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[
"If virtual particles are symmetric, how do black holes evaporate?"
] |
[
false
] | null |
[
"Virtual particles don't literally exist, and this description of Hawking radiation is meant to be a very cartoonish explanation for laypeople, it's not \"what's actually happening\"."
] |
[
"It matters because the idea of a particle and antiparticle spontaneously popping into existence and one of them falling into the black hole is not correct at all. That bears to resemblance to how Hawking radiation actually works. It's a cartoon picture for laypeople."
] |
[
"It matters because the idea of a particle and antiparticle spontaneously popping into existence and one of them falling into the black hole is not correct at all. That bears to resemblance to how Hawking radiation actually works. It's a cartoon picture for laypeople."
] |
[
"What are these ground formations in Sudan? Some of them look like purposeful markings."
] |
[
false
] | null |
[
"To me they look like round huts within walled enclosures. You can make out paths around them and a few of them seem to have pens attached. So, I think it's some tribal settlement."
] |
[
"Hmm an interesting point. But if they are human settlements, then they must be very old considering the desolate surrounding area. There is absolutely no water or vegetation for miles around so no one could survive there. "
] |
[
"They seem too well-defined to me to be old. There looks to be 'plenty' of trees and bushes around and they seem to be surrounded by small streams. And if those are pens then they must have livestock, maybe goats - they can eat pretty much anything.",
"I can't think of anything else it could be."
] |
[
"How can one measure the age of humans?"
] |
[
false
] |
I came across this about refugees in Sweden saying that adults are getting away with crimes by pretending to be under 15. I've wondered if there's any way to measure/verify the age of these people, since they throw away their IDs.
|
[
"It's easy you just saw them in half like a tree!",
"But seriously there's no way to exactly verify age since everyone ages differently. But there are ways to estimate like checking the wear on their teeth since more wear would mean they are older since teeth don't grow back. In addition xrays could be used to look at the wisdom teeth and see how matured they are which will give a good idea.",
"Another method using xrays would be to look at places where bones take longer to fuse. Areas like the wrists or ankles is a good place to look since there's lots of small bones there. If they really are 15 they would also most likely show evidence of growth plates in their long bones. Someone fully matured would not have growth plate activity and would most likely be fully calcified in an adult."
] |
[
"Very true combining several methods would be the most effective way to determine age but there's nothing foolproof"
] |
[
"Just as a little note, the plates in the bones aren't always a good indicator. I grew very fast so when I was 12, I had the bones of a 16 year old in terms of fusion."
] |
[
"If I move both my index fingers at once, am I sending one signal to both hands, or am I sending 2 individual signals? Is there a signal queue?"
] |
[
false
] | null |
[
"Lots of signals!",
"How are you moving your index finger? Just a quick movement and then stop? Sustained goal-tracking? Sustained proximal extension?",
"There is a swirl of signals operating between prefrontal cortex (probably both sides), supplementary motor cortex (probably both sides) and primary motor cortex (primarily contralateral to the moved finger); as well as between cortex, brainstem, cerebellum, thalamus, and back to cortex; and between cortex, basal ganglia, thalamus, and cortex. These are all for smoothing movements, planning movements, etc.",
"The final pathway is a series of pulses down the corticospinal tracts to alpha motoneurons in your spine, which send pulses directly to muscle fibers in your forearm and hand. Depending on how much effort you need, there may be more or fewer groups of muscle fibers contracting, and at different rates. The rates are governed by the spiking rate in the alpha motoneurons and the groups are governed by the activation pattern in the cortex and the spine.",
"With sustained effort, there will be a feedback loop set up with additional spike trains sent by intrafusal muscle cells and bag fibers both to the motoneurons and up the dorsal columns to the thalamus and the cortex to help regulate the muscle firing rate. If you're looking at your finger, that information can also be used as feedback. So now there's visual processing and flows from association visual cortex to prefrontal cortex.",
"There's no queue. Neurons send spikes, or ",
", at varying rates. They code for responses by the rate of spiking or sometimes by the timing of spikes. Spikes propagate from neuron to neuron by the release of neurotransmitters across small fluid gaps (the synapses). Of course spike trains can also lead to inhibition, setting a gate to interrupt spike propagation from other cells (analogous to a transistor); or they can cause changes in gene expression altering the properties of the target neuron (analogous to resetting circuit props in an FPGA).",
"So if you're extending both index fingers, you have bilateral corticospinal tract signalling, bilateral dorsal column signalling, and bilateral intraspinal, cerebellar, basal ganglionic, thalamic, visual, and prefrontal signalling."
] |
[
"I was a subject in a transcranial magnetic stimulation study that involved exactly that; moving index fingers. ",
"To calibrate the machine, they have to find your 'motor threshold'. They aim the TMS machine at your motor cortex, and stimulate the area of your brain responsible for moving your index finger (which feels pretty strange). The minimum strength of stimulation that causes your finger to move is your motor threshold. ",
"It's very distinctively one finger or the other, meaning that at least at the motor cortex level, moving both index fingers would be two separate signals. ",
"This doesn't necessarily mean that it isn't one signal somewhere else that's later split. It might originate as one signal higher up in your brain's control process, but I don't know enough to comment on that. "
] |
[
"I have a follow up question. ",
"I learned to spin a pen around my thumb with my right hand. It took weeks of practice to get it well because it requires quite a lot of fine motor \nskill.",
"\nThen I tried to do it with my left hand and I could do it on the first try. \nHow exactly does that happen? Is there a \"program\" designed to read other programs designed for my right half and relay/translate the output to my left half? Or if I train something for my right half is there some mirrored program being trained for my left half simultaneously?"
] |
[
"How much safer is bicycling with a helmet?"
] |
[
false
] |
From what I can tell from a few videos I've watched and the , cycle helmets do reduce head injuries, but their effects may be overstated. They mention a lot of different studies with different results, and some seem to propose that the positive effect of helmet use is negated by by drivers, and , (removed this as as MaliciousH has rightly pointed out this is a seperate issue). What I want to know in practical terms is, how much safer am I biking to get places with a helmet on. Edit: I would also be interested to know if a helmet has a similar protective effect if one is driving or walking.
|
[
"Thanks for your response, and glad to hear your friend was okay. Alas, an anecdote doesn't really answer my question."
] |
[
"I am going to throw out the increase risk taking and reduced cycling factors. Taking out increase risk taking since that is not a normal ride and really shouldn't happen. As for reduced cycling causing obesity, I am taking that out since its not a safety factor. So with that, I am going with just a normal, everyday urban bike ride.",
"A helmet is for most intent and purposes is just there to protect you from minor accidents and mistakes that can result in head injury from certain angles. An impact to the face will take you out with or without a helmet. A car going around and above 15 mph and colliding with you with mess up your day. Hell, even one going less than that could. ",
"So I hope I implied that a helmet is not going protect you everywhere on your body and in all all situations. With all that said, it is silly to impose a helmet law. A helmet should not be required but it is highly recommended for the sole reason of offering protection in the case of something bonking your head."
] |
[
"Thank you for your response, I've updated my question with your response in mind (I'm referring to risk compensation on the driver's part, and I've got rid of the obesity stuff). Do you have any sources on exactly how much safer they are?"
] |
[
"What are my chances of going through life without a life-altering condition (such as cancer, Parkinson's, diabetes, arthritis, etc) before the age of 70? [X-post r/answers]"
] |
[
false
] | null |
[
"I think it's pretty clear that OP is asking for disease statistics and is not asking for medical advice."
] |
[
"I study epidemiology and I don't think I've ever heard this question asked this way. The diseases you mention are so different from each other that it's not really an informative question. What are your inclusion criteria? Some types of cancer are easily treated. If someone has a mole removed that turned out to be cancer, with no additional treatment necessary, does that count? ",
"The odds of developing any disease depends on so many factors, including age, sex, weight, smoking, family history, and genetics.",
"FYI, the epidemiological term that you're asking about is survival analysis. Survival can refer to odds of not dying, and it can also refer to odds of not developing a given illness. A common method for survival analyses is Kaplan-Meier estimation. ",
"Here",
" is an example of a Kaplan-Meier plot. Both groups start at time 0 and p(survival)=1. As time progresses, p(survival) will gradually decrease. "
] |
[
"I meant any sort of condition that will negatively alter the way I go about my life."
] |
[
"What will happen to New Horizons after the Pluto fly-by?"
] |
[
false
] |
Do scientists know where it will be drifting? How much power does it have left? Will it continue to send us data? And if so, for how much longer? Is the NH team planning at all to examine other Kuiper Belt objects with it? And if so, how are they going to get to them? Does New Horizons have still-working engines that can propel it, or is it entirely relying on the gravitational pull of planets/other objects to slingshot its way around at this point?
|
[
"Do scientists know where it will be drifting?",
"Yes.",
"How much power does it have left?",
"According to the Wikipedia page, 228 W. This matches closely with the expected 5% power drop every 4 years.",
"Will it continue to send us data? And if so, for how much longer?",
"Yes. It's power supply should be good for about 10 - 11 more years.",
"Is the NH team planning at all to examine other Kuiper Belt objects with it?",
"Yes, this was one of the primary objectives.",
"And if so, how are they going to get to them?",
"Doing nothing would result in passing through the Kupier belt, so the key is adjusting trajectory to fly by objects of interest.",
"Does New Horizons have still-working engines that can propel it, or is it entirely relying on the gravitational pull of planets/other objects to slingshot its way around at this point?",
"It has 16 primary thrusters and 8 backup thrusters, using hydrazine propellant."
] |
[
"In the recent AMA they did, the mentioned they are going to see if they can steer it towards another Kuiper Belt Object. After that it will just drift off into space."
] |
[
"It is going faster than the solar escape velocity. New Horizons will not return to the sun. Incidentally the third stage booster for the launch is also going to leave the solar system."
] |
[
"Scientifically, how does tempered glass work?"
] |
[
false
] |
[deleted]
|
[
"Prince Rupert's Drops",
" are an interesting example of tempered glass. When molten glass is dropped into water it makes a blob with a long tail. The blob can survive being hit with a hammer, but if the thin tail is damaged the entire drop shatters. "
] |
[
"Tempered glass is strong because it is under considerable internal tension. Caused by the rapid heating then cooling under room temperature during the manufacturing process. However the smallest scratch or inclusion inside or the glass can lead to a stress concentration where if enough heat or stress is applied it releases all of the tension energy and shatter. ",
"It would be similar if you had a piece of rubber stretched very tightly over an object, if you were to put something like a small scratch or a pinhole in it it would eventually begin to tear just because of the shear tension. ",
"Edit: I forgot to mention the edges of the glass tend to be the most prone to cause the glass to shatter since the outside edges cool far more quickly than the center does."
] |
[
"Glass is a brittle, amorphous ceramic. One of the consequences of this is that it is quite strong in tension, but extremely weak in tension, due to the inevitable presence of tiny cracks and other flaws in the material that dramatically weaken it in tension (compression mostly forces the crack shut, so they don't have nearly as much effect there). ",
"To make tempered glass, you take molten glass and cool it down fairly rapidly from the outside in. The effect of that is that the outside will solidify while the interior is still molten, and then the interior solidifies afterwards. Now, most materials (including glass) expand when heated and contract when cooled (see ",
"thermal expansion",
"). As the exterior of the glass object solidifies, the still-molten interior can deform fairly easily to accommodate this shrinking. However, when the interior solidifies, it shrinks as well - but it's still bonded to the exterior, which cannot deform easily. The net effect is that stress is produced in the material, such that the outer layer is in compression (squeezing it smaller) and the interior is in tension (stretching it larger) such that the object stays attached to itself. Note that you have to be careful with this ... if the stresses are ",
" large, the whole object may simply shatter immediately from the internal stress. ",
"Now, remember how I said that cracks dramatically weaken glass in tension? Well, those cracks generally start at the surface of the object. If the surface is already in compression from internal stress, then any tension you apply has to overcome that internal stress before actually putting the material into tension. This makes the glass much stronger in tension (but weaker in compression, since that adds to the already-present internal stress). Also, once a crack ",
" begin propagating through a tempered-glass material, the large internal stresses generally encourage further crack propagation and ensure that the entire piece of material disintegrates very rapidly, as the internal stresses represent a lot of stored elastic energy that can be released by breaking and changing to a non-stressed state. ",
"When you put cold water on a hot glass object, the surface cools down much more quickly than the interior does. Going back to thermal expansion again, this means that the exterior is going to try to contract more than the interior does - but again, they are both solid and attached to each other, so instead stresses are generated to counteract the difference in deformation. This time the stress generated will be tensile on the surface and compressive on the interior. If the stresses generated this way are large enough, it can cause the object to shatter (this is known as ",
"thermal shock",
"). This is what caused that first glass to shatter. ",
"The coffee pot that survived the thermal shock may simply have been mechanically stronger, or it may have been a different type of glass with a lower ",
"coefficient of thermal expansion",
" (e.g. Pyrex), which reduces the magnitude of stresses generated by thermal shock and thus allows the material to survive very rapid temperature changes. "
] |
[
"Can someone explain the difference between SEM and TEM?"
] |
[
false
] |
[deleted]
|
[
"In an nutshell... In an SEM the detector looks at low energy \"secondary\" electrons produced from the uppermost part of a surface when it is bombarded with an electron beam. The sample can be any thickness. A more complete discussion is given ",
"here",
". In TEM, the detector looking at electrons from the electron beam that have ",
" the sample. This requires that the sample be thin. ",
"Here",
" is a brief description of TEM.",
"Edit: added TEM link."
] |
[
"Are you saying secondary electrons are reflected? No.. They are generated by interaction with the sample."
] |
[
"That's not true, either. There is a limited depth penetration (",
"interaction volume",
") depending on the sample material and electron accelerating voltage. The sample emits different radiation from different parts of the sample (and some is absorbed more from the sample before escaping). You can actually use this to your advantage when your sample is uniform on the surface but composed of different materials."
] |
[
"Could a quantum computer do this?"
] |
[
false
] | null |
[
"Assuming the scenario was about some sort of search in this large space of 216-digit numbers, quantum algorithms (",
"Grover's algorithm",
") can speed it up by a quadratic factor (from O(N) complexity, to O(sqrt(N)))."
] |
[
"No, it means that the two functions that describe the runtime of the two algorithms differ by a factor of x",
". For example, algorithm A takes N time, alg B may take N",
", and thus:",
"and so on."
] |
[
"Thanks for answering! Does quadratic factor mean that it reduces calculation times by 4?",
"I'm really sorry if that's a stupid question, but like I said, I've got a very basic understanding of math."
] |
[
"Does carbonated water chill slower than still?"
] |
[
false
] |
If you have otherwise identical bottles of carbonated water and distilled and placed them in the fridge, which one would "chill" the quickest (to the temp of the fridge ~3°C)? How would added solvents (i.e. in sodas) affect this? Also, how does pressure of the bottle itself have an effect? i.e. Shaking a fizzy pop bottle up so that it is highly pressured inside, as opposed to leaving the bottle 'unlidded' in the fridge?
|
[
"The molar heat capacity of a solution is going to be different from the molar heat capacity of pure water - for solutions of dissolved solid, it is lower.",
"The dissolved solids disrupt water's ability to hydrogen bond, and the ions form solvent cages. These and other factors reduce the water's ability to hold heat, and so they would change temperature faster, and hold temperature for less time.",
"I cannot speak to the efficacy of this rule for dissolved gases, but I would assume it is much the same. "
] |
[
"True, but question is, how is the speed affected? It does not directly matter what the freezing point is (which should lower with solvents or pressure) or whether or not it freezes at all, but the speed of which the drink can be chilled to the temperature of the fridge (3-5°C)"
] |
[
"True, but question is, how is the speed affected? It does not directly matter what the freezing point is (which should lower with solvents or pressure) or whether or not it freezes at all, but the speed of which the drink can be chilled to the temperature of the fridge (3-5°C)"
] |
[
"Does the portal of entry for a pathogen affect the symptoms that develop?"
] |
[
false
] |
For example, if my eyes are exposed to a pathogen that causes respiratory symptoms would there be any effect to them?
|
[
"Yes, that is how people get pink eye. It really depend on the virus or bacteria, but most pathogens can plant themselves in a variety of tissues and the symptoms will depend on the specific virus. ",
"The eyes are actually connected to the nose via lacrimal ducts, that is why people sniffle when they cry. So even if the virus is not a kind that causes pink eye, it will drain to the nose and then throat and infect what it may be best suited to infect."
] |
[
"Yes, portal of entry definitely matters.",
"An extreme example would be anthrax: there are three \"common\" subtypes of anthrax (none of which really exist in the US). Cutaneous anthrax occurs when you get the bacteria into a skin abrasion; this leads to local painless necrosis called an eschar. However, with antibiotics this is rarely lethal. There are no other systemic symptoms provided this is the only exposure. However, the gastrointestinal (from eating contaminated meat) or inhalation (from breathing bacterial spores in) are almost always fatal once symptomatic, and this is why anthrax is considered a biological weapon. There's tons more examples of this too, but anthrax is a really well defined disease with distinct clinical presentations dependent on location of exposure."
] |
[
"Yes, the route of entry will lead the pathogen to a specific tissue - either locally to where it arrives, like abrasions etc or to specific tissues, like the lungs for something inhaled. This will lead to a localised inflammatory response: the cut on your finger may cause swelling as the inflammatory response increases blood vessel \"leakiness\" to allow immune cells to arrive at the site of injury and subsequent oedema; the pathogen in your lung may cause coughing as your body tries to clear some of the excess immune cell-containing mucous that's slightly blocking some airways that your lungs are creating to protect them from the pathogen. Both of these could be caused by the exact same pathogen, but pathogens are also generally enter by only a few routes due to their specific biology (eg, water-born may require you to drink/swim in them so will likely first meet the GIT or abrasions, air-born most-likely meet the lungs, but may find abrasions or, as you point out, vulnerable tissues like eyes etc).",
"It is no longer a localised response if the pathogen is able to exfiltrate outside of that tissue leading to wider inflammation and symptoms... and at the extreme end leads to sepsis."
] |
[
"If humans could see in the infrared and ultraviolet spectrums, would our brain have to invent new colors to distinguish them? What would these colors look like?"
] |
[
false
] |
Would these new colors just look really deep violet, and really deep red? Or would they be new colors all together?
|
[
"In very layman terms:",
"Human eyes can detect light at \"visible-light\" wavelengths because of the special photosensitive cells in the retina. Three different cones that distinguish color, and rods that detect light of any wavelength within the range. All these different types of cells send signals to the brain, which combines them for interpretation. When a group of cones receive a bundle of incoming light (let's say, an equal amount of red and green), they all send signals (in this case, red cones and green cones signal \"on\", and the blue cones \"off\"). The brain processes all of this and we perceive it as \"yellow\" (somewhere in-between \"red\" and \"green\").",
"To be able to see infra-red or ultra-violet, we might need another type of cone. If that's the case, it'd be relatively easy for the brain to distinguish infra-red from red - if IR cones signal \"on\" and red cones signal \"off\", we'd perceive \"infra-red\". Rainbows would indeed have an additional color band. However, if (what are currently considered to be) the red cones simply start responding to infra-red light, our perception of red would simply extend to that. The rainbow would just be broader, in a sense. Even so, we might be able to distinguish \"IR\" from \"red\" by checking how much the neighboring green cones are responding. That gives the brain a hint about the \"deepness\" of the color.",
"Here's a Wikipedia link",
" to the article on cones, where you'll see the response curves for the different colors."
