Is it true that a rainbow requires an observer? Unlike a tree falling in a forest, which must certainly make a noise (IMHO),wouldn't the refracted light of a rainbow need to be seen to actually exist?

Is it true that a rainbow requires an observer? Unlike a tree falling in a forest, which must certainly make a noise (IMHO),wouldn't the refracted light of a rainbow need to be seen to actually exist?
All levels of vibration are remotely detectable by devices, and no observer need be present to record the event.

The light is still refracted, whether anyone sees it or not.

Is it true that a rainbow requires an observer? Unlike a tree falling in a forest, which must certainly make a noise (IMHO),wouldn't the refracted light of a rainbow need to be seen to actually exist?

This was somewhat tougher question decades ago, along the lines of Einstein's question to Bohr, "Do you really think the moon isn't there if you aren't looking at it?"

The standard answer now is that so long as any photons (and the wave functions of those photons) generated are interacting with other particles/wave functions on a large enough scale (including passing through the air), there would certainly be enough quantum decoherence to, in effect, collapse the wave functions of the photons. That would mean the photons would be in a definite state, and if the photons are there, in the proper wavelengths, so the rainbow would be.

That assumes we accept that the "wavelength" of light is the same as "color." On a more philosophical level, "color" is really an interpretation our brain makes as an easy way of discerning different wavelengths. Without a brain there, the photons would exist, and would each have a wavelength, but if you think of color as an artifact of brains interpreting stimuli, then without a brain you could not have "color," and that might lead one to conclude there is no "rainbow."

(The same can be said for sound, though, and you took a position on trees falling. One could argue in the same way that a falling tree would cause pressure waves in the air, what we call "sound waves", but without a brain to interpret, is a complex patter of pressure waves the same as "sound?")

Is it true that a rainbow requires an observer? Unlike a tree falling in a forest, which must certainly make a noise (IMHO),wouldn't the refracted light of a rainbow need to be seen to actually exist?
yes, an observer needs to be present to see the colors.
the droplets will still divide the the wavelengths but the colors will be absent without the observer.

Here's a live camera view of a waterfall. You can watch during the day to see rainbows appearing and you are not there.

http://www.google.com/url?sa=t&rct=j&q=rainbows%20from%20waterfalls%20web%20cams&source=web&cd=1&ved=0CDwQFjAA&url=http%3A%2F%2Fwww.fallsviewcam.com%2F&ei=_kyZT_XJLOa02gXf_YS4Bw&usg=AFQjCNEfD2zaceG23xfTNtK_3iQhVllCPw

On a more philosophical level, "color" is really an interpretation our brain makes as an easy way of discerning different wavelengths. Without a brain there, the photons would exist, and would each have a wavelength, but if you think of color as an artifact of brains interpreting stimuli, then without a brain you could not have "color," and that might lead one to conclude there is no "rainbow."

It really isnt on a philosophical level though, Is it? What began as a philosophical question, finished with a scientific answer.

Is it true that a rainbow requires an observer

The phenomenal appearance of a rainbow (the exhibited qualitative colors) is what requires at least a certain kind of sensory and cognitive system for organizing and discerning inputted data as such. Really, the manifestation of any spatially-extended form is dependent upon outer relations converging upon a receptive agent that can interpret that information (just try being dead and still having the world manifested as visual, audible, etc, evidence). The planet Mars, as it existed in itself, certainly wouldn't be a visual image of a red dot in the sky, or a round reddish body as viewed from orbit around it, or the flat landscape as apprehended from on its surface, or any of a variety of abstract technical descriptions in the physical sciences (what would brainless Mars or the brainless universe being doing dabbling in descriptions?). Things having their be-ing as observed bodies are as they are thought about or presented as existing outside themselves, as Mars or whatever exists to something else (humans in this instance).

Idealism was not about denial of things existing when not observed, but that they existed in some other manner than as conscious experiences or phenomena. Somewhere in either the Three Dialogues or Siris, even Berkeley eventually got around to acknowledging that a tree wouldn't be maintained as some biotic-like multiple-view set of perceptions in God, but in some noumenal-like way which he knew not what. Leibniz dropped the need for "God perceiving everything", but left God responsibility for his pre-established harmony; and then Kant dispensed with God altogether in his critique of theoretical reason, tossing a bone to theists only in his practical philosophy.

CC! It's a shame that they have a great mind like you, along with your body, just cutting grass.

