from outdoor hives that never bothered humans and thus were never were subject to pest control. But in the north where the winters are too cold for there to be any outdoor roaches to replenish the population, the next generation of roaches come mostly from indoor hives lucky enough to avoid being exterminated. And one way to be a cockroach lucky enough not to be exterminated is to happen be one of the weirdo roaches who, unlike all your brethren, happens not to like the taste of sweet things so you happened to avoid the poison bait. After several decades of using this type of bait on roaches, we've accidentally bred the sweet tooth out of them. But again, only in the north where there isn't an outdoor roach population to dominate the next generation when the indoor ones get killed off. In the south, the replenishment from the outdoor population overpowers this evolutionary effect making it mostly lost in the noise."
] |
[
"What determines the wavelength of a photon leaving the sun?"
] |
[
false
] |
I'm studying the light reactions of photosynthesis for biochem right now, looking at the page on accessory pigments. Obviously not all photons are created equal because plants have these pigments that specialize in absorption at different wavelengths. What determines the wavelength of a photon leaving the sun?
|
[
"The spectrum of light emitted by the sun is described by its blackbody radiation curve. ",
"Blackbody radiation",
" is emitted by all matter, in a spectrum whose shape depends on the temperature of the matter. Blackbody radiation is how infrared night-vision goggles work, and the reason why objects glow visibly when they get hot enough.",
"Here is a chart",
" of the solar radiation spectrum with the 5250C (5525 K) blackbody curve overlaid on it. They are not a perfect match because the sun is not a perfect blackbody and its surface temperature varies, but the fit is very good as you can see."
] |
[
"To add to what ",
"/u/wazoheat",
" said, the temperature used for the blackbody curve of the sun is the temperature of the surface. This is because the photons in the interior of the star (where it's much denser) are being emitted and reabsorbed so often that it takes them a very long time to reach the surface. Since the process takes so long, the photons come into thermodynamic equilibrium with the gas at each radius as they slowly meander their way out to the surface. At the surface, by definition, the density of the gas has dropped enough so that the photons are finally able to escape, and so we see a blackbody distribution of photons at the surface temperature of the star.",
"The temperature at the surface is governed by lots of other properties of the star, including it's mass, evolutionary stage, composition, etc."
] |
[
"This was helpful, thanks for your response! "
] |
[
"Do insects sleep, or have any comparable process?"
] |
[
false
] | null |
[
"/u/jokerzwylde",
"'s answer is not correct. Insects do have a type of rest that resembles vertebrate sleep in various physiological measures, and is distinct from torpor. For example, rhythmic and endogenously driven neural activity, increased threshold for response to stimuli, changes in breathing, changes in posture and reduced motion, regular circadian rhythm to sleep/wake patterns, and rebound sleep (increased sleep the day/night after being deprived of sleep.)",
"In honey bees, there is some really cool work to show that sleep deprivation results in poorer learning the next day.",
"See a related comment on a related question earlier today: ",
"https://www.reddit.com/r/askscience/comments/3pdwwo/how_do_some_insects_sleep_if_they_have_no_eyelids/cw65mvn"
] |
[
"i would go on to agree with ",
"/u/neurobeegirl",
" as torpor is an action of decreased physiological activity in animals (insects included) that is usually rooted in causes like lack of availability of food, environmental changes etc. making it something like hibernation but the insect sleep cycle is different. They do need rest like mammals as they need to rest their CNS. This is vital to their system and their survival like ",
"/u/BeardySam",
" had mention. That study was conducted by Univ of Penn. The fruit flies they tested quickly started to die.... ",
"All this said their sleep cannot be taken in the sense as tuned to our ideas (they don't kiss each other goodnights) but i guess they do cuddle up, check this video out for that ........",
"https://youtu.be/HiLWCf2MPHQ"
] |
[
"I've always really liked the experiment that was done to look for sleep/wake cycles in fruit flies. They had a whole bunch of very narrow tubes, like straws, with one fruit fly in each tube. A laser was shone through each tube about halfway up, and a counter was triggered every time the fly traveled through the laser, so that the number of counts was related to how active the fly was - how much it was moving up and down. They found a very clear 24-hour circadian rhythm, as during the night the flies tended to be much less active.",
"It's also true that flies tend to lay their eggs during daylight hours. We've taken advantage of that in the lab, tricking flies to reproduce more by exposing them to 24 hour light. Mwahaha."
] |
[
"Why does any system/particles/electrons/atoms tend to be on the position with the lowest energy state?"
] |
[
false
] |
I understand that the way electrons "fit" around the nucleus is such that they are in the lowest energy state possible. I'm also told that this is also the reason why atoms and various compounds/molecules are formed but why is this so? Is there any specific reason? Also how does the electron/atom "know" that it's in the lowest energy state and how it has to align itself?
|
[
"It doesn't go to the lowest energy state unless it has somewhere to dump its energy. Our everyday world is at a relatively low temperature, so that's pretty easy to do. In a closed system, the energy would tend to distribute itself evenly among the available atoms, because that's statistically more likely. If there's more energy than atoms, so to speak, the atoms stay excited."
] |
[
"If your molecule is in an excited state, depending on the state, it can fall to a lower energy level either by emission of light or by interactions with other molecules (collisions, vibrations). This process can happen spontaneously. In order to get back from the ground state to the excited state, it would have to be hit by an excitation of exactly the resonant frequency, which is just extremely unlikely at room temperature."
] |
[
"This is correct, and also leads to the fact that although things are usually in the lowest energy electronic state, they are often not in the lowest energy ",
"rotational state",
". Since the energy it takes to transition between rotational states for gases is comparable to the thermal energy in the air, molecules are frequently in excited rotational states unless you cool them down. The same goes even more strongly for things like spin states in NMR."
] |
[
"I was heating Hydrated Copper II Chlorate in a crucible, and some odd things occurred. Can you please explain the chemical processes involved?"
] |
[
false
] |
So, I posted initially about this a while back, but I have duplicated results more than just once, so I know it's not contamination within the crucible. So, Hydrated Copper II Chlorate: CuCl2, 2H20 heated in a crucible. So, initially, I had heated CuCl2, 2H20 in a crucible with a Bunsen burner. I was not regulating the heat at all. I know I boiled off the water quickly(turned from green/blue to brown), but then I wasn't sure what was really going on. The crystals melted and the substance started to produce gray smoke. On top of that, there were no longer just blue flames of a Bunsen burner. There were green flames with white tips. Here are the final results of the crucible. Here is the outside of the crucible: . Here is the inside of the crucible: . On the bottom should be CuCl2, but it isn't brown, it's black/gray. Now, in order to test to see if it was in fact the water that was doing the work of this, I did two things: First thing I did was place the Hydrated Copper II Chlorate in an oven at 108C to boil off as much water as possible. I then did my best to heat a second crucible of it, kind of as an empirical test to see when no more water would boil off(weighing constantly after short heating periods). I then proceeded to place both of these samples with nearly no water left over the burner. The samples melted, and left some gray residue and was very similar to the image of the inside of the crucible I posted above, however, the outside was untouched, unchanged. This tells me that the simple fact that I was heating/burning Hydrated Copper II Chlorate was the cause of the green/white flames on the OUTSIDE of the crucible. So, can anyone tell me what is going on when you heat/burn Hydrated Copper II Chlorate? Basically, what causes . Note: ALL images are high res, in focus, sharp, 3000x2000 EDIT: terminology/grammar
|
[
"First, just so we're clear. Copper chloride =/= copper chlorate. With the pedantry out of the way.....",
"The obvious question - did you test to see if the red material was copper (i) oxide? And that the gray residue is copper (II) oxide? ",
"That would be my initial suspicion. "
] |
[
"My immediate thought is that the dihydrate is rather readily ",
"decomposing",
" and that the anhydrous compound is less sensitive to decomposition. The chlorine gas is a byproduct of heating the dihydrate, which might be why you're seeing effects outside the crucible."
] |
[
"Yes, I know Copper Chloride =/= copper chlorate, my mistake, the naming conventions screw with me. ",
"I did not test for copper (i) oxide or copper (II) oxide. But I do believe you may be right. How would I go about testing that?"
] |
[
"I've seen reports that the Pfizer coronavirus vaccine may give up to 52% protection 10 days after the first shot. Does the Moderna data suggest anything like this as well?"
] |
[
false
] | null |
[
"Yes. Look at the ",
"FDA briefing document",
" for the Moderna vaccine, top of page 28. The curves for the vaccine and placebo group start to separate somewhere around the 2 week mark, which is well before the second shot is administered. So people who received the vaccine seem to be getting some protection relatively early with the Moderna, as the do with Pfizer vaccine."
] |
[
"Am I reading this correctly as 50.8% effective in the first two weeks after 1 dose, and 92.8% effective more than two weeks after dose 1?"
] |
[
"I'm seeing 50.8% in the first 2 weeks and 92.1% between 14 and 28 days after the first dose. This is from the table on page 28."
] |
[
"When we step on the ground, does the pressure kill any microscopic organisms?"
] |
[
false
] | null |
[
"Yes; ",
"Cryptobiotic Soil",
" found in desert environment is an example of microscopic organisms that are sensitive enough to human pressure.",
"Utah NPS",
" has a bit more explanatory detail than Wikipedia.",
"And just for fun, ",
"this",
" is what happens when you step on the soil."
] |
[
"what about in every day instances like walking on the sidewalk or through a yard? you mentioned that these particular organisms are sensitive enough to human pressure, but could you elaborate a little? I really don't understand microscopic scale organisms"
] |
[
"The pressure from human footfall doesn't kill microoganisms except in special cases like the one suggested by ",
". However, the pressure caused by farming with old-school tilling practices can have harmful effects on the soil structure itself where the pressure compaction will cause the creation of different, less fertile horizons in the soil profile. ",
"This incredibly dry video",
" put out by the USDA explains the benefits of minimizing soil pressure on farmed lands. "
] |
[
"If Mars has indications of flowing water, would that mean it had to have been raining on Mars?"
] |
[
false
] |
Assuming that the signs of flowing water actually indicate flowing water, what would cause it to flow? Does this mean that there would have been an evaporation cycle on Mars, complete with rain?
|
[
"Not necessarily, one thought is that there was a large body of water (/liquid) on Mars which was contained by a natural dam. This dam was then breached and there was a massive amount of ensuing flow. That flow would be sufficient to cause the valleys and river beds you describe.",
"https://books.google.co.uk/books?id=fuC04-ZOs9EC&pg=PA128&lpg=PA128&dq=mars+large+body+of+water+natural+dam&source=bl&ots=3GTNR9V8D5&sig=ulQB2Yv56fUPDbub7XBhuxqAmK0&hl=en&sa=X&ei=IHmKVaD2BJPX7Aa80oCABQ&ved=0CBwQ6AEwAA#v=onepage&q=mars%20large%20body%20of%20water%20natural%20dam&f=false"
] |
[
"Precipitation has been argued to be the source of water on Mars, but there are still some questions. There are an abundance of erosional/depositional features on Mars, including rivers, alluvial fans, deltas, and lake deposits. There are still some thoughts that you could develop many of these features through ground water seeping to the surface, eroding headwalls through processes like sapping (that we see on Earth in arid regions), with enough water exiting to eventually channelize and form the other features. The extent to which this process works without surface runoff (from rain) is still an open question on Earth (and thus on Mars, as is this our best analogue), and I think many people favor the idea of a brief period of Mars history with something like a water cycle, ",
"e.g. this discussion from several years back",
". Caveat being, I focus partly on geomorphology here on Earth, so I've not kept up with the arguments for Mars closely. Perhaps another more planetary panelist will weigh in."
] |
[
"There is probably some sort of water cycle on Mars, researchers are working on figuring out the details. ",
"Here",
" is an article describing a recent paper (link to actual paper in the article.) ",
"From the article: ",
"\"Based on a combination of data about Martian weather and soil conditions, the researchers conclude that salts found on Mars can pull water out of the thin atmosphere and may drive a daily water cycle.\" ",
"This may or may not end up being what is actually going on, it sounds good but remember that we have just a handful of missions actually collecting data on Mars and people are trying to work with what they can. Keep reading on the subject, more results will keep coming out. ",
"*Edit - this is about current conditions on Mars, I'm not sure if your question was about current or past conditions."
] |
[
"In reference to a person standing on the north pole of the earth, what direction is the sun moving around the center of the galaxy (Upwards/Side-wise/At an angle)?"
] |
[
false
] |
[deleted]
|
[
"This doesn't answer the question, and that last part isn't a very widely accepted hypothesis. "
] |
[
"It's moving in the general direction of the constellation Cygnus, almost 90 degrees from the galactic center, over 200 km/s relative to the center. If you were standing at the north pole, the direction of the Sun's motion would be a little less than 45 degrees above the horizon."
] |
[
"The Sun is moving around the galaxy clockwise when looking at the galaxy from one side, and counter-clockwise when looking at it from the other side. But it's also going back and forth from one side of the disc to another, and every time it travels through the middle of the disc it drags with it a ridiculous amount of asteroids which bombard the planets triggering cataclysmic extinction events on Earth."
] |
[
"How does being injected with a version of a virus or bacterium give our bodies the ability to become immune to certain diseases?"
] |
[
false
] | null |
[
"A little more in depth in case you are curious.",
"Your body is built to recognize foreign structures, usually proteins, that are not supposed to be inside it. These are called antigens.\nSome immune cells make antibodies ins that then hook on to these antigens. Other cells hunt down things with antibodies attached to them and eat them.",
"After this process is complete. Some of the cells that make that specific antigen are stored. If that antigen appears again, your body can now produce antigens very quickly. So quickly that in most cases the disease is prevented. ",
"Nothing is perfect though. Some viruses, like Influenza, mutate and exchange DNA wit other similar strains so fast that immunity to what is going around now does not mean you're immune to the same later.",
"Some vaccines, like Tetanus, target the toxins bacteria produce. If current, your immune system gobbles up the toxin and you're fine.",
"Your body has lots of barriers (membranes, mucus, acid, etc.) to keep things out of the bloodstream, so when vaccinating they have to be injected to get around them."
] |
[
"If that antigen appears again, your body can now produce antigens very quickly.",
"Just pointing out the typo. He/she meant to say your body can now produce ",
" very quickly. Antigen is a component that is recognized, antibody is one of several immune system molecules that bind to different antigens."