] |
[
"Depends.",
"We have 3 color vision \"cones.\" Each is activated by a specific frequency of light. Red, green, and blue. (Red actually activates a little bit past blue as well, to see \"purple\")",
"There are 2 ways we could see, for instance, ultraviolet:",
"Add a new cone for ultraviolet. You could not compare this color with your existing vision.",
"Stretch the frequencies that the existing cones work at. What looks red/orange would just look red. What looks purple would just look blue, etc., with ultraviolet appearing purple."
] |
[
"Thanks! So basically if we added a new cone, we could potentially have a new color, but if we extended the range of our current cones, we'd have no new colors, but we'd have a broader spectrum that covered more frequencies?"
] |
[
"Has anything new been learned about biology from superresolution microscopy?"
] |
[
false
] |
I know it can produce some pretty pictures, but has anything new been learned about biology?
|
[
"When I used it, it was treated like electron microscopy lite. It's just short of being able to visualize proteins directly, but is far faster and cheaper than EM. You don't need any special sample prep or need to spend hours pretending like you're friends with the creepy EM tech.",
"I used it to determine the spacing of chains of extracellular matrix proteins. I don't think the paper is out yet, but it was a much easier way of figuring out how the whole complex assembled under different conditions.",
"This isn't anything that couldn't have been done with EM and gold-labeled antibodies, but it was 10x as fast."
] |
[
"Oy! Every EM tech I've hung out with has been great. XD Go to better EMs! "
] |
[
"Google is your friend",
"So I don't come across as being a smartass - that is a nature article about the benefits of superresolution microscopy to biology since 2008 - including new discoveries about protein clustering in lipid rafts."
] |
[
"Can you improve your vision?"
] |
[
false
] |
I was wondering if it's possible to improve your vision without surgery, just through practice, including distance and reading etc. your eyes are a muscle, so can't you work it out? I have 20/15 vision, could I get that to 20/10 or better? Can it be used to slow down the decline in eyesight from aging?
|
[
"What you are referring to is called \"The Bates Method\" and has no scientific evidence to support the claims made. The American Academy of Ophthalmology did a study in 2004 on how effective The Bates Method is and while some people reported that their vision had improved, when tested the patient's vision had not changed.",
"From the article: \"No evidence was found that visual training has any effect on the progression of myopia. No evidence was found that visual training improves visual function for patients with hyperopia or astigmatism. No evidence was found that visual training improves vision lost through disease processes such as age-related macular degeneration, glaucoma, or diabetic retinopathy.\"",
"Web-MD Article on 'Natural Vision Correction'",
"AAO Study"
] |
[
"Ive been told that wearing glasses improves your vision, is this true? "
] |
[
"Short answer, no. Your eyes are basically nerves (or outpouchings of the brain) that have muscles to help them move and to focus light. Here's how it works and there are several limiting steps. Light from an object goes toward your eye. The light is refracted at the cornea (tears then cornea), goes to your lens and is refracted more. Light continues through the vitreous and is then absorbed by various photoreceptors which trigger a nerve impulse that is then sent to the brain for further processing. What really affects visual acuity (when you say 20/15, etc.) is limited by how tightly packed your photoreceptors are and how well your brain processes the information it gets. This is pretty much a physiological limit, like being short. When most people don't see well, it is usually due to a refractive error, or light not hitting the retina (where the photoreceptors are) in focus. There are some conditions, like amblyopia or convergence insufficiency, where practice and therapy can improve vision but little can be done to improve actual acuity. With that said, you can practice visual exercises to improve FUNCTIONAL vision, e.g. form discrimination, vergence ranges, etc., but that is a little different. As far as declining eyesight when aging, barring pathology and the natural process of cataract formation there is no reason for a person not to see 20/20 throughout life. Other aspects of vision do change as your get older, for example people are most sensitive to acuity loss due to glare as they age. This was a general response. I'll try to answer more specific questions with more specific answers. ",
"http://en.wikipedia.org/wiki/Visual_system"
] |
[
"Can we view the oscillating electrical and magnetic components of visible light on an oscilloscope?"
] |
[
false
] |
If we have a single color laser with some wavelength and frequency, can we view the (presumably sine?) oscillations of the electric and magnetic field using some type of antenna connected to an oscilloscope?
|
[
"QuasiEvil posted",
" a method that might be used to view the oscillation on a scope. I'm not very experienced with the equipment he mentioned there, so I can't comment.",
"But I can tell you that there are various types of ",
"interferometers",
" that can be used to directly observe the wavelength of light."
] |
[
"Thanks! Aren't interferometry techniques entirely optical based on interference / diffraction patterns? "
] |
[
"Yes, I realize this isn't quite what you were asking about, but it is the main technique for directly observing the wavelength of electromagnetic waves."
] |
[
"[psychology] has their been cases of different brain behavior in people that were brought up bilingual?"
] |
[
false
] | null |
[
"I'm not entirely sure what you mean, but yes, there is plenty of work done on bilingual individuals and how they process language in their brain"
] |
[
"What types of differences are apparent when you compare an individual raised with the ability to process two languages compared to an individual that was raised just knowing one language. ",
"Like what parts of the brain light up. or how do they perform social and academically. "
] |
[
"I would recommend making a new post with a clearer question like \"what are the neural differences between monolingual and bilingual individuals?\""
] |
[
"How powerful does a laser have to be to ionize the air around it and turn it into plasma?"
] |
[
false
] |
Hello! New poster here at /r askscience. Lately, i've been wondering about the ionizing effects of powerful lasers. It would be great to have someone shed some light on the situation. (pun not intended) Is there a specific wavelength that causes ionization? Is there an approximate temperature for the plasma that is formed after ionization occurs? Also, is there any way to measure the conductivity of plasma?
|
[
"I do this with my laser. It happens, at least in my case with the following laser characteristics: 80 mJ pulse, 9 ns FWHM, 1064 nm light, 16 mm beam, f=150 mm focusing lens.",
"Also, this paper helps.\n",
"http://jap.aip.org/resource/1/japiau/v111/i7/p073302_s1?isAuthorized=no"
] |
[
"It must have an energy greater than the ionization energy of the constituents of air.",
"Let's pretend that air is only made of diatomic nitrogen. I'm getting from Google that the first ionization energy of N2 is about 16 eV. That's the minimum possible energy needed to break an electron off of an N2 molecule. This corresponds to a frequency of about 3.9x10",
" Hz (or a wavelength of 7.75x10",
" m). ",
"Light at this frequency will be somewhere in the deep blue/ultraviolet region of the electromagnetic spectrum."
] |
[
"Thank you for answering!\nI will definitely be looking more into the linked paper."
] |
[
"How does pouring your beer down the wall of your glass prevent it from foaming up?"
] |
[
false
] |
I guess the prerequisite question is, how or why does beer foam form in the first place? And another tangential question: why do some beers foam so much more easily than others?
|
[
"Simpleton beer drinker here. All that co2 is trying to escape in the form of those awesome little bubbles that make your tummy feel so good after you shotgun a keyster. ",
"It starts with the first ~4 ounces of the pint. Think about dropping an egg directly into the bottom of a trashcan from the top. Chances are, the egg will break. If you slant the trashcan and roll it down the side, there's a chance it might not break. Basically the agitation from not only falling further and gaining more momentum but also falling directly on to a perpendicular surface (as opposed to a slanted one that will deflect it in another direction instead of just abruptly stopping it. Okay.",
"So after that point you've got a little beer in the glass. Let's imagine that bit of beer is a swimming pool and the beer flowing from the tap is a diver. When someone jumps in the water and does a cannonball, you know all those bubbles that come up while they're still underwater? It's air that was pulled down under the water with them. This is in a sense what is happening and the agitation releases more co2, most of which will be a five inch head in your six ounce pint of brew.",
"A good pour avoids that in somewhat the same sense that a diver would reduce their drag and displacement by doing a dive as opposed to a cannonball, thus disturbing the water less. ",
"I don't like to talk to people, so I spend my first few drinks at the pub thinking about beer. The above might be complete bullshit, but I hope it helps :) I never realized how much thought I put into beer while drinking it."
] |
[
"Hmn see I was thinking it was due to a lack of nucleation sites. As a smooth pour down the wall of the glass provides for a smooth film there are few if any local instabilities for the bubbles to begin to form at. As opposed to pouring into the bottom which creates all sorts of interesting flow patterns on the surface of the beer with the fluid from the bottle continuously breaking the surface of the beer in the cup. "
] |
[
"The foam results when CO2 comes out of solution. It's supersaturated with respect to the atmosphere when it comes out of the tap/bottle. When a bubble forms and comes to the surface, the bubble might normally pop in water. In beer there are proteins which decrease the surface tension of the solution, just like soap does. This stabilizes the bubbles. When you have a lot of those bubbles, you get foam. Compare how tonic water (almost no surfactant) foams to soda (some sugars) and then beer (lots of protein).",
"Here's a great illustrated article (not paper) from Physics today which goes over this topic:\n",
"Making a frothy shampoo or beer, Douglas Durian and Srinivasa Rhagavan",
"Why some beers foam more than others is that they have more surfactant molecules. In addition to the chemical equilbrium and surface chemistry behind the process, there are some mass transfer dynamics involved. As mentioned in the other posts, if you provide a lot of nucleation sites you'll evolve CO2 faster. Same principle as ",
"mentos in coke",
". If you shake or agitate the beer (like when pouring) you'll increase the rate of mass transfer from the liquid to the bubbles and your bubbles will grow faster. The reasons for this are increased gas-liquid interfacial surface area and thinner mass transfer film layer. Some manufactures want a thick foamy head so they engineered a device (",
"the widget",
") to increase the amount of foam that comes out when a can is opened."
] |
[
"When they say we're 99.9% genetically identical, is that looking only at protein-coding regions of the genome?"
] |
[
false
] | null |
[
"I'm assuming you mean percent identity between humans. I'm not sure exactly what the percentage identity is across the entire chromosome, but I wouldn't be surprised if it were 99.9% even including non-coding regions. Chimps and humans are somewhere around 99.5% identical in protein coding regions. It's hard to assess it with clear metrics, though, because what's the percent identity for a gene that's present in one species but not the other, or has a 3 amino acid deletion in one species but not the other?",
"Humans are not very genetically diverse compared to most species. It has been hypothesized that we nearly went extinct about 50-70,000 years ago, possibly due to the Toba supervolcano eruption. The human population at that time was estimated to have dropped to only a few thousand individuals. So we pretty much all share common ancestors not much further back than that. "
] |
[
"but I wouldn't be surprised if it were 99.9% even including non-coding regions. ",
"humans exhibit a large amount of copy-number variation, if you include copy-number variation (and the attendant non-coding regions of DNA that are dragged along the copy variant gens), humans can be VERY different:\n",
"http://en.wikipedia.org/wiki/Copy_number_variant",
"It is estimated that approximately 0.4% of the genomes of unrelated people typically differ with respect to copy number.[15] ",
"So including CNV, the average person drops down to 99.5% similar to each other. (the commonly given 99.9% value doesn't include CNV, since that number came from the Human Genome Project or whatever, and the extent of CNV in humans is a more recent discovery)",
"Also, this article I read recently puts some doubt on the previously held notion that we're not very genetically diverse (i.e. that our effective population is only 10,000):\n",
"http://genomena.com/ne/",
"\"Promisingly, the new papers on human rare variant burden use such tuning to re-estimate our effective population size to be on the order of millions, rather than mere thousands. Tennessen et al., for example, estimate the modern effective population sizes of Africans and Europeans to both be roughly half a million each; and Keinan and Clark estimate that European Nₑ is now roughly 1.1 million. \""
] |
[
"Yes. Deleterious selection keeps the protein coding regions so similar between humans. The VAST majority that deviate much from the functional DNA sequence for protein coding regions fail to mature; the small portion that deviate and do not die before maturity either represent neutral polymorphisms (observable in that multiple functional alleles exist for many genes) or they confer an evolutionary advantage. We have not figured out much about the function of truly non-coding regions of the genome, but selection will not act on sequences that do not affect fitness. Relevant: ",
"Neutral Theory of Molecular Evolution"
] |
[
"What is Yang-Mills gauge theory and why does gauge symmetry necessitate the Highs boson?"
] |
[
false
] |
So my current understanding is that all of the fundamental forces converge at high energies, and for this to be mathematically sound all of the forces' respective bosons must have the same mass. This means that they must all have 0 mass, and the effect of mass that we experience is a result of the bosons interacting with the Higgs field. Please feel free to explain it better than I have, and I would also like to know why the bosons all have to have the same mass, I've heard that this is to do with Yang-Mills gauge theory but I cannot find anything that explains it beyond that. Also, why must this mass be 0 (I'm guessing its to do with the photon and not wanting to break relativity by giving it a non 0 mass) and why the higgs field interacts with different particles fifderently. An overview of gauge theory would be helpful and feel free to indulge your mathematical urges if it helps explain things; I'm not scared. Thanks in advance EDIT: spelling, sorry about the title too, can't change that- god that's annoying...
|
[
"Let's address one point first, and then turn to the bigger questions.",
"So my current understanding is that all of the fundamental forces converge at high energies",
"This is just a theoretical conjecture. Our reasons for suspecting that this is the case are aesthetic, not empirical. ",
"Now--Yang-Mills, Higgs, and all that.",
"We start with electromagnetism. Electromagnetism can be understood as the theory that arises when we impose a certain symmetry on the equations of motion. This symmetry goes by the name of ",
". Let's deconstruct this term, in reverse order.",
"A ",
" is a transformation that leaves the equations of motion unchanged. Symmetries, in our present understanding, are about the most basic feature of a fundamental physical theory.",
"Now many transformations (think, for example, of rotations) have a size or an amount associated with them. In a global symmetry, that amount is the same everywhere (e.g., rotate everything by 30 degrees). In a ",
", the amount of the transformation can be different at different points in spacetime.",
"Warning: the symmetries we are going to look at are internal symmetries; that means we are not talking about transformations that move things around in space, but transformations that modify the identities of particles (sort of like swapping protons and neutrons, or shifting each proton into a mixture of 90% proton and 10% neutron and each neutron into a mixture of 90% neutron and 10% proton).",
"Finally, ",
" just tells us the mathematical form of the particular symmetry transformation that leads to electromagnetism.",
"Okay... Why do gauge symmetries matter?",
"In order to have a gauge symmetry (a symmetry where the amount of the transformation depends on where you are in spacetime), you need to have objects in your theory called ",
" which compensate for how the transformations vary from one point to another. Gauge fields give rise to forces, carried by ",
", the particles associated with those fields. In electromagnetism, this gauge boson is the photon.",
"Remember that ",
" in electromagnetism? There are other possible gauge symmetries which produce different particular transformations. One way to think about this, if you know a little math, is that while the ",
" means that objects can have charges represented by real numbers, in ",
", we have symmetries such that the corresponding charges can be represented as matrices. For the weak force, we need 2 by 2 matrices; for the strong force, 3 by 3 matrices.",
"Now when you have a Yang-Mills theory, the corresponding gauge fields are massless. More precisely, we cannot put a term directly into equations to give them a mass directly. In the case of electromagnetism, you could add such a mass term; this would mess many things up -- it would destroy the gauge invariance, and you would not get the electric and magnetic fields and forces with which we are familiar -- but it is not mathematically flawed. The resulting forces would be short range rather than long range, due to the mass of the modified photon.",
"But for Yang-Mills, you can't add a mass directly to the gauge bosons. The problem is that when we look at the weak force, we see that it ",
" a short range force. So we seem to be on the horns of a dilemma: we'd like to use a Yang-Mills gauge symmetry to explain observed forces, but this apparently won't be able to explain why it's short range.",
"Enter the Higgs mechanism! In a gauge theory, you can have a field -- we call it a Higgs field -- that interacts with the gauge fields (i.e., experiences the force associated with the gauge bosons) but has the peculiar property that the energy is minimized when that Higgs field acquires a non-zero value throughout space.",
"This non-zero Higgs value has several effects. First, it hides the symmetry underlying the equations of motion; the equations are still symmetries, but this low energy state is not itself symmetric. Second, it causes (some of) the gauge bosons to acquire non-zero masses, not because a mass was put in by hand, but because of how they interact with the Higgs field that fills space. This is how the W and Z bosons become massive (and is also what happens with electromagnetism in a superconductor). Third, this way of giving mass to gauge bosons ",
" the gauge symmetry, and so there is no mathematical problem when the gauge bosons get their mass this way. (Demonstrating this last statement carefully led to the Nobel Prize for 't Hooft and Veltman.)"
] |
[
"We don't know why there are the particular forces there are. What we do know is that the symmetry transformations for gauge symmetries correspoind to a mathematical structure called a Lie group, and there is a classification of Lie groups, and each of these leads to some particular matrix structure that will correspond to the form of the charge when we use that Lie group to construct a physical model. (Electromagnetism is really the degenerate case of a \"1 by 1\" matrix.)"
] |
[
"Great, thanks that really helped. Just out of curiosity, why are the strong and weak forces represented by higher order matricies?"
] |
[
"Is immunity backwards compatible?"
] |
[
false
] |
If someone develops immunity to virus B which evolved/mutated from virus A, does that person have immunity against virus A or have any advantage against being exposed to virus A that a person who has not been exposed to virus B would not have? What about the symmetrical question of when one has developed immunity against virus A before being exposed to virus B?
|
[
"It would depend on which epitote the body raises antibodies against. If it raised antibodies against a conserved regional of the virus then yes you would get immunity (cowpox and smallpox).",
"Often though, viruses containe only a couple simple genes and can mutant them all so fast very little is conserved."
] |
[
"Do anti bodies from different people target the same area of a virus? Meaning, are some people's antibodies randomly better at being \"backwards compatible\" or less sensitive to mutations?",
"Antibodies are generated more or less randomly. Some of them will end up responding to various small chunks, called epitopes, of any particular antigen, and then those are selected for efficacy. ",
"Yes, antibodies and their specific targets and therefore efficacy against specific strains of specific pathogens are highly variable from person to person. Not everybody will have the same degree of cross-immunity. ",
"Also, does the body stop the r&d phase of the immune response as soon as a good candidate is found? Or does it continue testing antibodies even after a good one has been found?",
"The sensitization of your immune system to antigen is a continuous and ongoing process. It's naturally self-limiting, because as your immune system produces more effective antibodies, less circulating antigen will be found and fewer naive B cells will be exposed and undergo the hypermutation process that generates the many slightly different antibodies of your immune system, In general, after an effective immune response is mounted, most of the antibodies present will be the highly effective antibodies that were previously evolved by your immune system, precisely because your body deliberately selects for those cells which are generating highly effective antibodies and it's likely that those are the ones which did a good job last time."
] |
[
"Do anti bodies from different people target the same area of a virus? Meaning, are some people's antibodies randomly better at being \"backwards compatible\" or less sensitive to mutations?",
"Also, does the body stop the r&d phase of the immune response as soon as a good candidate is found? Or does it continue testing antibodies even after a good one has been found?"
] |
[
"What the heck is going on with this warm weather all autumn/winter?"
] |
[
false
] |
I'm in school in the Albany, NY area and usually around early-mid October I can't go outside without a sweatshirt or risk immediate hypothermia. Today, I went to do some errands and I was walking around comfortably in a no-sleeve shirt and shorts. What's the deal? Is this the direct result of global warming, a lesser effect, an El Nino/Nina?
|
[
"Its el nino.",
"Global warming is a very very slow process that happens around the world. During the past 60 years the average global temperature has rose about 0.4celcius. If you are still in school it probably means that during your lifetime the global warming has only increased global temperature of about 0.1celcius. Something that would be compleatly impossible for you to notice yourself. Especially locally, the anual temperature fluctuations compleatly dwarf this change."