If two people are a couple of miles apart, don't they see the rainbow in slightly different form or orientation?

yes, an observer needs to be present to see the colors.
the droplets will still divide the the wavelengths but the colors will be absent without the observer.

Does that include all sky light?

Does that include all sky light?It depends on what you mean by "color." We define certain wavelengths as red, yellow, green, etc. Even if we're not there to see it, the light still has the same wavelength.

Now all animals don't see the same way. Our eyes have three kinds of photoreceptors; dogs have only two so they see much less variety of colors, and for compensation they see better in dim light in black and white. Cats have even worse color vision and even better night vision than dogs.

But many animals have more kinds of photoreceptors than we do. They can see clear up into the ultraviolet range. For example, this is how birds can tell males from females when they look the same to us: their feathers have ultraviolet pigmentation that we can't see.

Bees have something like seven different kinds of photoreceptors. The ultraviolet spectrum is a riot of color to them. That's how they can tell which flowers are ripe enough to have nectar.

yes, an observer needs to be present to see the colors.
the droplets will still divide the the wavelengths but the colors will be absent without the observer.

Colors are not an artifact of your perception, they are divided by the wavelength of the light present. If the wavelength is present, the color is there plain and simple.

http://en.wikipedia.org/wiki/Visible_spectrum

Colors are not an artifact of your perception, they are divided by the wavelength of the light present. If the wavelength is present, the color is there plain and simple.

http://en.wikipedia.org/wiki/Visible_spectrum

Taking into consideration what FraggleRocker said, I now glean something different from what leopold said.

I now understand that leopold means that the diffraction into red, orange, yellow, green, blue and violet still occurs, but without a human present to see it, the image is absent, since that particular image as we know it is a product of human perception. If some animal were to observe it, that animal's mind might project the whole spectrum into shades of red, so the coloring we know and perceive is absent.

This kind of reasoning goes along the lines of that familiar question: what if the color palette I see does not look to you like the color palette you see, but we can't corroborate this fact because we have no way to communicate our perceptions to each other exactly?

This kind of reasoning goes along the lines of that familiar question: what if the color palette I see does not look to you like the color palette you see, but we can't corroborate this fact because we have no way to communicate our perceptions to each other exactly?It's certainly true that I have no way of knowing what image pops into your mind when you see an object that I call "orange" or "blue." Nonetheless we both agree on which frequency of the light spectrum we call "orange" or "blue." In some cultures they break the spectrum down differently, for example making a fundamental distinction between orangish-red and a more pure red, or regarding blue and green as different shades of one color.

Nonetheless, if we are both shown an object that is a specific shade of red or bluish-green, and then shown ten objects in slightly different shades of each of those colors, we will unfailingly agree on which one is the same color as the original, even if we argue over that color's name.

My point was that this is not true over species boundaries. Blue and green look absolutely identical to a cat, and the subtle tinges of ultraviolet that distinguish a ripe flower from an unripe flower in a bee's eye are completely invisible to us.

Of course some people lack one of our standard three color receptors, so they see colors more the way dogs do and don't understand why we distinguish between shades that look the same to them. This is what we call "color-blindness." They're actually blind to only one of what we call the "primary colors," and their world is not the black-and-white that the term seems to imply.

Colors are not an artifact of your perception, they are divided by the wavelength of the light present. If the wavelength is present, the color is there plain and simple.

http://en.wikipedia.org/wiki/Visible_spectrum

The wavelength is there, but "color" is an interpretation of wavelength made by the visual cortex. It's no different than "sounds. There are complex compression waves that move through the air (or other bodies), but "sound" is an interpretation of those waves that is created in the eye/brain working in concert.

Proof of that is that some people are color blind. It's not that the wavelengths do not exist for them, it's that their visual systems do not process those waves in the same way most people do, in a way that does not result in them seeing the "color" is certain wavelengths in the way that others will.

It's certainly true that I have no way of knowing what image pops into your mind when you see an object that I call "orange" or "blue." Nonetheless we both agree on which frequency of the light spectrum we call "orange" or "blue." In some cultures they break the spectrum down differently, for example making a fundamental distinction between orangish-red and a more pure red, or regarding blue and green as different shades of one color.

