Wikipedia:Reference desk/Archives/Science/2017 April 1

= April 1 =

Repeated exposure and emotional response
When I first watched this YouTube video, my eyes were in tears, and my nose was runny. Now when I watch it again, it doesn't provoke the same response. Actually, the part where the guy pulls on the person's shirt to prevent a suicide attempt just makes me laugh. I don't get why I can sit in a comfy room and cry at the same time. Is my brain re-interpreting the video as a false alarm? 50.4.236.254 (talk) 01:10, 1 April 2017 (UTC)


 * Accustomisation is one term for this. Do we have an article on it ? StuRat (talk) 01:23, 1 April 2017 (UTC)


 * Once you've seen something new, the next time you see it the element of surprise is not there. ←Baseball Bugs What's up, Doc? carrots→ 02:09, 1 April 2017 (UTC)
 * That's not always true: some things have a physical power even when you know they are coming. When this happens, it tends to come from internal expectations generated by a work of art in which these things happen, which retain their power at every appreciation, instead of external expectations generated by the form or some conventions. Of course, this case isn't really relevant to this video. Double sharp (talk) 07:14, 1 April 2017 (UTC)


 * See desensitization. Matt Deres (talk) 17:22, 1 April 2017 (UTC)
 * Another article of relevance is Habituation - this is the process whereby an organism learns NOT to respond to a repeated stimulus. DrChrissy (talk) 20:37, 1 April 2017 (UTC)


 * The "most likely to succeed" part gets a laugh. That title never did make very much sense because they never say at what... now we know. ;) Wnt (talk) 12:49, 3 April 2017 (UTC)

Synchronizing cardinal grammeters
Anyone know of a machine that works to not only supply inverse reactive current, for use in unilateral phase detectors, but would also be capable of automatically synchronizing cardinal grammeters? PaleoNeonate (talk) 07:19, 1 April 2017 (UTC)
 * Most turboencabulators are capable of this. Andy Dingley (talk) 09:39, 1 April 2017 (UTC)
 * Yes, but you must ensure that the logarithmic casing is kept intact and secure or you'll end up with ordinal contamination. Matt Deres (talk) 16:12, 1 April 2017 (UTC)
 * Is your turboencabulator clad in unobtanium? If not, you can expect excessive reductoxidative corrosivity.  -- Jayron 32 19:50, 1 April 2017 (UTC)
 * Rasofractors do this or an Interocitor. Edison (talk) 01:00, 3 April 2017 (UTC)

Feynman Lectures. Lecture 51. Ch.51-2 Bore in a channel
I want to check 2nd quote. But I don't understand why did the mass (green on this figure) get a speed v. Can you explain that? I assume that the vgreen =0, vorange= 0 (everywhere except at the piston), at the piston x-component vorange, x= v, y-component vorange, y= v (cycloid trajectory). Is it correct?

And also can you give youtube video of the experiment shown in fig. 51-4? Username160611000000 (talk) 07:33, 1 April 2017 (UTC)