] |
[
"Is this the direct result of global warming, a lesser effect, an El Nino/Nina?",
"A bit of both.",
"Yes this is an El Niño year. And El Niño is part of the expression of a very large climatic response called ENSO (El Niño - Southern Oscillation), which has far reaching but locally quite varied effects throught the world. The main driver of El Niño is an E-W band of warm surface waters along the equatorial Pacific. In NE-North America, part of the response to an El Niño event is warmer winter températures. I'm further to the NE from where you are, in Québec City, and we've had unseasonably warm temps as well, we are getting our first snowfall as we speak. Normally the first snowfall which sticks to the ground around here is around the 3",
" week of November.",
"But ENSO is a normal part of our planets climate behavioral toolkit - where does climate change fit in? Well, one thing we've been seeing from studiying the multiple feedback effects built into ENSO is that warmer global températures seem to increase the frequency of El Niño events, as well as their intensity. The current El Niño seems to be one of the most intense ones on record (",
"reference1",
", ",
"reference2",
"), so the intensity of the current event ",
" be related to climate change."
] |
[
"So far it's been a fairly classic El Nino winter, yeah."
] |
[
"Why are absorption lines not lines?"
] |
[
false
] |
It seems that in every absorption spectrum you come across, you come across many as a physics undergrad, the spectral absorption 'lines' are not lines at all but sharp curves. What I mean by this is that they are finitely wide- (for example the solar spectrum - ) - whilst the energy required to promote an electron in an atom is supposed to be only one exact value. Which would make you think that the absorption should be at one wavelength and have no uncertainty in it, ie infinitesimal thickness to the absorption line. Can anyone explain why this would be the case? I have been playing around with the idea that some dopler shift may be the involved but I can't resolve it. HELP ME SCIENCE!
|
[
"There are many different sources of line broadening. The must fundamental limit is lifetime broadening: since an atom does not remain arbitrarily long in an excited state, the uncertainty principle, or if you prefer the Fourier relationship, guarantees that the line will have a finite width. ",
"Otherwise, any interaction may cause an increase in line width of the order of the transition frequency associated with the interaction. Examples for this are dipolar broadening, unresolved fine structure (Lamb shift and such), hyperfine structure, etc. You are also correct in that Doppler broadening can be important.",
"Very stable transitions are actually hard to get and a lot of effort is expended into having as sharp as possible transitions for use in atomic clocks or laser systems.",
"The eigenvalues of a composite quantum system are not \"supposed to be\" a single exact frequency. That is an approximation that is often made, but it's not how you should generally think about things."
] |
[
"Thermal doppler broadening is probably the biggest one in the solar spectrum - or astrophysics in general. Non-thermal doppler broadening (e.g. turbulence) is often the next biggest."
] |
[
"In chemical systems, like solution spectroscopy, every molecule is going to be experiencing a slightly different environment. These environments can have subtle, but sometimes large, effects on the absorption spectrum. An extreme example of this effect which shows up to a lesser extent within a single solvent is ",
"solvatochromism.",
"EDIT: ",
"Here's",
" a pretty picture which demonstrates the effect. The vials each contain two chemicals: A solvent and a \"pigment\" (the molecule actually giving the solution color). The color of the pigment is changing just because of the effect the solvent has on the quantum mechanical states in the light absorbing molecule."
] |
[
"Is there any form of matter that cannot be categorized on the periodic table?"
] |
[
false
] |
ie: is there any mass that breaks the standard rules of how elements work?
|
[
"Oh there's heaps. The periodic table is just for baryonic matter made up of protons, neutrons, and electrons. Anything made out of other subatomic particles won't make it into the periodic table. It doesn't include muons, neutrinos, or anything else in the ",
"standard model of particle physics",
". In particular, if dark matter really is some currently undiscovered subatomic particle (and there's good reasons to suspect it is), then like 80% of the mass of the universe is made up of matter that isn't on the periodic table."
] |
[
"The ",
"standard model",
" organises the fundamental particles, but it's not really an equivalent to the periodic table. The variation of behaviour in the elements on the periodic table is due to how the electrons on each atom interact with each other, that's Chemistry basically. The same kind of variation isn't really seen outside the elements, or at least we ourselves are made up of chemical elements and the vast majority of experience is too so it's not as well studied as Chemistry is."
] |
[
"Is there a periodic table-like equivalent to organize non-baryonic matter?"
] |
[
"What is happening physiologically when you have a “knot” in a muscle?"
] |
[
false
] | null |
[
"There really just has not been enough research into this area. For some reason, the tone in a local muscle group is increased, or part of the contraction does not completely release once the nerve signal has stopped, but the actual mechanism of what is happening is not really known. ",
"The blood flow and toxin theories are generally pushed by people selling something (therapies to increase blood flow or remove \"toxins\") but since people don't have muscles rotting off like they have leprosy and because you have working kidneys and a liver, it's not because of these things. ",
"That being said, it can have real consequences (pain, dysfunction, etc) and massage, stretching, physical therapy, etc can be quite helpful but ymmv on what helps you. If it is recurrent in a specific area, it's reasonable to seek medical care. Sometimes this could be a more serious issue or simply a posture/positioning thing that a physical therapist can help you work on."
] |
[
"We don't actually know. There's an area of higher muscle tone that you can feel, but we don't really know why they happen. Just that sometimes, through massage and/or relaxation, sometimes through activation and use, they go away. Not the same thing as a cramp, which we know well. Knots are sort of a mystery."
] |
[
"What is happening physiologically when you have a “knot” in a muscle? By knot I am referring to a tight or particularly sore area in a muscle belly. When palpated it can feel like a small lump or tense area. They tend to go away with stretching, and or some pressure to the area."
] |
[
"Why does paper 'remember' when it's been rolled up?"
] |
[
false
] |
As in, if I roll up a bit of paper and then un-roll it, why will it bend in the direction it's been rolled?
|
[
"The outside of the roll is under tensile stress. Therefore, the interface in between the paper fibres and the matrix is deformed more than the inside. When you let go of the roll, the paper recovers the elastic portion of the deformation, but not the plastic portion. "
] |
[
"When you fold a piece of paper, you break some of the cellulose fibers. As these are broken, the paper stays that shape, like when you break a stick",
"The same goes for rolling. Some of the fibers snap and somewhat 'hold' the paper in that position.",
"This",
" is a picture of paper under a microscope. Notice the fibers.",
"Unfortunately I couldn't find a picture of what it looks like folded, but you can imagine each of those fibers breaking like sticks and holding it in place. "
] |
[
"But your wording implied that most metals don't retain their shape when bent. Not only is that a false statement but that isn't even what shape memory alloys do. They will return to a predefined shape after being deformed. I guess it's relevant in that it's the opposite of what happens to paper after it gets deformed."
] |
[
"Why is it that, when light is out of focus, it always makes the shape of a hexagon or octagon?"
] |
[
false
] | null |
[
"This is only true if you take a picture of an out of focus light source and it happens because of the shape of the aperture blades in the lens.",
"6 bladed aperture: hexagon shape",
"8 bladed aperture: octagon shape",
"..and so on. That's why expensive lenses have more aperture blades to make that shape as round as possible.",
"You can even cut out your own aperture blades from cardboard and make fancy shapes like ",
"this."
] |
[
"That's because cameras use ",
"bladed apertures",
" that form polygons. When the aperture is fully open, they will get circular aperture though, since the blades are only require to change aperture size and the max aperture is static.",
"the 50mm f1.8 from canon is famous for having a 5-bladed aperture to reduce cost",
" "
] |
[
"The question has been answered, but the general term for this effect is ",
"bokeh",
", if you'd like to learn more. It can be used for some surprising things, like devices reading complex optical patterns without being focused!"
] |
[
"Ask Anything Wednesday - Engineering, Mathematics, Computer Science"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"It's a simple one, but I really like the ",
"Ideal Rocket Equation",
". The reason is, because it takes a concept that sounds pretty complicated, and then shows a really simple final result. ",
"The question this equation answers is: if I want to launch a rocket to a certain velocity (or change a rocket's velocity by a certain amount), how much fuel do I need? At first blush, it may not sound complicated, but think about what's happening. The last little bit of fuel needed only has to accelerate the rocket itself. The second to last bit of fuel has to accelerate the last bit of fuel, and the rocket. The third to last bit has to accelerate the second to last bit and the last bit of fuel, an the rocket. ",
"The ideal rocket equation is sort of a \"real world\" example of why differential equations are so powerful, because after you solve it, you find out that it is as simple as:",
"delta_v = v_e*ln(m0/m1) ",
"where delta_v is how much you want to change your velocity by, v_e is the velocity of your exhaust, m0 is how heavy you start off, and m1 is how heavy you end. "
] |
[
"Pi is related to circles, and circles are used in the definition of the trigonometric functions (Sin, Cos, ...). These functions can be approximated using infinite polynomial sums through their Taylor Series.",
"This series (in this case) is a perfect approximation, and for these functions has very simple forms. Also, because these are polynomial functions, their link to their trigonometric sources aren't obvious. For example, Euler showed that the infinite sum of 1/n",
" is Pi",
" /6 (called the Basel problem)."
] |
[
"Pi is related to circles, and circles are used in the definition of the trigonometric functions (Sin, Cos, ...). These functions can be approximated using infinite polynomial sums through their Taylor Series.",
"This series (in this case) is a perfect approximation, and for these functions has very simple forms. Also, because these are polynomial functions, their link to their trigonometric sources aren't obvious. For example, Euler showed that the infinite sum of 1/n",
" is Pi",
" /6 (called the Basel problem)."
] |
[
"How does changing the physical diameter (but not ratio) of two gears affect the resultant power/torque on a bicycle?"
] |
[
false
] |
Alright, so I am looking at some gear ratios for a single speed bike I am building up. Ideally I would like a bike with a 2.75 gear ratio (44 tooth ring up front, 16 in the rear) but due to some component sizing issues I am now looking more in the range of a 33 tooth front and 12 tooth rear, keeping that 2.75 ratio. Will this affect power output, torque, or any other factors that am not thinking of currently?
|
[
"Yes and no.",
"With larger diameter front gear, the rider does have greater leverage.",
"However, with larger diameter rear gear, gravity and friction also have greater leverage.",
"Ultimately what matters (except, as I mentioned, if you are concerned with stress on individual teeth) is not the rider's leverage against the chain, but the rider's leverage against gravity.",
"And since OP specified that he is maintaining the same gear ratio between the two designs under consideration, river's leverage against gravity is equal between the two, because rider's leverage gains in the front are exactly canceled out by gravity's leverage gains in the rear.",
"But yes, if you changed the size of the front gear without changing the size of the rear gear, you would be correct."
] |
[
"No, different tooth count, different gear diameter, just same ratio. Bike gears are more or less constant in tooth spacing. Sometimes there are different chainring widths and chain widths to match but I'm more concerned with the feasibility of changing up gear diameter without manipulating the ratio. "
] |
[
"No, different tooth count, different gear diameter, just same ratio. Bike gears are more or less constant in tooth spacing. Sometimes there are different chainring widths and chain widths to match but I'm more concerned with the feasibility of changing up gear diameter without manipulating the ratio. "
] |
[
"Would a blue whale feel the prick of a pin?"
] |
[
false
] |
As a human, one can noticeably feel the irritation or pain of something as small as a bug bite, even though the affected area is incredibly small in comparison to the human body. Neglecting chemical effects, would a larger animal (like a blue whale or elephant) have a proportionately higher threshold for what would be considered irritative/somewhat painful when compared to a human? I know this would be dependent on the location on the body of the animal, but I'm curious about the comparison in a more general sense.
|
[
"I have combed through available journals looking for any info like this. The closest I got was ",
"here",
", but I have no access.",
"What are your sources? What you say sounds plausible, but I'm skeptical without documentation."
] |
[
"I have combed through available journals looking for any info like this. The closest I got was ",
"here",
", but I have no access.",
"What are your sources? What you say sounds plausible, but I'm skeptical without documentation."
] |
[
"Nerves have two modes. On, and off. In us humans, a resting cell is negatively charged at -70mV to -80mV. Now some action happens. ",
"This causes sodium(Na+) gates to open up, letting some into the cell and depolarizing it. At a certain point of threshold many more sodium ions flow in, making it positive on the inside. This triggers a action potential. The amount required is aprox 40mV. As far as I can remember most mammals are in the same area. ",
"The thickness of the epidermis is a larger factor here, as well as nerve density. ",
"A quick search revealed that ",
"the epidermis of whales is very thick.",
"I highly doubt that the whale would feel pain from a jab of a pin, if even at all. Nerve density is also a large factor here. Don't want to go into guesswork on this so I'll leave it to someone else to figure if the nerves are dense enough to notice things this small. ",
"This last part is very situational on where you are poking, different density in different parts of the body. "
] |
[
"What is the smallest thing that you could set fire to?"
] |
[
false
] |
Like can you make fire on a micro/nanoscopic scale?
|
[
"You may find this entry useful: ",
"http://en.wikipedia.org/wiki/Combustion"
] |
[
"That depends what you mean by \"fire\". Do you mean rapid exothermic oxidation? Because that can happen at the molecular scale."
] |
[
"Ah saw the microcombustion section cheers mate "
] |
[
"Can someone explain how miRNAs produce gene silencing?"
] |
[
false
] |
I know the basics of miRNA but I know there are things called like RISC and argonaut proteins, but I don't know how they all fit together.
|
[
"Given your flair, I'm sure you know what a miRNA is, but in case anyone who doesn't bops in, miRNAs are short, noncoding RNAs - that is, they're only a few dozen bases long and don't code for a protein. They silence genes by binding mRNA - your run of the mill, protein coding RNA, which are much, much longer.",
"How does a miRNA do this silencing? Well, it gets bound by one of the Argonaut family of proteins, which then recruits a set of proteins called the microRNA-induced silencing complex (miRISC, or RISC). The basic gist of it is that miRNA acts like \"template\", giving the miRISC its specificity. It targets the miRISC to the matching mRNA. From there, all the silencing is done by the miRISC, not the miRNA itself. The proteins in the miRISC have many protein synthesis-inhibiting functions; for instance, some proteins in the complex can bind PABP, the polyA binding protein which binds the tails of mRNA and helps circularize the mRNA. miRISC binding of PABP prevents the mRNA from becoming a circle, and degrade the protective polyA tail. Preventing circularization and removal of the tail leaves the 5' cap (the other end) open to degradation as well, resulting in destruction of the transcript.",
"This is only one of several mechanisms - the miRISC can also block translation from happening, and the decircularizing of mRNA stops the ribosome from staying on the mRNA, reducing the efficiency of translation. For a very thorough review, check ",
"this paper by Fabian and Sonenberg",
".",
"Hope this helps!"
] |
[
"Your assumption is correct. Sequence complimentarity is a big factor in determining the fate of the target mRNA. siRNA's are derived from long introduced dsRNA and have high complimentarity to the target transcript. This high complimentarity activates the 'slicer' activity of the Argonaute (Ago) proteins in the RISC complex and cleaves the mRNA. Free ends of mRNA (lacking a 5' cap or 3' poly-A tail) are then targeted by cellular exonucleases and degraded. ",
"Here is the paper by Fire and Mello",
" which eventually led to a Nobel for discovering RNA interference.",
"miRNA do not always have perfect complimentarity with their mRNA target and do not necessarily activate the cleavage of the mRNA strand via Ago slicer activity. ",
"/u/chondroitin",
" gave you a great example of translation suppression by miRNA/RISC by binding the poly-A tail and circularizing the mRNA. I'll give you another: The Ago2 protein in the RISC binds the 5' cap of the mRNA. So the miRNA directs the RISC complex to a particular site on the mRNA transcript like the 3' UTR (untranslated region). Argonaute 2 has a binding domain that fits the 5' cap of the mRNA and sequesters the cap, circularizing the mRNA transcript and inhibiting translation initiation. ",
"Source: An mRNA m7G Cap Binding-like Motif within Human Ago2 Represses Translation"
] |
[
"Hey I found you're explanation to be really informative. I have a question though. What makes the RISC ",
" translation when interacting with an miRNA, and cause ",
" when interacting with a siRNA? I always thought it was because the imperfect matching up of the miRNA kept it from doing so, but that's just my assumption and it seems like a gross over simplification. "
] |
[
"All other factors being equal, who would win an arm wrestling match between two people with different arm lengths?"
] |
[
false
] | null |
[
"This is a fun question. It really depends on what \"all other factors\" means!",
"Now we just need some experimental data..."
] |
[
"A common physics 101 question asks a person to calculate the torque a bicep can exert on a forearm, assuming that the bicep connects to the forearm a short distance ahead of the elbow. So, for example, if they both have the same bicep strength (or their biceps is capable of producing the same amount of force), do they connect at the same distance from the elbow or do they connect at a proportional distance from the elbow, scaled with the length of the arm?",
"Like you said, the question boils down to your interpretation of \"all other factors being equal\" - this is simply a case where setting two specific qualities equal will guarantee that others must be unequal. "
] |
[
"Think about it like this, what is easier to swing, a sledge hammer or a normal hammer (assume the weight at the ends of the hammers are the same)."
] |
[
"What does our solar system orbit?"
] |
[
false
] |
Title explains
|
[
"It orbits the center of the Milky Way. ",
"See here",
"."
] |
[
"This is correct."
] |
[
"To explain a little further than snooptray, everything in our galaxy (including our solar system) is orbiting a supermassive black hole that is in the center of our galaxy. It's generally accepted that most, if not all galaxies have black holes in the center, keeping its contents from expanding into (more) open space. "
] |
[
"what would happen if a star gets caught in a supernova?"
] |
[
false
] |
Let's say for instance, there is a binary star system and one of those stars explode, (for whatever reason) what would happen to the other star? Would it explode too? Or would nothing happen to it?
|
[
"Numerous X-ray binaries are known, with a neutron star or black hole paired with a \"living\" star. This indicates that in at least some supernovae, a partner star can survive.",
"https://www.nasa.gov/mission_pages/chandra/news/binary-star-system-clues.html",
" discusses what's inferred to be a very young X-ray binary, mentioning that the orbit was presumably disrupted by the supernova - which the mass loss alone would do even without any force from the explosion. But the stars remained in a closed orbit instead of escaping each other.",
"Some examples aren't X-ray binaries. \"Gaia BH1\" is one of the closest known black holes to Earth, it's a binary of a ~10 solar mass black hole and a sun-like star with an orbital distance of 1.4 AU, discovered by precise position and radial velocity measurements. ",
"https://en.wikipedia.org/wiki/Gaia_BH1",
"As another answer mentioned, supernovae are often asymmetric, so I wouldn't be confident predicting that ",
" supernova can destroy its companion. A low-mass star in a close orbit caught by a strong direction of a supernova might be vulnerable. The asymmetry can also send the stellar remnant recoiling off at great speed; a former companion could survive but be left behind."
] |
[
"As I understand, the distribution of matter once a star has gone supernova isn't uniform. If you wrapped a sphere around the star and cataloged how much matter flew past each part of the sphere, it'd give you a very spotty sphere. If the partner star gets hit, likely it'll be torn apart and distributed chaotically alongside the supernova stuff. It might also supernova on its own? Stars are actually sort of fragile on such massive scales, so it'll either be ripped apart, and both fusion from pressure and gravity from proximity will stop, or it'll get compressed in the right way for fusion to be overwhelmed by gravity similarly to its parter, causing a sudden surge in fusion, blowing the star apart.",
"If it doesn't get hit, what you'll find is this untouched star orbiting the stellar remnant (either a neutron star or a black hole).",
"There isn't much middle ground, it'll either survive miraculously untouched, or the supernova will basically erase its former partner from history."