Inverted spectrum / qualia related fare keep hanging around as if no fatal criticism of such possibilities has been provided yet. But I agree that we have to assume humans are sharing the same operating system (barring minor perceptual and interpretative deviations and the more major ones that are known or detectable); or that we have no good grounds for assuming otherwise. And, if such inverted conditions were really that behaviorally and experimentally undetectable, then they could be ignored for never achieving a clinical status, anyway -- they would be unverifiable scenarios (amounting to metaphysical).

The wavelength is there, but "color" is an interpretation of wavelength made by the visual cortex. It's no different than "sounds. There are complex compression waves that move through the air (or other bodies), but "sound" is an interpretation of those waves that is created in the eye/brain working in concert. Proof of that is that some people are color blind. It's not that the wavelengths do not exist for them, it's that their visual systems do not process those waves in the same way most people do, in a way that does not result in them seeing the "color" is certain wavelengths in the way that others will.

Also, if these oscillating environmental energies (EM waves, atmospheric pressure waves, etc) had internal manifestations as images or sounds -- it would be a situation amounting to panexperientialism (http://en.wikipedia.org/wiki/Panpsychism). This as much applies to contact-related perceptions. A thorn doesn't possess "sharp pain" as part of its properties and the wafting molecules from rotten eggs don't have that strong odor literally inhering in themselves. These qualitative properties are supplied by the nervous and neural systems of a body or conscious agent in response to outer disturbances transpiring on its assorted kinds of receptive, sensitive tissue.

Proof of that is that some people are color blind. It's not that the wavelengths do not exist for them, it's that their visual systems do not process those waves in the same way most people do, in a way that does not result in them seeing the "color" is certain wavelengths in the way that others will.No, this is not true. Colorblind people have only two types of photoreceptors rather than the standard three. Their eyes literally cannot distinguish one-third of the colors that ours can. It's a physical difference, not psychological. The brain does not receive the signal because the signal is not sent; it has nothing to do with interpreting the signal.

CC! It's a shame that they have a great mind like you, along with your body, just cutting grass.

A kind of running joke as to the various things that "CC" could stand for. Next month it might be anything from "Cheap Copyreader" to "Conference Caller". Serves me right for randomly choosing a couple of letters for a username. ;)

Does that include all sky light?
light is tricky because it can either be particles or waves (apparently).
if light is considered solely as waves then yes.
the "tree in the woods" analogy is the same thing.
the tree produces the waves but the sound will be absent without the observer.

a similar analogy would be the transmission of radio and TV programs.
without the proper observer, a radio or TV, the programs will never be seen or heard.

My point was that this is not true over species boundaries. Blue and green look absolutely identical to a cat, and the subtle tinges of ultraviolet that distinguish a ripe flower from an unripe flower in a bee's eye are completely invisible to us.


Yes, good point, I actually had in mind the animals, such as certain insects and birds, that have ultraviolet perception. It's conceivable that all the colors we see would fit into that animal's perception in the way we see shades of red. (Assuming it sees them at all). That's sheer speculation, but one that considers what we might see if we looked through a system that compressed our visible range into the red band in order to reserve space for the shades of ultraviolet, which the system might remap into the bands that we perceive as orange through violet.

It remains an intriguing mystery as to how the continuum of wavelengths "appear" in the mind as hues. It does seem that in general each sighted species is endowed with a perception of spectral differentiation that has a benefit of distinguishing specific markers for essential needs such as food, mate, and camouflage. This, and perceptions like shape and patterns, are part of the larger question of what it means to assemble the pulses from the optic nerve into the phenomenon of sight, through many functional layers, resolving into the visual experience itself.

Now that PET scanning gives some clue about how brainwave patterns correlate to particular images (presumably a person looking at a rainbow might exhibit a particular pattern) we are practically left on the doorstep to continue to ponder what it really means to perceive anything at all.

light is tricky because it can either be particles or waves (apparently).
if light is considered solely as waves then yes.
the "tree in the woods" analogy is the same thing.
the tree produces the waves but the sound will be absent without the observer.

a similar analogy would be the transmission of radio and TV programs.
without the proper observer, a radio or TV, the programs will never be seen or heard.

Yes, I understand now you are addressing perception. I thought Epictetus was asking whether refracted light would propagate at all without observation. I thought maybe he was inviting discussion of what observation means. At first I thought you were requiring perception in order to have observation in that sense. I asked about sky light since it would necessarily be the result of atmospheric refraction.

