Wikipedia:Reference desk/Archives/Science/2015 October 23

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October 23

How can In-situ Fabricator grab bricks?

How can In-situ Fabricator grab bricks? See [1]. I thought at first that it had claws, but it does not grab them by the sides. It has a plate that pull the bricks up. (Close-up at the bottom of the linked article). --Scicurious (talk) 02:01, 23 October 2015 (UTC)

Around 1:55 in the video: https://www.youtube.com/watch?v=jjcXJ8EU48o It's suction, or a "vacuum gripping system with flexible sealing foam". See here for example, second picture and the "Modular Vacuum Grippers" section. Ssscienccce (talk) 02:48, 23 October 2015 (UTC)

Speed of Gravity

Before I decided to post this, I looked it up. The Wikipedia article on this subject is long, drawn out, confusing, and as near as I can tell, inconclusive. I looked at the talk page as well and it's even worse. So, my question: All the objects in our solar system are all pulling on each other all the time. They are also in motion all the time. So when the moon pulls on the Earth, is the pull coming from where it was a second and a half ago, or is it coming from where it is now? The moon is moving pretty quick, but in a second and half it's only going to a go about a mile. We can we tell the difference in the direction of the moon's pull, but can we determine it that accurately? 50.43.33.62 (talk) 04:44, 23 October 2015 (UTC)

I don't know how accurately it's been measured, but in theory it comes from a "current location" that's extrapolated from its location 1.5 seconds ago, which is very close to its actual current location unless something extraordinary happened in those 1.5 seconds. "Where it was 1.5 seconds ago" depends on your choice of reference frame, so the force can't come from there in a relativistic theory. It can't come from the actual current location because that location won't be available for another 1.5 seconds. -- BenRG (talk) 05:04, 23 October 2015 (UTC)

I think that explanation is too facile, since "where it is now" is also frame-dependent. Here's another attempt. Imagine a sphere with very long straight spines sticking out in all directions. If the sphere moves inertially, the spines always point toward where the sphere is "now" in any inertial reference frame. They don't lag behind the sphere because there's no relativistically invariant notion of "behind". That's how the fundamental forces work. On the other hand, if the sphere shoots bullets in all directions (in vacuum), the path of each bullet points back in spacetime (and hence in any spatial projection) to where the sphere was when it fired that bullet, not where it is now. That's how light works. -- BenRG (talk) 05:31, 23 October 2015 (UTC)

Here's an easy way to understand it: The moon moves in a certain direction, and it "releases" gravity. That gravity also moves! And it moves in the same direction the moon was moving when it released the gravity. So the pull of gravity is toward where you would expect the moon to be. Unless something changes the path of the moon. If that happens then the real location of the gravitation force, doesn't match where the force is felt. But only relativity noticed the mismatch, Newtonian physics assumes gravity moves at infinite speed. Ariel. (talk) 06:06, 23 October 2015 (UTC)

I have sometimes seen gravity of massive objects represented as a flat sheet with divots where those massive objects are. Those divots are circular and spread out evenly in all directions - like when you drop a round object into calm water. So presumably the idea would be that if one massive object is close to another, it's always somewhere within that divot. It doesn't suggest there is any "catching up" to do. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:32, 23 October 2015 (UTC)

The gravity field in the solar system (and I suspect throughout the universe) is static. Therefore gravity forces dont have to travel: they are already there. We are still trying to detect gravitational waves with the LIGO experiment. To date none have been found. I think this is what the Wabbit was trying to say, I think, in its own innocent way.--213.205.252.46 (talk) 14:45, 23 October 2015 (UTC)

It? Ahem.

If gravity affects space itself, then looking for gravity waves might not work. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:54, 23 October 2015 (UTC)

This is one of those things that is a semantic distinction which is hard to get at, and sometimes people are answering two different implied questions, which is why we have some confusion. There's two questions really we need to get at:

• At what speed does gravity itself travel?
• At what speed will objects respond to gravitational forces?