] |
[
"When injected with the low doses of said virus, your body automatically builds up specific antibodies to that virus - that's the whole purpose of your immune system - it's just doing exactly what it was designed to do. If there's a glitch in your system, or if your immune system isn't strong enough, it won't properly develop the antibodies which is why vaccines aren't 100% effective."
] |
[
"Would a superconductor pass through a walk through metal detector without being detected?"
] |
[
false
] |
As walk through metal detectors rely on metal disturbing a magnetic field, and superconductors through the Meissner effect eject magnetic fields, would a walk through metal detector (like at airport security) detect a superconducting superconductor?
|
[
"Superconductors do expel magnetic fields, but they distort the outside field in the process (see the middle image in ",
"this figure",
"). So since the magnetic field is still distorted, I would imagine that the metal detector would go off with just superconductor. However, if you were to put a ",
"magnetic cloak",
" through a metal detector (in which the 'pushing out' effect of the superconductor is perfectly cancelled out by a ferromagnetic material 'pulling in' the field) you could pass through undetected. However, airport security might still flag you for additional screening if you carry a box of liquid nitrogen through the metal detector.",
"Edit: As I understand it, the perfect cancellation also assumes a static magnetic field, and I'm not sure how a time dependent field (as is present in many metal detectors) would effect it. ",
"This article",
" suggests that its possible in a dynamic field however, you may just have to tweak your cloak to fit the field and frequency range that the metal detector operates at."
] |
[
"I don't think so. While the superconductors would reduce the I",
" R power losses in the conductive windings, there would still be eddy current losses in the non-superconducting ferromagnetic core."
] |
[
"Is it possible to build 100% efficient transformers using super conductors?"
] |
[
"If electric motors replace internal combustion engines in vehicles, will we ever face an \"ozone pollution\" problem?"
] |
[
false
] | null |
[
"Actually, there already is an ozone pollution problem. From ",
"Wikipedia",
":",
"Low level ozone (or tropospheric ozone) is an atmospheric pollutant. It is not emitted directly by car engines or by industrial operations, but formed by the reaction of sunlight on air containing hydrocarbons and nitrogen oxides that react to form ozone directly at the source of the pollution or many kilometers down wind.",
"Also from the looks of it, at least on the Prius, the motors in use are fully magnetic (brushless), therefore they do not contain an ozone-producing spark gap. As long as the car doesn't have spark gap motor, it shouldn't produce ozone.",
"However, if the electricity running the car came from a fossil-fuel source, even a fully electric car will have a significant carbon (and ozone) footprint."
] |
[
"You might want to rephrase your answer so you don't get a pedant response.",
"By that, I mean even if you stopped all pollution from internal combustion engines, tons of our pollution comes from ",
"other sources",
". So someone might try to answer your question without really addressing the problem you were thinking about.",
"I'm also really curious to know what the effects would be if somehow pollution were greatly diminished."
] |
[
"If electric motors replace internal combustion engines in vehicles, will we ever face an \"ozone pollution\" problem?",
"Not with brushless motors, or motors that either prevent or suppress any sparking of their brushes, easily accomplished. Ozone is not an issue for a properly designed electric car, and that car is also more efficient for having prevented ozone generation."
] |
[
"Why does it seem that Animalia, according to estimates, has by far the greatest biodiversity of all the kingdoms?"
] |
[
false
] |
It seems a little counter-intuitive that the results of this study on the number of species on Earth (2011) suggests that the most biodiverse group of organisms on Earth are the animals. The study predicts roughly 7.7 million species of animals, but just 298k of plants, 611k of fungi, 36k of protozoa and 27k of chromists. Apparently prokaryotes, such as bacteria and archaea, are a different matter since we've catalogued so few of them, but Protozoa are very well catalogued so it can't be due to their microscopic nature. It just seems a little unintuitive that animals, some of the largest, most complex organisms on Earth and, from what I understand, the ones requiring the most resources-per-size (due to not being autotrophs and having to derive energy from plants(?)), are the most diverse group of organisms. Honestly, my guess would be that all microscopic life would vastly outnumber the species-count for all multicellular organisms; they require less space, and they can evolve faster. Actually I'd expect that a huge amount, like, times several thousand, of microscopic organisms would be completely unknown to us, simply because they're invisible, and there are so many places to search. And even disregarding microscopic life, I'm surprised that fungi and plant don't at least approach animal biodiversity. Does biology have any theories to explain this trend (assuming that the estimates are close-to-correct)?
|
[
"The thing about protozoans is that they can display the same range of variance as any eukayotic organsim, but they only have one cell. By this I am talking about the levels of organisation. We will use the example of the human skin ",
"epidermis",
". In the lowest level, there melanocytes, which determine skin colouration. So we have the lowest level of organisation: the cell. When you 'zoom out', you can see tissue, which is when there are a bunch of melanocytes working together. When you 'zoom out' even more, you can see the whole epidermis, which is made up of many different types of cells - an organ. When you 'zoom out' even more, you can see a lot of organs like the heart, the kidneys, the brain, and the skin. This is an organism. The reason as to why there is so much variation between animals and protozoans is because an animal has all of this which can vary, wheres a protozoan is just one cell, and so animals will always beat that in terms of variation (prokaryotes are different because there is just so much variation in prokaryotic structure). Chromists are very similar to prokaryotes in this respect. As for plants and fungi, they are just simply not as complex as animals are, and so display less variation."
] |
[
"Well, it's a little difficult to have 100% facts for things like this, but that is the closest explanation to a fact. When it comes to asexual organisms, it is said that if they share 98.7% or more of the genome then they are of the same species."
] |
[
"I see. Is this pretty solid fact, or just a theory? Also, a common definition of species is a group of individuals who can breed with each other. But how do we apply this to asexual organisms? How do we define species in Protozoa or Bacteria?"
] |
[
"What would happen if something were to collide with the Sun?"
] |
[
false
] |
Seeing as how the Sun is a giant ball of plasma, what would happen if an object could withstand the heat and collide with the sun? Would it shoot through the other side and continue on its journey? or would it kinda go splat on the surface?
|
[
"You need to clarify your question. Are you asking if something can shoot a hole through the Sun like a bullet through a wall or something like that?",
"The Sun is a solid object. Yes, it is giant ball of gas/plasma, but it is also extremely dense. It is not sparse enough for an object to pass through it without hitting any matter.",
"If we imagine something could survive the heat and pressure then it would either have to punch a hole in the Sun or stop or be destroyed by the impact. "
] |
[
"It depends on the object, but it's likely that it would be crushed and slowed to a stop before it could get near the core of the sun. ",
"To keep the sun from collapsing, the inner part of the sun has to be hot enough to produce sufficient thermal pressure to counteract the enormous weight of the hydrogen and helium gas pressing down on it from all sides. The surface of the sun doesn't have much outside gas pushing down on it, so it can stay relatively cool with a lower pressure. However, the deeper you get into the sun, the pressure and temperature of the surroundings will increase. By the time you get to the core, you'll find that it's ",
"20 times denser than iron",
" and at a pressure billions of times greater than the atmosphere of the earth. "
] |
[
"Well sure, I guess I should have clarified, I was just assuming the 'ship' was powered and/or the object had a great enough velocity to pass through.",
"If in free-fall then yes, it would come to rest."
] |
[
"Can UV light kill fleas?"
] |
[
false
] |
Can UV light wands like one really kill fleas or their eggs?
|
[
"UV light can kill pretty much anything, if you leave it under the UV long enough. It's used pretty commonly as a disinfectant in labs and hospitals already, though sterilisation cycles are generally minutes to hours long depending on what you're trying to kill (bacteria, fungus virus, bacterial spores). ",
"This thing in particular? I'm pretty sceptical. It would depend on the strength of the UV light. It says it works in 10 seconds. I reckon that would make it absolutely deadly to be waving around in the air without any safety equipment. UV light is not a toy, and is especially damaging to eyes and other fun things. So chances are it's a bit bullshit, as they would have to reduce the power enough to make it 'safe', which would also make it useless. ",
"It is also an absolutely unnecessary device for personal use."
] |
[
"It might be able to kill their eggs.",
"UV is ionizing radiation, like gamma-rays, x-rays and such stuff, but it's at the very weakest end of the scale. So weak that we can laugh at it with impunity, because it can't even penetrate skin. There are only two areas on the whole body that is susceptible to UV-light (assuming you have no open sores), and that's the eyes.",
"UV light isn't just dangerous to your eyes because the retinas doesn't contract (because the eyes can't sense how much light is coming in), but it's actually radiation of the ionizing kind.",
"Germs and such have no skin - they have a pitiful membrane that's totally not up to the task of blocking UV-rays, and as such, ten seconds of UV-light fucks up their DNA and gives them instant-death-cancer (to put it in a way that's not technically true), and the same ",
" be true for the eggs of fleas and bedbugs.",
"I'm pretty certain, though, that it's wholly ineffective against adult fleas - they have a chitinious armour and everything.",
"One last thing - ten seconds is not very much, so the device would have to be pretty powerful. A lot of the information on the page is overblown and bordering on untrue. See here, for example:",
"That would mean they're inside the mattress.",
"You can't light ",
" the mattress.",
"Apart from that, they also sell detox aids and holistic health.",
"I'd say \"UV-light can kill flea eggs. Their UV wand probably can't\"."
] |
[
"It might be able to kill their eggs.",
"UV is ionizing radiation, like gamma-rays, x-rays and such stuff, but it's at the very weakest end of the scale. So weak that we can laugh at it with impunity, because it can't even penetrate skin. There are only two areas on the whole body that is susceptible to UV-light (assuming you have no open sores), and that's the eyes.",
"UV light isn't just dangerous to your eyes because the retinas doesn't contract (because the eyes can't sense how much light is coming in), but it's actually radiation of the ionizing kind.",
"Germs and such have no skin - they have a pitiful membrane that's totally not up to the task of blocking UV-rays, and as such, ten seconds of UV-light fucks up their DNA and gives them instant-death-cancer (to put it in a way that's not technically true), and the same ",
" be true for the eggs of fleas and bedbugs.",
"I'm pretty certain, though, that it's wholly ineffective against adult fleas - they have a chitinious armour and everything.",
"One last thing - ten seconds is not very much, so the device would have to be pretty powerful. A lot of the information on the page is overblown and bordering on untrue. See here, for example:",
"That would mean they're inside the mattress.",
"You can't light ",
" the mattress.",
"Apart from that, they also sell detox aids and holistic health.",
"I'd say \"UV-light can kill flea eggs. Their UV wand probably can't\"."
] |
[
"If a large amount of hydrogen falls into a black hole, will it start fusing inside the black hole's event horizon?"
] |
[
false
] | null |
[
"No, as it would still be accelerating towards the singularity.",
"Think of a water going down a drain.... the water doesn't increase in pressure / clump together just because it passes the point of no return (event horizon).",
"Now, a more interesting question would be what happens to a star already undergoing fusion as it passes the event horizon of a supermassive blackhole....."
] |
[
"If all that hydrogen is getting slammed into a singularity, wouldn't it be under enormous compression?"
] |
[
"This is a somewhat complex question, because fusion can happen in the accretion disc outside of the event horizon, but doesn't specifically happen because of passing the event horizon. ",
"If you are asking if a non-fusing hydrogen cloud passes the event horizon, whether it will start fusing, I believe the answer is no, the tidal forces will vastly outstrip any gravitational attraction between the hydrogen atoms themselves.",
"Now, for already fusing atoms passing the event horizon, they would probably continue to undergo fusion until the tidal forces rip the core apart. "
] |
[
"Seeing as sperm need a specific temperature to thrive, and that a laptop heat exhaust port is generally in the right area, how much laptop use per day would be an effective spermacide?"
] |
[
false
] |
Im just curious. Could it be effective? To further clarify my question: How much computer (laptop specifically) usage would it take to be an effective method of contraception.
|
[
"Funny: about 3-4 hours of video games and porn a night should ruin your sex life sufficiently.",
"Honest: There is no guaranteed level. Tight underwear, laptop heat, drug use, etc. Pick your favorite \"lowers sperm count\" method, and the result is merely a reduced chance of conception. So if you're TRYING for a kid, you need to avoid all of those activities. However, for effective contraception, you should be using a variety of contraceptive measures. What I call a \"defense in depth\" approach. All methods can fail. Condoms or another barrier method are typically the most effective method, but oral contraception (or something similar) are also very effective. Used together, you can virtually eliminate the risk of pregnancy, but even then there are cases of pregnancies that have resulted. Using your laptop as your preferred method of contraception is likely to result in a Father's Day card sooner rather than later."
] |
[
"Yup! It is called Laptop Thigh, Toasted Skin, or, ",
"Erythema Ab Igne",
".",
"The temperature of a laptop sitting on the thighs can reach 44°C, or higher if this blocks the ventilation fan. At least 10 cases were reported between 2004 and 2010, usually the left leg. ",
"ONE",
"Another",
"And another",
"study"
] |
[
"How about some references for this? "
] |
[
"what reasons could there be for apparent higher salinity in certain parts of oceans that go against the norms?"
] |
[
false
] |
I live in North Queensland, Australia and a friend of mine from Maine recently commented that the ocean here is considerably more salty in comparison to Maine. while I realise that salinity varies throughout the oceans, from what I have found, this is very much against the usual trends, as the North Atlantic ocean apparently has a higher average salinity than the Pacific and salinity generally increases further from the equator, due to lower precipitation. What reasons could there be for this and could the presence of the Great Barrier Reef play a part?
|
[
"You are correct that in general, the surface North Atlantic is saltier than the South Pacific. However the Gulf of Maine is considerably fresher due to all the rivers which flow into it and the fact that it is isolated from the open ocean by Georges Bank. The salinity level in the Gulf of Maine is about 33 parts per thousand while most of the North Atlantic is ~ 35.5 parts per thousand. "
] |
[
"The presence of a river mouth could be a factor that is confounding his observations. Where exactly is he comparing? "
] |
[
"ah yeah, fair call",
"she's from Lewiston, not sure which bit of the coast she'd be referring to, I think it was a general observation of places she's been throughout new england"
] |
[
"When rubbing a wine glass with a finger to produce a tone, why does the finger have to be wet?"
] |
[
false
] |
You probably all know the story: I get bored, there's a wine glass on the table, I start to play with it, exploiting one of its resonance frequencies by rubbing it in a certain way with the finger. I know why that tone comes about and what influences its frequency. But what I don't know is: why does it require a wet finger? Can one of you guys help me out?
|
[
"Seems to me it's just because you want to lower the coefficient of static friction.",
"When your finger is dry and you're just about to break static friction and start sliding across, you're forcing with some very large shear. You break static and then you're finger jumps pretty far and you get stuck again. So the forcing looks like delta functions spaced by too long a period.",
"And as we all know, we want to force close to the resonant frequency. So wet your finger lower the coefficient and it will be much easier to break in to sliding at it will happen more often.",
"More importantly I've heard that the glass has to be crystal."