I was prepared to offer a chloroplast as an observer. It then occurred to me that refraction within the lens and vitreous humor of the eye, and then again at the nerve net in the retina where at last the photon sets up the electrochemical propagation of a colored pixel down the optic nerve, would present the argument that all visual perception is of refracted light.

I see now that you were simply addressing perception.

The wavelength is there, but "color" is an interpretation of wavelength made by the visual cortex. It's no different than "sounds. There are complex compression waves that move through the air (or other bodies), but "sound" is an interpretation of those waves that is created in the eye/brain working in concert.

Proof of that is that some people are color blind. It's not that the wavelengths do not exist for them, it's that their visual systems do not process those waves in the same way most people do, in a way that does not result in them seeing the "color" is certain wavelengths in the way that others will.

I don't understand how you not seeing it makes it not there. The wavelengths are still scattered if your there or not.

light is tricky because it can either be particles or waves (apparently).
if light is considered solely as waves then yes.
the "tree in the woods" analogy is the same thing.
the tree produces the waves but the sound will be absent without the observer.

a similar analogy would be the transmission of radio and TV programs.
without the proper observer, a radio or TV, the programs will never be seen or heard.

If the waves are there, the sound is there plain and simple. If I put a microphone there to record the waves and play it back I hear the sound. There same information is present whether or not someone is there to hear it.

Is it true that a rainbow requires an observer? Unlike a tree falling in a forest, which must certainly make a noise (IMHO),wouldn't the refracted light of a rainbow need to be seen to actually exist?
In my opinion there are two distinct plans.
One is the reality and another is our perception and reflection of this reality in our mind.
It would be interesting to analyze the interdependence of these two plans.
Especially if our perception and reflection in our mind, change the reality.

Yes, good point, I actually had in mind the animals, such as certain insects and birds, that have ultraviolet perception. It's conceivable that all the colors we see would fit into that animal's perception in the way we see shades of red. (Assuming it sees them at all).I haven't read that much about this, but so far it seems that animals who can see into the ultraviolet range have more kinds of photoreceptors than we do, so they do indeed see a wider spectrum than we do: all the colors we see and then more. For a bee with his seven receptors to our three, it's probably a whole octave more.
It does seem that in general each sighted species is endowed with a perception of spectral differentiation that has a benefit of distinguishing specific markers for essential needs such as food, mate, and camouflage.Our species is an interesting case study. All of the other primates are grazers, but as our brains grew larger and we invented hunting tools, we evolved into the planet's apex predator. The only other predators whose eyes I know anything about are dogs and cats, and compared to their vision ours is still that of a grazer. Our night vision is desperately poor but in good light we can tell the ripe fruits from the green ones and the poisonous mushrooms from the nutritious ones. That's a skill that was vital to our herbivorous ancestors but today all it's good for is making a slightly tastier salad to garnish our slab of meat.

Oh yeah, and appreciating art!
we are practically left on the doorstep to continue to ponder what it really means to perceive anything at all.This is supposed to be the Century of Biology, as the last one was the Century of Physics and the one before the Century of Chemistry. But I don't know if that's supposed to include psychology or we'll have to wait another hundred years for it.

Is it true that a rainbow requires an observer? Unlike a tree falling in a forest, which must certainly make a noise (IMHO),wouldn't the refracted light of a rainbow need to be seen to actually exist?

How is saying this any different then saying if no one oberserves the sun it is not there? Both are physical phenomena that don't need you.

I wondered often, how we would perceive the reality if we would have more sensors.

Electroreception (http://en.wikipedia.org/wiki/Electroreception) , Magnetic-field perception (http://www.unc.edu/depts/geomag/PDFGeomag/2010LohmannNatureQ&A.pdf) , Non-human senses (http://en.wikipedia.org/wiki/Sense#Non-human_senses)

I wondered often, how we would perceive the reality if we would have more sensors.

Electroreception (http://en.wikipedia.org/wiki/Electroreception) , Magnetic-field perception (http://www.unc.edu/depts/geomag/PDFGeomag/2010LohmannNatureQ&A.pdf) , Non-human senses (http://en.wikipedia.org/wiki/Sense#Non-human_senses)

It would look cool for a while I'm sure, but would the information be useful or just confusing?