The answer to the questions then ALSO depends on which theory of gravity you're working from. For example, if you're working with the as yet unsupported graviton theory, then gravity is modulated by force carrier particles, and the answer to both questions is "the speed of light". If you're working under general relativity, then gravity isn't really a force, it's a property of space-time, and as an existing property, it does not properly "travel", and the first question is meaningless. The second question would still be the speed of light, however. --Jayron32 15:02, 23 October 2015 (UTC)

Gravitons don't really change anything. If you quantize a classical field theory, you get particles as a side effect. The particles don't replace the field, and shouldn't be confused with classical particulate matter. The best answers to your questions could be debated, but shouldn't be different in classical vs quantum field theory. -- BenRG (talk) 21:42, 23 October 2015 (UTC)

• I always thought the Tests_of_general_relativity#Perihelion_precession_of_Mercury was due to the propagation of gravity being at the speed of light, and not instantaneous. I may be totally off there, and our article doesn't make that claim. But if the difference is not due to the speed of propagation of gravitic changes, what is it caused by? μηδείς (talk) 19:24, 23 October 2015 (UTC)

(Disclaimer: I'm not a physicist) In a sense your statement is true, because gravity having a finite speed of propagation is one of the things underpinning general relativity. By contrast, Newtonian mechanics predicts that gravitational effects propagate at infinite speed. But the explanation I've heard for the precession of Mercury is that when you get sufficiently close to a very massive body like a star, spacetime is warped enough that you start seeing effects that differ from Newtonian predictions. Mercury is close enough to the Sun that these effects become apparent. As you might know, Newtonian mechanics is still a good approximation for how gravity behaves, in most cases. Relativistic effects only become significant once you get close to a large enough mass, or get up to significant fractions of c. The ultimate demonstration of this is, famously, a black hole; as just one example, close enough to a black hole (but still outside the event horizon), it's impossible to stay in an orbit around the black hole, because spacetime is so distorted. But, you can still maintain your position if you can apply enough force to avoid being pulled towards the black hole, say by pointing a sufficiently powerful rocket engine towards it. --71.119.131.184 (talk) 20:23, 23 October 2015 (UTC)

Mercury's anomalous precession is due to the non-flat spatial geometry around the sun. specifically the fact that the circumference of a circle is less than 2π times the radius. It may disappear in an appropriate c→∞ limit (I'm not sure), but it's not caused by the gravitational force "lagging behind" in the sense of aberration. If there were aberration (if the force was toward the optical position of the sun), orbits would gain angular momentum and spiral outward. This was historically used as an argument against gravity having a finite speed (at least a speed comparable to the speed of light). See Speed of gravity#Laplace. -- BenRG (talk) 21:32, 23 October 2015 (UTC)

Thanks, @BenRG:, I was afraid someone might say that. I am only just educated enough in physics to comprehend your very helpful answer. μηδείς (talk) 04:02, 24 October 2015 (UTC)

General relativity is the gateway ref here, but from context above I think it's worth pointing out gravitomagnetism, gravity waves etc. In electrostatics things get complicated when the charges move; the same is true for gravity. How complicated can be illustrated by weirdness ranging from the Tipler cylinder to less apocalyptic frame dragging around compressed stars, even to Mercury. But nobody wants to work out tensors with a pen and paper on a homework problem, so our awareness tends to shy away from this part of the theory. Wnt (talk) 21:25, 23 October 2015 (UTC)

When I was in college, I asked this of a professor who had done work in General Relativity. He said the speed of light. Bubba73 ^{You talkin' to me?} 04:06, 24 October 2015 (UTC)

How old is the Suidae family?

--Romanophile (talk) 08:18, 23 October 2015 (UTC)

Possibly Eocene, definitely Oligocene, but to quote this paper on the phylogeny, "The Paleogene history of Suidae is still almost unknown and the early evolutionary history of the family is therefore poorly documented". Mikenorton (talk) 08:38, 23 October 2015 (UTC)

Yes, our article on the peccaries agrees that they were differentiated in the late Eocence or early Oligocene.

This is a rather technical question; is it just a matter of curiosity, or are you looking for a source for scholarly purposes? μηδείς (talk) 03:57, 24 October 2015 (UTC)

I would tell you, but I dislike you. --Romanophile (talk) 06:46, 25 October 2015 (UTC)

Yes, given your edit history, I can see why. μηδείς (talk) 02:33, 27 October 2015 (UTC)

Romanlover might have been trying, in his clumsy way, to make a joke - as if to answer his own question as to whether great apes have a sense of humor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:14, 27 October 2015 (UTC)

Why does hair growth in the ear increase among elderly humans?