] |
[
"Crystal will resonate much better than ordinary glass but ive gotten notes out of plenty of cheapo wine glasses"
] |
[
"Actually what we call glass and \"Crystal\" glassware are both amorphous. They for the most part do not have a aligned molecular structure at all. Crystal tends to make a better sound and look nicer because the heavier atoms make a denser material with a higher refractive index as well as the high elasticity making the sound \"ring' better."
] |
[
"Can we measure the width of one single strand of human DNA?"
] |
[
false
] | null |
[
"Cool. Thanks. I know I could have done that but I wanted a little more communication around the topic. "
] |
[
"I'm not sure what you are looking for other than a numeric value that you can find with a Google search. "
] |
[
"Google it"
] |
[
"Bio/Physics Question : Why is valence in the denominator of the Nernst Equation?"
] |
[
false
] |
Hi guys! I'm a Neuroscience PhD student who had a minor in physics and for some reaosn I can't physically intuit why valence is in the denominator of the Nernst equation, which to refresh your memories is roughly V = [(RT)/(zF) ]* ln [Co]/[Cin] I've gone through the derivations, which make mathematical sense as to why z is on the bottom. However, I can't understand why divalent ionic species would result in a smaller potential than monovalent species. Is it because of charge charge interactions between the divalent species such as Ca 2+ that would cause greater repulsion on either sides they occupy? I know that V goes by 1/r, but how is it that this would result in an exact difference by a magnitude of 2 eludes me. Thanks guys!
|
[
"That's not valence in the denominator, it's the number of electrons transferred in the electrochemical process. Voltage is J/C, which means a reaction that releases 1000 kJ spread amongst 10 electrons has a higher voltage than the same 1000 kJ spread amongst 20 electrons. That's all there is to it. Ion size, charge, and other specifics can be included in the equation, but they are minor correction factors that could give non-ideal behavior as predicted by the Nernst equation."
] |
[
"I'm sorry I'm a bit confused (it's Monday). Doesn't charge of the ionic species = valence? ",
"Also, if you have a greater difference of electrons per each side (greater charge separation = higher voltage)- such as in 20 electron example by which you can only have 20n differences on each side of the membrane this would invite a greater V if you assumed you only had a concentration of 2 atoms or something? To clarify, if you had 2 atoms of Na and the equilibrium potential lent itself to have 1 atom per side of membrane this would result in X volts. However, when you have 2 atoms of Ca2+ -again assuming Veq would be 1 atom per side - then the equilibrium potential would be X/2, which still doesn't physically make sense to me. "
] |
[
"Nernst Equation is derived from a system where the chemical and electrical gradients of a system are at equilibrium. That is chemical gradient = electrical gradient. So, NRT* ln(Co/Cin) = NzFE",
"Solving for E will put z in the denominator. ",
"Now for why divalent ions would result in a smaller potential. Look at the equation, and assuming you are comparing two situations where the concentrations of ions are the same but one situation has monovalent cations and the other has divalent cations. Since the concentrations aren't changing, that side of the equation is the same for both situations. N cancels out, and F is the same for both equations, so the only variables are z and E. If z doubles, (1 to 2) E must half. ",
"http://www.st-andrews.ac.uk/~wjh/neurotut/mempot.html"
] |
[
"Blindfolded at birth?"
] |
[
false
] |
If a child were blindfolded right after they were born, and left blindfolded, would this effectively make them blind later on in life? Or is the visual cortex already fully formed by this stage?
|
[
"There are many cues for depth order other than disparity (like looming and occlusion). Disparity selectivity requires input from both eyes. These inputs are segregated in the lateral geniculate nucleus, and mixed in visual cortex. In the critical period, access to disparity cues reinforces inputs to both eyes together, and this is required for the thalamic (lateral geniculate) inputs to remain active in the same cortical columns. Without disparity cues, there are retinal waves in each eye that are independent, and the thalamus wires each eye's inputs to primary visual cortex separately. ",
"Studies of humans with strabismus are used to argue that this same critical period, described in detail in the cat, applies to humans. "
] |
[
"There are many cues for depth order other than disparity (like looming and occlusion). Disparity selectivity requires input from both eyes. These inputs are segregated in the lateral geniculate nucleus, and mixed in visual cortex. In the critical period, access to disparity cues reinforces inputs to both eyes together, and this is required for the thalamic (lateral geniculate) inputs to remain active in the same cortical columns. Without disparity cues, there are retinal waves in each eye that are independent, and the thalamus wires each eye's inputs to primary visual cortex separately. ",
"Studies of humans with strabismus are used to argue that this same critical period, described in detail in the cat, applies to humans. "
] |
[
"Of course, unless that is not true. ",
"http://web.mit.edu/newsoffice/2007/blindness-0214.html",
" ",
"Also, I doubt Hubel, Weisel, or Stryker or Antonini would agree with you (I know all four of them). Early experience is essential for disparity selectivity - so people with blindness until they are 6-7 years old would not be able to see depth from disparity (think Magic Eye pictures). "
] |
[
"Please help me understand delayed choice quantum eraser"
] |
[
false
] |
So I've read its description on Wikipedia but still don't quite get it. Scientists see interference only when they have no means of understanding what slit the photon went through. They don't see pattern when they can know which slit was used even if they can know it after "signal" photons interact with detector. The question is, what will signal detector D0 show while "idler" photons are still traveling, if detectors D3/D4 will be away - on the moon, for example? Also, sorry if my question is dumb or badly worded.
|
[
"for some reason this question comes up from time to time and doesn't generally get much in the way of answers. I don't know much about it myself, but I'd suggest searching this subreddit for \"quantum eraser\" to see some previous discussions. (I'm going to go try to read up on it in the meantime)."
] |
[
"I think, from my reading of this, that D0 is guaranteed to show a hit, because it doesn't record \"which\" slit the particle travels through. D0 acts as a \"trigger\" of sorts. When it receives a photon it asks which of the other detectors have received photons. Now, a proper experimental setup will have put the appropriate delays in the logic to account for distances to the several detectors."
] |
[
"It may be that I am not fully appreciating the weirdness of this experiment (I only just read about it on wikipedia), but I don't think anything is happening that would seem surprising assuming ",
"Many Worlds Interpretation",
".",
"I don't have time right now to give you a full explanation (sorry!), but essentially all quantum events that \"could\" happen in multiple ways ",
" happen in all these ways. When you observe that the particles go one way or the other, doing so necessarily entangles the particles comprising ",
" with those of the experiment. So if there are two ways the photons could have gone, there is a version of you that sees them go one way and a version of you that sees them go the other.",
"Basically, you'll branch off if there's a causal relationship between the path of the photons and the state of your brain. Again, wish I had more time to go into detail here, sorry. But it shouldn't matter ",
" you observe the particles doing one thing or another because ",
".",
"So don't think of it as affecting something that happens in the past, but only as ",
".",
"You should really read up on MWI though, because like I said though this explanation doesn't do it justice."
] |
[
"Do satellites maintain the same velocity forever?"
] |
[
false
] |
Today in my physics class we talked about the gravitational field and about the elliptical orbit of satellites. My question now is if the satellite would continue to be accelerated and slowed down by the gravitational field of the earth forever? And if so wouldn‘t that mean that no energy is converted (for example in heat)?
|
[
"I'm going to answer your question, but just because somebody will \"correct\" me if I don't touch on it first: in an elliptical orbit, the velocity does change, because the speed and direction of the satellite's motion is changing throughout the orbit. But of course I understand what you mean - whether an orbit loses energy, or whether it can keep on going on forever.",
"In practical terms, yes, orbits can and do lose energy. In particular, this happens in low Earth orbit, because there's still a very thin amount of atmosphere up there. This produces a weak drag force, which has to be countered. The International Space Station actually has to have little boosts now and again, or else it will start to slow down and fall to the Earth.",
"Satellites and the Earth are also not perfect spheres, and there are also other gravitating bodies in the solar system. These effects can produce mild torques on satellite orbits that can cause their orbits to precess. If things are aligned right, this can sometimes add up to quite a significant effect.",
"But even in an idealised universe where you can ignore all of those effects, the system will still radiate gravitational waves, which means that the system is ",
" slowly losing energy, and the satellite could theoretically slow down and plummet to Earth. But in reality, for anything but the most massive objects, this is absurdly slow. Real satellites would be affected more by space gas or the Moon or Jupiter than by gravitational waves."
] |
[
"Small quantum effects like photons from starlight will always affect the orbit. But you can't measure it anyway. ",
"Radiation pressure from the Sun (it's a star!) is a measurable effect."
] |
[
"Small quantum effects like photons from starlight will always affect the orbit. But you can't measure it anyway. ",
"Radiation pressure from the Sun (it's a star!) is a measurable effect."
] |
[
"Why does Saturn have a hexagonal shape at its north pole?"
] |
[
false
] |
posted an image of Saturn's north pole:
|
[
"This recent article",
" appears to shed some light on the mystery patterns and formation of the storm. Basically, the giant storm seems to operate like jet streams on Earth and this is why the shape remains consistent. Seasonal variations on Saturn don't seem to affect its pattern or shape, so both are part of an extensive wave from deep down in Saturn's atmosphere."
] |
[
"Previous ",
"thread on this topic",
". ",
"Relevant paper: (PDF) ",
"A laboratory model of Saturn’s North Polar Hexagon",
" by\nAguiar, Read, Wordsworth, Salter, Yamazaki ",
"Video: ",
"https://www.youtube.com/watch?v=n_c9A9Auf0A"
] |
[
"On Earth, jetstreams are basically caused by prevailing westerly winds that are a result of vortexes formed through the rotation of the Earth and its atmosphere. In-depth explanation here: ",
"http://www.pilotfriend.com/av_weather/meteo/prv_wnd.htm",
"Not really sure about other planets but it probably follows the same principle."
] |
[
"When you re-experience something in life, like a song, or a TV show you've seen before, does your brain fire the same synapses from the original experience, or does it create new connections? Or both?"
] |
[
false
] |
In other words, how does remembering work from a technical point of view? I just woke up from a dream where a song I remember from years ago was playing very vividly in my head. It got me thinking about how memory works in the brain. When you re-experience something, I imagine your brain would have to do several things at once: a) find the memory in your head in order to recognize that it's something you already know, b) follow along a chain of memories as the experience happens again to confirm that it's the same experience, c) create a new copy of the memory so that you remember that you heard that song today, and not in 1994. d) possibly many more technical mechanics I'm not even aware of, which is why I'm asking. How does it actually work? And when we get that deja vu feeling, which part of this process is failing?
|
[
"I can't answer your original question (if our brain fires the same synapses from the original experience) but I wanted to say two things that I did learn before and might make some sense here. 1 - When you access your memory of something you saw, heard or of an event, you will be changing the original memory. It's not like a photograph you look at and it's always the same every time you look at it. You'll change the memory you had. So I'm guessing it will not be like the original experience (maybe the feeling you associate with the memory is maintained... But this is just a guess!). 2 - Last time I looked it up, I discovered there were many theories as to how and why we have deja vu. The explanation I learned in psychology and the one I personally found more acceptable is that it occurs because our brain skips the short term memory step. I'm not sure if that's how you call it in English but we have short term memory and long term memory. In deja vu the information or brain is receiving skips the short term and goes straight to the long term memory giving the impression of that moment being a memory of something we already did. But then again, it's one of many theories. "
] |
[
"Yeah, that deja Vu segment is correct in English. Exactly how I would've worded it."
] |
[
"Hey guys, this is pretty close to one of the issues that I study. We do believe that replaying a memory in one's head does involve reconstructions of something like the original experience in sensory cortices. For example, auditory cortices appear to be activated in specific ways when we recall the sound associated with a visual stimulus. ",
"One way we have of testing these things is through what is called MVPA: multi-voxel pattern analysis. With neuroimaging data, you can train a machine-learning classifier to identify which stimuli correspond to which patterns in sensory cortex. For example, an algorithm can learn to identify which picture from a set of pictures a person is looking at based on activity patterns from his or her visual cortex. This is quite easy to do. ",
"Then, to test the issue at hand, we can then ask the person to recall the same images, and compare the classifier's ability to decode the information from visual cortex during this imagery-from-memory experience. In other words, can the classifier that is trained on data from perception still identify the data from recall? This could only be the case if the patterns are shared across perception and imagery. ",
"It turns out that the patterns are indeed very similar, supporting the idea that memory involves re-instantiating neural patterns in sensory cortex that are just like the ones at initial perception. As an example, I point you to ",
"this study",
" by Johnson & Johnson from last year. ",
"edit: wording improved"
] |
[
"Is arachniphobia (the fear of spiders) biological or cultural?"
] |
[
false
] |
Copied from my comment for better clarification: To make my question easier for you to understand, is the fear of spiders hardwired into the human brain? (I've never seen a spider or anything like it before but somehow I have a fear of it.) Or is it simply a product of human intelligence? (I know that a spider has killed someone before and therefore I will have a fear of it.)
|
[
"Depends what you're asking. ",
"The ",
" is an innate reaction to something recognized as a threat and is considered rational. A ",
" is an irrational fear. ",
"Are you asking if it's rational to be afraid of something you know may threaten your health, or are you asking if it's natural to irrationally react to arachnids as if they are threatening even if it's unclear?"
] |
[
"To make my question easier for you to understand, is the fear of spiders hardwired into the human brain? (I've never seen a spider or anything like it before but somehow I have a fear of it.) Or is it simply a product of human intelligence? (I know that a spider has killed someone before and therefore I will have a fear of it.)"
] |
[
"I'll just throw it out there that, in my opinion, this literature (on innate fear of snakes, spiders, heights, etc.) is plagued with methodological and theoretical problems. So if someone thinks they have an answer to this question, then he/she needs to make sure that all limitations are acknowledged. That person also needs to define what they mean by \"innateness.\" ",
"There's a bunch of studies (e.g., ",
"here",
") that ",
" an innate \"fear\" of snakes (etc.), but there are tons of confounding variables and potentially misguided theory (e.g., on defining the emotion of \"fear\"). ",
" But perhaps someone else has some insight that I do not."