h_1)$$, we get: $$gh_2 (h_2-h_1)>^? g({h_2}^2-{h_1}^2) +   h_1  v^2$$ Using final Feynman formula $$u^2 = gh_2(h_1 + h_2)/2h_1$$, we get: $$v^2=u^2\tfrac{(h_2-h_1)^2}{{h_2}^2}=0.5gh_2(h_1+h_2)\tfrac{(h_2-h_1)^2}{h_1{h_2}^2}=0.5g(h_1+h_2)\tfrac{(h_2-h_1)^2}{h_1h_2}$$ $$gh_2 (h_2-h_1)>^? g({h_2}^2-{h_1}^2)  +   h_1  \cdot 0.5g(h_1+h_2)\tfrac{(h_2-h_1)^2}{h_1h_2}$$ $$gh_2 >^? g(h_2+h_1)  +   0.5g(h_1+h_2)\tfrac{h_2-h_1}{h_2}$$ $$h_2 >^? h_2+h_1  +   0.5(h_1+h_2)\tfrac{h_2-h_1}{h_2}$$ $$0 >^? 0.5{h_2}^2+h_1h_2-0.5{h_1}^2$$
 * Assuming all the Feynman text is correct I write next: $$E^{(a)}_{pot}=(\text{mass}) g (\text{heigth}) = (\rho h_2 v\Delta t )g (0.5h_2) $$ $$E^{(b)}_{pot}=(\text{mass})  g (\text{heigth})=(\rho(h_2-h_1) u\Delta t  ) g (0.5(h_2+h_1))$$ $$E^{(b)}_{kin}=0.5 (\text{mass})  v^2 =0.5 (\rho h_2u\,\Delta t - \rho h_2v\,\Delta t)  v^2$$ We need to check  $$E^{(a)}_{pot} >^? E^{(b)}_{pot} + E^{(b)}_{kin}$$ or $$E^{(a)}_{pot} =^? E^{(b)}_{pot} + E^{(b)}_{kin} + U$$
 * $$0.5(\rho {h_2}^2 v\Delta t )g  >^? 0.5(\rho({h_2}^2-{h_1}^2) u\Delta t  ) g  + 0.5 \rho h_2\Delta t(u - v)  v^2$$ $$ {h_2}^2 v g  >^? ({h_2}^2-{h_1}^2) u  g  +   h_2 (u - v)  v^2$$ Using conservation of matter $$vh_2 = u(h_2 -
 * Last statement is true only when $$h_2\in (-2.4h_1;0.4h_1)$$, so Feynman text that initial energy is enough for the falling water and the churning if $$h_2>h_1$$ is wrong. It's even not enough for Feynman (a) to (b) scenario. Where is my mistake? Username160611000000 (talk) 19:58, 1 April 2017 (UTC)
 * By more careful inspection of Feynman text I found that I need include work: $$A_\text{by piston}+E^{(a)}_{pot} = E^{(b)}_{pot} + E^{(b)}_{kin} + U + A_\text{by water}$$ We need to show that U>0 $$A_\text{by piston}=(\text{force})\cdot (\text{distance})=(\tfrac{1}{2}\rho g{h_2}^2)(v\Delta t)$$ $$A_\text{by water}=(\text{force})\cdot( \text{distance})=(\text{force})\cdot (0.5\text{acceleration}\cdot \text{time}^2)=\text{force}\cdot \tfrac{0.5 \text{net force}\cdot \text{time}^2}{\text{mass}}=(\tfrac{1}{2}\rho gh_1^2)\tfrac{0.5(\tfrac{1}{2}\rho gh_2^2 - \tfrac{1}{2}\rho gh_1^2) \cdot (\Delta t)^2}{\rho h_2u\,\Delta t - \rho h_2v\,\Delta t}$$ $$A_\text{by water}=(0.125\rho gh_1^2)\tfrac{ g(h_2^2 - h_1^2) \cdot \Delta t}{h_2(u - v)}=(0.125\rho gh_1^2)\tfrac{ g(h_2^2 - h_1^2) \cdot \Delta t}{uh_1}= (0.125\rho h_1)\tfrac{ g^2({h_2}^2 - {h_1}^2) \cdot \Delta t}{u}$$
 * $$A_\text{by piston}+E^{(a)}_{pot} = E^{(b)}_{pot} + E^{(b)}_{kin} + U + A_\text{by water}$$ $$(\tfrac{1}{2}\rho g{h_2}^2)(v\Delta t) + 0.5(\rho {h_2}^2 v\Delta t  )g  = 0.5(\rho({h_2}^2-{h_1}^2) u\Delta t  ) g  + 0.5 \rho h_2\Delta t(u - v)  v^2 + U + (0.125\rho h_1)\tfrac{ g^2({h_2}^2 - {h_1}^2) \cdot \Delta t}{u}$$ $$g{h_2}^2v  +  {h_2}^2 v  g  = ({h_2}^2-{h_1}^2) u  g  +  h_2(u - v)  v^2 + \tfrac{2U}{\rho\Delta t} + 0.25 h_1\tfrac{ g^2({h_2}^2 - {h_1}^2)}{u}$$ $$2vg{h_2}^2  = ({h_2}^2-{h_1}^2) u  g  +  u\cdot 0.5g(h_2+h_1)\tfrac{(h_2-h_1)^2}{h_2} + \tfrac{2U}{\rho\Delta t} + 0.25 h_1\tfrac{ g^2({h_2}^2 - {h_1}^2)}{u}$$ $$2u\tfrac{h_2-h_1}{h_2}g{h_2}^2  = ({h_2}^2-{h_1}^2) u  g  +  u\cdot 0.5g(h_2+h_1)\tfrac{(h_2-h_1)^2}{h_2} + \tfrac{2U}{\rho\Delta t} + 0.25 h_1\tfrac{ g^2({h_2}^2 - {h_1}^2)}{u}$$ $$2{h_2}  = ({h_2}+{h_1})     +   (0.5h_2-0.5\tfrac{{h_1}^2}{h_2}) + \tfrac{2U}{\rho\Delta t ug(h_2-h_1)} + 0.25 h_1\tfrac{ g({h_2}+ {h_1})}{u^2}$$ $$2{h_2} = ({h_2}+{h_1}) + (0.5h_2-0.5\tfrac{{h_1}^2}{h_2}) + \tfrac{2U}{\rho\Delta t ug(h_2-h_1)} + \tfrac{0.5 {h_1}^2}{h_2}$$ $$0 = -0.5{h_2}^2+{h_1}{h_2} -0.5{h_1}^2 + \tfrac{2Uh_2}{\rho\Delta t ug(h_2-h_1)} + 0.5 {h_1}^2$$ $$0.5{h_2}^2-{h_1}{h_2} =    \tfrac{2Uh_2}{\rho\Delta t ug(h_2-h_1)} $$
 * $$U=0.25(h_2-2h_1)(h_2-h_1)\rho ug\Delta t$$ We see that U is positive if $$h_22h_1$$, which  again  doesn't coincide Feynman. But if I remove last term $$A_\text{by water}$$ in energy conservation law, I get $$U=0.25\tfrac{(h_2-h_1)^3}{h_2}\rho ug\Delta t$$, which coincides Feynman. I don't understand is last term $$A_\text{by water}$$ necessary and why. Explain this, please. — Preceding unsigned comment added by Username160611000000 (talk • contribs) 15:04, 2 April 2017 (UTC)