What biologically clicks at that later stage in life to stimulate follicles in the ear? 20.137.7.64 (talk) 14:35, 23 October 2015 (UTC)

Who says it does? ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:52, 23 October 2015 (UTC)

Wikipedia. "Hair growth within the ear canal is often observed to increase in older men" Me: why? I see a mention of the Y chromosome in that link #2, but nothing relating the age factor.20.137.7.64 (talk) 15:04, 23 October 2015 (UTC)

Lots and lots of people claim this, surely you've heard of the notion? It may even be true. Here's some coverage from Popular Science [2], and here's [3] some coverage at Straight Dope. SemanticMantis (talk) 15:02, 23 October 2015 (UTC)

This is a pretty comprehensive answer from a Newspaper health column, noting that, during the aging process, the cycle of growth and shedding of hair changes, so that hairs that would have normally been shed after only a short time may remain and continue to grow for longer times. The reason why this happens in old age among men is not entirely known, but it is suspected that it may be due to the cumulative effects of testosterone on the hair cells in those body areas. That is, it isn't the momentary level of testosterone in the body, but rather the fact that an older man has had many decades of a certain level of testosterone in the body, and the cumulative effects of testosterone changes the way hair grows, which is why older men have hair growing out of various body parts that they didn't notice in their youth. That makes some sense (though as noted, it's a speculative reason, and not entirely well understood), since one of the effects of testosterone is increased hair growth. --Jayron32 15:55, 23 October 2015 (UTC)

It is not well documented that there is an increase in the quantity of hairs. Pretty much everyone has some hair inside their ears - they are just small and thin. They go from the anagen (growing) phase to the catagen (stop growing) phase very quickly. As people age, many areas of the body tend to have hairs that stay in the anagen phase longer and longer. So, the hairs grow for a longer period of time - getting longer than thicker. Therefore, if it is true that the quantity of hair remains constant, the length and thickness of hair will increase. Unfortunately, it is not known what causes the change in anagen duration. Testosterone is a prime suspect, but the actual mechanism has not been published in any of the AMA journals (I did a very wide search, but it is possible I missed one). 199.15.144.250 (talk) 16:38, 23 October 2015 (UTC)

From an evolutionary POV, we should also ask what the evolutionary advantage was, of prolonged exposure to testosterone causing changes in hair growth patterns. Knowing people's ages is important for survival of a group, and this is just one of many age markers. For a practical example, a tribe might put more weight on the advice of elders, who presumably have more experience, and more hair in the ears might be one way to identify such elders. StuRat (talk) 20:46, 23 October 2015 (UTC)

I have the feeling that any effect from testosterone on ear hair is probably not driven by evolution. Testosterone does have well-documented effects on hair follicles, specifically the androgenic hair, but those effects are along the lines of signaling sexual maturity. Not every characteristic of an organism is the direct result of natural selection; some things are just random. Evolution is a messy and chaotic process, and we need to be careful not to assume every trait is the result of a "just-so story". --71.119.131.184 (talk) 21:34, 23 October 2015 (UTC)

Yes, what you are mentioning is spandrel (biology). I suspect ear hairs must be developmentally more closely related to beard hairs, given the latter don't seem to suffer the ravages of old age, but that's just my guess. μηδείς (talk) 22:22, 23 October 2015 (UTC)

Just for the fun of it I will mention the wonderful product at cat-ears.com, which is intended to reduce wind noise when cycling. Ear hair has a potential benefit of providing noise cancelling function. See also "dead cat" windscreens for microphones. Or it could be a spandrel, hard to say :) SemanticMantis (talk) 22:52, 23 October 2015 (UTC)

I am jealous. Back when I rode bikes they didn't have helmets. I do still have the scars.... μηδείς (talk) 03:47, 24 October 2015 (UTC)

Deriving energy from air pressure changes

If you have a large air reservoir, such as a cave system, with a small opening (perhaps one you sealed up), I would expect that air would blow in and out of that opening at high speeds, and thus could power a windmill, whenever the air pressure changes. Has this method ever been used to produce energy ? StuRat (talk) 21:06, 23 October 2015 (UTC)