Colors are not an artifact of your perception, they are divided by the wavelength of the light present. If the wavelength is present, the color is there plain and simple. ...At best that is only partially true, but mostly false. Yes if a "white" sheet of paper is illuminated by one narrow band of visible wavelengths, it will produce some neural activity in all of the three retinal detectors. The relative intensity of these three channels is what make you call it for example yellow.

However there does not need to be any of that wavelength band entering into your eye for you to see "yellow." By careful adjustment of the intensity of three different wavelengths (say each one at the wavelength of the peak sensitivity of the three different color receptors), you can again make the identical relative neural activity in the three channels. That is all your brain has to work with, so of course you will again perceive the light as yellow.

Edward Land, inventor of the polaroid film process developed a theory of color called Retinex Theory of color. Details at: http://www.trincoll.edu/depts/ecopsyc/courses/retinex.html

Which exploited this fact (closely related to "color constancy" - fact that a leaf still looks green even if the illumination has no "green" light say when only illuminated by the very reddish orange setting sun). Here is an image with only red wavelengths + uniform white light, but parts of image definitely are not just different intensities of pink.
http://people.msoe.edu/~taylor/eisl/land/hamb.gif
"This idea was first demonstrated by Edwin Land, the founder of Polaroid, in 1959 by using two slide projectors. Each projector had a black and white slide in it, and one projector had a red filter in front of it. Oddly enough, recent updates of psychology textbooks seem to omit any mention of this experiment." image and this quote from: http://people.msoe.edu/~taylor/eisl/land.htm

Land gave this demonstration (and many others) while speaking at JHU. I was an amazed graduate student in the audience, as prior to his visit I believed falsely what most believe: I.e. that wave lengths present determine the perceived colors.

By the way you already know the simple theory you believe (wave lengths present determine color) is false. Just take piece of green paper, cut it into two small pieces. Place one on large blue sheet and the other on a yellow sheet - the two greens will be very different in perceived colors.

Summary: color perception is far more complex than most believe. Part of the reason you see leaves as green in the setting sun light, is you know the leaf is green. To remove this "knowledge effect" experimenters use different size adjacent rectangles each with different spectral reflectivity (but some pairs identical), called Mondrian patterns. More on them, "color constancy" & Retinex theory here: http://www.neuronresearch.net/vision/files/retinex.htm

It would look cool for a while I'm sure, but would the information be useful or just confusing?
I personally would want. About others I can not pronounce.
(How about an electrician with electroreception, or a sailor (explorer) with magnetic-field perception !? :cool: )

How is saying this any different then saying if no one oberserves the sun it is not there? Both are physical phenomena that don't need you.
and that's the point.
the sensation of sound is not a physical phenomenon.

at best that is only partially true. Yes if a "white" sheet of paper is illuminated by one narrow band of visible wavelengths, it will produce some neural activity in all of the three retinal detectors. The relative intensity of these three channels is what make you call it for example yellow.

However there does not need to be any of that wavelenth band entering into your eye for you to see "yellow" By carful adjustment of the intensity of three different wavelengths (say each one at the wavelenth of the peak sensitivity of the three different color receptions, you can again make the identical relative nerual activity in the three channels. That is all your bain has to work with, so of course you will again perceive the light as yellow.

Edward Land, inventor of the polaroid film process developed an theory of color called Retinex Theory of color. Details at: http://www.trincoll.edu/depts/ecopsyc/courses/retinex.html

Which exploited this fact (closely related to "color constancy" - fact that a leaf still looks green even if the illumination has no "green" light say when only illuminated by the very redish orange setting sun). Here is an image with only red wavelenths + uniform white light, but parts of definitely are not just different intensities of pink.
http://people.msoe.edu/~taylor/eisl/land/hamb.gif
"This idea was first demonstrated by Edwin Land, the founder of Polaroid, in 1959 by using two slide projectors. Each projector had a black and white slide in it, and one projector had a red filter in front of it. Oddly enough, recent updates of psychology textbooks seem to omit any mention of this experiment." image and this quote from: http://people.msoe.edu/~taylor/eisl/land.htm

Land gave this demonstration (and many others) while speaking at JHU. I was an amazed graduate student in the audience, as prior to his visit I believed falsely what most believe: I.e. that wave lengths present determine the perceived colors.

By the way you already know the simple theory you believe (wave lengths present determine color) is false. Just take piece of green paper, cut it into two small pieces. Place one on large blue sheet and the other on a yellow sheet - the two greens will be very different in perceived colors.