] |
[
"Described by Einstein's theory of relativity, there are some wonky consequences of extremely strong gravity, but outside of the relativistic zones, it's normal gravity. If the sun was replaced with a black hole of the same mass, nothing about the solar system's orbits would change.",
"The same with a star going supernova next to its binary partner. A lot of the mass was thrown off as the brilliant nebula that will hang around the pair and glow for decades, but much of the mass is still concentrated in the dead stellar core, which is either barely holding itself together as a neutron star, or has/will soon collapse(d) into a black hole, becoming much much much smaller than it used to be as even a neutron star. Its partner will stay untouched, maybe it will enter an elliptical orbit (same energy in moving around the black hole, but the black hole has less mass, so it pulls slightly less, meaning the remaining star can swing outwards more than it used to), but unless it somehow slips very close to the black hole, it won't actually be inexorably pulled into it."
] |
[
"If RGB LEDs can produce 256^3 colors, why haven't there been any preset colored lights that mimic the color of tungsten bulbs?"
] |
[
false
] |
I was thinking of this because I was looking at my new LED Christmas lights. I understand it's more cost effective to slap standard red, green, blue and yellow LEDs on a string, but I personally know many people, especially older folk who miss and prefer the old style tungsten lights. But these colors should be able to be reproduced by RGB LEDs and sold at a premium as a perfect copy of old style tungsten strings, no? Why haven't I heard of this? Also what about regular ceiling lights? Could tungsten also be reproduced with RGB LEDs and sold at a premium?
|
[
"The issue at heart is that Tungsten bulbs produce broad wavelength light and RGB LEDs produce three very specific wavelengths. The eye only has three types of cones so theoretically an RGB LED should be able to exactly reproduce the response that the eye interprets from a Tungsten bulb. ",
"The complication is that objects do not reflect all light equally, anything that is not pure white/gray/black reflects and absorbs light differently. For a very simple example, imagine that you have an RGB system where blue is around 480nm, green is around 580nm, and red is around 640m. Now imagine you have an object that very selectively absorbs 580nm and 640nm light, it will look very blue when illuminated by the RGB system. If you shine light from a Tungsten lamp on that object, the red and green will still be visible because a broad spectrum of light is still available around the absorbed wavelengths, so the object will look more white.",
"Here",
" is an example where a group is using a 9 color LED system to more accurately reproduce the reflective appearance of a Tungsten bulb, essentially by making a more broad band light source."
] |
[
"LEDs can be used to produce light similar to tungsten filament bulbs, but the RGB approach is not the most successful so far. Better results have been achieved by using UV or blue LEDs, then converting the light with a special coating, similar to fluorescent tubes. Check ¨",
"this model from Philips",
".",
"More compact designs have been developed, in some cases the \"coating\" (called phosphor, though it is not the chemical element phosphorus) is inside a module that we call the LED, so the light that the LED itself produces by electroluminiscence is never seen directly. That's how most commercial LED lighting works."
] |
[
"What about pixels on an LED display? Those should be capable of 16 million. "
] |
[
"Are there any added benefits to working out at high altitudes other than increased lung capacity?"
] |
[
false
] |
Are there any other repercussions from working out at a higher altitude (say 7,000ft)? Does the "lack" of oxygen make our muscles more efficient ? Also, if your body was used to being at said altitude, would you be less susceptible to the symptoms of hypoxia (12,500ft and up) in an un-pressurized aircraft?
|
[
"As Deus_Ex_Corde already pointed out, you'd also produce more red blood cells. But to confuse matters a little bit, modern training research recommends that you ",
" at high altitude, but ",
" at low altitude.",
"Most of the altitude-related physiological adaptions happen independent of whether you're working out-- just living there is sufficient. But if you then go downhill to do your training, you are able to train at a higher intensity than if you did your training in the thinner air. ",
"Edit: and you would be somewhat less susceptible to things like altitude sickness and hypoxia. "
] |
[
"Yes, at higher altitudes the body produces more red blood cells to transport oxygen in order to make up for the thinner air. It's very common for top athletes to train at higher altitudes than their event is taking place in order to gain an advantage, many athletes also sleep in pressure chambers that simulate a thinner atmosphere. The higher number of red blood cells means that the cv system is more efficient in getting oxygen muscles so they can work for longer periods before having switching to anaerobic respiration.\nThere's also something called blood doping where an athlete will inject himself with more blood prior to an event to confer the same advantages."
] |
[
"Your lung capacity wouldn't really change. Most adaptations are hematologic and metabolic/mitochondrial. "
] |
[
"Why do current-carrying wires have multiple thin copper wires instead of a single thick copper wire?"
] |
[
false
] |
In domestic current-carrying wires, there are many thin copper wires inside the plastic insulation. Why is that so? Why can't there be a single thick copper wire carrying the current instead of so many thin ones?
|
[
"A single wire that's thicker will be harder to bend. It will also fail entirely when it breaks.",
"Multiple thin wires will allow easier manipulation of the wire overall. Also if any part breaks, it's just a few strands that break (usually the ones on the outside of the bend). The break won't affect the wire because the current still travels alongside through the unbroken strands.",
"Tl;dr greater flexibility and more durable wires."
] |
[
"Electrician here, that wire is called \"stranded\" and has applications that are more beneficial than \"solid\" wire. You mention it's easier to bend, but sometimes it is more useful to have solid wire, where it will stay where you bend it. It has more memory, which is what we call that. There are other factors to consider but I thought I'd mention that!"
] |
[
"Solid wire is easier to connect to wiring devices with screw terminals, switches and receptacles etc. Bend a loop in the wire , hook it under screw and tighten. Stranded wire unwravels and spreads out, doesn't stay under screw neatly. Now connection are often \"quick connect\", strip wire stick it in hole. These are usually designed for solid wire only."
] |
[
"What is the most controversial or contested concept in your field? How great is the disagreement?"
] |
[
false
] | null |
[
"I am a philosophy major... its all controversial and contested. "
] |
[
"1) The clean baby hypothesis. This yo-yos back and forth every few years, with evidence going either way. Most people go along with the yo-yoing, claiming that it's right in some cases and wrong in others. Some are very die-hard on it. Most agree that greater exposure to antigen at a young age will decrease atopy down the road, the controversy is how important it is in conjunction with other factors and what antigens are \"best\" for prevention without risk.",
"2) The Dutch hypothesis. This states essentially that asthma, COPD, and emphysema are all one disease and should be treated and researched as such. More extreme versions say that asthma is actually early-stage COPD. The other camp says it's bullshit and COPD is very different from asthma in fundamental pathogenetic ways.",
"3) Mucoid vs biofilm in cystic fibrosis. People with CF get chronic infections, and these bugs form a community in the lungs. What is not known is if these communities are true biofilms or just alginate overproducing mucoid strains of bacteria. What makes this especially hard is that there is not a good definition of an in vivo biofilm, and it's very likely that mucoid bugs are forming biofilms as well as a side effect of their mucoidy. At this point, though, it still remains a chicken and egg type of controversy (which makes it important in pathogenogenesis. Mucoid conversion is often due to a null mutation followed by selection and is therefore hard to revert. Biofilms are regulatory events and can revert with environmental stimuli)",
"4) Another would be the hypoxia problem. Most tissue culture experiments have been done in room air +5% CO2. So that's 20% O2, ~75% N2 and 5% CO2. The problem is that with the exception of the very upper reaches of the respiratory tract (nose, mouth, trachea, and maybe mainstem bronchii), there is nowhere in the body that has 20% oxygen. It's always lower, and often much lower. Cells and tissues have major signaling arms dedicated to sensing and responding to oxygen, and these signaling pathways have significant crossover with inflammatory pathways. The people that promote the hypoxia problem say that because you are doing the experiments in a high-O2 environment, you are hitting those pathways. Skeptics counter that the pathways are mostly geared to sense low oxygen concentrations, and there is evidence that they are self-regulating. They say the pathways can adjust to new oxygen set points over the course of days. I personally say the skeptics just don't like the idea of potentially having to reevaluate decades of research. The sensor pathways may well be self regulating, but that's not the only player here. ",
"There are probably others, but that's what I get off the top of my head. Very field specific. "
] |
[
"most controversial point: does it work...",
"(nuclear engineer, fusion)"
] |
[
"Help with my Thought Experiment?"
] |
[
false
] |
I came up with this while looking over the special relativity stuff for my A Level, so I may not be able to do it because I don't know "higher" stuff, but here goes. Imagine a perfectly smooth, spherical planet. The circumference of the circle at the widest point is 0.9 light years (it's a big planet). I, and my family, live on this circumference. I can run at 0.9c. If I run at 0.9c around the circumference (so the journey takes 1 year), what will happen to me and family's relative ages. Will I be older, younger or the same age than if I hadn't embarked on my epic trek? My guess was I would be younger, due to the time dilation as a result of me running at 0.9c, but what about the centripetal acceleration towards the centre of the planet and the effect that has (I think GR comes in here, but I don't know)? Thanks for any answers.
|
[
"assuming that you will stay on the ground (gravitational force is greater than the centripetal force) then you would have experienced the journey as taking 0.45 years. T = t /sqrt(1-v",
" /c",
" ). If you want to know if the assumption is correct, you need to specify the mass or density of the planet. M > r*v",
" /γ for you to stay on the ground, assuming no drag or lift from friction. where M is the mass of the planet, r the radius, v your speed, and γ the gravitational constant. "
] |
[
"The centripetal acceleration would actually be the only thing that makes you appear younger than your family at the end of the trek, as it were. Time dialation in special relativity is a two-way street. If your frame differs from your family's frame by velocity alone, you will both think that the other is younger. Only via the differing acceleration do you both agree that you have experienced less time."
] |
[
"Wait, really? So does that mean that, in the famous Twin Paradox, both twins would think they were older than the other? Do you have links that expand on this?"
] |
[
"Why do so many animals have 4 limbs rather than 2 or 6?"
] |
[
false
] |
[deleted]
|
[
"Yes, absolutely. What most biologists believe is that amphibians, snakes and lizards, turtles, crocodiles, birds, and mammals are all descended from a single common ancestor who lived about ~400 million years ago. As a matter of fact, the scientific name for this whole group of land-dwelling vertebrates is the tetrapods, which literally means \"four-foots\". It's likely that this ancestor had 5 toes/fingers as well!",
"We don't know exactly what this common ancestor looked like, but we've found quite a few fossils of creatures around the era we believe they first evolved that give us a decent idea--",
"probably somewhere between modern salamanders and modern lungfish/mudskippers",
"Now, obviously not all of the descendants of this creature have four limbs and five toes. Snakes are an obvious example, but it's believed that their immediate ancestors had legs and they evolved to lose them to fill a particular niche in their environment. Clearly, it worked well for them, since there are tons of snakes all around the world.",
"There's still quite a bit of debate about exactly how the tetrapods are all related to eachother, but the general idea is that amphibians branched off first, with the remaining 3 big groups being snakes/lizards/turtles, crocodiles/dinosaurs/birds, and mammals. \"Reptiles\" doesn't tend to be used in scientific contexts anymore, because crocodiles are probably more closely related to birds than they are to lizards, so any definition of reptile that wasn't arbitrary would have to include birds too.",
"Also, just a quick note that there are many, many more living animals with 6 limbs on the planet right now rather than 4 limbs, as insects are by far the most numerous animal group."
] |
[
"FYI, insects are part of a larger class of animals called arthropods (means \"jointed legs\"). Arthropods also include crustaceans like crabs/shrimp, millipedes/centipedes, and arachnids like spiders/scorpions. The technical name for the group within the arthropods that includes insects is the hexapods, which means \"six-foots\".",
"This is a very high level summary",
" of the most current \"family tree\" of the major groups of animals. This is still not settled yet, and we don't know much about how or exactly when these large groups appeared or split off from eachother.",
"FYI:"
] |
[
"FYI, insects are part of a larger class of animals called arthropods (means \"jointed legs\"). Arthropods also include crustaceans like crabs/shrimp, millipedes/centipedes, and arachnids like spiders/scorpions. The technical name for the group within the arthropods that includes insects is the hexapods, which means \"six-foots\".",
"This is a very high level summary",
" of the most current \"family tree\" of the major groups of animals. This is still not settled yet, and we don't know much about how or exactly when these large groups appeared or split off from eachother.",
"FYI:"
] |
[
"Any scientific research re: what dinosaur's eyes looked like?"
] |
[
false
] |
When I look at a hawk's eye, I can't help but wonder if that's what a oviraptor's may have looked like, for example. Is there any research out there on what form dinosaurs' eyes might have taken?
|
[
"Not really, the preservation potential of soft tissues is low enough - the preservation of the squidgy bits of eyes is practically zero.",
"Certain things can be inferred from muscle marks on skulls, and some work has been done on older forms of life with hard lensed eyes (trilobites I know for a fact an acquaintance of mine did her PhD on) but otherwise we don't really know."
] |
[
"The image of dinosaur's are unfortunately more of a theoretical image. They have the bone structures and yes as bobreturns said, they look for muscle markings, but because they have the same inner-bone structure that we still have, we do not have enough tissue information to confirm how they actually look, as only things such as fossils can give us more realistic depictions because of exoskeletal remains and tissue impression. We know birds and reptiles have evolved from the same structures, so we often use their outer characteristics as a model, but we cannot say for sure."
] |
[
"Too bad! I read recently that a researcher was able to theorize what sounds a dinosaur might have made by examining the bones in which vocal cords (or related organs) are housed. I was was hoping similar research may be possible in this case. "
] |
[
"Question about Light: What Happens to It? (See Inside for more explanation)"
] |
[
false
] |
[deleted]
|
[
"Not only has time stopped, but the universe is infinitely thin in the photons direction of travel. To the photon, the universe appears to be traveling at the speed of light. By the lorentz transform, the universe is infinitely short in its apparent direction of travel. To the photon, the electron in the sun that emits the photon and the electron in your eye that receive that photon are actually touching."
] |
[
"It can be absorbed, bounce off or be absorbed and a new photon emitted.",
"If it is absorbed it adds energy to the thing absorbing it (the object heats up a bit). ",
"The law of Conservation of Energy says that all energy in a closed system can be accounted for. It can not be destroyed. It can change forms but in the end it is all accounted for.",
"This will bake your noodle though:",
"From the perspective of the photon (if it had one which it doesn't) they are absorbed as soon as they are emitted. Even if they cross the universe."
] |
[
"It would \"think\" it is absorbed immediately because in its perspective, time is stopped, essentially because the speed of light is so much faster than everything else. "
] |
[
"Did early trees decompose? Looking for article/video/evidence that fungi didn't have the capabilities to break down tree matter when it first evolved."
] |
[
false
] |
This got shot down in ; hopefully it fares better here. I feel like I saw a video or read an article article on fungal evolution relating to woody plants on reddit, but I can't find it here or anywhere. Another part of me thinks it came from the BBC's Private Life of Plants series, but I haven't been able to find the goods from there either. Can anyone help me out? Or am I going crazy and making shit up in my head?
|
[
"It is mentioned in ",
"this",
" BBC documentary that fungi were unable to decompose wood for some time.",
"\nIf I remember correctly, that documentary was posted in ",
"/r/todayilearned",
" some time ago."
] |
[
"This might help: ",
"http://en.wikipedia.org/wiki/Carboniferous#Rocks_and_coal"
] |
[
"Perfect! This is exactly the documentary I remembered. It comes around 28 minutes in.",
"The original TIL post may have either been for that moment, or for the moment two minutes earlier with a fungus taking over the mental faculties of an ant."
] |
[
"Is the ice at the north and south poles floating like giant ice cubes or are they sitting on the bottom of the ocean basically acting like land?"
] |
[
false
] |
I want to know if theyre basically just giant ice cubes that are melting or if they're so heavy they're sitting on the bottom of the ocean.
|
[
"The North polar ice cap is mostly sea ice that floats on top of the Arctic Ocean. The South polar ice cap rests mostly on Antarctica as a continental glacier, although some portion of it extends into the oceans."
] |
[
"The north pole is a giant mass of ice, not just foating but attached to Canada, Russia, and other far northern countries. It isn't frozen all the way down, there is a large amount of ocean underneath it with a lot of unique types of life. The south pole on the other hand is a land mass like any other, though it's size is increased by ice on the surface of the ocean."
] |
[
"Ok thank you because i was wondering how such a large glacier could possible stay at the bottom and also this explains whybtye sea level change would be so drastic."
] |
[
"How am I able to see stuff in our universe without other stuff getting in the way?"
] |
[
false
] | null |
[
"tl;dr space is really, really empty."
] |
[
"Because there's not that much stuff in the universe. Stars are ",
" and nearly everything we see when we look up at the sky isn't individual stars, but whole galaxies. It takes a ",
" of matter to absorb or scatter the light from a single star, much less a whole galaxy. And the universe simply doesn't have that much matter in it.",
"The average density of mass in the universe is thought to be comparable to one hydrogen atom per ",
" of empty space. And, of course, nearly all of that mass is contained within stars, which are the things that are pumping out light at us.",
"So wondering why we can see distant stars is kind of like wondering why you can see the light from your reading lamp even though your room is packed wall-to-wall with air."
] |
[
"Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.",
"Space is mostly empty."
] |
[
"Were there once trees everywhere?"
] |
[
false
] |
[deleted]
|
[
"It depends on the biome and local climate, but for instance, most of Central Europe was once covered by thick deciduous forests. Chopping down forests for timber, firewood, and for making room for farmland and pastures started in the antiquity, but major deforestation in Europe occurred in the early industrial age when massive amounts of ",
"charcoal",
" were produced to fuel factories, steel mills in particular. This was before fossil fuels became widely used, and indeed fossil fuels became a thing because forests in Central Europe were basically all used up. "
] |
[
"Thanks for the reply! Exactly what I wanted to know."
] |
[
"Conversely, in America, there are more trees now than there were 200 years ago. Much of the land used for farming back then is now forest again."
] |
[
"Why have we not come up with a better way of generating electricity?"
] |
[
false
] | null |
[
"We have developed other ways, but they are more expensive up front and therefore see little investment. For example thermoelectric generation gets power from a heat difference. You see it in lots of weird places (from satellites to the smoke stacks of 18 wheelers) but it's too expensive for generating enough power for the whole populous. ",
"Another part you seem to be missing is that the concept of a turbine from its most basic elements is the same, but the actual practice has been improved since the invention. This is why new technologies have so much trouble keeping up. For every advancement in new technologies, there is an advancement in turbines that makes them more efficient and raises the bar higher for the new techs."
] |
[
"Don't knock it if it works. They have a maximum efficiency of 50% according to the Carnot cycle. Solar cells have a maximum efficiency of ",
"http://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit",
"33.7%, the Shockley-Queisser limit. And to approach that limit you need very expensive components and precisely made solar panels. Spinning magnets are much easier to scale up.",
"Edit. Yes, you can beat the limit with extremely expensive components and special set ups, as detailed in the wikipedia article. Mostly with multiple layers and mirrors and lenses to concentrate light. This is relevant for things like spaceships, where any extra weight is incredibly expensive. For your average user though the limit is pretty hard."
] |
[
"This is inaccurate. Not wrong, just inaccurate in saying that solar cells have a maximum efficiency of 33.7%.",
"The Shockley–Queisser limit only applies to cells with a single p-n junction; cells with multiple layers can outperform this limit. In the extreme, with an infinite number of layers, the corresponding limit is 86% using concentrated sunlight.",
"It's also kind of silly to discuss the maximum efficiencies at this level when talking about a 'better' way to generate electricity, as the OP is. This is because the sun's rays are free and readily available and solar cells require close to zero maintenance. 'Better' doesn't necessarily mean 'more efficient', though efficiency would probably be a factor."