To store and then release energy, something along those lines can be done: Compressed air energy storage. As to producing energy, if air is blowing in and out of somewhere, that's wind. You don't need to force the air through a confined space to make it turn a windmill. If you do, you lose some of the energy available to turn the windmill. Compressing a gas heats it up, and some of the heat will be transferred to whatever it's in contact with. --71.119.131.184 (talk) 21:23, 23 October 2015 (UTC)

I don't think you got the gist of the Q. The air pressure differential between the air inside and outside the cave will cause wind to blow, and that differential will occur whenever the air pressure rises or falls due to changing weather. Sure, you can put windmills in other places, but this one would provide energy at different times than those, and perhaps fill in the gaps. StuRat (talk) 04:42, 24 October 2015 (UTC)

You would need an enormous cave to get the benefit of slight changes in atmospheric pressure, and the cave would need to be well-sealed without openings elsewhere. You could generate electricity only during changes in pressure, so the system would not be cost-efficient. I don't think it has ever been tried. Dbfirs 09:10, 24 October 2015 (UTC)

My great-grandparents owned a good-sized cave that we used to visit when I was a kid. I don't recall any significant wind blowing in or out. From the standpoint of atmospheric dynamics there's no reason there should be (assuming the cave system is effectively closed). Shock Brigade Harvester Boris (talk) 18:31, 24 October 2015 (UTC)

I don't understand your comment. Air pressure outside changes with the weather. Air then needs to move into or out of the cave to equalize the pressure. If there is a large opening, or many small openings, that wind going in or out may not be noticeable. But, a huge cave with a small opening should provide a strong wind for an extended period, until the pressure equalizes. It might be particularly useful to charge batteries to light the cave, say if the cave is nowhere near the power grid and not in a location that gets much sunlight or regular wind (perhaps because it's in a jungle). Of course, getting in and out of the cave, past the windmill, could be problematic. A separate, sealable door would solve that. StuRat (talk) 20:55, 24 October 2015 (UTC)

Sure, there would be a flow of mass in an out of the cave. But would the mass exchange produce a "strong wind"? Instead of arguing generalities try putting numbers on "huge cave", "small opening", and working it out. The math is not hard. Assume dp/dt of 100 Pa/hr, which is a reasonable value for pressure change following a frontal passage. For simplicity you can neglect the effect of adiabatic expansion on temperature of the air in the cave. Shock Brigade Harvester Boris (talk) 21:30, 24 October 2015 (UTC)

No need to speculate - there is a device called the "Atmos clock" which is powered in exactly the way you describe. The problem is that you're going to need a very large, well-sealed cave in order to generate much energy. It doesn't take much to power a clock. SteveBaker (talk) 02:18, 25 October 2015 (UTC)

That's interesting, but it uses a very small pressure chamber, while mine would be massive. Surely enough to power some LED lights to illuminate the cave. StuRat (talk) 03:46, 25 October 2015 (UTC)

I suppose you could use it to signal the approach of an anticyclone or depression, but a barometer would be simpler. The cave system might keep a battery charged to power a few LEDs when a series of fronts are passing, but a small windmill on top of the cave would be more reliable as a regular source of electricity, and much less expensive to install. If you have a particular cave in mind, try burning a candle in the entrance to see what the airflow is like. Dbfirs 07:07, 25 October 2015 (UTC)

Just for some back of the envelope calcs, if that clock uses an air reservoir 1 meter cubed, and my cave is 1 cubic km, that's a billion times more air, so should produce a billion times as much electricity. That should be a significant amount of power. StuRat (talk) 01:43, 26 October 2015 (UTC)

Those clocks use expansion of a liquid from temperature changes. I know of no clock that uses airflow, and the diurnal temperature change outside the cave would have little effect inside. Dbfirs 12:15, 26 October 2015 (UTC)

It's hard to believe that putting a wind turbine in front of the mouth of a cave would produce more energy than just sticking the exact same turbine outside to catch the wind. There are many problems with this scheme - one being whether enough of the air inside the cave would flow outside before the pressure reversed again. The actual mass of air moving from inside to outside might not be that much - especially if the pressure difference is small. The size of the passageways and their degree of convolution would matter because it would limit the rate at which the pressure could equalize. Also most caves have numerous small entrances and cracks leading to the surface - if those aren't plugged, then you'd lose a lot of airflow that way. SteveBaker (talk) 17:20, 26 October 2015 (UTC)