] |
[
"Why is the \"Many Worlds Interpretation\" not just crazytalk?"
] |
[
false
] | null |
[
"Because, when you think of it that way, it's not actually The Many-Worlds Interpretation, but a watered down, bastardized, pop-sci version of it. Unfortunately, it's the only version that the public ever hears.",
"From the now deleted text of your submission (a pity you removed it, because it's hard to understand ",
" you think it's \"crazy\" unless you explain it):",
"to spawn an entirely new, and fully complete universe",
"No such thing ever happens. This is an intrusion of the Copenhagen thinking, and then a further intrusion from classic-physics thinking. From a pure Many-Worlds frame, wave function collapse never happens; both particle and observer always and ever exist in multiple states; it's only that, after the observation, particle and observer become entangled, and stuff appears to \"congeal\" (but it really doesn't).",
"From M-W, all possible past ",
" future \"Universes\" already and forever exist. But they are not full-blown, collapsed, classic-physics universes, but are merely sets of particle states. This is the key, and as long as you remember it, M-W is not so bewildering: the \"universe\" is merely a collection of particle states; it's not a brand-new copy with new particles.",
"If you're worried that too much \"particle stuff\" is created at each \"branching\", understand this: the \"stuff\" of each particle is \"distributed\" among all its possible states. It's not like there's a new electron for each state, but it's the same electron existing in all those states at once. The \"branching\" is not the recreation of the whole cosmic background anew, just because an electron \"chose\" A instead of B, but it's an entanglement between electron and observer that gives \"the stamp of approval\" to A instead of B.",
"But there's a whole'nother scenario where the electron \"chose\" B instead, which is just as valid, except it's completely removed from the other scenario - might as well be like a \"separate universe\" for all we care.",
"Here's an explanation which is more competent than my rough sketch, coming from a proponent of M-W:",
"http://www.askamathematician.com/2011/11/q-according-to-the-many-worlds-interpretation-every-event-creates-new-universes-where-does-the-energy-and-matter-for-the-new-universes-come-from/",
"Further reading:",
"http://www.askamathematician.com/2010/10/q-copenhagen-or-many-worlds/",
"http://www.askamathematician.com/2012/08/q-is-there-an-experiment-which-could-provide-conclusive-evidence-for-either-the-many-worlds-or-copenhagen-interpretations-of-quantum-physics/"
] |
[
"Hmm, I didn't delete anything...",
"OK, so would it be fair to describe our entire universe as a giant superposition of all possible states? It's not so much that they're separate universes, but separate physically possible states for this one universe? If that's a reasonable description, intuitively, I feel like there might be some connection there to the holographic principle. If the entire universe were a giant superposition of states, isn't that basically what a hologram is?",
"When referring to \"another universe\" you'd really just be referring to one particular superimposed state, sort of like viewing a hologram from a particular \"angle\"? You can't really say that any particular point of view is \"reality\", because as soon as you look at it from a different \"angle\" you see something different. ",
"When someone like Michio Kaku says that there would be an infinite number of \"me\", in an infinite number of states, in an infinite number of universes, each with infinitely small variations between them, is that really doing a disservice to the many-worlds concept?",
"If I'm understanding you correctly, it intuitively makes a lot more sense to me to describe one universe in a superposition of states, rather than describe it as distinct, multiple universes. I guess I can see how it would be useful to conceptualize any one of these possible \"congealed\" states as if it were it's own universe, but really is it describing just one \"possible\" state that one particular observer perceives from their particular perspective? ",
"If an electron \"chose\" option A instead of B, can it be said that the universe congealed around option A, and that option B never ",
" happened, or is the fundamental point here that we can't really say that either one actually happened, because some other \"observer\" somewhere else in the universe in a different reference frame may, or may not have seen the same \"event\" occur in the same way?"
] |
[
"would it be fair to describe our entire universe as a giant superposition of all possible states?",
"In a sense, yes, but as soon as you're inside and start interacting with it, bam, wave function collapse (as a copenhagian would put it) - or so it seems for you (as a many-worlder would quickly add).",
"It's not so much that they're separate universes, but separate physically possible states for this one universe?",
"That's the gist. It's one single giant pile of dust (not many), but each little mote enjoys simultaneously all its own possible states (unless you \"observe\" it).",
"I feel like there might be some connection there to the holographic principle",
"That thing has a very specific meaning, unrelated to this topic:",
"http://en.wikipedia.org/wiki/Holographic_principle",
"When someone like Michio Kaku says that there would be an infinite number of \"me\", in an infinite number of states, in an infinite number of universes, each with infinitely small variations between them, is that really doing a disservice to the many-worlds concept?",
"It' a valid question. But the reply is - so how else would you describe these things in a pop-sci context? After all, for all practical purposes, these ",
" indeed ",
" separate universes, except without the massive inflation of \"new stuff\" being \"produced\" all the time.",
"Popularizing science the correct way is very hard. You need to make compromises, and inevitably you lose parts of the message.",
"I think Kaku does a very good job overall.",
"If an electron \"chose\" option A instead of B, can it be said that the universe congealed around option A, and that option B never actually happened, or is the fundamental point here that we can't really say that either one actually happened, because some other \"observer\" somewhere else in the universe in a different reference frame may, or may not have seen the same \"event\" occur in the same way?",
"\"Observer\" is a misleading word. It's more correct to say that \"particle\" and \"observer\" are interchangeable, and \"observation\" really just means \"interaction\".",
"When you \"observe\" the electron (when the electron and you interact with each other - and therefore the electron also \"observes\" you), then option A really does happen - for you and all parts of the Universe entangled with you. If you don't \"observe\" it, then both A and B happen at once."
] |
[
"What is the loudest sound physically possible"
] |
[
false
] |
At witch point is it impossible for a sound to get louder? How many decibel? It would also be interesting to know how low and high in pitch a sound can be.
|
[
"I don't think there is a limit to the volume of sound. Sound is a localized variation in the density of the medium that is traveling outward from the source. ",
"Even if the local distortion is so violent that the air molecules become ionized, the atoms are still there and will still propagate the sound wave.",
"I suppose if the vibration of the medium material is so large that the velocities of the molecules become relativistic, you would start to approach a fundamental limit. But as to what that would translate to in terms of decibels is not an equation I know of (not that it doesn't exist)."
] |
[
"So you're saying there is one?",
"I Already figured out that the lowest possible frequency would relate to the age of the universe. "
] |
[
"First of all there are many different kinds of decibels, I think what you're talking about is dB (SPL) or \"sound pressure level\". 140 dB SPL is the painful upper limit of human hearing, 0 dB SPL is the lower limit. Some volcanoes have been said to be much greater than that, Mt. Krakatoa supposedly hit 272 dB SPL. Some microphones are rated as high as 180 dB SPL.",
"I suppose the high dBSPL threshold would be where either the air turns into a plasma from overheating or turns into a liquid from compression. Not sure where that would be and I can't really do the math.",
"The frequency high and low bounds would be the bandwidth of air. The upper limit is when the wavelength of the sound approaches the average distance each molecule travels between collisions. At this point the sound is distorted.\nThe low bound would depend upon the medium, namely the length of the medium. The longest possible distance for a sound wave to travel on earth before meeting up with and interfering with itself would be around the equator, about 40,000km.... ",
"wave velocity = frequency * wavelength",
"so",
"340 m/s = frequency * 40,000km (speed of sound in air is about 340 m/s)",
"so the frequency of a sound wave that stretched around the equator would be about 0.0000085 Hz, which is a slightly flat D about 25 octaves below middle C",
"Edit: That sound wave traveling around the equator would take about 32 hours to complete the trip. And the high frequency threshold I've seen for sound waves in air is ~3GHz",
"Edit 2: I just read that at around 194 dB SPL sound begins acting like a shock wave instead of a sound wave."
] |
[
"Why do we use CO2 for sparkling drinks rather than any other gas?"
] |
[
false
] |
Just curious.
|
[
"Carbon dioxide, CO2, is more soluble in water than most common gasses. The solubility of a gas is proportional to pressure, ",
"Henry's Law",
", and the ",
"Henry's Law constant for CO2",
" (3.4x10",
" mol /L-atm) is one to two orders of magnitude greater than for the other atmospheric gasses: 6.1x10",
" for nitrogen and 1.3x10",
" for oxygen. So you can dissolve more CO2 in a given amount of beverage than you can N2 or O2. But you could use other gasses, and I believe Guinness does just that, using N2.",
"Another reason may have to do with taste. When CO2 dissolves in water it forms carbonic acid, H2CO3. This is a weak acid, so it could give some zap to the flavor, although the phosphate buffers in soft drinks may override this. Perhaps a food scientist could address the effect on flavor.",
"Less common gasses would be more expensive of course, but could in principle be used. N2O (nitrous oxide) for instance, is nearly as soluble as CO2 (",
"Henry's Law constant of 2.5x10",
" mol/L-atm",
".) This could make an interesting drink since N2O is commonly known as ",
"laughing gas",
"."
] |
[
"Food scientist here to address the effect of carbonic acid on the overall flavor: yes, it will add up to the flavor but also gives in-mouth texture and the scratchy effect on the throat. It also lessens the sweetness from the sugar and other sweeteners which (along with cold temperatures) makes them feel \"refreshing\". It also helps stabilize colors and aroma compounds. So if we use a different gas, soda will feel sweeter, heavier and not as refreshing.",
"As a side note: it's also the main reason carbonated beverages are easier to damage teeth as they combine with sugar and also the reason why coke cleans jewelry and toilets.",
"Edit: I stand corrected: I forgot about the lovely phosphoric acid in coke which is actually the one that makes it clean jewelry. However, coke is the only beverage to add enough phosphates to create phosphoric acid in such a quantity that it can clean it."
] |
[
"But you could use other gasses, and I believe Guinness does just that, using N2.",
"Yes, they do but only for cans. They're also using a special container inside the can. If you buy bottled Guiness you'll get CO2 - tastes very different."
] |
[
"If I double the mass of explosives (from 50kg to 100kg), does it double the size of the explosion?"
] |
[
false
] |
If I had a warhead that contained 50kg of explosives and has a blast radius of 100m, would doubling the explosives content result in a linear increase of the blast radius? I need to characterize the difference in blast radius between two weapon systems, but this is not my area of expertise. Thank you for your help!
|
[
"No, it wouldn't be linear. If you double the radius of a sphere you get a sphere with eight times the volume. So if you had only twice the explosives there's no way you'd be able to have the same pressure at the surface of a sphere eight times bigger. The blast radius would be approximately proportional to the cube root of the amount of explosives."
] |
[
"I don't think so. It's not how much Uranium there is, it's how much of it fissions. if twice as much fissions, you'd have twice the energy."
] |
[
"A purely fission bomb has to be designed such that it starts with sub critical masses of uranium and then goes past critical mass when detonated. Its actually a major challenge of design to get as much of the uranium fuel to participate in the explosion as possible, I think the for the Hiroshima bomb 64 kg of uranium was used and less than 1 kg actually underwent fission. Once the reaction gets going the fuel itself is going to be torn apart, and it winds up effectively not part of a critical mass. ",
"Ivy King had around twice as much uranium as Little Boy but around 33 times the yield. But there are a lot of design aspects in that, its not just fuel. Ivy King had to spread the mass over a hollow shell to be subcritical, and then use 92 explosives spread around it to compress it, and that inward force lets the nuclear reaction proceed further. So while Little Boy was roughly 1.5% of its fuel used Ivy King was around a third of its fuel burned. ",
"Design is such an important feature, and the design has to accommodate the amount of uranium, if you had just doubled the uranium in Little Boy, it would have exploded when it was being built because it would have been already super-critical. It has to be designed to take subcritical mass distribution and make it supercritical in a controlled way. ",
"With conventional explosives you can just add more, with a nuclear explosive you have to design it for the amount of fuel. "
] |
[
"Are there any exceptions to Newton's Laws?"
] |
[
false
] | null |
[
"Newton’s laws are violated (need to be modified) at relativistic speeds."
] |
[
"as in when approaching the speed of light?",
"any other examples?"
] |
[
"as in when approaching the speed of light?",
"Yes.",
"any other examples?",
"Quantum effects."
] |
[
"How different are different sperm cells in a single 'batch' from eachother?"
] |
[
false
] |
[deleted]
|
[
"The reason you and your brother look different has more to do with the process of meiosis (when the sperm and egg are formed) than random mutations or epigenetics. I'll skip some details, but basically, your father has 46 chromosomes that he can ",
" pass on. During meiosis, these 46 chromosomes are split up and randomly assorted into the sperm. So a single sperm inherits 23 chromosomes.",
"Since the chromosomes split up randomly, there are over 8,000,000 (2",
" ) different combinations of DNA that a single sperm can inherit, not including the enormous amount of variation that you can get from crossing over (which ",
"/u/gebraroest",
" mentioned). Don't forget, your mother also went through meiosis to create an egg, which also has over 8,000,000 unique combinations.",
" Every sperm is different. The probability that you would inherit your unique set of chromosomes is less than 0.000000000000016%. The probability that you and your brother would inherit the exact same set of chromosomes is 0.00000000000000000000000000024%."
] |
[
"I will note a bit of a bias in your statement: if any of those things had happened and you ",
" here, you wouldn't be able to be astounded by the improbability of your existence. "
] |
[
"The probability that you would inherit your unique set of chromosomes is less than 0.000000000000016%. The probability that you and your brother would inherit the exact same set of chromosomes is 0.00000000000000000000000000024%.",
"Actually, those probabilities are the same. I think in the latter case you mean the probability that you have your exact same set of genes ",
" your brother does too. "
] |
[
"If two cyclists - one 50kgs and one 100kgs ride up a hill, will the heavier cyclist have done exactly twice the work?"