] |
[
"Is there a reason large Submarines tend to have relatively small propellers?"
] |
[
false
] |
[deleted]
|
[
"They're ",
"not small",
". As you can see, the diameter of the screw is almost identical to the diameter of the hull. That is relatively huge by comparison to non-submarine marine standards. ",
"See this photo",
" to see a cruise ship screw in comparison to the actual ship. As you can see, the relative size of the screw is tiny compared to a submarine. It might be hard to tell since the submarine screw picture does not give you a scale, but the modern nuclear submarine screw is actually bigger than that cruise ship screw. I cannot release actual dimensions (they're highly classified), but those pictures give you an idea.",
"The screw is designed to operate at lower RPM, while producing large amounts of thrust while minimizing noise. Another important factor is to maximize the RPM before cavitation occurs. The US (and other countries) have spent billions of dollars in developing their own highly classified designs to achieve these goals. That picture of a submarine screw I posted are very old, and the design has evolved much from that time. The recent revolution in computers has allowed us to perform complex Computation Fluid Dynamics and Finite Element Analyses of the screws to better optimize them. The result is a screw that varies it's pitch thickness and width as each blade fans out radially, thus allowing the maximum thrust to be achieved with the least amount of noise and cavitation.",
"More modern US submarines use ",
"propulsors",
". ",
"Here",
" is a picture of a shrouded US Submarine propulsor."
] |
[
"What do modern subs use as a propulsion mechanism if not propellers?"
] |
[
"On topic, I hope: in 2007, it was revealed that a Google Maps satellite took a picture of a US Navy submarine propeller (screw)-- otherwise a very highly classified object that hasn't been seen by the public for decades. The Navy knew they didn't have the legal authority to request takedown of the image, and also handily avoided the \"Streisand effect.\"",
"Source from Navy Times (behind paywall)",
"Article from stuff.co.nz",
"The image from Google, you can see it's almost the same diameter of the submarine",
"Close up of screw"
] |
[
"Why do we yawn?"
] |
[
false
] |
Having a discussion at work as to why we yawn. Is it a leftover evolutionary trait or is it a reaction to oxygen deprivation or neither? Thanks
|
[
"We still don't know. There are many theories, such as it being an evolutionary adaptation (possibly related to showing of teeth), but the most recent one is that we use yawns to ",
"cool our brains",
". The interesting thing about contagious yawning is that it seems to be confined to only humans, chimps and possibly dogs. People don't seem to find them contagious until they're about 4 years old. Recent studies show contagious yawning may be linked to one's capacity for empathy. One ",
"study",
" showed that autistic children were less susceptible to contagious yawning than non-autistic children, suggesting some social element that could be linked to empathy."
] |
[
"video answer:\n",
"http://youtu.be/jGIbUK4nw00"
] |
[
"Wow that's pretty fascinating. I was curious about how a yawn could be contagious but forgot to ask that in the op. "
] |
[
"How do those sealed ecospheres sustain life?"
] |
[
false
] |
I've occasionally seen in stores a small glass sphere, completely sealed, with little shrimp living in them. Supposedly they will live a few years in this environment, and I'm wondering how? I wouldn't expect there to be enough diversity in there to sustain life.
|
[
"Here's one of 'em.",
"Sunlight enters the sphere, causing algae to grow. The shrimp use the oxygen produced by the algae, and eat it as a sustainable food source. The shrimp in turn produce carbon dioxide and other nutrients required for the algae to grow. That's the jist of it."
] |
[
"I got one of these last year, and from my observations the branch / twig serves as a surface for algae grow on.",
"Mine is similar to the one linked above, but maybe bigger? I think this is ",
"the one",
".",
"It is amazing that the shrimp can survive that long."
] |
[
"Is the tree branch there to provide materials at it decays, or just for aesthetics?"
] |
[
"Do ribose or deoxyribose have any other uses besides forming the backbone of nucleic acids?"
] |
[
false
] | null |
[
"Ribose-5-phosphate is an important product/intermediate of the ",
"pentose phosphate pathway",
", which is very important for the production of NADPH, which is a reducing agent that helps to protect against oxidative stresses. R5P is also a precursor for synthesis of some amino acids such as ",
"tryptophan",
". ",
"Ribose is also a component of ",
"ATP",
" and ",
"cAMP",
", which are important for energy storage and cellular signalling, respectively. "
] |
[
"Came here to say all of this. \nAs for deoxyribose, I have never heard of it being involved in anything but DNA structure - I could be wrong.",
"This wouldn't fly in ELI5, but here's a link to the ",
"KEGG page for R5P",
".",
"KEGG is the go to resource for molecular metabolic information. Click around, it should have 'all' known pathways that ribose is involved in."
] |
[
"This isn't ELI5!"
] |
[
"What's the physics behind hourglasses?"
] |
[
false
] |
As an example, how can one calculate the amount and granularity of sand that is needed for an hourglass to last t time, given the hourglass' shape, size, and radius of the orifice? Also what does holding an hourglass at a certain inclination imply? Can "sand" in this case be considered a thick fluid, and would this fall under fluid mechanics? Thanks.
|
[
"Flow of granular solids is definitely ",
" the same as flow of fluids. In particular, flow rate of a liquid through an orifice would change as the pressure in the liquid changes (so the flow rate of a \"water-glass\" would drop as the water level in the top bulb dropped), while for granular materials the flow rate tends to remain relatively constant. ",
"This paper",
" discusses a mathematical model for the flow rate of granular materials through an orifice, including equations. "
] |
[
"Well, the truth is that they don't calculate this sort of thing. :) The design is based on past experience and the amount of sand is calculated (more or less) by trial and error. Obviously for mass produced hourglasses you just have to figure out a certain volume of particulate once.",
"Pretty sure the sand cannot be considered a fluid here... though even if it were I think it would be a non-Newtonian fluid, which makes things trickier. Even if you ",
" want to try and calculate things, it would mostly be based on empirical data. It is on a larger scale at least. Movement of granular materials is a complicated topic..."
] |
[
"Thank you for that paper. Granular mechanics looks like a fascinating topic."
] |
[
"When did humans start cutting their hair?"
] |
[
false
] |
Many animals groom themselves, but I don't think anyone of them actually cuts their hair. Did we start cutting our hair when civilization "happened", or did we already do it before? I imagine that it's relatively uncomfortable to hunt deers and stuff with long hair.
|
[
"This is a major problem in archeology as well. We literally have no knowledge of how peasants constructed their less impressive houses out of wood and grasses because those materials disappear."
] |
[
"This is a major problem in archeology as well. We literally have no knowledge of how peasants constructed their less impressive houses out of wood and grasses because those materials disappear."
] |
[
"Well, the ancient Egyptians used wigs... So I would imagine well before then? It's really hard to scientifically say when humans started cutting their hair, as the practice doesn't exactly leave obvious evidence. That said, I would imagine that the practice came naturally to tool using homosapiens after they figured out you could cut substance A with substance B."
] |
[
"Buffers in the human body"
] |
[
false
] | null |
[
"I'm a chemist, not a biologist, so there may be conditions I am unaware of in the human body that make things more complicated. That said, I think what you are looking for is the Henderson-Hasselbalch equation.",
"pH = pKa + log ([A",
" ]/[HA])",
"pKa is something you will usually have to look up on a table, depending on the buffer system you're looking at (and can get a little complicated with polyprotic acids and bases). ",
"Here",
" is a worksheet with several problems worked through and ",
"here",
" is a discussion of pKa.",
"Does this answer your question?"
] |
[
"yes! thanks so much. :)"
] |
[
"Well, the best way would be to measure it because this formula is only going to give you a ratio. But for example:",
"pH = 6.1 + log (HCO3-/H2CO). So at pH 7.4 -> 7.4 - 6.1 = log (HCO3-/H2CO3) -> 1.3 = log [HCO3/H2CO3] -> 10",
" 1.3 = [HCO3-/H2CO3] = 19.95/1. So for every ~20meq/L of HCO3-, there will be 1meq/L H2CO3. ",
"In a normal person at normal pH, HCO3- is around 26 (22-29meq/L), so H2CO3 is present at around 1.3meq/L (because 26:1.3 is 20:1). If the pH changes, that means the ratio changes. So if pH = 7.0 -> 7-6.1 = log [HCO3-/H2CO3] -> 10",
" 0.9 = 7.94 HCO3-/1 H2CO3. The ratio is now ~8:1, meaning that the person is acidotic. If the ratio shifts the other way (say 25:1) the person will be alkalotic. But the only way to know the exact values in a given person is direct measurement (because take a CO2 retainer patient, like emphysema: if their bicarb were 52meq/L and H2CO3 were 2.6meq/L, they'd still have a normal pH around 7.4)."
] |
[
"Will any sort of reading actually damage my eyes?"
] |
[
false
] | null |
[
"link"
] |
[
"Note: AskScience removes and downvotes jokes, memes, anecdotes, ",
", medical advice and other violations of our guidelines."
] |
[
"Note: AskScience removes and downvotes jokes, memes, anecdotes, ",
", medical advice and other violations of our guidelines."
] |
[
"What is the difference between a 2.8 dual-core processor from today and a 2.8 processor from a few years ago?How is todays processor better?"
] |
[
false
] |
It would be like comparing a 2.8 dual-core i5 and a 2.8 dual-core pentium D. I know the i5 has some better cache, but what actually makes it a better processor?
|
[
"Hey, a question in my field for once! (well, almost)",
"One thing that nobody has brought up yet is memory bandwidth. Memory bandwidth is the rate at which you can feed data to the processing areas of the processor. Bandwidth has traditionally scaled slower than clock speed, so it's become an increasingly important issue. Bigger caches are one solution to memory bandwidth, bigger data buses (think plumbing for data) are another. The more modern processor will probably have bigger caches and faster memory buses."
] |
[
"Within one line of CPU's you can still sort by clock speed, but if you want to compare one line to another there's just so many variables that you really need to look at benchmarking results."
] |
[
"I would like to point out that clock rate is only a good descriptor of performance when comparing CPUs from the same architecture. Even during the Pentium 4 days, clock rate was meaningless as AMD processors were far faster on an IPC basis and even different Pentium 4's had different performance per clock, with the 3.2GHz Prescott probably being the worst. Basically clock speed has always been a marketing gimmick with the Pentium 4 being the poster child for Intel's lust for clock."
] |
[
"Why is water a better indicator of life on other planets than the presence of volcanic activity or lightning storms?"
] |
[
false
] | null |
[
"Astrobiologist here. Volcanic activity and lightning are thought to have been important in the formation of life on Earth, but may not be important for life on other planets. Volcanic activity can effect global atmospheric chemistry in ways that could potentially be measurable with near-future observing technology, but looking for lightning on an exoplanet is like looking for signs of static shock on my finger from Jupiter -- it's a very very small signal placed at a huge distance. ",
"It is easier to find water in the atmospheres of planets in habitable zones with significant amounts of water, since water vapor can be found high in the atmosphere, where we are most likely to detect molecules with current observing techniques. Volcanic activity on Earth, for example, only leaves small traces in the atmosphere today. Astronomers at the University of Washington are currently trying to look for trace evidence of volcanic activity in Venus' atmosphere (though not for life-search purposes, in that case)."
] |
[
"Water is a necessary medium through which many biochem reactions proceed. It is 100% necessary for carbon based life forms.."
] |
[
"What we can do is look for non-equilibrium chemistry. For instance, if you were to study Earth's atmosphere from a distance (as we do with exoplanets) you would notice tons of O2 in the atmosphere. You can figure out how much sunlight strikes the Earth, and how quickly O2 molecules would be destroyed by sunlight. It turns out that the timescale for complete O2 destruction on Earth by UV radiation from the sun is less than a few million years, so if you saw an atmosphere like Earth's for a similarly sized planet at a similar distance from a similar star somewhere else in the Universe, you would know that there is some non-equilibrium process producing O2 on Earth. It could be a poorly understood chemical reaction, but really that's all that life is, it's a series of chemical reactions that use energy to manipulate their surroundings. This is your first sign of a \"biomarker\", a chemical signature that could indicate that metabolism is processing a foreign atmosphere.",
"This kind of study is independent of what the chemistry of that life is -- it works just as well if you're calculating the half life of sulfuric acid, methane, or other molecules in an exoplanet atmosphere, and that way carbon-based, DNA-centric life need not be anthropically invoked to find life. We can hypothetically detect any kind of metabolism if it effects the atmosphere of its planet enough."
] |
[
"Flying ant day (UK) - where do they all come from?"
] |
[
false
] |
Each year, the media goes nuts in the UK as the flying ants are invading! This happened where I am (leeds) yesterday and is when flying ants emerge enmass for a very limited time. I grew up in Australia and saw this happen there too, but you would generally see more ants about all of the time of a similar size. In the UK, you hardly see any for most of the year, and then they are tiny little things, not the huge ones we had flapping about yesterday. Is this a species that dwell underground, unnoticed for the rest of the year or are they general ants that sprout wings for this one specific event and we notice them more when they are trying to overthrow society?
|
[
"Most (if not all) ants have their colonies underground.",
"\"Flying ant day\" is when queen ants grow their wings and emerge from their home colonies. They then mate a bunch and go somewhere else to start a new colony. This is all timed very specifically so \"flying ant day\" is more or less a regular yearly occurrence."
] |
[
"To be clear, they're virgin queens, or \"queens in the making\". So the \"one-queen-per-colony\" rule doesn't apply to them."
] |
[
"But, so many Queens? Can one colony have many? "
] |
[
"Can an occluded artery affect its parent-artery?"
] |
[
false
] |
[deleted]
|
[
"Yes. Bleeding into a body cavity adjacent to a major artery can create enough pressure to press down on the artery and close it off. This usually occurs in the limbs and is known as compartment syndrome. That said, in compartment syndrome, small blood vessels are affected before the big ones - it's really the pressure on small capillaries that does most of the damage."
] |
[
"Yes. Bleeding into a body cavity adjacent to a major artery can create enough pressure to press down on the artery and close it off. This usually occurs in the limbs and is known as compartment syndrome. That said, in compartment syndrome, small blood vessels are affected before the big ones - it's really the pressure on small capillaries that does most of the damage."
] |
[
"It wouldn't likely have a large impact on the more proximal arterial system. If you occlude a major artery (ie. cross clamping in a vascular surgery) like the aorta you'll definitely have major short term effects. Since your heart is still pumping out the same amount of blood into a system which has decreased in size due to the occlusion then your blood pressure will have to increase as a result. Sometimes this rise in blood pressure rises to a dangerous level which may lead to damage like stroke, arterial dissection, or damage to your other organs. But your heart and the rest of your unaffected arteries and veins have feedback mechanisms to return back to a normal blood pressure, thus your heart will start pumping out less blood and your other vessels will dilate to accommodate more blood to lessen your blood pressure. Most thrombus or emboli are not big enough to fully occlude these major arteries though, so major occlusions like this they just get stuck in the vascular bed of an organ and cause them ischemia if not enough collateral blood flow exists, but have little to no effect on the rest of your vascular system. A pulmonary embolism is the best example of a relatively small occlusion that can have devastating effect on your cardiovascular system. A reasonably sized clot can occlude the place where your pulmonary artery splits into each lung. Since your entire circulation passes from your venous system through your lungs, a clot here could cut off the flow of blood for your heart to pump out and also cause the right side of your heart to fail since it's pumping against a brick wall."
] |
[
"Science and Philosophy of Science"
] |
[
false
] |
The philosophy of science is a subject I have heard a little about, and have only the most passing acquaintance with; I'm terribly underinformed on the subject, and would probably embarass myself if I tried to discuss it seriously, but I was wondering: for scientists, how important a subject is the philosophy of science? Are the questions it raises crucial to the pursuit of science itself--that is, do scientists have a lot of interaction with the subject--or is it more tangential, more of a side commentary on all things sciencey by people interested in the intersection of science and philosophy? I guess I'm asking because I am slightly skeptical of philosophy in general (I don't think it's all balderdash, but a good deal of it fails to impress or even interest me, which probably says more about me that it does philosophy), and I'm wondering if the insights offered by the study of the philosophy of science are of pratical use to scientists. And for those who are more knowledgeable on the subject than I am, would you say that the tradition of philosophy of science is more closely allied to "pure" philosophy, or "pure" science?
|
[
"I'd say it's very important in that understanding the philosophy of science is necessary in order to honestly carry out the scientific process.",
"We follow the basic methods of science because they have been shown to work. Make an observation, develop a hypothesis, and design an experiment to test that hypothesis. Designing and carrying out an experiment to test this hypothesis is what makes science so difficult--but doing so correctly is what furthers human knowledge. If you can rule out all confounding factors and place good probability on the validity of your hypothesis, then you've helped mankind.",
"\"Scientists\" that don't follow the philosophy of science very often produce results that are just false, but sometimes subtly so. Confirmation bias, personal testimony, inadequate controls...the list of potential confounding factors is enormous in science, and one has to realize ",
" we make such strict controls in order to know which ones to implement.",
"The philosophy of science is, in my opinion rather simple: it's to discover the truth, and only the truth. To find a cause an effect, you essentially have to eliminate every potential alternative cause and isolate the \"true\" one. The scientific method is, thus far, the best way to do so."
] |
[
"I'd say most scientists don't care about it in their day-to-day work.",
"or is it more tangential, more of a side commentary on all things sciencey by people interested in the intersection of science and philosophy?",
"That one. Science is so incremental that any single person or group will have a certain system that they perturb, and then humanity will have some updated information about that system. How this fits into the big picture of science is important, but doesn't affect how they do their jobs. Rarely do people push the boundaries of knowledge like Einstein did."
] |
[
"I was thinking of philosophy of science in terms, not just of the basic elements of the scientific method (which are definitely part of it), but more sophisticated concepts like what you might see on the ",
"relevant Wikipedia page",
" or over in [",
"r/philosophyofscience",
"](reddit.com",
"/r/philosophyofscience",
")--scientific realism, the problem of induction, theory-dependence of observation, etc.",
"I have to confess, my instinct (which is in this case strongly informed by my own bias, and a worldview that tends to divide everything into \"verifiable fact\" and \"personal opinion\") is that most philosophy of science, beyond basic experimental rigor like what you describe, is the idle speculation of armchair observers of science--like that SMBC comic about the difference between a science enthusiast (who can recite pi to dozens of decimal places) and an actual scientists (who knows it to one if he's lucky--since he knows he can just go look it up if he needs to).",
"For instance, ",
"in this discussion",
" someone posted the following in reply to a comment of mine:",
"When natural philosophers ... first tried to create a sufficiently useful temperature scale, one of the first things they did was try to combine different systems of measurement; this required the ontological assumption that some measurable property existed 'out there' regardless of how you measure it. Remember, since they were inventing the linear thermometer, they had NO empirical ... reason to believe this, but their efforts proved fruitful.",
"But I'm wondering how relevant the thorny philosophical issues behind such assumptions are to the actual business of science. Does a scientist seeking to measure temperature for the first time actually wonder \"Gee, assuming I can come up with a useful temperature scale requires certain ontological assumptions,\" or do they just fiddle around until they invent the thermometer? While considering the ontological assumptions that underlie the invention of a useful temperature scale is actually pretty fascinating, it doesn't strike me as ",
" for trying to figure out the world around us. I don't meant to imply philosophy is bunk--things can be much more interesting than they are practically useful--but I suspect a good deal of the philosophical interrogation of science isn't actually terribly useful when it comes to the ",
" of science (i.e., blowing stuff up or looking at it through telescopes). However, as I said, I'm not very well versed in the subject, and I'm curious about what people who actually know what they're talking about have to say on the subject."