Color perception

Hey baseball bugs, I've always wondered if different people see and experience color in totally different ways. I'm also at a loss on how to either prove, or disprove this notion. Here's what I mean. Is it possible that when I see the color red for instance, that it's actually someone elses green? How can we be sure that we all perceive the correct colors? I'm confused. — Preceding unsigned comment added by 80.195.27.47 (talk) 22:47, 23 October 2015 (UTC)

Yes, humans have been discussing this for a long time, see qualia and refs therein. SemanticMantis (talk) 23:31, 23 October 2015 (UTC)

Do you not remember being taught colours when you were very young? We learn to associate the standard names with whatever variation we perceive. Some societies use very different names, so learn to "see" a slightly different spectrum. Dbfirs 00:38, 24 October 2015 (UTC)

There is actually a recently discovered objective answer to this question, referenceable to a very reliable source. Since my name is [not] Bugs I won't post it. μηδείς (talk) 03:44, 24 October 2015 (UTC)

@Medeis: Would you kindly clarify the second part of that post. Are you saying that you also post under the name Baseball Bugs? Akld guy (talk) 05:14, 24 October 2015 (UTC)

Oops. added the missing "not". μηδείς (talk) 16:38, 24 October 2015 (UTC)

Thank you. It simply didn't occur to me that there might be a skipped word there. Akld guy (talk) 18:14, 24 October 2015 (UTC)

I think it's rather obvious that Medeis meant to say that his name isn't bugs and that he was making a snarky critique of the fact that the OP addressed their question to Bugs specifically for some reason. I've no idea why the IP would directly inquire of Bugs for an answer to that question in particular, but I'm even more confused (as I have found myself on a not small number of occasions...) as to why Medeis feels a passive-aggresive response improves a situation like this.

Anyway, turning to the actual question at hand, SemanticMantis was quite right to point the OP to qualia. I'd add for the OP only that, while there are deep questions of subjectivity implied here that have largely thwarted ancient philosophers and modern cognitive scientists alike in trying to nail down, as someone who comes from a deep background in visual cognition, I take the pure subjectivity/"we can never really know if what we experience is close to what others experience" notion with a grain of salt. While consciousness and experiential sensation are as-yet poorly-defined and -understood phenomena, we do know a decent bit about the mechanics of the systems implied in their creation. That is to say, we may not know all the ins-and-outs of how conscious experience arises from the sensory organs and the brain, we do know how a great deal about the mechanics of said sensory organs and we know which areas of the brain are involved with the creation of specific types of sensory phenomena, and a fair bit about their general structure. And one of the things we know is that, much like other neural modules, they tend to be pretty similar across members of a given species. So, while there's really no way any of us will ever know for certain, I suspect that (assuming you have generally typical vision in the empirically testable sense - no colour-blindness, no impairment of vision arising from defects in the eyes or visual centers of the brain) you and I see "red" in very much a similar fashion. Certainly, it's highly unlikely that what I experience as red, you experience as green and vice-versa. While the philosopher in me must concede that there is no way to know for certain, or even to conceptualize what it might be like to experience another's senses, as a scientist with experience in this area, every materialist clue I know of leads me to believe that we're mostly experiencing the same colors from a given source of stimulation.

For me, the much more interesting question is, what is like to experience reality from the perspective of a creature that has an entirely different kind of sensorium or even a different type of modality to a sense we are roughly familiar with? What's it like to see colours we don't have names for because of different types of ocular photoreceptive cell sensitive to different wavelengths of light, or because the mechanics of the eye cause it to focus in a different way, or because the visual array processes that data drastically differently because of the ecological niche in which the organism evolved? I've spent a great deal of my life wondering about and studying those questions and it's a funny thing to pre-occupy oneself with, because at the end of the day, I'm forced to admit that I'm no closer to an answer for the subjective questions that then arise than literally any other human who has ever existed! To say nothing of speculating on what it might be like to "see" in ways that don't involve photoreception but may use similar areas of the mammalian brain to construct a 3D environment from other sensory modalities. Here's an old chestnut for you: do bats dream in sonar? Snow ^{let's rap} 09:23, 24 October 2015 (UTC)