Pine trees
I actually have 2 questions. This is the background. I have three pine trees growing on a patch of land in the back of my house. That patch is about 60-70 feet in circumference or perhaps 28 x 15-20 feet. This is what happened.

(1) Last November I looked at one of the pines and saw that the tree was dying. We had a very dry summer. Many needles were yellow. I don't know if that's my neglect or the previous owner's or both. In short I began watering the tree and the other one, which was also affected but not to the degree. Unfortunately I don't remember precisely how the needles looked when I started but it seems the yellow parts are receding. We had winter, of course, when I did not water them. My question is: Is it realistic to expect that the needles will completely become green eventually?

(2) Now I have an idea to plant shrubs around the patch, along those 60-70 feet. I want the shrubs to form a complete green wall without gaps and be about 3-4 feet high. My purpose is to protect the birds that eat the birdfeed I spread for them between the trees. They get scared when people pass by. Also I noticed 2 weeks ago that two ducks tried to make a nest there, at least they were sitting there between the pines but too much human traffic eventually scared them away. The human traffic is essentially myself. I need to pick up the newspapers and drive out of the garage. Life it tough for wildlife and I want to help them as much as I can. So, my question is: will the shrubs help to keep the moisture for the trees or take the moisture from them? Thanks, - --AboutFace 22 (talk) 18:16, 1 April 2017 (UTC)


 * Have a look at Browning of Evergreens. Alansplodge (talk) 19:38, 1 April 2017 (UTC)

@Alansplodge, it is an interesting reading but I don't think it answers any of my questions. Thanks anyway. --AboutFace 22 (talk) 23:32, 1 April 2017 (UTC)