] |
[
"I work in facility that has consistent, and high static discharge. Management is at a loss and employees are/have gotten hurt. How can we prevent static discharge and protect ourselves?"
] |
[
false
] | null |
[
"Workplace safety is far outside the purview of this subreddit. This is something that requires an expert who can personally evaluate the situation. "
] |
[
"In regards to preventing safety incidents sure, but if they won't protect us, how can we stop it from happening. Wire strap etc. I would give more examples but that is kinda why I asked. "
] |
[
"I get what you're saying, but there's no way we're qualified to offer safety advice. This is an OSHA issue. "
] |
[
"how do photons of different amplitudes all do the speed of light?"
] |
[
false
] |
[deleted]
|
[
"Photons don't have amplitudes in that sense, really. The ",
" of ",
" is a function of photon flux; in other words, ",
" passing through a given surface in a given time means brighter light, and fewer photons means dimmer light.",
"It's only sort of meaningful to talk about the \"wavelength\" of a photon. Photons have exactly two properties: energy and spin orientation. When you get a bunch of photons together of the same energy, the phenomenon that results looks like a self-propagating electromagnetic wave with a wavelength proportional to the energy of each photon. But that's a property of ",
" — that is, tons and tons of photons all considered together — and not individual photons by themselves.",
"A statement that we ",
" make about a photon using the language of waves is about the ",
" that a photon will be found in a particular place. This probability can be described, mathematically, using a wave function, and the wavelength of that wave function depends on the energy of the photon. But we can't really emphasize strongly enough here that the wave function is a ",
" not something that actually exists. When we talk about the probability of finding a particle interacting at a certain point in space, we're do so using the language of waves, but that's a description of the ",
" and not anything physical.",
"Essentially? Photons don't really ",
" as ",
" They are field quanta, which means they play by the rules governing field quanta. They aren't waves, and they aren't little cannonballs.",
"Oh, and as for detecting polarization, you stick a polarizer in front of the light and a detector behind it. If the detector pings, a photon got through the polarizer. If not, not."
] |
[
"But people said earlier that light is brighter when it has a higher amplitude.",
"Intensity is a function of photon flux. ",
" photons, in other words.",
"Even if they don't exist as things, which I agree with, they still have amplitudes.",
"Not in the sense you asked about, no. A photon has no property which relates in any way to brightness.",
"Let me put it in terms of an analogy. How crowded are you? I'm asking how crowded you are, just as a person. Meaningless question, right? \"Crowdedness\" isn't something attributable to ",
" It's a concept that applies only to ",
" and is a function of how-many, how-dense and how-quickly.",
"Well how do you know what polarization the polarizer is giving - linear, circular, or elliptical?",
"This is a subtle point, but an important one: A polarizer does not ",
" despite the name. Rather, it's a ",
" that permits the passage of photons of a certain type.",
"So you use the kind of polarizer, and in the appropriate spatial orientation, to permit the passage of the kind of light you want to detect."
] |
[
"This is a subtle point, but an important one: A polarizer does not polarize, despite the name. Rather, it's a filter that permits the passage of photons of a certain type.",
"I also think that this is misstated or incorrect. A polarizer does change the polarization state of any light that is filtered through. ",
"This can be shown both by classical wave mechanics and quantum mechanics - one gets the exact same answer either way.",
"The experiment to show this is as follows:",
"Filter a beam of light with a vertical filter, and then with a horizontal filter, and all of the light will be blocked.",
"Then put a 45 degree filter between the vertical and horizontal filters, and about 12% of the light will get through the three filter combination. ",
"It is a lot of fun to see people freak out when they do this in an intro. physics lab."
] |
[
"Looking for a Feynman Poster"
] |
[
false
] |
Anyone know where I can find a good one? Google, amazon, ebay etc. don't seem to be very helpful so far. is sweet, but the only place that has it in stock has it for like 8 hundo. Thanks guys!
|
[
"You could try making your poster at home with the ",
"Rasterbator",
". No hi-res image required."
] |
[
"A redditor (mamerong) put ",
"this",
" together based on a submission last month and provided the high-res images."
] |
[
"Glad you like it! I just realized that the \"NO\" looks like \"ON.\" I'll fix that, and post it here in a bit."
] |
[
"Do plants get climate shock when being moved to the other hemisphere?"
] |
[
false
] |
Like say a full grown tree from the north hemisphere is moved to the south hemisphere during January.
|
[
"Plants in general have a ton of different receptor pathways to regulate their response due to environmental changes. However stuff like you are describing can put these cycles out of phase. Plants are for example known to show Jetlag. After a few days however, the regulatory enzymes are updated through stuff such as duration/intensity of sunlight, etc. And start to put the cycles responsible for the plants response back into phase. So for your described problem, the plant would for a few days be jetlagged just like us humans would, which would most likely make them more susceptible to the current conditions, but after some time they would be able to adjust."
] |
[
"Biocontamination. ",
"That tree has has developed over hundreds of millions of years for its site specific region. It would most likely not do well unless you could find a duplicate similar habitation with exacting environmental controls. ",
"Many trees cant make a transplant from a higher elevation even within your own region. ",
"The real problem is the millions of bugs catching a ride on that tree. ..they could wreck the local system"
] |
[
"Most plants do in fact experience some form of climate shock. Even as much as moving a plant outdoors in the spring after keeping it indoors is not good for them, and it is recommended to slowly acclimatise them to a colder climate. This is in part because most plants have certain molecules that help them function effectively in colder temperatures, which they need to generate before they may survive there."
] |
[
"How did nasa know the voyagers left the solar system?"
] |
[
false
] |
[deleted]
|
[
"\"The solar system\" here means ",
"heliopause",
", the point where the solar wind of charged particles from the sun tapers off between 75 and 90 times the distance between Earth and the sun. Both Voyagers have tools to measure the solar wind, powered by good old bomb manufacture waste product plutonium-238 and still communicating with Earth even after all this time.",
"You could make a case that the solar system includes the truly vast and very widely spaced comets in the Oort cloud, which Voyager 1 will not enter ",
"for 300 years",
" and will not exit the outer edge of the cloud for 30,000 years."
] |
[
"!remindme 30000 years"
] |
[
"I was legit confused by this point when NASA first announced that V1 had left the Solar System. I even tweeted in during their press conference announcing the achievement, and my question about the Solar System extending to the Oort Cloud was asked to Ed Stone. He seemed annoyed."
] |
[
"How can the Universe be infinite if it expanded from a point?"
] |
[
false
] | null |
[
"At what level of math do you want? In addition to what I linked, there are also two other relevant links in that FAQ which explain that the universe does not expand \"into\" anything, and some other relevant info on expansion which are germane. The fully mathematical description is that the universe is described in relativity by an object called the ",
"FLRW metric",
", which determines how lengths are measured between two points and how that length changes with time. The Big Bang singularity corresponds to taking a certain limit of this metric where at some finite time in the past, all distances became infinitely close. This description does not single out a certain \"point,\" it applies to the whole universe whether it is infinite or not."
] |
[
"Please read the ",
"/r/AskScience",
" FAQ before posting. There is a ",
"whole section on the big bang",
" which explains that it was not a point, and how the universe can be infinite. "
] |
[
"It doesnt have my specific question"
] |
[
"Will sunscreen block UV light if sprayed on glass?"
] |
[
false
] |
Well its more of; Does sunscreen need a flabby moist tissue (skin) to soak into to provide the UV protection, or could you just spray it on glass with the same effect? If someone has a UV light meter to test it out, i would love to see the results. Before posting, it just occurred to me that glass inherently scatters light rays because of (im guessing) the impurities?. So would you even get sunburn behind uncoated glass?
|
[
"Glass is a very effective barrier for UV light. For example, from my experience as a chemist, when I have studied the UV spectrum of a molecule (i.e. what wavelengths of UV-light that are absorbed by a molecule) then I need to put a solution of the molecule in a QUARTZ (not glass) container the UV light cannot get through glass."
] |
[
"Yes. It blocks UV light because of the titanium oxide pigments in it. The particles are smaller than the wavelength of visible light so it lets visible light through (if you get the clear kind), but it still reflects UV. It doesn't have any special reaction with your skin.",
"Glass also blocks UV light. From what I can find, you can still get sunburned because it lets UVA through, but in general, so does sunscreen."
] |
[
"Some qualifications - soda lime glass blocks UVB but allows some UVA through. Quartz glass ('fused silica') allows a significantly larger amount of UVB through. Flint glass, borosilicate, and other types may allow differing amounts. ",
"Normal window glass is soda lime glass. However, a particularly old window may have been made of something else - and a newer window may be made of plastic - probably polycarbonate or poly(methyl methacrylate), each of which have different transmission spectrums."
] |
[
"Why fever is the most common symptom in infectious diseases?"
] |
[
false
] | null |
[
"Because a first line defense for the human body is to raise its own temperature. Many diseases can not survive in a body that has a temperature above average. (This is part of the reason that dogs do not suffer from some human illnesses)",
"",
"Edit: OMG That was my first award ever and it made me feel special. Thank you!"
] |
[
"Because most diseases can survive a lower temperature, often by going into a hibernation of sorts. It's actually one of the reasons we're afraid of arctic thawing. Some people a long time ago died from diseases that don't exist anymore and if their bodies thaw, the diseases may still be infectious. ",
"But even our own bodies can't survive if our temperatures rise just a few degrees. Get a temperature above 105F and your brain starts boiling (not literally) in its own juices. That said, there is far more of your own cells than of any disease. Raising your internal temperature and killing yourself a little bit is a small price to pay to kill a whole lot of the other stuff."
] |
[
"Many biological proteins are sensitive to temperature. A small change in temperature can cause proteins to denature (change shape) and lose their functionality.",
"Human proteins are stable in this temperature range. But bacterial and viral proteins may not be. By raising the body temperature these invasive proteins can be disabled.",
"The same denaturing process is also used in food preparation through cooking and this also reduces the chances of bad bacteria surviving the process.",
"Denaturing on Wikipedia:",
"https://en.wikipedia.org/wiki/Denaturation_(biochemistry)"
] |
[
"Elementary Students' Responses to Your Answers!"
] |
[
false
] |
First of all, I want to apologize for the delay. Graduation, moving out, moving back in, and getting settled took a bit more time than I thought it would, and this is the first chance I've had to sit down and relax. I would like to thank the AskScience community for the fantastic contributions you have made. This experiment has been a huge success. The children were stoked at the opportunity to speak to real scientists. They could barely hold still as I was passing out their responses, and were silent for a good five minutes (a complete rarity!) as they read through them. Then, the class erupted in "What did you get? What did you ask? Who answered yours? Woah!" and so on. Most students were very eager to write back, with some addressing comments directly to specific users, and other addressing comments to the entire comment tree. However short their responses may be, I can promise you every single student was thrilled with this experience. They were asking questions they really wanted to know the answer to. A huge thank you goes out to who Skyped in to the class from Scotland (to NYC!) The students were thrilled to not only talk face to face with a scientist, but one from another country! Overall, this experience was amazing, and I have all of you to thank. My only regret is I will not be able to repeat this exercise for another two years; this was only my student teaching. Now I'm off for a year to volunteer in the Marshall Islands (no luck with the internet there!) and then a year to complete my graduate studies. When I finally settle in to my own classroom, I would like to repeat and expand upon this entire process, if that's all right with the community. Some ideas I have tossed around: Students submit questions on a weekly basis, and the top questions get submitted to AskScience Student-generated questions leading to inquiry based experiments and research and lessons Having a monthly Skype session with scientists from different fields I cannot thank all of you enough for this being such a huge success. Without all of your support, expertise, and generosity with your time, this could not have happened. I hope this is a sign of the direction Education is turning. On Monday, I will email their teacher with any responses you have for them, so she can print them out and give them to the children. Unfortunately, that will be the last correspondence between you all and them. Again, I cannot thank you enough. This has been an amazing experience for everyone involved, and it is one I plan to repeat!
|
[
"No, Ms_Christine, thank ",
" ",
"For being daring enough to try this experiment. ",
"For being kind enough to return with the responses. ",
"For giving us this opportunity.",
"This is the coolest thing that's happened in this subreddit, and I ",
" hope other teachers step forward and give it a shot.",
"Good luck in the Marshall Islands! "
] |
[
"You know what? You're totally correct. I apologize for that, and particularly for my tone and choice of words. It was a good question, and don't stop asking them!",
"Side note: I woke up this morning to my girlfriend saying \"You got burned by a sixth grader.\" I can honestly say that that's never happened to me, and that I totally deserved it. "
] |
[
"In response to, ",
"\"What is the extent of the known universe? Do you support the theory that our universe is part of a multiverse?\"",
"Dear ",
"A_Dog_Named_Bob",
",",
"I respect your accusation that most of the kids would be \"parroting\" from the TV or internet, but you are mistaken with us. We have studied some of this science for a while. I have been interested in the universe since 4th grade. Of course, I don't know as much as a scientist who is an expert in this subject, but you take us WAY too lightly. It is true that initially my question was not about Quantum Physics, but that does not mean us 6th graders know nothing about it. We are smart.",
"Dear ",
"halberdier85",
",",
"Thank you for your response! You helped me understand this topic much better. I did not know most of the stuff you responded about the universe. I appreciate your help and I am grateful to you for answering.",
"-M.M"
] |
[
"Why is it when you have a high fever from the flu, you don't sweat, but as soon as the fever breaks, you start sweating a lot?"
] |
[
false
] | null |
[
"Think of the hypothalamus as a thermostat and think of a fever as \"air conditioning\" and shivering as \"heating\".",
"When the body detects a pyrogen (bits and pieces of various microorganisms that trigger a fever) the \"thermostat\" in your brain resets itself to a higher temp (lets say 101F instead of the normal 98.6F). The body now thinks that you're cooler than you should be so it turns on the heat (you begin to shiver). After you shiver, and you get under a ton of layers of clothing or blankets, you eventually reach the 101F. Microorganisms tend to have very specific temperature requirements to survive and \"the body knows this\". After hanging out at 101F a little while, the microorganisms die and there are less and less pyrogens around to keep the setpoint of 101F in the hypothalamus. The hypothalamus now \"resets to 98.6\" and your body does what it needs to do to cool down -> turns on the air conditioning (you start to sweat, shed all the layers that you previously sought, etc.)",
"The point being, you only sweat when there is a need to cool down and you only shiver when there's a need to warm up. This need is determined by what your temperature is relative to what your temperature \"is set at in the hypothalamus\"."
] |
[
"The flu isn't what gives us the fever, it's your own body that raises it's temperature in order to fight the flu better. Sweating is our primary controllable cooling system, so by stopping this mechanism, your body will quickly heat up.",
"Once the fever breaks (flu defeated), your body wants to go back down to a normal body temperature as fast as possible, so the sweating/cooling mechanism is set to 100%."
] |
[
"Hypothalamus."
] |
[
"Does HVAC “Heat Dumping” have any effect on global warming?"
] |
[
false
] | null |
[
"Hi strong_grey_hero 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.",
" ",
" "
] |
[
"Planetary Sci"
] |
[
"Planetary Sci."
] |
[
"Why do some people shudder when touching some textures?"
] |
[
false
] |
For example when touching sandpaper or a pumice stone.
|
[
"People may have an anecdotal response to the topic - so the replies technically should be downvoted and removed from this subreddit as you say. This would comply with the rules of ",
"r/askscience",
". ",
"However the original question is not focused on the content of the personal experiences but on the cause of those bodily reactions. I hope this means the post is safe. Indeed a Mod has already provided some guidance on this very point - ",
". "
] |
[
"People may have an anecdotal response to the topic - so the replies technically should be downvoted and removed from this subreddit as you say. This would comply with the rules of ",
"r/askscience",
". ",
"However the original question is not focused on the content of the personal experiences but on the cause of those bodily reactions. I hope this means the post is safe. Indeed a Mod has already provided some guidance on this very point - ",
". "
] |
[
"I have a similar \"problem\" with writing with pencils; shivers run up and down my body whenever I do. It's the weirdest thing considering I don't do this when I write with a mechanical one or a pen."
] |
[
"If we were to position a satellite at 1 lightyear from Earth and had it take picture of the planet, would what we see date from a year ago?"
] |
[
false
] |
That is assuming that we have optic that can see that far of course. In the same vein, would an advanced civilization possessing such optic see Earth and the human race as it was X years ago, X being their distance in light year from Earth?
|
[
"Theoretically, if you could travel faster than light, you had a perfectly flat and reflective mirror, and a powerful enough telescope, you could witness just about any event from the past that took place under an open sky."
] |
[
"Yes. Earth would be earth of last year if you were on the satelite.",
"This is not unexpected or some weird aspect of relativity, this is just regular it takes time for light to travel (just like it takes time for sound to travel). E.g., if someone a \"sound-minute\" (approx 20km ~ 60s*340m/s) away from you made a variety of loud noises, you would hear the noises a delay of 1 minute."
] |
[
"If you were in the sattelite, yes. Receiving the signal from the satellite in Earth would take a year, so people on Earth looking at the satellite images would actually be seeing Earth from two years ago.",
"And to the second question, the answer is yes."
] |
[
"Light and atoms"
] |
[
false
] |
Imagine you had a piece of iron (or any other solid), that was just one atom thick. Would light be able to pass through this?
|
[
"Mostly. It can absorb and scatter some light, but if it's only a single atom thick, there's a pretty large probability the light will simply pass through it. Already gold leaf, the thinnest metal you'll easily produce, is fairly transparent, and it's on the order of thousands of atoms thick. (0.1 micrometers)",
"A layer that thin also won't have the same absorption properties as the bulk material. Once you get down to the nano-scale, the size of the material has a large effect on how it absorbs. (",
"image",
" of the diameter dependence of the color in gold nanoparticles)"
] |
[
"Er, most of an atom is surrounded by a space full of electrons. Although being quantum objects, electrons don't have any particular location. So atoms are surrounded by what's more like a 'cloud' of electron density, the density being where they're more or less likely to be located. "
] |
[
"Er, most of an atom is surrounded by a space full of electrons. Although being quantum objects, electrons don't have any particular location. So atoms are surrounded by what's more like a 'cloud' of electron density, the density being where they're more or less likely to be located. "
] |
[
"Why is the amp a fundamental SI unit instead of the coulomb?"
] |
[
false
] |
It seems to me that charge is a more fundamental quantity than current. Why is it done this way?
|
[
"An ampere is simply a coulomb per second, it doesn't functionally matter whether you use a coulomb or an ampere as your base unit. ",
"However, an ampere is much easier to measure. The SI ampere is currently defined through the force between two wires."
] |
[
"It's easier to measure an ampere than a coulomb, and the point of SI units is that they're easily reconstructed."
] |
[
"Coulomb is derived from ampere and is considered a derived unit while amp is a fundamental SI unit. ",
"Similar case with meters and m/s. Meter is the fundamental unit while m/s is a derived unit."
] |
[
"Please help debunk this zero point energy sorcery on TEDx (Rodin Coil Vortex Based Math)"
] |
[
false
] |
Here is the TEDx talk in question. This video is claiming that with some strange math we can be on the verge of zero point energy. Does this mad scientist have something going on here, or is this way to out there to be plausible?
|
[
"Just a note, for debunking stuff ",
"r/skeptic",
" can be good."