] |
[
false
] |
Let's assume they are on identical bikes and their frontal profile is identical (which is obviously unlikely but it makes life easier) so air resistance is not a factor. Will the heavier rider have done exactly twice the work add the lighter rider? Logic tells me that the potential energy of the heavier rider should be double that of the lighter rider, but I didn't do physics at school, so I could well be wrong. If both riders were running a power meter (powertap, quarq etc) well that show double the work having been done? And what is the appropriate measurement for that? Watt hours? -----EDIT----- Thanks for the great answers everyone. I didn't expect this to hit the front page - this is my first ever post to Ask Science. I posted it a few days ago and it got deleted - I pored over the submission rules to see what had gone wrong but it had just got caught in the spam filter - and now here it is on the front page! Submitted it when I went to bed and woke up to 400 odd comments - am working through them now. And to everyone who said it wouldn't be double due to bike weight you are absolutely right. I should have had a 50kg rider and a 110kg rider both on 10kg bikes. But that is why I don't even science, bro.
|
[
"You are right in that the heavier cyclist would have performed twice the work against gravity, i.e. raised their gravitational potential energy twice as much (W = mgh). But the heavier cyclist would effectively do more work due to having to do more work against friction and drag. He also spends more energy pedalling as he has heavier legs.",
"And what is the appropriate measurement for that? Watt hours?",
"You can measure work (and heat and energy) in many ways. Joule, Newton meters, Watt hours, Coulomb Volts etc. With mechanical work, such as cyclists riding up a hill, I would use Newton meters or Joule.",
"EDIT: To reply to the most prominent follow-up comments:",
"I included the weight of the bicycle as well as the clothes, helmet and other carried items/accessories in the cyclist. If we only count the weight of the cyclist, the heavier one would do a little less work against gravity.",
"While leg weight doesn't contribute to any work against gravity. You do have to push with your legs to apply force to the pedals, and to make your legs move you have to overcome their inertia which is proportional to their mass.",
"I cite an ",
"example I made earlier",
":",
"Imagine if you are on a stationary exercise bicycle with no resistance and had to carry a certain amount of weight. If you carried that weight in a back pack it would make almost no difference, but if the weight were strapped on your feet it would make it harder to pedal as it would increase the inertia of your feet."
] |
[
"If the problem is reduced to the ideal case - no air resistance, weightless bikes with frictionless drivetrains, inflexible wheels with no slippage, then yes, the heavier rider will have done twice the work.",
"You can see in all the other answers that there are a lot of other factors (air resistance, bike weight, tire flex, etc.) that can be added to the equation to get a more precise answer."
] |
[
"Watt is a unit of power, but Watt hour is the unit of work (power x time)"
] |
[
"I will get hell for this question but here goes... If homosexuality is something people are born with, then wouldn't natural selection and their preference to be with the same sex and more than likely not reproduce delete the homosexual trait?"
] |
[
false
] | null |
[
"This is a very common question. See, for example:",
"http://www.reddit.com/r/askscience/comments/lbt6d/what_role_does_homosexuality_have_in_human/",
"http://www.reddit.com/r/askscience/comments/f85jq/if_homosexual_tendencies_are_genetic_wouldnt_they/",
"Also see wikipedia: ",
"http://en.wikipedia.org/wiki/Biology_and_sexual_orientation#Sexual_orientation_and_evolution"
] |
[
"Alrighty thanks! This is kind of a follow up then. If they did crack the genetic code for homosexuality, could gene therapy then be used to make someone straight? Say a gay man really desired to have a family with his own genetic children and wanted a straight lifestyle (completely hypothetical). Could he attempt to change that? "
] |
[
"That's supposing that (a) there is a genetic basis, and (b) environmental effects are secondary to genetic effects. Without knowing the answers to those questions, it's impossible to do more than speculate."
] |
[
"Do women really have worse circulation than men, or is it some kind of confirmation bias-based myth?"
] |
[
false
] |
I have always noticed women seem to have cold feet/hands compared to me, even if it isn't really cold. I was just watching an episode of Scrubs which reminded me of it. Googling provided come quite vague answers, the top one being from the Daily Mail. Is this a real thing? Why?
|
[
"http://circ.ahajournals.org/content/115/7/823.full",
"Further evidence that may help to explain variations in coronary artery disease outcome are gender differences in vascular structure. Women typically have smaller and less compliant conduit arteries than men. This is true even after adjustment for differences in height, weight, and blood pressure.",
"While it's true to an extent, I'm not sure whether that difference in arterial size would be enough to cause a significant difference in the temperature of the extremities."
] |
[
"I've seen this question addressed in ",
"/r/askscience",
" before, and I seem to recall the consensus being that the feeling of being cold was inversely related to body mass. So women of lower body mass will generally feel colder than a man with more mass."
] |
[
"This",
" is a very detailed study to answer your question."
] |
[
"Why does James Webb Space Telescope needs to be in L2 lagrangian point? What are the benefits other we don’t worry about losing orbit..."
] |
[
false
] |
Edit - other than we don’t need to worry about losing orbit time to time ..
|
[
"Thermal control. In Low Earth Orbit (LEO), you don't only have to worry about the Sun heating your satellite, but also ",
" reflects 39% of sunlight and emits infrared at the same time. James Webb is designed to observe in infrared, so the instruments themselves have to be kept very cold to reduce thermal noise in the observations. In fact they have designed it for temperatures below -200°C! This would be too hard to maintain if you have visible ",
" infrared coming from both sides at times.",
"The most intuitive answer would say that in L2 Earth blocks most sunlight. This isn't actually true for JWST because it will be placed in a halo orbit with a radius of 800,000 km, so Earth will never be in line between the Sun and the telescope. ",
"http://www.stsci.edu/jwst/overview/design/orbit",
"Still, the benefit of not having to deal with planetary infrared is already a good improvement. Also the fact that all sunlight is coming from the same direction is good, so you can just put a solar shade to have a permanently cold side. (Not trying to imply that maintaining such a low temperature is going to be easy, but definitely not as hard as in LEO).",
"Losing orbit is actually still a concern. L2 is an unstable equilibrium point. If the satellite moves away from this point perpendicularly to the Sun-Earth line then the combined forces of the two major bodies would pull it back into L2 (in fact it will be in orbit around that point), but if the movement has a small component that is parallel to the Sun-Earth line then it risks of being pulled into a heliocentric orbit that is no longer dominated by Earth, or falling down into an ellipse coming close to LEO or even crashing against Earth. For that reason it will need thrusters to compensate for perturbations. That said, there isn't much atmospheric drag as in LEO and the Moon is too far away to cause a strong gravitational influence, most of the force it will have to account for is solar radiation pressure which is very small."
] |
[
"The most intuitive answer would say that in L2 Earth blocks most sunlight. This isn't actually true for JWST because it will be placed in a halo orbit with a radius of 800,000 km, so Earth will never be in line between the Sun and the telescope.",
"When you said Earth \"blocks ",
" sunlight\" at L2, I had to know how much is most... So here are my quick envelope numbers:",
"Earth's L2 is approximately 1.5M km beyond the Earth as viewed from the Sun. ",
"Given AU = 150M km, R",
" = 695700 km, R",
" = 6371 km, Earth's umbra extends toward L2, on average, about 1.38M km.",
"This leaves L2 deep in the Earth's antumbra, but directly illuminated by about 15% of the Sun's photosphere as well as sunlight refracted by the Earth's atmosphere."
] |
[
"From the point of view of an object at SEL2, the earth, moon and sun all occupy the same small region of the sky. So all three heat sources can be blocked with a small shade. This leaves most of the sky to radiate heat into. ",
"Since JWST is an infrared scope, staying cold is important.",
"WISE was an earlier infrared scope. Being in low earth orbit nearly half the sky is filled with a 300 K heat source (the earth). Besides the earth it also had to shade itself from the sun.",
"Staying cold at SEL2 will be much less difficult."
] |
[
"What's actually happening when you go temporarily blind for standing up too fast?"
] |
[
false
] | null |
[
"Your heart needs to pump at a slightly higher pressure to move the blood up to your brain, since it must now fight gravity. It takes a little while to adjust, so your brain becomes slightly blood (and oxygen) deprived for just a little while, causing your vision to momentarily degrade."
] |
[
"This process is called orthostatic hypotension, if anyone is interested for more information."
] |
[
"the temporary stroke part. it's because of hypotension that the arterial supply becomes insufficient. the neurons don't get oxygen or glucose or anything else, because it just stops. they then start going through the initial phases of cell death. then supply is returned (hopefully) when your homeostasis regulatory mechanisms cause the sympathetic nervous system to upregulate and the parasympathetics to slow down, thereby increasing arterial blood flow to the brain."
] |
[
"Do astronauts have difficulties with swallowing and digestion?"
] |
[
false
] |
Would weightlessness mean that food and water floats around inside your body, making digestion hard? If so, how is it dealt with?
|
[
"After the point of swallowing food is moved by a series of muscle contractions, and the stomach is cinched off from the esophagus by a sphincter muscle so that stomach contents cannot passively enter the esophagus.",
"While this process can proceed normally in zero gravity, a few problems do arise... ",
"I believe there are issues with acid reflux as stomach acid can sometimes creep through the sphincter when not assisted by gravity. Same principle as when peoples acid reflux is worsened by laying down.",
"Another issue is burping. We kind of take burping for granted, but the air in our stomach only collects at the top because gravity pushes everything else down. Without gravity, it's basically impossible to burp without vomiting a bit at the same time. I have heard that astronaut Jim Newman dealt with this by jumping off a wall of the space station, momentarily collecting the contents of his stomach at the bottom, allowing him to quickly burp."
] |
[
"The oesophagus has sphincters to help push the food you swallow into your stomach, by contracting the oesophagus at the \"end\" side of the chunk of food and dilating it in the front while the food progresses in the direction of the stomach. Gravity helps getting the food down but isn't necessary for the swallowing part, as you already have a biological mechanism for it.",
"I can't say for digestion though."
] |
[
"My understanding is that GI tract primarily uses ",
"peristalsis",
" to move food along, not sphincters. As such, it would not be directly affected by the presence (or lack there of) of gravity."
] |
[
"What would happen if we got a bunch of single protons (with no electrons) and compressed them all together?"
] |
[
false
] |
[deleted]
|
[
"It’s depends on the energy at which you compressed (or ",
" to compress) them together. Protons repel each other due to their like charges. At very short distances, the (usually) attractive nucleon-nucleon interaction will begin to dominate over the electromagnetic repulsion. However a system consisting of only two protons has no bound states (which clearly remains true for a system consisting only of A protons with A > 2).",
"Even if you press them together really closely so that the nuclear force takes over, you won’t be able to form a bound system unless some of the protons change into neutrons via some weak interaction."
] |
[
"The first step in that chain is a weak reaction which turns a proton into a neutron."
] |
[
"Isn't that the answer to his question then? At a certain point, you get a fusion process identical to what happens in stars. "
] |
[
"Why is the \"p\" sub-level the most stable?"
] |
[
false
] | null |
[
"So the p orbitals of quantum number n are lower in energy than the s orbitals of the next principal quantum number",
"Okay, so then why is the p orbital of quantum number n lower in energy than the s orbitals of the ",
" quantum number?",
"Maybe I'm just not understanding, so could you clarify with an example?\nSay, why the 3p orbital has a lower energy than 3s?",
"Edit: Sorry, did not mean lower energy. I meant that a filled 3p is far more stable than a filled 3s."
] |
[
"Okay, so then why is the p orbital of quantum number n lower in energy than the s orbitals of the same quantum number?",
"They're not. The order of filling is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, ..."
] |
[
"It's empirical. The rule is simply a description of what was observed experimentally. It answers \"how?\" and not really \"why?\" It does a decent job of predicting configurations for neutral atoms, but like all things in chemistry, there are situations when it doesn't apply.",
"You'll need to dig deeper into quantum mechanics for a more satisfying answer."
] |
[
"Why is plastic so hard to breakdown?"
] |
[
false
] | null |
[
"The long polymers that make up plastic are extremely stable chemical structures that were invented very recently in evolutionary history. For any organic substances to be broken down into units that can be used by life decomposers that can recognize the substance and catalyze breakdown reactions need to exist. Since plastic is made from fossil fuels it is organic and in theory will eventually be broken down whenever appropriate decomposers evolve. In some landfills we’re starting to see bacteria that are actually breaking down simpler plastics. Eventually species will exist that can break all sorts of plastic down. ",
"This is actually an active area of research that should be heavily funded (in my opinion). Using controlled conditions to drive the evolution of plastic decomposers would solve a lot of problems if successful. It also theoretically allows us to select for species that will decompose these plastics in a way that doesn’t contribute further greenhouse gases.",
"Edit: grammar"
] |
[
"A similar thing happened in the Carboniferous Era, when plants evolved lignin but bacteria and fungi hadn't evolved to break it down so a lot of it just kept piling up, got buried, and eventually formed an estimated 90% of the coal that's ever been produced on Earth."
] |
[
"There are plastics that aren't hard to breakdown they're just limited to nich uses.. The reason plastics in use don't breakdown is people dont want plastics that breakdown. Nobody would want waterbottles that dissolve in water or breakdown from being left in sunlight. They don't want food containers that are easily broken down by common bacteria."
] |
[
"What forces are at work that make cheerios floating in milk have a tendency to group together as they move around?"
] |
[
false
] | null |
[
"Surface tension is at the heart of it.",
"Milk is water-based and as such, has a rather high surface tension. This means that very light materials, such as cheerios, not only float along the surface, but seem to \"repel\" the liquid. They're not actually hydrophobic, of course, that would be a pretty useless trait for cereal, but because water is polar, H2O molecules love sticking together. That means that near a cheerio, milk molecules will prefer to be close to other milk molecules rather than the non-polar cheerio.",
"This effectively creates a \"dent\". You can observe this if you look closely. The cheerio seems to be sitting in a little crater of milk, an effect only possible due to surface tension. When two cheerios come into contact, their \"craters\" unite. This is energetically preferable, as the crater's lip length is now smaller than if there were two craters. Remember how H2O molecules like sticking together? Separating them requires energy input. This means that increasing the lip length, i.e. increasing the number of water molecules not surrounded by other water molecules requires an energy input.",
"Due to internal friction, energy input into the system will eventually \"dissipate\" and turn into negligible heat. As a result, the cheerio-milk system will stay in a state of least potential energy, or in other words it will prefer that cheerios stick together once they come into close proximity.",
"EDIT: It's worth noting that this behaviour fundamentally changes depending on the material. If you remember high school science, you'll remember that water in thin glass tubes tends to curve upwards at the edges. Glass, like water, is quite polar, meaning the two will attract and water will actually ",
" to be in contact with glass rather than not. As a result, a polar material with the same density as cheerios would not exhibit the clustering behaviour seen in cereals."
] |
[
"This is actually called the ",
". It's an interplay of surface tension and buoyancy.",
"Here are a couple of links:",
"http://www.damtp.cam.ac.uk/user/dv211/cheerios.html",
" ",
"http://en.wikipedia.org/wiki/Cheerios_effect"
] |
[
"When two cheerios come into contact, their \"craters\" unite. This is energetically preferable, as the crater's lip length is now smaller than if there were two craters. Remember how H2O molecules like sticking together?",
"To expand on this, surface tension always acts to try to decrease the surface area of the liquid. This is why drops and bubbles tend toward spheres: because spheres have the least surface area for a given fixed volume."