And do androids dream of electric sheep? Richerman (talk) 09:33, 24 October 2015 (UTC)

The OP had asked a question on the language desk that mentioned colors, and I was one of the responders. As to why he singled me out here, I expect he was drawn by the charismatic nature of my user ID. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:14, 24 October 2015 (UTC)

• To add some pointers, this question was first posed by John Locke in the 17th century, and has been discussed by philosophers ever since. It is generally known as the inverted spectrum problem, and remains very controversial. Looie496 (talk) 12:20, 24 October 2015 (UTC)

@Looie496, SemanticMantis, Dbfirs, Medeis, and Snow Rise:commenter think answers in philosophy category, not science desk, humanity deskMahfuzur rahman shourov (talk) 15:16, 24 October 2015 (UTC)

This is a very interesting question with regards to animal behaviour. Some animals (e.g. some birds, rodents, fish) are visually receptive to UV (most humans are not because it is blocked by the cornea). My understanding that the signals from the cones are not kept separate, but are summed, so animals with UV reception do not see just additional colours in the UV part of the electromagnetic spectrum, but all their perceived colours are changed. Some vipers and invertebrates "see" in infra red!DrChrissy ^(talk) 18:41, 24 October 2015 (UTC)

Quite right on the first point, although I'd used a different term than "summed". Suppose we had a tetrachromat (an organism whose eyes has photoreceptors keyed to four different spans of wavelength of light), as opposed to the three humans have. Let's further suppose that three of those cell types are identical to the three humans have. That creature's eyes would not be able to just perceive an extra 25% of colours. Rather they would be capable of discerning a 100 times as many hues. And virtually everything they saw would have a different colour from how we perceive it, because it would be "tinged" in ways we can't perceive.

On the other hand, just because you have an eye capable of absorbing a photon of a particular wavelength and translating that to the firing of a neuron does not mean you automatically get all of the benefits of "perception" of all of the "colours" that can come from combining all such stimuli into a hundred million hues, because this perception arises as much out of how the nervous system of the organism utilizes that information as it does the raw data itself. So even though there are creatures who do in fact have four or more types of photoreceptor in their ocular organs, all evidence suggests that they actually "see" colour in a much more limited fashion, as the visual cognition portion of their brains are generally vastly more simplistic than our own. They are probably just perceiving a very small number of colours from within the span that their eyes can detect, because those wavelengths happen to correspond to environmental ques that are important to them in their ecological niche.

I think it's also important to distinguish in your pit viper/invertebrate example that these are actually two vastly different modes of sensation. Those snakes that are sensitive to distal/non-tactile heat perception accomplish this feat through a specialized organ that actually perceives the heat itself. This is very different from those organisms who see into the infrared (or, as is often more accurately the case the "near infrared") spectrum through photoreception. The radiative source may be the same for both, but the mechanism for perception of it is worlds apart. Snow ^{let's rap} 21:34, 24 October 2015 (UTC)

The question is easily answered. Many, many people are colorblind (I'm not considering the kind where they can't see any colors - but rather the various kinds where color perception is somehow reduced or limited). Those people quite clearly see color differently than those of us who have full color vision - yet they assign the same names and associations to those colors - and very commonly don't realize that they are colorblind until some specific incident makes it obvious. John Dalton was the first person to comment on the subject - even though there must have been millions of color blind people before his time. His remarks are quite telling: "...that part of the image which others call red appears to me little more than a shade or defect of light. After that the orange, yellow and green seem one colour which descends pretty uniformly from an intense to a rare yellow, making what I should call different shades of yellow".

But an enormous number of people before Dalton must have gone through their entire lives not realising that what they were seeing as "green" was really "yellow" (or whatever).