 * Shrubs will have much shallower roots than the trees, so will be taking water from a different place. However, if there isn't enough rain, they might soak it up before it sinks to the tree roots.  So, watering may still be required.  As for existing yellow needles turning green again, probably not, but those needles may fall and be replaced by new green ones. StuRat (talk) 02:02, 2 April 2017 (UTC)


 * The yellowing may be caused by more than simple lack of water; needle blight is another possibility, but there are others. We're unlikely to be able to say whether adding shrubs will help or damage the trees; the sharing of water and nutrients, even in a small ecosystem, can be extremely complicated. Besides the plants themselves, soil conditions and drainage patterns will play a part. In the very simplest terms, any plants you add will require water for their own purposes and lose it through transpiration, but they may help if there's nominally enough water, but it's being lost through surface runoff. Be aware that many plants struggle to survive under evergreen trees; the soil pH tends to be acidic and the year-round foliage doesn't help. Even dripping resin may be a hazard. Plenty of online forums have suggestions for shrubs that thrive in those conditions, however. Here's one that seems germane; but there are plenty of others; Googling shrubs under pine trees will get you far. Matt Deres (talk) 02:35, 2 April 2017 (UTC)

@StuRat & @Matt, thank you. I appreciate the information. --AboutFace 22 (talk) 15:57, 2 April 2017 (UTC)

Extraterrestrial eyes that absorb non-electromagnetic waves
Is it possible for extraterrestrials to have eyes that see non-electromagnetic waves(correction:eyes that see in non-electromagnetic waves)? — Preceding unsigned comment added by Uncle dan is home (talk • contribs) 20:13, 1 April 2017 (UTC)
 * If they were eyes, by definition they would see some form of electromagnetic radiation. That's what an eye is.  You have organs that detect mechanical waves.  Those are called ears.  -- Jayron 32 20:16, 1 April 2017 (UTC)

Yes,but ears are for hearing, not seeing.Uncle dan is home (talk) 20:35, 1 April 2017 (UTC)
 * I think what Jayron is saying is that this a circular question. We define eyes by saying they are organs that are responsive to visible light, i.e. within the electromagnetic spectrum.  Therefore, organs that are sensitive to non-electromagnetic radiation would not be "eyes".  I suggest you re-word the question. DrChrissy (talk) 20:45, 1 April 2017 (UTC)


 * A simpler question might be whether "aliens" could have eyes that see invisible (to humans) electromagnetic waves. We already know the answer, as several Earth species can do this. Some insects can see ultraviolet, and some flowers have patterns on their flowers that are only visible thus. Bees can see (and use to navigate) polarised light, allowing them to steer by the Sun, even under cloud. Some snakes and other reptiles have thermal sensors which can detect long-wavelength infra-red. Andy Dingley (talk) 20:53, 1 April 2017 (UTC)
 * Andy, I know that several species of snake are sensitive to infra-red, but I don't know about other reptiles. Please could you point me in the direction of species I should be looking at. DrChrissy (talk) 21:24, 1 April 2017 (UTC)
 * I may be wrong here, as it's certainly controversial and they're nowhere near either as good at it, or with such obvious organs, as the crotalinae. But AIUI, there is some opinion that both the heloderms (venomous, so a useful one-bite attack) and the iguanas (which really predate, not just hang around waiting) may have some similar ability. Andy Dingley (talk) 22:01, 1 April 2017 (UTC)
 * Cheers - I will have look into it. Another example is an insect that seeks to lay eggs in recently burned tree stumps - sorry, I forget the name of the animal for the moment, but I seem to recollect it can detect bush fires from miles away. DrChrissy (talk) 22:31, 1 April 2017 (UTC)

How do I cross out my question? — Preceding unsigned comment added by Uncle dan is home (talk • contribs) 21:09, 1 April 2017 (UTC)
 * You can do this by placing text around the text, but probably not worth it. By the sounds of it, you wish to withdraw the question and that is sufficient.  DrChrissy (talk) 21:17, 1 April 2017 (UTC)