] |
[
"I've seen babies with glasses. Assuming they can't read a chart or communicate a lens preference, how on earth do doctors figure out their prescription?"
] |
[
false
] |
I guess this also applies to non-verbal adults who get glasses. Is there a kind of test that just pops out a prescription? If so, why do we have the whole "what letters can you read" and "do you like 1, or 2 better" process?
|
[
"Opthalmologists can analyze the optical system by observing how the light goes through the eye back to the retina. It's not as accurate as the normal methods, but it's usually good enough, especially for babies and the like who can't yet read."
] |
[
"the process is called 'retinoscopy'",
"https://en.wikipedia.org/wiki/Retinoscopy"
] |
[
"Many times, babies with glasses have them for other eye conditions, not to correct their vision. Sometimes, it’s to protect their eyes; for example, children with poor or no vision in one eye wear glasses to prevent injury to the other eye, which could be blinding. Other times, children might wear special glasses to prevent the worsening of eye misalignment or other conditions as they grow."
] |
[
"What does \"conservation of angular momentum\" really mean?"
] |
[
false
] |
Suppose I have some object tumbling about in space (no gravity, no air resistance). I know how to compute its angular momentum vector, and I know that it is conserved. Is there a way to understand this vector intuitively? It's not the axis of rotation, right?
|
[
"A football tumbles when its axis of rotation is not in line with the axis of the football (i.e. tip to tip). The axis is not changing, at least not without an applied moment. "
] |
[
"Keep in mind that vectors have a magnitude and a direction, but ",
" necessarily a starting or ending point. The angular momentum vector is ",
" to the axis of rotation, but it could be thought to be anywhere in space. As for sign, curl your fingers on your right hand in the direction of rotation and your thumb is pointing in the direction of the vector."
] |
[
"A couple of things. Remember that L = I * omega, where I is a tensor and omega and L are vectors. Therefore, L is not in general parallel to omega, which is what is really parallel to the axis of rotation.",
"Also, although L has to be conserved, since I * omega is a tensor-vector product the components of omega ",
" vary. Remember the ",
"tennis racket theorem",
" where when an object has three non-equal moments of inertia, rotation about an axis corresponding the middle moment of inertia is unstable. In this case, tumbling ensues.",
"Also, in a non-conservative case, imagine a bottle filled with a viscous fluid is spun about its minimum principal moment of inertia. The viscous fluid will decrease system energy, so 1/2 omega * I * omega needs to decrease. There is no external torque however, so I * omega needs to stay conserved. What happens is the rotation switches to being about the maximum principal moment of inertia, which allows energy to be minimized."
] |
[
"Why is economical growth necessary in a rich country?"
] |
[
false
] |
I am an environmental scientist/manager living in a rich country (Germany). There is a strong believe among my peers that we should just stop growing for the sake of the environment and work for subsistence alone because if there continues to be as much as there is now we got enough for everyone. Would it be possible to switch our national economy into zero growth mode (in a situation where the population is completely in favour of it) in a globalised economy? Or would we actually lose our absolute level of wealth/opportunity if we stopped growing? Economic reasoning (Had some economy classes, so I understand core concepts) or links would be appreciated. I found a similar topic via the search but there were no convincing answers in there.
|
[
"In the U.S. economic growth is necessary to help offset the debt we have accumulated. The government borrows money with the hope that our economy will grow at a higher rate than the interest rate on the loan. ",
"As for your peers concern about economic growth affecting the environment, this paper helps cover some key points and states there isn't a strong relationship between the two\n",
"http://www.nber.org/papers/w4634",
"\nThis is most likely due to the fact that growth can come from more efficient means of using raw goods instead of harvesting more goods (better fertilizers or harvesting techniques as opposed to growing more corn)",
"A 0% growth rate would not be sustainable, at least not with the current system. People would be much less likely to invest money (profitable returns are less likely), social programs would become more of a burden on current generations and there would no longer be a reason to save your money in a bank, meaning less loans and mortgages being lent to the people who need them. This would lead to less people taking risk by starting their own businesses or enterprises, leading to less competition in the market as the current providers of goods go out of business or form cartels to maximize profits.",
"If there is anything you would like me to go more depth in, let me know!"
] |
[
"The problem with sustainable environmental policy is that there needs to be policies that individually deal with each form of nonsustainable environmental use, you can't just assume that you've solved your environmental problems via an aggregate change.",
"For example, suppose the economy stopped growing so that the GDP per capita in Germany stayed at about 29,000 EUR, but people in Germany decided that they would spend their leisure money buying say imported rainforest hardwood. The economy is stable, but the environment is still exploited unsustainably, you haven't solved the problem you want to address. If you want to stop an environmental problem you need to target that problem. If you want a generally better environment, then you need to target lots of problems at once. There isn't a way around this and any single study will inevitably only look at a subset of all the environmental problems that exist."
] |
[
"It's not just the government though, all lending is based on the prospect of growth. Banks can lend more money than they actually have on hand because they've calculated (or at least attempted to) how much money they'll have in the future. This of course is based on the idea that the people they've lent money to will have more money in the future than they do right now, which is essentially the essence of growth."
] |
[
"Could a weaponized version of a particle collider be created in the near future?"
] |
[
false
] | null |
[
"In addition to that, the beam would quickly lose energy in the air due to collisions with molecules. There is a reason the beam is kept in a high vacuum."
] |
[
"The LHC has about 1000 beam bunches, each with about 10",
" protons, so roughly 10",
" protons total. After the upgrade, these protons will have 6.6 TeV of energy. Taking that 1 TeV ~ 1.6 ergs, this means that if you dumped the ",
" set of bunches onto a target, you could deposit at most 1.1x10",
" ergs or 110 MJ of energy. 1 gram of high explosive releases 4200 J, so for comparison, the total beam energy of the LHC is equivalent to firing off about 30 kg of high explosive. ",
"The upshot is that even if you were to weaponize it, it wouldn't be that impressive in terms of kinetic energy. Particle accelerators of the sort we use in particle physics make for rather inferior weapons. "
] |
[
"Those charged particles at the LHC produce additional radiation (consisting of photons) due to radial acceleration during their circular trajectory: ",
"Synchrotron radiation",
". This is actually a type of radiation that seems to be weaponized right now since it can be also produced by electrons in a compact machine, a so called ",
"Free-electron laser",
"."
] |
[
"Do cables between Europe and the Americas have to account for the drift of the continents when being laid?"
] |
[
false
] | null |
[
"I am in the submarine cable business, and can answer: No, there is not compensation as drift is inconsequential (2.5 cm or 1 inch per year). One reason is the bottom of the ocean is not flat - but has mountains and valleys like dry land, so extra cable is 'payed out' (let off the ship) to fill in the valleys so the cable isn't left suspended between peaks. Think of paying out rope from the back of a helicopter over the alps. If you just let out a meter for each meter of flight, the rope would be suspended across all the valleys. If there is any wind (equivalently sea currents for undersea cables) it would rub through the rope where it contacts the peaks. So the bottom line is there is excess cable laid just to accommodate the topography of the ocean bottom, so the inch/year is not an issue.",
"Hope this helps!"
] |
[
"The cable laying is suprisingly well controlled these days. They first have a map of the ocean floor. Then they have a 3-d model of the ship, plus currents, plus cable properties. ",
"So, if the cable has to go over a ridge, they make sure it isn't hanging.",
"This video does a good job explaining it ",
"https://youtu.be/j6p0Mf_CAvg?t=1m17s"
] |
[
"Near the shoreline or in areas where there is risk of external aggression (anchor dragging, fishing nets, etc.) the cable is armored and very, very tough. In deep water, however, the cable is exposed polyethylene about an inch in diameter. I don't know of anything special being done in areas of special abrasive concern. (As I answered elsewhere, I'm an optics/electronics guy, so I hear stories from the route planning/laying guys, and I haven't heard anything. There are only a few cable designs - basically heavily armored, lightly armored, and 'bare'. I suspect if there is a troublesome abrasion area they might deploy the lightly armored stuff.)"
] |
[
"What makes a virus more transmissible?"
] |
[
false
] |
[deleted]
|
[
"Things that make viruses more transmissible are usually related to their envelope proteins, replication speed, or fusion/entry mechanisms. ",
"We don't have much info yet, but in the case of Coronavirus (a enveloped, single stranded, + sense RNA virus), that means that there was a slight mutation which A) helps the virus attach to more receptors than just the ones we're used to and enter cells more quickly, B) replicate more quickly C) Exit from the cell it infects more quickly D) hang out in cell types that are easier to exhale (higher up in the respiratory tract) or E) survive the environment (outside of a host) for a little longer.",
"It's unlikely that the new strain causes it to hang in the air longer (that would be a significant mutation as opposed to a smaller one we're expecting) and it could affect viral load through the aforementioned mechanism of replicating faster. But no one is quite sure yet, hopefully it's not a significant change to the spike protein (kinda unlikely but nothing is for certain with this wacky virus)."
] |
[
"Will the current vaccines defend against this mutation?"
] |
[
"As long as the structure that the vaccine is targeting doesn't change, it should be ok."
] |
[
"Can you give yourself diabetes by drinking too much soda?"
] |
[
false
] |
Like say... Mt Dew? How much would it take and for how long? And would this be reversible with diet change or permanent?
|
[
"I assume by 'diabetes' you mean Type II Diabetes mellitus. ",
"If you drink high-energy drinks and fail to excercise enough to burn off the energy, leading to weight gain, then you could in fact develop this condition, but it would not be the direct result of the soda. Type II diabetes mellitus is considered a lifestyle disease with genetic components that can increase risk. Since obesity is such a huge risk factor for the disease, only soda that was in excess of your dietary requirements would be an issue. If you only have mountain dew occasionally, and not to excess, you would have no problem, and in fact mountain dew itsself does not 'cause' diabetes any more than potato chips or cake 'causes' it. ",
"A sedentary lifestyle and inadequate excercise, leading to obesity, would put you at greatly increased risk. It's short-sighted to say '[food/drink x] causes diabetes' when it is a complex disease with multiple risk factors.",
"Wikipedia link to relevant section:\n",
"http://en.wikipedia.org/wiki/Diabetes_mellitus_type_2#Lifestyle"
] |
[
"Eat lots of fruit instead! It's got just as much sugar, but also lots of fiber to slow things down to a healthy level. "
] |
[
"Mt. Dew has 55mg of caffeine per 12oz can (4.6 per oz). Coffee typically has 80-135 per 8oz cup (10-16.9 per oz). So 2 or 3 cans of Mt. Dew is like a cup of coffee. Both that and the sugar could be causing you issues but your description sounds like a sugar issue to me. ",
"Processed sugar is not good for you so weaning yourself off of it is a good thing. I completely avoid it. Don't add it to anything, don't drink soda, etc. My family has a history of type 2 diabetes (and we are not generally overweight people) so I figure may as well give yourself every advantage you can and avoiding sugar is an easy one to do."
] |
[
"Electrodeposition deposition of iron from iron oxide for mars mission?"
] |
[
false
] |
Ok, so out of curiosity i have been trying to figure out how a martian colony could operate without continuous support from earth which would cost trillions. A significant problem i have encountered is the lack of carboneous material to smelt ore with. Can any other method like galvanic processes be used to make metal out of ore? Would it be practical? What chemicals would need to be producable by the martian colony to make it feasible?
|
[
"Dead wrong there. Iron is made by burning coal with iron ore, which reduces Fe2+ and Fe3+ into Fe. You dont need just the heat, you also need something to make the chemical reaction happen. ",
"Electrical furnaces are used to make steel. After reducing iron ore into iron, you end up with around 4% carbon in it. If you heat it up and blow some air into the liquid metal, the carbon present will react with the oxygen in the air blown and you end up with steel, which has a much lower carbon percentage (in the order of 0.1%)"
] |
[
"Precisely. This is why everyone is so keen on Mars as a target for colonization. It has tremendous amounts of resources that can be made use of with even a small amount of industrial infrastructure. Within the first 1-2 decades of a Mars colony being setup they'll be able to not only produce basic necessities like propellant (for the return trip) and fuel for energy storage or ground transportation but also food from local crops, plastics, concrete, iron/steel, aluminum, glass, etc. The sorts of heavy bulk materials that can be used to build local structures with the addition of imported high-tech bits and pieces, greatly boosting the effectiveness of whatever equipment is shipped to the planet and putting the colony on a road to self-sufficiency. If you look at other potential colonization locations they would be much more dependent on shipments from Earth for much longer and not have such a rapid creation of local industrial infrastructure."
] |
[
"Please detail the process of smelting iron with electricity. I have read about aluminum smelting using electricity but couldn't find anything on iron."
] |
[
"If I want the heaviest 3cm ball, what available element should I choose ? Why not a stable form of Uranium ?"
] |
[
false
] |
I always wondered about a very heavy matter that I can feel the weight in my hand, but I heard that Uranium is not so much denser than gold for example. Is there a metal that is not dangerous for my health (is there Uranium which is always stable ?), and dense enough to feel something that is heavy even if small ?
|
[
"There are a few metals that are heavier than gold, but generally are more expensive. Gold is about 19 times as heavy as water, osmium and iridium are about 22. Tungsten is almost as heavy as gold but less expensive.",
"The reason that density isn't directly correlated with atomic number (gold at 79 is like 50% heavier than lead at 82) is because the atoms are arranged differently. Gold atoms are arranged in the most efficient way (the way oranges are stacked at groceries) while uranium is more like a cubic structure with lower density. Lead is the same structure as gold but the atoms are farther apart, 500 picometers for lead and 400 for gold."
] |
[
"Uranium orthorhombic but I called it like a cubic to simplify things.",
"Like I said, the lattice constant of lead is about 21% greater than that of gold, so the density ratio is about 1.21",
" x 197/207 = 1.68 (which is close to the actual difference in density). This then shifts the question to \"why does gold have a smaller lattice constant?\" which I don't know the answer to."
] |
[
"1) For a 3cm diameter sphere the most dense naturally occurring element (Osmium) would weigh about 320grams",
"2) There is no stable form of Uranium but natural Uranium is not very dangerous in low quantities if held in the hand because it decays so slowly you get very little radiation exposure from it"
] |
[
"How likely is it that bacterial diseases will eventually adapt to all antibiotics?"