I wouldn't say what I said was false, just that it's not the complete story and the color can be influenced in other ways, but these thing of which you speak have to do with your PERCEPTION of the color, if the wavelength is there, the color is still there. If you take a spectrometer and measure the spectrum coming off of the green paper in your experiment, its still green. The overwheleming blue simply confuses your visual processing. The wavelengths are still determining the color either way. If you put another color of paper that was also capable of changing your perception of the green paper, would it not be a different color percieved then if it was on the blue paper? The wavelengths are not changed, only your perception of them and I would bet that this perception change is related to the other wavelength present, which still means that the wavelength determines the color.

and that's the point.
the sensation of sound is not a physical phenomenon.

Sound is the movement of air molecules, how is that not physical????

Sound is the movement of air molecules, how is that not physical????
uh, the transverse waves are the physical phenomenon.

... (1)The wavelengths are still determining the color ......(2)The wavelengths are not changed, only your perception of them and I would bet that this perception change is related to the other wavelength present, which still means that the wavelength determines the color.No you are so convinced of the false idea that you confuse wavelength with color.

For example a "color blind" person (or non human) does experience the same wavelengths but not the experience the same color. Even just your memory can change the color you perceive. You can perceive blue color when there is only uniform white light present. (Just stare at a bright yellow spot for a minute, then look at the white wall.) Of course if you had stared at bright blue spot for a minute then exactly the same light from the white wall will cause you to see yellow spot. Ergo- wavelengths need to be present but do NOT determine the perceived color. Thus the only truth in your statement I numbered (1) is:.

(1) If no wavelengths are present then you see no color.

Point I was trying to get you to understand was that no matter what set of wavelengths is present, if their intensities are adjusted to make the same relative neural activity ratios in the three different color receptor cells as when only single wavelength we call yellow is present, you perceive yellow EVEN IF NO WAVELENGTHS EVEN CLOSE TO YELLOW LIGHT ARE PRESENT.

(2) Yes the wavelengths (and their relative intensities, plus 6 or more other factors) do determine the color perceived but their is no simple connection between wavelengths present and color perceived.

I wouldn't say what I said was false, just that it's not the complete story and the color can be influenced in other ways, but these thing of which you speak have to do with your PERCEPTION of the color, if the wavelength is there, the color is still there. If you take a spectrometer and measure the spectrum coming off of the green paper in your experiment, its still green. ...Your confusion is most clear here. There is no color with, in, or at the spectrograph - only EM energy of some wavelength. Color is NOT same as wavelength. Color is sensation, a qualia, created in a brain.

You do not have any "perception of the color." Color IS a perception, just like fear, pain, etc. and other qualias

Sound is the movement of air molecules, how is that not physical????No, you are still confused. Sound is a brain created qualia, sensation. What is physical is the compressive density wave traveling it the air, usually.

Can't win um all I guess :)

If two people are a couple of miles apart, don't they see the rainbow in slightly different form or orientation?No, but one may see a more complete or intense rainbow. It shape and angular relationship to them will be exactly the same. This is true because the rainbow is not a physical thing that can be looked at from different angles or perspectives. It very definitely requires an observer to exist. It is a creation of the observerīs mind, is not a physical object:

http://eo.ucar.edu/rainbows/RNBW5.GIF

As at Earth the sunīs rays are essentially parallel (0.5 or less degrees of angular divergence) any one water drop sphere will send to your eye only one color. Lets assume, just to be clear, that the drop of the illustrationīs blue ray is entering your eye. (Its red ray is passing below your head. It might even strike the ground a mile in front of where you stand.) Another drop higher above it can send its red ray to your eye. I.e. coming to your eye are rays at 40 & 42 degree rays. You assume, correctly, that the 42 degree or red ray is from a higher source than the blue 40 degree ray. Thus you perceive the red color as coming from an arch larger than the blue color arc you perceive.

Every observer of every rainbow always sees the red arc 2 degree wider, higher, etc. than the blue arc – Thus the shape of all rainbows for all observers who see one is identical, but again, one may see only a small part of the rainbow arc if there are not water drops where they need to be for him. You can make a quite nice rainbow with fine mist garden hose, if you know how.* Also if you know where to look occasionally you can see the much weaker larger rainbow. It has the red arc inside the blue arc. I have seen it a dozen of so times.