Is it possible for ETs to have organs that 'see' in non-electromagnetic radiation/waves? Not hear smell,touch, or taste, but see.Uncle dan is home (talk) 21:28, 1 April 2017 (UTC)
 * You are talking about organisms that we do not even know whether they exist. How can you possibly expect a sensible, evidence-based answer to this question.  Is it relevant that today is April 1st? DrChrissy (talk) 21:47, 1 April 2017 (UTC)


 * Sure it's possible. Anything you can imagine is "possible". ←Baseball Bugs What's up, Doc? carrots→ 22:07, 1 April 2017 (UTC)


 * The definition of 'see' is 'perceive with the eyes; discern visually' so the answer is no. Bats can find their way around by echolocation and dogs by smell but we don't call it 'seeing'. Richerman    (talk) 22:17, 1 April 2017 (UTC)
 * When you see a dream, are you using your eyes to see? ←Baseball Bugs What's up, Doc? carrots→ 22:24, 1 April 2017 (UTC)
 * I never say I see a dream. I just say I dream. --Lgriot (talk) 15:54, 3 April 2017 (UTC)


 * A quick question before I make a fool of myself - What type of energy is gravity...is it electromagnetic? I think not, but I am not a physicist. DrChrissy (talk) 22:38, 1 April 2017 (UTC)
 * OR alert Here is the reason why I asked the above question. It is believed that some birds may actually visualise magnetic fields.  It is also believed that some animals navigate using gravitational fields (Lednor AJ, Walcott C (1984) The orientation of pigeons at gravity anomalies. J Exp Biol 111:259–265.)  Here comes the leap of faith - what if the animals navigating using gravity also visualise these energy fields? DrChrissy (talk) 23:16, 1 April 2017 (UTC)
 * Well, as chocolate is an octave of solar energy, anything is possible.
 * This is just about the point at which language starts to break down and woo-woo creeps in. What does "visualise a field" mean?
 * It's studied and recognised that pigeons (maybe others) can sense a magnetic field. Specifically they can measure the direction (but not the strength) of the Earth's magnetism, which is a vector field. Others, such as heat-sensitive snakes, can measure the strength of a scalar field by either thermal or smell strength sensing, and by head movement or tongue flicking can use this to determine a good target vector for a strike. But very few organisms, except some mathematicians and physicists, can really visualise a field, let alone a vector field. Sensing one directly is (AFAIK) impossible. You can either image and visualise an image plane (the solid angle over which you can "see") or you can scan by moving your sensor around the field and so visualise a constructed volume. But nothing gets to "perceive" a volume of a field directly. Some SF novels (the Lensman series) have included this ability. Andy Dingley (talk) 23:42, 1 April 2017 (UTC)
 * I am getting a little lost in the terminology you use above, but I think I am in broad agreement. My understanding is that pigeons (hens and turtles also detect magnetism) have magnetite in their brains (hens have it in their beaks[Freire, R.; Eastwood, M.A.; Joyce, M. (2011). "Minor beak trimming in chickens leads to loss of mechanoreception and magnetoreception". Journal of Animal Science. 89: 1201–1206. doi:10.2527/jas.2010-3129.]).  Presumably, the signals from the magnetite being stimulated is transferred to the brain which is then transferred to the eyes.  So, this actually gets back to Bugs' question about when we dream, are we "seeing" what we dream about.  Unless there is evidence that magnetism/gravity is detected through the eyes, I don't believe it fulfills our common understanding of "seeing". THat's just my take on the way we use terms. DrChrissy (talk) 00:00, 2 April 2017 (UTC)


 * I think two things must be distinguished - the physical mode (light, sound) of the stimulation and what the perception feels like to the creature. "Eyes" suggests the OP meant the former, but "not hearing, but seeing" suggests it's the latter. Either way, anything is possible - aliens could have organs that respond to non-EM stimulation and the subjective quality of that perception is akin to "seeing" (or "hearing.") Dawkins had an argument (I forget in which context) that bats could, in principle, perceive different kinds of echo as different colors (because the neurocircuitry got coopted or something.) Asmrulz (talk) 05:13, 2 April 2017 (UTC)
 * I think what you might be referring to is called Synesthesia in humans. DrChrissy (talk) 20:27, 2 April 2017 (UTC)