] |
[
false
] |
We're told that if people continue to use antibiotics in the manner they do, then bacteria will eventually become resistant to them, making our antibiotics useless. Is this really true? What would happen to us if they do become resistant?
|
[
"In the absence of antibiotics, populations of bacteria lose their immunity since there are costs to maintaining it that cause them to be less competitive with other bacteria. ",
"http://www.tufts.edu/med/apua/about_issue/about_antibioticres.shtml#5"
] |
[
"You're right, if we rotate antibiotics using one until it becomes ineffective, then switch to another type, the previously ineffective one will return to being effective in time. It will no longer be desirable for the microbes to maintain resistance since the antibiotic is no longer in the environment. This means if we use antibiotics appropriately AND people complete their regiments which is the leading problem to contributing to resistance, antibiotics should last us a long while. Microbes can't adapt to what's not in their environment. "
] |
[
"samspot has explained quite well why you're wrong.",
"Antibiotic rotation, when implemented and properly controlled and maintained is an extremely effective plan."
] |
[
"Night Terrors in Children - What is the current thinking on their cause and treatment? [X-Post]"
] |
[
false
] |
I always thought that sleep-walking and night terrors was a mostly fictional thing elaborated by film-makers. I found out a while ago that these are very real things and that very little seems to be known about them. Psychologists (?) of Reddit - what light can you shed on the subject? (XPost from AskReddit since I got zero response - wrong sub?)
|
[
"Sleepwalking is real and not unusual, especially in children. Night terrors / sleep terrors are also real, if less common. Both are considered NREM parasomnias (behavior during sleep, specifically the non-rapid eye movement part of sleep). They're classified as 'arousals' from NREM sleep, but sleepwalking individuals are not really 'awake,' even if they're doing complex behaviors like opening doors.",
"These sleep disorders can run in families and probably have a genetic component. As they involve arousals from NREM sleep, they may be associated with other sleep arousals or parasomnias: sleep-disordered breathing, restless legs, periodic limb movements, etc.",
"Sleepwalking tends to go away as children get older, so first line therapy is behavioral: sleep hygiene, scheduled nighttime awakenings, securing dangerous objects, etc."
] |
[
"Yes, waking them up before the typical time of sleepwalking is supposed to prevent subsequent sleepwalking."
] |
[
"Keeping the area safe is an obvious one but what about scheduled awakenings? Is this to break the pattern?"
] |
[
"It is seen with certain cave-dwelling species like salamanders, lizards, and even mammals that evolved to have blindness due to the lack of light in the environment. Why do fish on the deep ocean floor still have functioning eyes when their environment has no light to begin with?"
] |
[
false
] | null |
[
"Several things: first, many large eyed deep sea fish are actually midwater fish. They migrate toward the surface at night to feed and have some dim lighting deep in the ocean during the day, so eyes are still useful for seeing in a way they aren't in pitch darkness. The really deep abysmal fish sometimes do have tiny eyes.",
"Second, biolumenescence is common in the ocean and rare in caves. It's useful to have eyes to see it.",
"But why is this the case? The huge difference between the ocean and subterranean habitats is that the ocean is a massive open space while most subterranean habitats are networks of tiny, twisting channels (open caves are rare). Even in the lightless deep ocean, something making a flash of light can be seen from a long way away through the clear water. But underground, you can't see through rock so biolumenescese isn't as useful. So few things make it and few have reason to look for it."
] |
[
"One main difference between the deep sea and caves is that caves are absolute darkness, no light is gonna penetrate the cave walls. The deep sea however is still illuminated by the surface sunlight down a long way. It averages 200m to reach 1% of surface sunlight, but with more sensitive eyes many fish can see each other using just tiny amounts of light, and so eyes can be useful down to extreme depths. However if you look at creatures that live not in the water column but on the abyssal plain, they tend share the eyeless and translucent features of most cave animals much more as there is no light at those depths and bottom dwelling fish stay on the bottom, as opposed to fish in the water column who may participate in the diel vertical migration and be exposed to much more light.",
"",
"Bioluminescence is also a consideration but that exists in caves as well."
] |
[
"https://youtu.be/CHmPL1QUmHw",
"Source: ",
"https://qbi.uq.edu.au/article/2021/12/deep-sea-fish-eyes-are-not-freaky-accident"
] |
[
"Is Spontaneous Human Combustion real?"
] |
[
false
] | null |
[
"Hi TheDuples thank you for submitting to ",
"/r/Askscience",
".",
" Please add flair to your post. ",
"Your post will be removed permanently if flair is not added within one hour. You can flair this post by replying to this message with your flair choice. It must be an exact match to one of the following flair categories and contain no other text:",
"'Computing', 'Economics', 'Human Body', 'Engineering', 'Planetary Sci.', 'Archaeology', 'Neuroscience', 'Biology', 'Chemistry', 'Medicine', 'Linguistics', 'Mathematics', 'Astronomy', 'Psychology', 'Paleontology', 'Political Science', 'Social Science', 'Earth Sciences', 'Anthropology', 'Physics'",
"Your post is not yet visible on the forum and is awaiting review from the moderator team. Your question may be denied for the following reasons, ",
"/r/AskScienceDiscussion",
"There are more restrictions on what kind of questions are suitable for ",
"/r/AskScience",
", the above are just some of the most common. While you wait, check out the forum \n",
" on asking questions as well as our ",
". Please wait several hours before messaging us if there is an issue, moderator mail concerning recent submissions will be ignored.",
" ",
" "
] |
[
"Chemistry"
] |
[
"Thank you for your submission! Unfortunately, your submission has been removed for the following reason(s):",
"/r/AskScience",
"guidelines",
"If you disagree with this decision, please send a ",
"message to the moderators."
] |
[
"Why does every element have the same number of protons as it does electrons?"
] |
[
false
] |
It can't be as simple as "it needs a neutral charge". It's just too uncanny that literally every element has an equal number of protons and electrons.
|
[
"If there are more protons than electrons, it is a positively charged ions and electrons are attracted to it until it gets neutralized. If there are more electrons, it is a negatively charged ion and the extra electrons are repelled by the nucleus until it is neutralized. If there are the same number, neither happens."
] |
[
"It is energetically favorable to be neutral. Atoms behave as in \"trying\" to have the lowest potential energy as possible.",
"That being said, the number of electrons in an atom can be temporarily different from the number of protons, because ocasionally that means having a lower total potential energy in a system. Of course, that would result in another atom (or collection of atoms) having to gain or lose the same number of electrons."
] |
[
"Another way to answer your question:",
"In a closed system, we know electrical charge is conserved. We also know things that aren't repelling or attracting each other must be electrically neutral. We know stuff doesn't spontaneously fly apart.",
"We've isolated charged particles in experiments, and charge is conserved, so there are always charged particles. Therefore stuff having NO charged particles in it is not an option to explain its overall neutrality and not-flying-apart-ness.",
"So the charged particles that make up things must be near each other in a neutral configuration -- we call these atoms, or molecules."
] |
[
"What are sunspots?"
] |
[
false
] |
[deleted]
|
[
"they are at temperatures of roughly 3000–4500 K (2727–4227 °C), the contrast with the surrounding material at about 5,780 K (5,510 °C) ",
"2727 °C vs 5,510 °C, a 'few thousand degrees' seems reasonable. Unless you're just disputing the \"only\" part. "
] |
[
"Darker, cooler areas of the sun. Only a few thousand degrees cooler though.",
"They are caused by the sun's magnetic field and the sun spots themselves often have a polarity."
] |
[
"Darker, cooler areas of the sun. Only a few thousand degrees cooler though.",
"That doesn't seem right. The surface of the sun has about 5000-6000 K, so a few thousand degrees less would be quite a bit."
] |
[
"Do men's voices get progressively lower forever?"
] |
[
false
] | null |
[
"Yeah, I see your point. Maybe it depends on what types of strains you put on your voice throughout your life. "
] |
[
"Not for ever, no. Eventually they die.",
"Seriously though, elderly men tend to have higher-pitched voices than young or middle-aged men (compare Grandpa Simpson), so that would suggest the answer to your question is \"no\"."
] |
[
"Yes, he is fictional, but he represents the stereotypical elderly man whose voice has become higher-pitched.",
"EDIT: fixed pronoun"
] |
[
"How do the sleeping patterns of modern westerners compare to people throughout history and people living in more primitive societies?"
] |
[
false
] |
I often wonder how natural our sleeping pattern is. We have artificial lights and amusements like TV to extend the day well past sunset. Our wake up times are dictated by the clock because we have to go to work or school and these places are run on a tight schedule. I can't help but think that sleeping patterns would be quite different without technology and in a less organized society. Perhaps there would be more seasonal variation and we would sleep more during winter. I haven't been able to find much information on this subject at all.
|
[
"Until someone qualified to answer comes by, I found the wiki section on the ",
"Anthropology of Sleep",
" quite interesting."
] |
[
"Thank you for that link. I've always suspected my natural clock is longer than 24 hours, so it's interesting to see that was one of his findings."
] |
[
"Thank you for that link. I've always suspected my natural clock is longer than 24 hours, so it's interesting to see that was one of his findings."
] |
[
"How do you simulate audio acoustics in software?"
] |
[
false
] |
Not sure if I phrased the question properly or not. I'm working with my nephew on some high school physics stuff for fun and he asked me, knowing that I've got a degree in Computer Science, how computers can simulate the generation of sounds like the human voice. Now I'm curious as to how one would model this mathematically to create the sounds. Even something as simple as an air current moving across the top of a bottle would explain a lot.
|
[
"Because the actual physical systems behind the human voice are so complex, the most common (and most frequently successful) approach for synthesizing the human voice is to analyze the properties of the sound, and model the simplest system that would have those properties. So instead of having a software model of the voice box, mouth, throat, tongue, head, etc. we analyze the sound of the human voice, and note that it has specific properties we can describe and model (eg. a fundamental pitch, a distinctive harmonic series, formants), and then model a simple system sharing these properties. A useful keyword to look up would be \"formant synthesis\".",
"That is, when the sound of a human voice is even being truly synthesized.",
"In practice it's most common to use small fragments of recordings of human speech (individual fricitives and vowel sounds etc.) and arrange, combine, and repeat these recordings of mouth sounds to construct speech, in a way that is relatively agnostic to any of the interesting physical or sonic features of the original. This might be synthesis of words, but the sounds themselves are just human mouth sounds that are cut and pasted and rearranged, not really synthesized. You could say it's less like CGI and more like photoshop.",
"Regarding the \"blowing over a bottle\" example, you can make a somewhat similar comparison with flutes. There's a CPU intensive physical model which isn't used much - it's expensive to calculate all the turbulance equations, and the results just aren't very convincing given the amount of effort, there's usable models based on the primary properties of the resulting sound and reverse engineering a DSP system that will model those properties, and by far the most commonly used is based on a recording of a human playing a flute, with some simple logic for altering the pitch or changing the duration of the note."
] |
[
"In the audio engineering world, there are reverb plugins (software programs) that simulate different reverberation surfaces and materials. This is generally done one of two ways: with an algorithm or with an impulse response. Algorithms are less cpu-intensive, are more malleable (size, density), but impulse responses are generally held to be superior in sound quality. An impulse response is created by putting a microphone in a room with a tone generator that sweeps the range of human hearing and modeling how the tone as it returns back to the source has been changed. Algo's are a little more mystifying to me, but I think it's just people tweaking lines of code, based on known acoustic principles of certain materials, until it sounds right. An IR is the sound of that one particular room, whereas algos are more \"imaginary.\"",
"This isn't exactly \"human speech\" but in audio, you're likely dealing with one or the other.",
"EDIT: He might be interested in a relatively cheap app called Audulus that works like Max MSP but is much simpler. You can still do amazing things with it, though: ",
"http://www.matrixsynth.com/2015/01/cogito-cartesian-sequencer-for-audulus.html",
"EDIT 2: Here's a fully-functioning vocoder that was built from the ground-up in Audulus (kinda similar to your voice synthesis thing) ",
"https://youtu.be/mchKwAYAUzE"
] |
[
"To add to ",
"/u/seventeenletters",
"' excellent answer:",
"Although it is exceptionally difficult to recreate believable real-world instruments using physical modelling (we usually use samples, due to the complexity outlined), approximately modelling the individual components commonly used within instruments is more manageable: such as a string being plucked, say, or a bell being struck. ",
"What this allows is for the creative modelling of instruments not physically possible (a solid wooden instrument the size of a house, being struck with a drumstick, say, that then morphs into a hollow metallic instrument over the course of 10 seconds.)",
"If he has access to a Mac, an exploration of a synth like Apple's ",
" in Logic, might be an enjoyable, hands-on, exercise for your nephew. It contains many of the core concepts used within physical modelling of acoustic instruments. It's a complex instrument, but a bright high school student would eat it up."
] |
[
"How do underwater cables deal with tectonic rifting? Is it even an issue?"
] |
[
false
] | null |
[
"It is key to remember that plate motion rates are ",
"slow",
", typically a few mm per year up to a few cm per year, so steady plate motion does not pose a particularly large hazard (and is easily accounted for with a small amount of flexibility in the cable, etc). Submarine telecommunication cables do get cut from tectonic associated hazards, usually underwater landslides or turbidity currents associated with earthquakes, but breaks in cables ",
"can occur for a variety of reasons",
", with the largest source of breaks being human caused (fishing trawlers, anchors, etc)."
] |
[
"One thing I have wondered about lifting a long cable miles from the seafloor is how the cable does not snap under its own weight when it is lifted from the sea bed. Is it designed to be almost neutrally buoyant in the water? Otherwise I would think the tension on a cable that is miles long would snap it or at least greatly strain it and possibly damage the core inside the armor."
] |
[
"One thing I have wondered about lifting a long cable miles from the seafloor is how the cable does not snap under its own weight when it is lifted from the sea bed. Is it designed to be almost neutrally buoyant in the water? Otherwise I would think the tension on a cable that is miles long would snap it or at least greatly strain it and possibly damage the core inside the armor."
] |
[
"What are some examples of self-organization in your field of study?"
] |
[
false
] |
I am curious about how self-organization manifests in math, physics, chemistry, biology, computer science, sociology, etc. What, and how, do group patterns or traits emerge that are not exhibited by individual group members? If you could give a specific example of something within your field of expertise, I would greatly like to know =)
|
[
"For clarification: are you asking about emergent self-organization in the science itself, or in the body of scientists?"