*Even make the full 360 degree circle, but you will need help. I.e. someone else makes the mist for you in front you, when you are say looking out from a second story porch but sun must be coming from your back side. (House can not be blocking the sun.)
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This is same story for the 22 degree halo sometimes seen around the moon, but it is a little more interesting in its physic. If you shine a beam of monochromatic light thru a prism its direction of travel will change. Exactly how much depends upon the angle the incident ray strikes the first surface of the prism. If your “prism” were a hexagonal ice crystal, as your twist the crystal you will find that the beam is always bent by at least 22 degrees.

Thus in addition to the moon light going directly to your eyes, a part of the sky say 23 degrees from the direct line of sight with ice crystals can bend a little moonlight back, thru 23 degrees into your eye. That at 22 degrees can too, but that at 19 degrees cannot. I.e. the inter edge of the moonīs halo is quite sharp but the outer edge does not really exist – the halo light bent thru 25 degrees is just much weaker, etc.

No, but one may see a more complete or intense rainbow. It shape and angular relationship to them will be exactly the same. This is true because the rainbow is not a physical thing that can be looked at from different angles or perspectives. It very definitely requires an observer to exist. It is a creation of the observerīs mind, is not a physical object:

http://eo.ucar.edu/rainbows/RNBW5.GIF

As at Earth the sunīs rays are essentially parallel (0.5 or less degrees of angular divergence) any one water drop sphere will send to your eye only one color. Lets assume, just to be clear, that the drop of the illustrationīs blue ray is entering your eye. (Its red ray is passing below your head. It might even strike the ground a mile in front of where you stand.) Another drop higher above it can send its red ray to your eye. I.e. coming to your eye are rays at 40 & 42 degree rays. You assume, correctly, that the 42 degree or red ray is from a higher source than the blue 40 degree ray. Thus you perceive the red color as coming from an arch larger than the blue color arc you perceive.

Every observer of every rainbow always sees the red arc 2 degree wider, higher, etc. than the blue arc – Thus the shape of all rainbows for all observes who see one is identical.

------------------
This is same story for the 22 degree halo sometimes seen around the moon, but it is a little more interesting in its physic. If you shine a beam of monochromatic light thru a prism its direction of travel will change. Exactly how much depends upon the angle the incident ray strikes the first surface of the prism. If your “prism” were a hexagonal ice crystal, as your twist the crystal you will find that the beam is always bent by at least 22 degrees.

Thus in addition to the moon light going directly to your eyes, a part of the sky say 23 degrees from the direct line of sight with ice crystals can bend a little moonlight back, thru 23 degrees into your eye. That at 22 degrees can too, but that at 19 degrees cannot. I.e. the inter edge of the moonīs halo is quite sharp but the outer edge dose not really exist – the halo light bent thru 25 degrees is just much weaker, etc.

Your perception of the rainbow can be differrent due to the things you spoke of earlier, but the scattered light that rainbow is made of is there whether you see it or not. It is not an artifact of your eyes or a hallucination due to a malfunction in sensory perception. Other animals can probably see them as well as long as there vision is sharp and sensitive, but they would be shades of grey rather then color, depending on the animal.

Can't win um all I guess :)Well at least you can learn - more that I can say for about half of the posters I correct.

Point I was trying to get you to understand was that no matter what set of wavelengths is present, if their intensities are adjusted to make the same relative neural activity ratios in the three different color receptor cells as when only single wavelength we call yellow is present, you perceive yellow EVEN IF NO WAVELENGTHS EVEN CLOSE TO YELLOW LIGHT ARE PRESENT.

(2) Yes the wavelengths (and their relative intensities, plus 6 or more other factors) do determine the color perceived but their is no simple connection between wavelengths present and color perceived
Interesting posts Billy T, thanks

Is it true that a rainbow requires an observer? Unlike a tree falling in a forest, which must certainly make a noise (IMHO),wouldn't the refracted light of a rainbow need to be seen to actually exist?

Actually the tree falling in the forest makes a shock wave in the air that isn't sound until a brain processes it as such....

Actually the tree falling in the forest makes a shock wave in the air that isn't sound until a brain processes it as such....
I think the rainbow is the same. The conditions for a rainbow are there, but you do need an "observer". A camera will work. BTW - Polarized sunglasses may cancel the rainbow effect.