] |
[
"thanks"
] |
[
"Why not search for 'vortex math' here and you'll find a good number of funny threads, not least ",
"this one in the math subreddit",
". It's just another crackpot; stereotypically so, even. And TEDx apparently ",
"removed the video",
" after belatedly realizing how nutty it was. "
] |
[
"Do individuals with \"light\" eye color (Blue or Green) have an increased sensitivity to sunlight?"
] |
[
false
] | null |
[
"That is the reasoning behind the smudges, but it has been proven to be ineffective "
] |
[
"Logically they would, the iris works as a sphincter, closing to block light in bright conditions, the pigment it contains provides this barrier. \nHence light-sensitivity is a problem associated with albinism because albinos lack pigment in their irises. There's are at high risk from being blinded from sun exposure. Whether the difference between blue and brown eyes is really practically significant - someone with access to science journals with actual studies and statistics can wade in there. "
] |
[
"Absolutely, and for the same reason that you see athletes with black smudges under their eyes. Dark colors absorb light and light colors \"reflect\" it."
] |
[
"Why do antidepressants cause weight gain?"
] |
[
false
] | null |
[
"The main question is fine, but we do not allow the posting of personal medical info. Please delete the text of your post."
] |
[
"I’ve removed the personal medicine info.",
"or did you mean the entire body?"
] |
[
"The text of the post still has an implication of asking for some sort of advice (e.g. \"should I stop doing X\") -- I forgot to mention that in my last comment, but we also do not allow requests for advice, especially medical advice (please see the posting guidelines). If you have a concern about a medication you are taking, you should speak with a physician. ",
"Because the post is a little old at this point, I recommend making a new one with just the title and no personal information whatsoever in the text."
] |
[
"Why is a swab required to be inserted deep into your nasal cavity to determine a positive or negative covid case, yet it can be spread merely by speaking too close to somebody?"
] |
[
false
] | null |
[
"I've been explaining it as that you might be able to see birds in your garden, but the best way to know if birds are nesting is to look in the nests. Coronavirus infects the tissues at the back of the throat, so swabbing there is the best place."
] |
[
"I've been explaining it as that you might be able to see birds in your garden, but the best way to know if birds are nesting is to look in the nests. Coronavirus infects the tissues at the back of the throat, so swabbing there is the best place."
] |
[
"By speaking, a smaller amount of viral droplets is expelled. This might not be enough to produce an accurate result. The concentration may be too low for the disease to be detected, however it might not be too low to infect a person - remember than not that many particles are needed to start an infection.",
"Using a swab, on the other hand, basically guarantees a pristine and trustworthy sample, and it is therefore much more reliable, if a bit uncomfortable.",
"Edit: sorry, there were some grammar mistakes"
] |
[
"If I have a block of aluminium with a hole in it and i warm it up. Does the hole get smaller or larger?"
] |
[
false
] | null |
[
", regardless of whether they consist of metal or the lack of metal. Any holes or other features will expand at the same percentage as the entire block, estimated by multiplying the thermal expansion coefficient of aluminum (around 0.00002 per °C) by the temperature increase.",
", depending on the specific conditions. Finite element analysis may be needed to predict how the size and shape changes for a certain feature.",
"Any answers that state unequivocally that the hole will grow are interpreting your question to mean the former case."
] |
[
"Hole gets larger, since the whole chunk expands linearly, like when you zoom a photo everything gets larger",
"This is a somewhat common technique for fitting bearings on shafts, you heat up the bearing so the hole gets bigger and then you can fit it on the shaft and let it cool down"
] |
[
"Nah. Liquid nitrogen is often used. This might be when the heat would do too much damage to the encasing part or when it is simply too large to heat up efficiently."
] |
[
"Do the electrons of an atom interact between each other?"
] |
[
false
] |
[deleted]
|
[
"Yes. Atoms hold electrons as different energy levels, and there are a limited number of electrons that can occupy various levels. Generally the low energy levels fill up first, so the mere presence of some electrons in an atom forces other electrons to occupy higher energy levels.",
"I'm sure someone else can give a more complete answer."
] |
[
"They do interact and this fact is what makes solving multi-electron quantum mechanics problems difficult. The potential energy term in Schrodinger's Equation can be split into an externally applied potential and an interaction potential. In an atom, the nucleus is often assumed to be constant and more or less classical for calculating electron properties so the external potential is typically the nuclear charge. This is simple and can be specified from the begining.",
"The interaction potential is the effect of electron 1 on electron 2. But you can't know the effect from electron 1 until you solve for its wavefunction, which will include an effect from electron 2. It is a sort of catch 22 situation where you can't solve for the wave function until you know what it is.",
"The interaction potential makes Schrodinger's Equation nonlinear and untractable analytically for more than one electron. Instead it is solved using a numerical method like ",
"density functional theory",
" or ",
"Hartree-Fock",
". Basically, you make a guess at the electron wave function, put it into the interaction potential term in Schrodinger's equation, solve for the wavefunction, compare it to your guess, make a correction, and repeat until it hopefully converges."
] |
[
"In addition, the inner electrons partially screen the outer electrons from experiencing the attraction of the nucleus. This has profound effects and explains a lot of the trends we see in the period table of the elements."
] |
[
"Would the Monty Hall problem/paradox be affected by an outsider?"
] |
[
false
] |
So today in my Econ course we were discussing the Monty hall problem and some one asked the question of whether bringing in a second person would affect the probability. So the set up would be that you have some one pick the door and then have Monty open his door. You then bring in a outsider and tell them the current door and that they can choose to switch if they want. Would this second persons probability be 50/50 or would it remain the same as the classic problem.
|
[
"The answer remains the same: you should switch, and switching gives a 2/3 chance of winning.",
"What do we mean when we ask what the chance of winning is anyway? In particular, what does it mean for the contestant to have a 2/3 chance of winning if he switches? We mean that if the contestant were to play this game many times (so each time the doors are closed and the prize locations are randomized again), then if the contestant takes the strategy of always switching doors, then he will win 2/3 of the games on average.",
"So now modify the game in the following manner (just to make your formalism more precise). Set up the game as usual. Then Monty Hall rolls a three-sided die (or a 4-sided die with a \"roll again\" side for those paying careful attention), which effectively picks a door for the contestant. Then Monty opens a door subject to the usual rules. Then he brings in the contestant who has been in another room the whole time. The contestant comes in to see 1 of 3 doors open and is asked whether he wants the door that Monty rolled or the one he didn't. Which door should the contestant choose? He should choose the door that was not rolled. In fact, the optimality of switching doors is independent of whether the contestant knows the rules, i.e., the host's behavior in choosing which door to open. Of course, if the contestant doesn't know any better, he will not ",
" that he should switch. So the contestant will think he should choose 50-50, but it is still true that he has a 2/3 chance of winning if he switches.",
"We can modify the problem further by modifying the host's behavior. What if Monty offers a switch only if the contestant picks a losing door? So Monty rolls a three-sided die. If it is a winning door, he rolls again. If it is a losing door, he brings in the contestant from the other room, and offers a switch. The contestant may think to choose 50-50 if he has no information on the host's behavior, but it is still true that the contestant will always win if he switches.",
"So the chance of winning on a switch, which is determined by the overall chance of winning after playing the game many times, is not dependent on the contestant's knowledge of how the game has been set up. The only factor is the host's behavior. If the host's behavior does not change from the classical set up, then the chance of winning on a switch is always 2/3. An entirely ",
" question is what the optimal strategy of the contestant is, given his knowledge. This is a so-called ",
". Clearly, if the contestant has no knowledge about how the host behaves, then his optimal strategy is to choose to switch 50-50. (Obviously, if he plays the game many times, he will likely deduce that there is actually a 2/3 chance of winning on switch, and so he can update his strategy after each play.)"
] |
[
"Ah. I thought you meant Monty picks randomly which door to reveal"
] |
[
"Thank you very informative."
] |
[
"Is there any reason why every element isn't radioactive?"
] |
[
false
] |
I was reading about bismuth, which you all likely know was discovered to be radioactive but with a half-life so ridiculously long that we only recently noticed the decay. This got me to thinking about the possible radioactivity of other elements. Is there anything preventing or any theoretical reason why every other element isn't similarly radioactive, i.e. with a huge half-life? Are we absolutely certain that, say, iron isn't radioactive with a 10 year half-life? How do we know?
|
[
"For radioactive decay there needs to be a energetically favourable decay channel, that minimizes the energy of the nucleus. I'll refer you to the liquid drop model of the nucleus. So while C14 will decay to N14, C12 is stable. However even though the models of nuclear physics are pretty nice, better models could arise where elements formerly considered stable would be radioactive. Also in some extensions of the standard model of particle physics even the simplest element, hydrogen, may decay with a half life of 10",
" years. "
] |
[
"Basically:",
"The strong force(strong interaction) is 100 times as powerful as the repelling effect created by the electromagnetic force, but the electromagnetic force has a larger 'range'. So, two protons next to each other are attracted to each other by a force 100 times stronger than the force that is pushing away.",
"The strong force doesn't really affect protons that are more than 1 unit away. If you imagine P1-P2-P3-P4-P5 to be protons, the Strong force only works on the adjacent proton so P1 affects P2, but not P5, whereas the repellent force of electromagnetic energy (due to each being a positive charge) means P1 is pushing away P 2-5.",
"Imagine the scene from Cliffhanger, where Stallone is trying to hold on to the girl to stop her from falling. If his grip was the strong force and gravity was the electromagnetic force, there is no chance that she would ever fall, his attraction would prevent it. But if you add more and more people, the chance that ONE of them will lose their grip increases until it becomes inevitable.",
"Edit:",
"I suppose it is possible. But the timeline on which this would become apparent is likely too large to actually observe."
] |
[
"Magic numbers. They come about from solving out the quantum equations. Certain numbers of protons /neutrons are more stable than others. So two is a magic number. A helium nuclei consists of two neutrons and two protons. It is very stable. For the island of stability, it is thought to fall on a proton magic number. It should be noted that the island of stability is not stable. It is just more stable than the surrounding isotopes. "
] |
[
"When you light a propane torch, why does the fire not also ignite the gas inside the canister?"
] |
[
false
] |
[deleted]
|
[
"Propane requires oxygen to burn. It only gets enough when it exits the nozzle into the atmosphere. The velocity and pressure of the gas coming out blocks any significant amount of oxygen from getting into the canister."
] |
[
"As a teenager I learned this while prototyping potato guns and experimenting with different types of fuel. ",
"I thought using propane would work great, but I would just get a \"thhwwwuump\" and the potato would barely make it out. ",
"The reason hair spray and similar aerosols works so well is because there is oxygen in the propellent that forces the fuel out of the can. That's also why these form impressive makeshift flamethrowers. ",
"I wasn't able to get my hands on a can of oxygen, but you could buy nitrous oxide at the local... adult store. ",
"Anyways, add a few valves, combine a little propane and half a whippet and you can shoot a potato farther than you can see. "
] |
[
"And why is that? Anything other than a perfect stoichiometric mixture and the rate of deflagration should be lower, and therefore the breech pressure should be lower. You make it sound like it's more dangerous if you get the mixture wrong, have I missed something?"
] |
[
"How long could a bodybuilder with 2-4% body fat survive without food? How would this compare to a person of the same weight with a normal body fat percentage?"
] |
[
false
] |
My impression was that during starvation the body first digests all the glucose, then all the fat, then all the muscle, which results in death because internal organs are unable to function. I am wondering if that means that body builders, though heavy, would not be able to survive as long without food as other people of the same weight.
|
[
"Great response, thank you!"
] |
[
"Great response, thank you!"
] |
[
"Fat holds more energy per unit mass than protein."
] |
[
"Is it possible to visualize electric current more accurately than the typical hydrology analogy?"
] |
[
false
] |
I understand that electric current is the flow of electrons from an area of negative charge to an area of positive charge, and I understand the analogies to flowing water we use when we talk about circuits, but what is happening inside that wire when I attach it to a voltage source? Is there a more accurate way of visualizing how the current actually propogates or is this something beyond our current understanding?
|
[
"A couple pedantic things. First, current is in general the net flow of any electrical charge. For example, in some semiconductors current is carried by positive \"holes\" rather than electrons. Or you could create an ionic fluid where positive ions flow in the direction of an applied electric field but that brings all sorts of complications beyond the traditional notion of current. Second, it is better to say that electrons flow from an area of lower electric potential to higher electric potential (or in other words they flow in the opposite direction of the electric field; this is flipped for positive charges). ",
"What is \"really\" happening at the microscopic level is a little unwieldly to treat fully in a quantitative sense but you can get a decent qualitative understanding. ",
"Let's talk about everything in terms of conduction electrons being the mobile charge carriers, ie. we are considering a traditional conductor. The instant you attach a battery to a circuit an electric field propagates through the circuit at the speed of light due to the local potential gradient (voltage difference) introduced by the battery. Electrons proceed to locally distribute themselves along the outside of the wire so that the net electric field everywhere points exactly along the length of the wire rather than towards the edges. This happens automatically by an effective feedback mechanism. If initially there is some net field towards the edges, charges will build up on the edge and this build up will eventually cause the net field to be along the wire. Once this transient state reaches equilibrium--which takes ",
" small fractions of a second--current has a steady value. Here I have ignored the fact that electrons in a circuit will ",
" have a random velocity which is more often ",
" in the direction of the net electron flow. What the battery does is increase the likelihood that this velocity vector is in the direction of the electron current (opposite direction of \"conventional current). ",
"This initial transient state and eventual equilibrium surface distribution is treated in detail in an undergraduate text by Chabad and Cherwood, an excerpt of which you can find ",
"here",
" (see diagram on p766). However I in general do not recommend this text."
] |
[
"Electric current flows from high electric potentials towards low electric potentials. Since the direction of electron flow is the reverse of current flow, this means that electrons flow towards higher electric potentials if they are able to do so.",
"In a wire, every atom has some electron/s that are moving around, jumping from atom to atom. When the wire isn't connected to anything else / isn't subject to any magnetic fields / etc., then the electron motion is random - that is, the direction of electron motion over the entire wire averages out to zero - there's no net electron flow.",
"When you put that wire in a circuit with differing electric potentials at each end, then the electrons in the wire change their jumping a little bit. The greater the potential difference, the more electrons will jump to atoms closer to the higher potential. Some of the electrons will still be moving in other directions, but there will be a non-negligible net electron flow. Inverted, that's the electric current."
] |
[
"This is much more rigorous explanation than mine. Give it upvotes!"
] |
[
"Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology"
] |
[
false
] |
Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...". Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists. Please only answer a posted question if you are an expert in the field. . In short, this is a moderated subreddit, and responses which do not meet our quality guidelines will be removed. Remember, peer reviewed sources are always appreciated, and anecdotes are absolutely not appropriate. In general if your answer begins with 'I think', or 'I've heard', then it's not suitable for . If you would like to become a member of the AskScience panel, . Past AskAnythingWednesday posts . Ask away!
|
[
"Will medical advances ever allow humans to achieve immortality?"
] |
[
"Why do so few scientists seem to have a good grasp of the history or philosophy of science, and why are these subjects not mandatory for matriculation from science degree programs?",
"I’ve many people in the sciences right through to post-doctoral work and tenured academic positions who are brilliant in their field but have never actually studied the foundational philosophical works that the scientific method emerged from.",
"This seems invaluable to truly understanding why one’s field is critical."
] |
[
"Two factors I can think of - first is that the amount of material students need to learn before they can start doing new research expands every day, so it becomes increasingly difficult to provide a solid foundation, especially if you want students to have a broad base. That means there’s less time for more meta or philosophical grounding. Second, and maybe more important, is that departments and professors are often extremely territorial, so getting people to reduce their component of a curriculum can be a major political problem. ",
"Put more simply, if you want students to learn something that isn’t currently in the curriculum, you have to decide what’s going to get cut."
] |
[
"Why does getting something wet make is softer?"
] |
[
false
] |
I was thinking about this in the shower. It's where I do all my great thinking. Is it only cellular based objects that this can happen to? What would be the equivalent for a hydrocarbon substance?
|
[
"When a material gets wet (meaning soaked with water), how \"soft\" it gets, if at all, depends on the nature of the chemical bonds in that material. Water molecules are polar and will undergo hydrogen bonding with polar molecules of the material. As water molecules associate and interact with the material, they will also weaken and break bonds between the molecules of that material. You can think of the material as being partially dissolved in a way. As bonds weaken and break, the material becomes softer and more flexible. Remove the water, and those bonds in the material will reform, restoring its hardness and rigidity. However, since the molecules were more free to move around with their bonds weakened from moisture, they won't necessarily settle/return to their previous form when moisture is removed.",
"This is why water damage will mess up the pages in a book. The water will associate and interact with the cellulose molecule chains, weaken bonds, and allow the molecules to move around more freely. When the moisture evaporates, the cellulose bonds regain their original strength but with with different arrangements and orientations than they previously had because the molecules were moving about more freely.",
"This can happen with any substance whose molecules have polarity (allows water to interact/bond) and whose bonds are weak enough (some molecular interactions may simply be too strong for moisture to mess around with)."
] |
[
"Things which absorb water will swell when wet and the modulus will be decreased. They get less stiff. In fibrous things, those fibers will bend more easily and it will feel softer. ",
"Polymers swell and soften when exposed to the right solvent (if they are not highly cross-linked) and hydrocarbons are often good solvents for polymers - so start with things made of polymer fibers and look for solvents for the polymer in question. "
] |
[
"Why would swelling make an object more pliable? Decreasing modulus, getting less stiff, and bending more easily are just three different ways to say the same thing."
] |
[
"How are viruses weakened for live vaccines?"
] |
[
false
] |
[deleted]
|
[
"There are multiple ways of weakening - or ",
" - a virus for use as a vaccine. The most straightforward and historically-used method is by ",
" (i.e. replicating the virus repeatedly over time using new cells for infection) the virus on a cell-type that is non-human. For example, if you wanted to create a live-attenuated vaccine for SARS-CoV-2, you could - in theory - try replicating it over and over and over again in a civet or cat cell line. Eventually, the virus may adapt to that cell line and lose its virulence against a human host. The key is to identify viral strains that are adapted to the non-human cells, but still maintain some capacity to replicate in a human - otherwise we would never mount an effective immune response to that virus. ",
"Another newer method is by intentionally introducing mutations into the genome of a virus that result in attenuation in humans. This is essentially directed evolution in the sense that the goal is the same as the prior method - accumulating mutations that reduce its virulence in humans - but more controlled and quicker."
] |
[
"I suppose my answer depends on what you mean by \"trial and error.\" ",
"Take the measles vaccine for instance. ",
"This paper",
" describes the process by which the first measles vaccine was developed: \"After 3 years of work (involving 24 passages through human kidney tissue culture, 28 through human amniotic cell culture, 6 in fertilized hens' eggs, and 13 in chick embryo cell cultures)...\" In this case, the virus is passaged through ",
" different cell-types multiple times in order to produce a virus that is no longer capable of causing disease in humans (side note: the person that discovered measles' ability to replicate in other cells won the Nobel Prize for their work). They would have had various tests throughout the process to determine if the virus had accumulated enough attenuating mutations to consider it a vaccine candidate. Or, for another example, the very first vaccine widely used was a smallpox vaccine that was quite literally just a related virus that infected cows - cowpox. You can think of this cowpox vaccine as a 'naturally' live-attenuated vaccine because it had essentially been 'passaged' through generations of cows and therefore had not evolved much virulence in humans, but was still related enough to smallpox that our immune system could generate antibodies that would recognize smallpox.",
"So in a sense, yes, there is a degree of trial and error when considering the virus' evolutionary pathway. But, I'm hesitant to use trial-and-error as it may imply that there's more randomness - and possible risk - to vaccine development than there really is. Attenuation does not always work - and can contain some ",
" risk - which is why all the other various vaccine 'platforms' exist (inactivated, subunit, adenovirus, etc)."