] |
[
"I am asking about emergent self-organization in the science itself. "
] |
[
"I feel that this may only be tangentially related, but some researchers interested in rhythm, timing, and beat induction take a dynamical systems approach to describing rhythmic movement, with interest in nonlinear oscillators. I will quote Beek et al. in ",
"Rhythm Perception and Production, Desain & Windsor eds.",
": ",
"The nonlinear oscillator approach views rhythmic movement and the physiological process that accompany it as manifestations of dynamic pattern formation or self-organization (",
"Beek, Peper, & Stegeman, 1996;",
" ",
"Haken, 1996",
")."
] |
[
"When I blow out a match or a candle how exactly is the flame extinguished?"
] |
[
false
] | null |
[
"This question has been asked numerous times in the past. Use the search! The last time I saw this question asked I responded:",
"You are removing the fuel. A candle flame consists of a pocket of vaporized fuel (wax) whose surface burns, fed by oxygen. When you blow out a candle you are blowing away that pocket of vaporized fuel before it has a chance to be replenished. You have blown out the candle. The candle remains hot enough for a while to continue issuing fuel vapor, but you have blown away the burning surface that previously provided enough heat to ignite the vapor.",
"A match is similar -- it's not just that you are reducing the temperature (as others have asserted) but that you are removing the vaporized fuel. The match will continue to be hot and will emit some ignitable vapor for a short time after it has been blown out, but since the flame is gone the source of high-temperature ignition is gone, and it can no longer self-ignite. "
] |
[
"And if you had a candle with a wick which burns at a much lower temperature you would have a trick candle."
] |
[
"And if you had a candle with a wick which burns at a much lower temperature you would have a trick candle."
] |
[
"When does cancer become terminal?"
] |
[
false
] |
People with cancer survive with an operation or some sort of medical treatment but when the doctor says it's terminal, when exactly does that happen and what does it mean? Is it possible to survive after the cancer has been termed as terminal?
|
[
"Quote: ",
" ",
"Cancers typically become terminal when the growth of malignant cells impedes major organ function or have reached a level of metastasis (widespread growth throughout the body) where surgical removal is no longer an option and chemotherapy or radiation are either unsuccessful or would only further weaken the patient's body, and the only option left is to make the patient comfortable as they die (how long this takes is entirely based on the particular type of cancer and case specifics).",
"There have been many cases where a prognosis of \"terminal\" has been reversed due to aggressive treatment via new techniques or simply by virtue of the tumor growth stopping or reversing on its own, but ",
". Often the media makes major news out of people surviving Stage 4 cancer, but these should not be considered statistically relevant cases, rather as remarkable ones due to various special circumstances."
] |
[
"Adding to the other answers. ",
" means fatal. When a doctor calls cancer terminal, they've judged it to be advanced enough that you could never survive. There are sporadic cases of people surviving \"terminal\" cancer, which means they were somehow lucky, and that the doctor was wrong."
] |
[
"Generally it is when it reaches what is known as stage 4 also known as metastasis or metastasized, they then become lethal as they spread to the liver, lungs or bones, basically to other places than when they originally formed and then disrupt the operation of key organs in the body - ",
"https://youtu.be/Q5--K1nUOM4"
] |
[
"What is the relationship between the surface tension of water and how large raindrops are?"
] |
[
false
] |
[deleted]
|
[
"It's a power relation, not an exponential.",
"f(x) = x",
" : Power relation",
"f(x) = 2",
" : Exponential relation"
] |
[
"Maximum drop diameter before droplet breakup goes as the square root of surface tension. So for a droplet to have twice the diameter, the surface tension would need to be four times as large, and so on."
] |
[
"Just to clarify, that's an exponential relationship because 2",
" = 4. So for triple the diameter, you're looking at nine times the surface tension."
] |
[
"Newton's Law: If a spaceship is moving in a vacuum, uses the chemical energy of half the fuel to accellerate (Kinetic energy), then the other half to brake aka accellerate in the opposite direction, where is this energy now?"
] |
[
false
] | null |
[
"In the motion of the particles that were shot out the back and front of the ship."
] |
[
"Less fuel is required to stop the motion than to start it, as the craft is now lighter (by the amount of fuel it burned to accelerate to that speed in the first place).",
"In fact it turns out that the fuel burned when the craft is at higher speeds imparts more energy to the vessel than that burned at lower speeds (for both acceleration and deceleration). This is known as the ",
"Oberth effect",
", and it's because you've already imparted kinetic energy to the fuel by accelerating it before it was burned, so it becomes more effective. "
] |
[
"Disregarding relativity, you can imagine this scenario instead as being a yourself, hopelessly stuck in the center of a frozen frictionless pond.",
"You can toss a shoe one way to get moving, and toss your other shoe to slow down again.",
"The math is the same...except that rocket fuel isn't tossed all at once, so you'll have to integrate its cumulative effect."
] |
[
"How fit did nature intend humans to be?"
] |
[
false
] |
Today, humans can live despite being morbidly obese and unable to sprint half a kilometer. But if we were to look at homo sapiens 50,000 years ago, how fit and physically capable would their genetics have optimized them to be? Would they be on par with athletes? Or would they simply be by today's standards "above average". Would they be able to sprint long distances, would they tire easily? What would their body fat% typically be, and what would their musculature be like?(a picture would be great for this) EDIT: There seems to be a lot of confusion over what I'm asking. Take a seal, it needs a lot of fat. Its genetic make-up is conditioned for an organism with a high body fat percentage. The seal would obviously not be able to properly fulfill its niche if it had 5% body fat. What about a human? What is its ideal composition(body fat, musculature, stamina) for fulfilling its niche based on its genetics?
|
[
"Nature didn't intend anything."
] |
[
"Just like the best way for a seal to be a seal is to have a lot of fat",
"Is that the best way? It's a possible way for the seal to avoid extinction. But I think I understand your question - you're essentially asking \"if somewhere deep in the rain forest a group of people had survived without technology for tens of thousands of years, how would they compare to today's athletes?\", yes?",
"To answer that, you'd have to look at the niche in which human beings existed. As omnivores, they'd be able to find sustenance by foraging as well as hunting. Are there animals like buffalo available? What about predators? Are you allowing for primitive tools such as simple spears and axes here?",
"I'm not really sure how you'd define optimal, but certainly being able to run would have been beneficial. We're not the fastest species out there, so we're not going to outrun many other species, nor are we particularly strong, or endowed with sharp claws or anything like that. Early man would have had to make up for that by being mobile, able to both sprint over short distances and run over long distances. However,they'd be generalists, whereas modern athletes are specialists. Michael Phelps is a gifted swimmer for example, but he's not the world's greatest weight lifter. I suppose the closest sport you could find would be something that involves a lot of running, perhaps a triathlon or something similar? ",
"Regarding body fat percentage, food would have been more sparse back then. The reason why we gain weight so easily is that our body tries to store energy, because evolutionary speaking the idea of having a guaranteed, nutritious meal coming up 3 times a day is extremely new. Back then it was more along the lines of gobble up what you can because who knows when you'll eat again. So your body fat percentage would be directly related to how lucky and successful you were as a hunter / forager. ",
"You brought up seals, they obviously need a lot of fat because they live in a very cold environment. The location / climate zone of your hypothetical tribe would probably factor into the body fat answer as well."
] |
[
"Title of the thread is very misleading. Rephrasing the question, it might sound like \"How athletic were early humans compared to modern athletes?\""
] |
[
"Why are there random colorful dots/noise in videos shot in the space station?"
] |
[
false
] |
Example:
|
[
"It is cosmic ray damage as others have said, but what surprises me is that they don't have cameras which mask defective pixels. On a pro video camera, every time an auto black balance is done, the masking circuit adds bad pixels to its list and covers them with adjacent pixel information. ",
"I work on pro cameras which travel by air a lot (WH Pool), and they get more defective pixels than cameras which don't fly. "
] |
[
"A reasonable assumption would be that they want the raw material, in case it's needed later. Masking bad pixels can be done in post processing.",
"Say, for example, that someone comes up with some cool way to use those dead pixels to give some kind of reading of cosmic radiation (just an unlikely example from the top of my head). In that case, it would be nice to have that information available in the existing data, instead of having it destroyed in the camera for convenience reasons."
] |
[
"There's a lot of cosmic radiation up there. Mainly from the sun, but also from elsewhere. And there's no atmosphere to protect you from it."
] |
[
"If you generated a large random sample of numbers, and then converted those numbers to binary, would there be roughly equal amounts of ones and zeros?"
] |
[
false
] |
If not, why not? Also, would it make a difference whether the numbers you randomly generated were small or large numbers? That is, if you set limits on the generated numbers, would a sample including 1-999,999 be substantially different than 1-99 after both sets were converted to binary? EDIT: when I was forming the question, I wasn't thinking of making the binary strings any set length. However, I see now that a binary number without leading digits will start with a 1 and never a 0. Thank you for the answers, everyone!
|
[
"You'd have more 1s than 0s. The higher your range, the closer the ratio will be to 50:50.",
"Think about it this way... Let's take a set of 3 digits and consider every possible combination of 1s and 0s:",
"000,\n001,\n010,\n011,\n100,\n101,\n110,\n111.",
"Basically what we have here is an equal number of 1s and 0s, because ever place holder can be a 1 or a 0. For any given combination, we can swap 1s and 0s to get a \"complement.\" It shouldn't be hard to see that this would be true no matter how many digits we extend the problem to.",
"But notice that the first half of the sets on that list aren't how we would write a number. We don't write leading zeros. It's not \"001,\" it's just \"1\". It's not \"010,\" it's just \"10\". So if the we have an equal number of 1s and 0s, but then toss out a bunch of leading zeros, it should be obvious that there will be more 1s.",
"Now let's stick a 1 in front of each set above:",
"1000,\n1001,\n1010,\n1011,\n1100,\n1101,\n1110,\n1111.",
"These ARE numbers. Before we stuck a one on the front we had equal numbers of 1s and 0s. We don't have to toss out a bunch of zeros now, but we've also added a bunch of 1s.",
"Let's say N is the number of digits we choose- so in this case you have N=4. The total number of sets (assuming the first place is a 1) is 2",
". Here we have 8. There are equal amounts of 1s and 0s in the three rightmost places. So the number of 0s is (N-1) x 2",
" / 2= (N-1) x 2",
"= 3x4 = 12. We have the same amount of 1s in those places, plus the leading 1s. So the number of 1s is (N-1) x 2",
" / 2 + 2",
" = (N+1) x 2",
" = 5x4 = 20. Total number of digits is N x 2",
"= 4x8 = 32. ",
"The percentage of 0s would be [(N-1) x 2",
"] / [N x 2",
"] = (N-1) / (2N).",
"That's for a given number of digits. If you're randomly choosing numbers within some range then you'd have to sum up the numerator and denominator for N=1 through N=whatever you're capping it at. And if you're choosing decimal numbers then these formulas don't work because you might not be grabbing from the full set of combinations for a given N. (e.g. if your range is 13 then the last two combinations above get left out) But for large numbers (i.e. large N) I think these are mostly negligible, thanks to N being in the exponent.",
"If we take the limit (of the percentage of 0s) as N goes to infinity then you get infinity/infinity. If you apply L'Hopital's rule you're left with 1/2 as the limit. ",
"So... there will be more 1s than 0s. The discrepancy will be larger for small numbers. For very large numbers the ratio ",
" 1:1.",
"For a range of 1-128 (N=1 through N=8) ",
"I get the percentage of 0s as 43%",
".",
"For a range of 1-1048576 (N=1 through N=21) ",
"I get the percentage of 0s as 47.5%",
"."
] |
[
"Benford's law is for logarithmically distributed numbers. If this is a uniform distribution from 1-999,999, it won't apply."
] |
[
"It entirely depends on how you want to represent the numbers and the set of numbers from which you choose.",
"Let's take your case of 1-99. Every number in this range can be represented in 7 bits (2",
" > 99). But taking a random sample of those numbers will not result in an equal distribution as 100-127 are not represented in the sample and so there'd be a bias towards 0 or 1.",
"But we never really represent anything in 7-bits. Modern computers use 4 main representations:",
"1/ 32-bit integers [1]",
"2/ 64-bit integers (\"long\")",
"3/ 32-bit floats [2]",
"4/ 64-bit floats (\"double\")",
"Almost all floating point numbers will introduce some inaccuracies and will have a bias towards zero unless you include negatives. So if you want uniformly distributed zeros and ones, you'll want to go with integers.",
"For unsigned integers (e.g. not supporting negatives) generating random numbers between 0 and 2",
" -1 or 2",
" -1 for ints or longs respectively will result in roughly a 50/50 distribution of zeros and ones in your data set.",
"Anyway, if you need random zeroes and ones, just run a python script like this and adjust NUM_BITS as necessary.",
"import random\nNUM_BITS = 32\nprint \"{0:b}\".format(random.getrandbits(NUM_BITS))\n",
"[1] ",
"https://en.wikipedia.org/wiki/Integer_(computer_science)",
"[2] ",
"https://en.wikipedia.org/wiki/Floating_point"
] |
[
"Why haven’t we cloned any extinct animals such as the dodo?"
] |
[
false
] | null |
[
"Its very very difficult to do, but there are people working on it. However there are also some debate if its ethical to even do it. In my opinon, which doesn't matter, Id say it be amazing to bring back animals such as the thylascine who recently went extinct and we are positive its from humans, and dodos are probably fine as well, its just a matter of what to do with them. They cant really be returned to Mauritius as there are predators there now, so we could either farm them like chickens, or keep them as pets (or both I guess). But when it gets all the way back to mammoths is when it gets really controversial, mammoths went extinct along with massive apex predators such as American lions so we would need to return those predators as well if we planned to put them in north America which isn't a great idea as now its heavily populated by humans. (Also there is a chance that mammoths went extinct from something other than humans). However siberia is a location they could be put back in. Its been found that mammoths helped keep permafrost frozen which is certainly a good thing but theyd still probably need their ancient predators returned as I doubt a tiger would even try to eat a mammoth. Which makes bringing them back even harder."
] |
[
"The short answer is yes it's possible (but extremely expensive, way past the point of not worth it) to create an intact copy of the Neanderthal genome, but you wouldn't be able to manufacture a faithful clone of an actual Neanderthal due to maternal effects and epigenetics"
] |
[
"Because the samples of DNA we have are insufficiently good mostly.",
"Follow up question for any actual experts: If we spent the time and money to print off, say, a neanderthal genome from scratch, could the resulting DNA be used to make a clone?"
] |
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