The physical data for rainbows and falling trees are present. Outside agencies are capable of detecting and interpreting such an event. The degree to which the data is interpreted is subject to the interpretive capabilities of the observer. Ergo, interpretation of the physical data can vary.

... Polarized sunglasses may cancel the rainbow effect.An interesting comment, I had never thought of. Yes the light of the rainbow is probably somewhat (50%?) polarized, but different parts with different orientations. I.e. if view thru polarizer, some part should dim as the polarizer is rotated; which part that is will move along the arc.

Brewsterīs angle effect is why:

http://upload.wikimedia.org/wikipedia/commons/thumb/6/65/Brewsters-angle.svg/250px-Brewsters-angle.svg.png Note there are 2 internal reflections inside the drop for EACH ray color: http://eo.ucar.edu/rainbows/RNBW5.GIF
but the only transmitted ray illustrated is the one that comes to your eye as a rainbow. Also the second internal reflections are not illustrated (for the normally seen rainbow - but the second would if figure were explaining the weaker, rarely seen, "reversed" rainbow as for it there are three internal reflections.)

http://upload.wikimedia.org/wikipedia/en/math/f/a/c/fac3d3f1752c49cf18fadee84b22d112.png

where n1 is the refractive index of the initial medium through which the light propagates and n2 is the index of the other medium or the medium into which part of the light is transmitted. Air in the rainbow case. Normally, as shown in the illustration, n2 > n1 but not for the rainbow. I.e. the beam incident upon the reflecting surface is already inside the water drop and n2 is essentially 1.0 of air. After the sun light internally reflects off the “back side” of the drop the some what polarized reflected beam is still inside the drop, on its it third interaction with the air/water interface.

At that 3d interface the transmitted beam will become even more highly polarized than the internal beam striking the 3d interface. Iīm too lazy to try to compute the two angles of incident for the 2n & 3d internal interface reflection, but if either of them, especially the 3d, is near the Brewster angle, then the rainbow rays entering your eye should be quite polarized.

Taking 1.5 as index for water, the Brewster angle IN RADIANS, is ~(2/3) where I have made slightly improper use of the fact that for small angles the arctan, in radians, is just the (n2/n1) ratio. As a radian is about 57 degrees, (as I recall) the Brewster angle is about 2x19 = 38 degrees.

The internal angle of incident in rain drop illustration looks to me to be a little larger, so effect would not be perfect polarization, but for the careful observer, probably noticeable if one rotates the polarizer – sees a slight dimming swing along the arc of the rainbow with that rotation.

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BTW 1, for the same EM wave scattering physics that makes the Brewster angle effect, the blue sky is highly polarized in a ring around the sun. I.e. that part of the sky where the sunlight has scattered thru 90 degrees to get to your eye, but once again what part you will see almost dark (thru polarizer) will change as you rotate the polarizer. This is a simple experiment all should do when you have a cloudless day. PS - Donīt look at the sun, even thru polarizer. The dark spot in the blue sky is far from the direction of the sun.

BTW 2, instruments exist that use Brewster angle effect to quickly and accurately measure the index of refraction of clear liquids. I used one in a summer job with a small oil company (Lion Oil). They had hired me to evaluate the makerīs claims for his new, tiny, curved, perforated metal chips as a distillation column packing material.

First day on the job I mixed 55 gallons of toluene with 55 of benzene and spent the rest of summer trying to separate them by a less than three meter tall distillation column filled with his packing material. My best separation gave that column 22 "theoretical plates," which is quit good for that length column. (The column performance depends upon how quickly and when heat is applied to the boiler tank - that is what I varied each day.)

I wrote my report, and headed back to Cornell, and never learned if they spent a million or so dollars buying his expensive metal chips based on my report. I measured the degree of separation with the instrument I mentioned as existing - it sort of looks like a microscope, but is hinged to allow a drop of liquid to be place between two glass plates.

Nobody on Sciforums would argue the interpretation of the double slit experiment that "matter does not exist unless it is observed".

This is a Dr. Fred Alan Wolf view. (he is Dr Quantum)
http://www.youtube.com/watch?v=DfPeprQ7oGc

Einstein and most Sciforum members will argue that the moon is there even if it is not viewed by anyone.

I have been in a position to measure and document recurring paranormal psychic hits beyond scientific explanations, and until I see a valid explanation I am open to a multitude of theories regarding Youngs experiment.

But a rainbow needing an observer would be the same argument as a tree needing an observer in my opinion.