 * It's a matter of semantics. We don't see anything in dreams - we imagine we see them and we can only do that because we have seen things before and dreams are constructed by rehashing memories and constructing new scenarios using them. We imagine we see because the visual cortex is active. People who have been blind from birth don't see in their dreams. In the same way a person who is hallucinating doesn't really see things that aren't there - they imagine they see them.  And bats don't see by echolocation - they have a perfectly good visual system for that. The question should really be could aliens perceive their world by detecting non-electromagnetic waves and the answer to that is yes. We use our visual system to construct an internal model of our surroundings so we can find our way around and that can certainly be done in other ways using different stimulii such as changes in gravity, sound etc. but it's not actually seeing unless the definition of to see is changed.  Richerman    (talk) 11:28, 2 April 2017 (UTC)

Can modern humans live on a wild food diet?
Domesticated plants are more edible and tasty than their wild counterparts. Domesticated animals are tamer and can be bred to be bigger than their wild counterparts. But if there were an apocalypse and all of a sudden humans don't have access to instant food in the supermarkets and restaurants, can humans survive on local, wild food (such as dandelions, wild berries, grass, pine nuts, acorns, clovers, earthworms, snails and slugs, insects, insect larvae, arachnids, crustaceans, tiny fish, and seaweed)? Is it possible, in a post-apocalypse scenario, to domesticate local wild plants and animals and mushrooms? 50.4.236.254 (talk) 23:00, 1 April 2017 (UTC)


 * Wild animals come in various tasty forms, and some would be trivially easy to capture and breed and raise for meat. What sort of apocalypse would kill all the vegetables and grains that we normally eat? Greglocock (talk) 01:47, 2 April 2017 (UTC)
 * I have read that honey bee populations are disappearing, and some plants are animal-pollinated in order to produce fruit. Without the honey bee, there will be fewer fruits and vegetables on the market. 50.4.236.254 (talk) 02:11, 2 April 2017 (UTC)
 * The problem is that those have been bred for their appeal to the human appetite, not for their ability to survive on their own. This means that without farmers to spray insecticides, provide water, keep birds from eating them, plant their seeds, etc., they would die off as quickly as chihuahuas in the wild. StuRat (talk) 01:53, 2 April 2017 (UTC)
 * A random selection from our local creek suggests that globe artichokes, rhubarb, garlic, potatoes ,rosemary, strawberries, blackberries and horseradish all self seed and are practically bullet proof. And i can assure you that grass grows just fine even if I'd rather it didn't.Greglocock (talk) 02:53, 2 April 2017 (UTC)
 * Sure, it's possible to start over and domesticate all new plants and animals, but that would take centuries. Probably not all of our current domesticated species would be lost, so it would be better to start with those which remain.  Also, see seed bank for one attempt to prevent extinction of species like this. StuRat (talk) 02:08, 2 April 2017 (UTC)
 * A human, or all humans? Some humans still live as hunter-gatherers, so the answer to "Can a human live on wild food?" is "Yes". But there is not even remotely enough wild food to support all humans on Earth. Agriculture is the thing that allowed large, settled human populations. And today's human population of over 7 billion is only possible because of industrialized agriculture. See: Green Revolution, Haber process, carrying capacity, world energy consumption. --47.138.161.183 (talk) 03:37, 2 April 2017 (UTC)
 * How many humans might still be around in a "post-apocalypse scenario"? ←Baseball Bugs What's up, Doc? carrots→ 04:24, 2 April 2017 (UTC)


 * The food doesn't look good :(. Count Iblis (talk) 04:55, 2 April 2017 (UTC)


 * Something that killed humans would probably kill everything else too, or contaminate the soil so heavily that nothing would grow for decades. So unless you like to eat cockroaches, I'd say if you survived the initial cataclysm you were out of luck! --TammyMoet (talk) 10:53, 2 April 2017 (UTC)


 * I disagree. Biological warfare, in particular, could kill large numbers of humans and leave everything else untouched. StuRat (talk) 19:56, 2 April 2017 (UTC)