SteveBaker (talk) 02:15, 25 October 2015 (UTC)

For colorblindness, see the third section of Wikipedia:Reference desk/Archives/Science/2015 October 17, where we discuss the "EnChroma" company's new glasses that help alleviate some of the problems caused by colorblindness. Nyttend (talk) 02:25, 25 October 2015 (UTC)

Notice though that there is a subtle difference between what you are discussing and what the OP was inquiring about (as I read the question anyway). Those with colourblindness simply have a lower number hues that they can see. But they don't perceive red as green and vice versa, as the OP was inquiring about. The colours they are physically able to precept, they presumably see the same as anyone else capable of perceiving that colour. Or perhaps not, but that's the philosophical question the OP is raising, anyway. There's a difference between the question of what a person perceives based on the adequacy of the mechanisms that receive the sensory stimuli and the question what a person perceives based on how their minds process that information and the confusing issues of subjectivity raised thereby. Today we can easily test and account for the former (not withstanding the fact that, as you say, many people throughout the ages probably had no idea they were colourblind) but we have absolutely no way to validate the latter. Snow ^{let's rap} 02:49, 25 October 2015 (UTC)

You'll have to forgive me, @Snow Rise: some patience for having no desire to directly answer an OP whose very question is worded as a challenge to a rather well-esteemed good-faith regular here. Especially when that regular has been the subject of direct attacks against his user name for the recent passing season.

There is indeed a peer reviewed university professor whose work does show that one can in reality prove that certain people with a rather unusual genome do have a reversed color spectrum compared to that of the conventional population, and Locke's hypothesis is both answered in full and disproven.

I have both that post-grads' paper proving that Locke's notion can be shown to be false, and his college textbook which disproves the supposition. But for some strange reason, I don't feal like bothering to answer, given the way the question has been posed. TANSTAAFL. μηδείς (talk) 04:50, 25 October 2015 (UTC)

Was referencing Bugs by name meant as a challenge to him? Even if the OP had a difference of opinion with Bugs in another thread elsewhere, the wording here didn't seem terribly confrontational ("Hey Bugs, I've always wondered..."). Anyway, even if you are correct and you didn't feel compelled to provide a substantive answer to the question, surely the best option is to provide no answer at all, rather than a passive-aggressive "I could tell you but I'm not gonna, nyah."

Anyway, getting back to the issue at hand, I'm confused as to what you mean by "a reversed colour spectrum"; perhaps direction to the relevant research or some sort of contextualization would help to make sense of that statement, but as it stands, it's word soup. No one has a personal colour spectrum; the colour spectrum is simply a representation we use contextualize the qualia associated with the sensations which result from perceiving certain wavelengths of light. Saying you can reverse that is like saying you can reverse the smell of something; it just doesn't make any kind of sense.

Furthermore, I think you've either misunderstood the question or your source if you feel that there is any way to empirically validate that the subjective experience of identical stimuli represents an identical experience between individuals. This is one of the oldest and most unapproachable questions in the history of philosophy, science, and indeed human experience broadly and I'm pretty sure we'd have all heard about it if someone had found a way to prove this and frame it in a manner that made any kind of sense in natural language.

All of that said, I'd love to see the paper to which you allude; this area used to be my bread and butter and I'm always happy to hear of perspectives within it. Snow ^{let's rap} 09:24, 25 October 2015 (UTC)

TheDress is probably as good empirical evidence as any that people with apparently normal vision _don't_ perceive colours similarly. Tevildo (talk) 16:15, 25 October 2015 (UTC)

I beg to differ; I think that example is great empirical evidence that even in this era of science and technology, most people aren't scientific. They don't understand that even when we address a difficult problem we must do so methodically. Most commentaries that I have read on this "phenomenon" imply that the authors don't understand the very essential basics of how digital imagery works on modern computer hardware, ... but it's worse than that! They don't even understand the scientific method. If everybody was tested in controlled conditions with a calibrated display on one computer, with one well-understood color image pipeline, we could draw conclusions about cognitive perception of colors. But, in the case of millions of independent internet commentators who all have "opinions about color," we had no methodology! The ensemble of subjects was a massive distribution of "independent observers" who all reported subjective opinions based on viewing unknown and widely diverse source images (not every copy of the image file distributed on the many different websites and sources across internet was anywhere close to bit-identical!) Thousands, if not millions, of diverse source image data were applied through each individual observer's personal computer or mobile device, all using different software and hardware processing stacks to convert from a compressed image file, rendered to a colorspace in software or hardware, and then output to millions of individually-owned displays, whose software, firmware, and hardware calibration, quality, and default settings are all unknown. The human test subject viewed the result in an unknown room, in unknown conditions, at unknown time of day, with unknown physiological and psychological conditions.