] |
[
"You've sent me into a very interesting rabbithole. Thank you for your detailed answers!"
] |
[
"I saw two points of light both originating from a single source. What happened?"
] |
[
false
] |
I took a (sfw) and was able to see my shaver charging through the curtain which illuminated two different parts of the curtain. (see my crude ) I used my hand as a reference, as that usually refocuses my eyes forcing them to see in sync with each other again ( ), I'll see 2 of my hand ( ). In this case, neither happened and I was able to point back and forth between the two points as if there were two light sources. Part of me wants to delve into theoretics here and wonder if there were actually 2 of light. Is this theoretically possible? Is there a much more explanation?
|
[
"This is really tough to answer without knowing all the exact details of the situation. My guess would be that the shaver light was reflecting off of something (mirror, wall nearby?) And in the dark, that secondary source would still appear as a light \"source\" and not \"just\" a picture in a mirror. Or perhaps the light refracted through water in the curtain (though that sounds unlikely to me. Did the spots move if you tilted your head somewhat? ",
"(I personally think the medical stuff is a bit of a red herring here. It's probably a simpler explanation from some optical property of the room)"
] |
[
"wow, thanks for replying. ",
"I will check for mirror reflection, however the walls I can probably answer outright: they are beige and the light source simply isn't strong enough to reflect with any kind of accuracy. I understand what you mean by the reflection appearing as a secondary source in the dark though, so I'll see if that was it. And of course, I will also try tilting my head.",
"Thanks again for replying. I will get back to you.",
" ",
" ",
" ",
" ",
" ",
" ",
" ",
" "
] |
[
"Ok, first, the reflection can be seen through the curtain and there are clearly 2 different \"sources\", however the mirror fogs up within the first minute or two and the reflections visibility through the curtain ceases.",
"Second, when tilting my head, the points of light followed my eyes. (point 1 for left eye, point 2 for right eye)",
"Third, after deliberately making the single source appear as two by shifting the focus of my eyes, it became painfully obvious what was happening, though it does not answer my question yet.",
"Here is some more proprietary but relevant information, and I do my best to make sure there are no misguiding fishies here:\nIf I focus on what is closest to me, I see it as one object, and everything behind it as two: (",
"like this",
"). Alternatively, if I focus on the background, I see it as one object, and the closer object as two (",
"like this",
"). ",
"Given the circumstances, it seems that just like in the first illustration, the charger light was being doubled since it was farther, and the curtain/hand was in focus since it was closer, making it appear as though 2 sources of light were hitting the curtain. I would say it's probably an illusion of some sort, but I'm still perplexed... Technically I saw 1 curtain with 1 light source hitting it in 2 spots. Whether an illusion or not, I still saw it. This leaves me wondering again the same thing I asked previously.",
"I appreciate in advance any more time or effort you spend helping me reach a conclusion."
] |
[
"Why hasn't \"synthetic blood\" been successfully made yet?"
] |
[
false
] |
In an age where entire organs can be grown in vitro, and prosthetics can be hooked up to a person's nerves, it just seems barbaric that we hold huge blood drives so that people can have their blood sucked out, only to be stored, and then pumped into someone else who needs it. I realize that blood is a complex tissue, but couldn't there be some sort of generic liquid containing plasma, some sort of erythrocyte substitute (seems easy enough to produce synthetically), white blood cells (perhaps produced in vitro), and whatever proteins are absolutely essential for human survival, that could be pumped into someone's body when needed? The only issue I can think of is antibody related. Regardless though, if a person is being filled with someone else's blood, then they're receiving antibodies that weren't originally there. Obviously I'm missing something here, can someone help me out?
|
[
"Sure it can be synthesized from cell culture, but why would you want to spend millions to produce a substitute, when you've got 7 billion blood \"farms\" walking around? Blood is really complex stuff and chances are that the incidence of complications relating to synthetic blood would be higher than the incidence of infection from donated blood on a large scale."
] |
[
"As I understand it... It has.",
"http://www.popsci.com/science/article/2011-05/synthetic-blood-substitute-derived-cow-plasma-saves-womans-life"
] |
[
"Transfusion of blood products is tailored to the need of the recipient.",
"You nicely pointed out some of the main things we think about when we talk about blood's role in the body, namely gas transport (by RBCs), immunology (WBCs), buffering of solutes and transport of proteins (plasma). Plasma also contains clotting proteins, and platelets.",
"Donated blood is separated into all these different parts and a patient will receive just plasma, or packed RBCs, or platelets, or some combination depending on what they need. Sometimes they'll receive all the constituent parts of blood in separate bags. Why not just give whole blood? It's hard to match donor to recipient, and it's hard to store. RBCs are good frozen for about a month, and plasma for longer than that, but platelets have to be kept warm and \"agitated\" so they don't become activated and blow their wad before it's time.",
"So living cells are tricky to store. That's the long-and-short of it. Researchers have thus been focusing on making a synthetic product that does one job of blood without the pesky necessity of keeping it alive or keeping it frozen. Hemoglobin-based-oxygen-carrying solutions (HBOCs) are the most recent step towards a blood substitute, as mentioned in the popsci article. ",
"The concern regarding HBOCs is that serious and fatal complications have occurred shortly after administration in some patients. They're still being studied but aren't approved for use in the US. ",
"I don't know how or if a synthetic platelet could be made, but perhaps someone will figure that out soon. As far as WBCs, I don't see a synthetic version being feasible - so much of how your WBCs work is based on their development and ability to recognize your cells as friendlies rather than enemies. As we learn more about how B and T cells are prodded into replication, we might have a better solution, though."
] |
[
"Serious Computer Question - Running Multiple Virtual Machines on One Physical Machine"
] |
[
false
] |
I'm a PC gamer/enthusiast. I work at a small machine shop. There are multiple archaic (Several Intel PII's and PIII's) computers still working overtime to help get our work done. All these machines do is surf the internet, send emails, edit spreadsheets, print labels, and run small inventory programs. I was wondering why it isn't commonplace to have a more powerful machine run several simultaneous virtual machines instead of individual workstations that are rarely used to their full potential. My idea involves a powerful workstation with (For example) a quad core Intel I7 920 with 12GB of memory. Why would it be impractical to have three users, each with 3GB of memory and a single processor core dedicated to their tasks, attached to this computer? I'm talking about having one computer with three monitors, three keyboards, and three mice attached with three different people logged into three different user accounts. The remaining unused core and unused 3GB of ram could be used for system tasks. Some motherboards have multiple network adapters that could be attached to two different ports on a router to improve bandwidth. Why don't developers develop an OS with this capability? The hardware would appear to be able to support such a thing, so what makes it so impractical? I brought this idea up to another computer gamer/enthusiast friend and he didn't have an answer for me. Any thoughts? TL;DR Why can't one modern computer running one operating system support three different workstations with three different users at the same time?
|
[
"Such operating systems do exist, the capability is called ",
"multiseat",
". Doing it on Windows is pretty tricky because of license considerations, doing it on Unix variants is relatively straightforward.",
"It isn't especially common because hardware is quite cheap and deploying it on a large scale within a business means IT has to do a lot of work they likely aren't too familiar with. It isn't a question of technical capability but of configuration and continuing support.",
"e: I didn't consider the virtual machine aspect. It really doesn't add much because you require a multiseat-capable OS to make the multiple keyboards and monitors work for distinct users anyway, so you're basically taking a standard multiseat setup and only allowing each user to run the VM program and interact with the VM inside it."
] |
[
"This is done more commonly by have a very powerful server that can host multiple user sessions concurrently (upwards of 50 and sky is the limit depending on hardware) and then have many very cheap computers (thin clients/terminals) which are basically a monitor, keyboard/mouse, cheap processor and a network card.",
"Your model would introduce a couple of constraints that don't allow it to scale well, notably the need to have to physically connect the monitor/keyboard/mouse to the computer. with the Thin client/server model, you can have your workstations as close or as far from the server as you want, as the only thing connecting them is the network.",
"Vmware, Citrix, and Microsoft all have their own brands of this solution."
] |
[
"I see. Would this idea be suitable as a midrange option?",
"I'm going to use the company I work for as an example. We have 10 computers in the building. 2 are used for engineering, so they would probably need to be standalone (Seeing as how they need to run Autodesk Inventor and various other CAD programs). The remaining 8 computers are used for mundane things. Email, internet, shipping, light duty programs for the CNC machines and CMM, and inventory software. Would it be practical to put one of the workstations I described in the office under a desk somewhere with three users? We have a separate building across the street that houses 75% of our company's assets, manufacturing equipment, personnel, and the main office. The building I work in is somewhat of a half-baked attempt at expanding the business to handle more customers. If something like I'm describing were to exist my thinking is that one machine could be used for an entire row of cubicles in our other building, replacing individual workstations. Would this be a viable option over a thin client/expensive server for a small-medium size company?"
] |
[
"How do we know the speed of light is a limit and not a threshold?"
] |
[
false
] |
We know electrons behave like both particles and waves, so could electrons accelerated to the speed of light behave like photons? That would make electrons and photons the same particle just in different conditions. I realize we can't make an electron travel at the speed of light, but if we could, is it possible?
|
[
"That it's a limit comes from special relativity where the energy required to accelerate a particle with mass to the speed of light is multiplied by the Lorentz factor = (1- (v",
" /c",
" ) )",
"When v = c the Lorentz factor is infinite, thus it takes infinite energy to reach c and it's not possible to go beyond it since if v > c, then the entire equation becomes imaginary (square root of a negative).",
"115 years of experimentation has supported special relativity completely and not one experiment (at least none that haven't been disproved) has ever provided evidence to suggest special relativity is false, so that's a lot of evidence in support of it being a limit.",
"That would make electrons and photons the same particle just in different conditions.",
"No. electrons and photons differ in multiple ways, not just velocity.",
"so accelerating an electron to c if it were possible wouldn't make it a photon. At least based on what we know. Given a system of actual infinite energy who knows what the hell would happen."
] |
[
"None. One thing to note is that the electron is only moving at almost-light-speed to our perspective. The electron always \"perceives\" photons as traveling at the speed of light relative to itself. So in that sense, no matter how much you accelerate, you never actually get any closer to traveling at light speed in your own frame of reference."
] |
[
"If you give an electron an energy of 0.511 MeV (the same as its rest energy) it flies at 87% the speed of light.",
"If you give an electron an energy of 5.11 MeV (10 times its rest energy) it flies at 99.6% the speed of light.",
"If you give an electron an energy of 51.1 MeV it flies at 99.995% the speed of light.",
"If you give an electron an energy of 511 MeV it flies at 99.99995% the speed of light.",
"If you give an electron an energy of 5110 MeV it flies at 99.9999995% the speed of light.",
"If you give an electron an energy of 51100 MeV it flies at 99.999999995% the speed of light.",
"All this has been verified experimentally. Increase the energy of a fast electron by a factor 10 and you get two additional \"9\" in the expression, i.e. you reduce the difference to the speed of light by a factor 100. But you'll never reach it, no matter how much energy you give the electron."
] |
[
"How likely is it that there is a cave underneath me right now?"
] |
[
false
] |
[deleted]
|
[
"Unlike the movies, you won't find open areas like caves as you would travel or drill to the center of the earth. The pressures are too great that the cave would simply collapse. ",
"Most caves are from dissolved limestone or are left over lava tubes. So unless you have had recent volcanism or live in an area with limestone formations, you won't be likely to find caves. "
] |
[
"Very unlikely. England covers 160,000 square km. The cave systems are restricted almost entirely to the limestone outcropping areas, which is 30-40% of the area. So the chances are immediately favourable that there is NOT a cave below, even if there are caves below 100% of the remaining area. However, caves are not that extensive. Even allowing for a (vastly over-inflated) of 10 km",
" total area for each of those 60 caves, you have 600 square kilometers of caves under perhaps 60,000 km of potential area. So, if we vastly exaggerate the numbers, there ",
" be a 1% chance of a cave under your feet, if you live on limestone. Taking the UK as a whole, there would be a 0.3% chance.",
"In actual fact the chance is much lower, as cave systems in the UK tend on the whole to be localised, layered, and much smaller than the sizes I've quoted above.",
"Once you're down to a few kilometers depth the overburden pressure makes caves unstable, so you don't tend to find any. There are certainly none in the mantle or core."
] |
[
"But a cave is clearly not infinitessimally small. Even at the cm to meter scale holes are defined as porosity, not caves. Every definition I've seen of a cave requires it to be big enough to get a person in."
] |
[
"I know this might be seen as a 'joke' question, but I'm honestly curious: If the placebo effect is real, do researchers also see 'placebo side effects' during double-blind trials?"
] |
[
false
] |
Are subjects told about which side effects they might experience before-hand, or do they go in completely 'blind' as to what they might encounter? Also, I know researchers or clinicians have to say 'This is a study for an Alzheimer's drug' or whatever, but do you think it could possibly be better to not let the people know what the research is actually testing for? (I understand this is extremely problematic, ethically, I just think it would be an interesting way to possibly avoid the placebo effect altogether). (edit: I think I missed the part where I could tag my post, obviously, this is medicine, or maybe biology?)
|
[
"Yes, and it even has a name: the ",
"nocebo",
" effect. There have been ",
"studies",
" that show these negative effects. Mind you, the side effects are not always the same as the effects of the actual drugs, but they can happen."
] |
[
"You may tell them that the drug has side effects, and despite it being a sugar pill, they still experience the side effects they assumed the real drug would give them."
] |
[
"Nope. ",
"Placebo: I give you a piece of sugar, and tell you it'll fix your illness, and it does.",
"Nocebo: I give you a piece of sugar, and tell you it'll make you sick, and it does.",
"A placebo and a nocebo may be chemically identical; the difference is what I say to you."
] |
[
"With the sun entering a solar minimum, could this slow the effects of climate change in terms of warming the planet?"
] |
[
false
] |
I've been seeing a lot of articles about the sun entering it's solar minimum phase from relatively reliable news sources. It got me thinking... Would the solar minimum cool the planet giving humanity a better shot at fixing climate change or am I completely wrong in that thought?
|
[
"No.",
"For one thing, we are currently in solar minimum and climate change hasn't gone anywhere. Solar activity is expected to ramp back up over the next few years to a max in 2026ish and then another minimum in about 2031.",
"The reason why it makes almost no difference is that the total energy coming from the Sun varies by only an EXTREMELY small amount between min and max (although there is a little bit of complex atmospheric effects due to the increase in euv light)."
] |
[
"the total energy coming from the Sun varies by only an EXTREMELY small amount between min and max",
"To put some hard numbers of this, ",
"here's",
" a graph of Total Solar Irradiance (= energy from sunlight) over the past few decades. You can see there is a clear 11-year cycle, but even at the absolute daily extremes we're talking about the difference between 1359 and 1364 Watts per square meter.",
"Per the Stefan-Boltzmann law, it turns out that planetary temperature varies as Irradiance",
" power. That means the ratio between hottest and coldest the planet will be due to this variation is...",
"(1364 / 1359)",
" = 1.0009",
"In other words, the hottest the planet will get due to solar cycles is about 0.09% warmer than the coldest planet will get. Given that Earth's average temperature is about 288 K (15 C, 57 F), that means we're talking about a temperature difference of...",
"288 K * 0.0009 = 0.26 K",
"...or about 0.5 F."
] |
[
"Isn’t the Stefan-Boltzmann law about blackbody radiation? Not really an expert.",
"Also 0.26K isn’t a BIG deal but since a a few K will be enough to have devastating effects it could buy us, like, a year or 2?"
] |
[
"Can you get sick (catch a disease) from someone who isn't sick themselves?"
] |
[
false
] |
Might be a basic question, but I've been wondering.
|
[
"Yes. They may have immunity but still carry the disease. See ",
"Typhoid Mary",
" as one famous example."
] |
[
"Yes. If someone is a carrier of a disease, but immune to it or not showing symptoms, it would be possible to get the disease from someone who isn't sick in the usual sense. It's not possible to get sick from someone who isn't ",
" by a disease, though. But it's possible to be infected and not show symptoms or be sick for someone diseases."
] |
[
"Also, you may still carry the bacteria/virus/pathogen in your body but it might be at an undetectable level for whatever reason. For example, during HIV infection your initial viral load is extremely high but settles down once your ",
"immune system responds",
" and can become undetectable in your blood after treatment despite the virus persisting in your cells and some tissue. In cases like this where the person may not ",
" sick they may still carry the pathogen and pass it onto others."
] |
[
"How do eyes lose their visual acuity?"
] |
[
false
] |
How does the visual acuity of so many young people deteriorate to the point of needing glasses? What is happening inside the eyes as people slowly lose their sight? Why is this so common now? How do objects such as computer/tv do aid the progress?(assuming that it does)
|
[
"TL;DR: Visual acuity in younger people usually deteriorates because of refractive error within the eye, as opposed to any sort of disease or pathology. The most common refractive error is myopia, and the most common form of myopia is axial myopia, whereby the eye grows and extends its length, causing images from distant objects to focus in front of the retina, instead of on the retina itself. This causes image blur, and image blur causes acuities below 20/20.",
"Bonus: 20/20 is not actually all that good of acuity. Most younger patients should be able to achieve 20/15 if they are true emmetropes.",
"The longer version: \nLike I said before, the most common form of refractive error is myopia, which is an eye that focuses light in front of the retina. If this is because the eye is too long, it is called axial myopia. If it because the eye, usually the cornea, which is the primary refractive surface of the eye, is overpowered, it is called refractive myopia. Axial myopia is more common.",
"Myopia rates are increasing very rapidly in some countries. In the US, roughly half of the population is myopia. In some asian countries, like China, myopia rates have reached nearly 90% of the population.",
"It was originally thought that prolonged nearwork caused myopia. Doing nearwork puts the image of whatever you are looking at behind the retina, causing the crystalline lens within the eye to work to move the image back forward onto the retina. It was thought that the eye then adapts to this by increasing its length so that the lens has to do less work. New research now shows that while prolonged nearwork does play a role, not enough time outdoors, looking at far away objects, actually has an even larger impact.",
"Of course, in addition to these theories, research also shows the number one indicator of whether a child will have myopia, is having two parents who have myopia, so there is a large genetic component.",
"Much less common than myopia is hyperopia, where the image from a distant object is focused behind the retina. Small to moderate amounts of hyperopia can be corrected by the lens within the eye, in a process similar to viewing objects at near explained above, which is called accommodation. ",
"Unrelated to myopia and hyperopia is astigmatism, where the cornea is oblong shaped rather than spherical. Many people liken this to a football vs. basketball analogy, which is fairly accurate. Astigmatism causes there to be 2 different powers needed to correct the eye, as opposed to just one in simple myopia or simple hyperopia."
] |
[
"Unfortunately, the eye rarely shrinks (except for when the eye \"dies\" in a situation called ",
"phthisis bulbi",
").\nThe best you can do is attempt to control the myopia progression. There are all sorts of ways to do this, and it is currently a very prominent research topic. The absolute best way to use ",
"atropine",
", which paralyzes the muscles of accommodation. Atropine is crazy interesting, and maybe worth reading about. Another interesting way is to use ",
"Orthokeratology",
", which is a contact lens that you wear overnight, and when you wake up, your myopia is corrected for the day!"
] |
[
"Thank you for the response! Now I'm wondering is there any way the eye can revert back go its original length to restore vision?"
] |
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