The failure to control the easy parts of the problem demonstrates the main issue with pop-science discussion about "qualia" and "psychoperception." We have a lot of very difficult unsolved problems related to cognition; but we also have a lot of very difficult, already-solved problems related to optical physics, computer image processing software, human eye anatomy, and so on. You can't expect to make forward progress in understanding of cognition and perception if you dive right into the "unsolved" parts without thoroughly understanding the already-solved parts!

We already know, from controlled experiment, that room lighting changes perception of color. Blood pressure, blood oxygenation, sleep deprivation, age, general health, eye health... all affect human vision. If we wish to test color perception on an audience, we must control for these known effects!

About the only thing we can learn from this "experiment" is that even many educated people do not really know the nitty-gritty details about how bits in a computer system actually get converted back into real actual colored photons. However, lots of people are ready to draw profound conclusions about mass psychology and color perception of those unknown photons!

Nimur (talk) 22:57, 25 October 2015 (UTC)

The matter is even more complicated than all that. Point in fact, this phenomena has been studied in a controlled manner with regard to some of the psychophysical phenomena you reference, but, even so, far from this phenomena providing "empirical evidence that people with apparently normal vision _don't_ perceive colours similarly", it actually just further highlights how difficult the question raised by the OP is. Even if we somehow found a way to control for all of the above criteria (a tall order indeed), and the many other possible conflating factors in the stimulus, the environment and the individual, we still would be no closer to answering this question empirically. Because we have no way to dependably measure the element which is actually being tested for. You could have identical displays, under identical conditions, and you could even (brain in a jar style) hypothetically plug those people's optic nerves into identical artificial eyes to look at the dress, but at the end of the day, what is being reported is still a subjective experience. And we have no way to share that experience than with human language. So one person says he bands are gold and another says they are brown. How do you know that they aren't actually seeing the same thing but just associate a different word with it?

I absolutely agree with you that there are a lot of factors here that need to be controlled for that people just don't intuitively appreciate as a general rule. But ultimately that's just a side issue. Even though we don't remotely have the technical ability to control for all of those factors, those still represent the "easy" part of the problem faced here. The real difficult part is not just something that is beyond our current level of technical expertise, but which we can kind of see how we might approach it if we only had vastly more sophisticated technique (as with the examples you listed above) it is something so confusing and beyond our ability to conceptualize that we just don't even yet have the first idea of how to tackle it, or even how to properly describe what it is we are really trying to measure. It just goes too far beyond the sort of phenomena our minds are intuitively designed to understand, and there's even a certain concession amongst cognitive scientists that it may be something we can never understand. Snow ^{let's rap} 23:32, 25 October 2015 (UTC)

Am is confuseding. I been commenter think answers in philosophy category, not science desk, humanity desk been being? μηδείς (talk) 02:44, 27 October 2015 (UTC)

Unfortunately, when it comes to cognitive science broadly (and the hard problem of consciousness in particular), it's pretty much impossible to disentangle the neuroscience/biophysics from the philosophy, even with regard to most of the particular discrete phenomena. The field is largely defined as an attempt to marry the difficult question of what exactly thought is with our materialistic understanding of the mechanisms which seem to, in some sense, give rise to it. This is definitely the right desk for the question, but you're never going to get an answer in this area which turns entirely on a mechanistic and fully satisfying explanation. At some point in the study of consciousness, even the most brilliant minds have to abandon empirical tools and rely to some extent on first principles extracted from philosophy. Anyone who studies cognition has to make their peace with it, early on.

And that's not to say that there need be any compromise of the scientific method in the formal study of mental phenomena; as with many areas of physics you just have to accept that there are some missing pieces that, if you look at them too directly, seem to call the whole extended framework into question and there's just no way of knowing when, or even if, those conflicts will ever be resolved by human minds. So, not to be pedantic, but wherever there is a complex problem that defies human intuition, philosophy is bound to play an important role. I think anyone who studies at the frontiers of science (certain areas in particular) develops a healthy respect for the fact that philosophy and science are really just terms for different stages of a unified process. But this issue is only now tangentially related to the OP's inquiry, so I'll leave it at that. Snow ^{let's rap} 03:46, 27 October 2015 (UTC)