Light - solid, liquid or gas?

I have a related question, how is the red, green and blue derived from light?

Sure if we scatter it, they will appear, but in the light where is the red, green and blue?

Why red, green and blue?

Also, can radiowaves etc. also be broken down into red, green and blue, if not, why?

 

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Hello, Billy T,

I've no disagreement with the science you've presented but from the experience as having been a teacher for many years, I do have to mildly disagree with your approach.

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If too much depth is presented too early, the result - all too often - is a confused, bewildered student who feels overwhelmed. Too many of them will wrongly assume that "this stuff is just deep for me."

On many occasions, I've had a bright student raise a topic in class - a valid question that arose from something we were currently studying - and while attempting to answer it saw dismay spread across several other faces. They simply were not ready for that level of the topic.

Make no mistake here, I'm absolutely not in favor of "dumbing down", but one has to recognize that there is certain danger when moving too fast. Sadly, I've seen it happen more times than I care to count. Students require time to develop a feeling of confidence and comfortable familiarity at each plateau along the way before being forced to take the next plunge.

 

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light and radio waves are the same sort of thing (described by the same Maxwell's equations, but following Light's advice, I suggest you not bother with that now.) They do not really have any color. They have frequency and intensity. Color is a perceptual thing that happens in the brain, and it does not take much of one to derive "color" experience. Gold fish can do it better than humans can, and so can bees. I.e. the range of frequencies they can see and interpret as colors is larger than one octave, almost two while humans respond to less than one octave. (All the flowers you see as white, have very distinct colors to the bee, presumably beautiful colors, as that is how they know which is currently giving nectar. Bees see well out into the UV.)

If you are "color blind," you have only two different types of "cones" in your retina but normally there are three for humans and four for gold fish. These cones respond to the frequencies differently. Low frequency visible light will make the "red" cones respond more etc.

So coming to the brain are three different sets of responses of different type of nerves in the eye. It is sort of like a triangle - you could describe the location of any point in the triangle by telling the three distances for each of the corners. Or you could tell other combinations of information.

The "red, green and blue" dots you see on your TV up close are approximately best matches for the three different color cones in your eye, but even in grade school you learned of the three primary colors. They could be any set of three that are quite different from each other and any particular mix of the three corresponding intensities would still specify (to the brain) what the color is.

We call a set of basics descriptors "the basis set" (reasonable name is it not?). The red/ green/ blue basis set is not the only one used in the brain. In fact in V5 area of the brain (if memory is not failing me) we unconsciously convert to another "basis set." For example, in the red/green axis set of nerves, a high rate of neural firing means "Red" and a low rate means "blue" (or the other way round - I forget which way it is.)

The activity of one subset of V5 nerves encodes the "red/green axis" another subset encodes the "blue/yellow axis" and still a third set the "light dark axis." If you have been following you might say: "Hey you said there were three primary colors, how can you encode color in only two subset of nerves?"

Well, think of that triangle again. (You may have even seen a "color triangle" in a paint store, if not a psychology book.) If I tell only how far the color spot inside the traingle is from two of the corners, you know what color I am referring to. Beyond V5 in the brain, that is all your color system works on.

You can confirm that in some sense "blue is the opposite of yellow" at the perceptive level: Fixate a bright yellow spot (stare at it for two minutes, then look at a white wall - you will see a blue spot of the same size.

99% of the people who have any explanation for this will give you, at best, a half correct answer. It is true that you have metabolitically exhausted the cells that respond to yellow light, but not just in the retina. In V5 also and there, AFTER the transformation from the original basis set to the one used later in the brain, is where "blue is the opposite to yellow."

But as Light said/ advised me/ this is too much all at once, so just file it away and recall later.

 

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That was excellent, Billy T.!

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Going just a bit farther usually doesn't create any problem and I don't feel that you overloaded him. In fact, I believe you employed the best style found in a teacher's toolbox - providing just enough beyond the answer to pique his curiosity.

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Well done.

And I'll add just two more small things. First, in direct answer to his question "where is the red, blue and green in white light?", they (and the other colors) are all present IN the white light. Our color receptors and the mental interpretation we give to beam of light containing all the colors in the proper proportional balance is to "see" it as white.

While at another end of the spectrum (small pun), consider the action of pigments. We've just established that white light contains all colors, so what happens when white light strikes a pigmented object?

A pigment exhibits it's color by absorbing parts of the light and reflecting other parts. For example, blue paint is reflecting blue light. If we add red paint to the blue, it will now reflect green light. If we carry this experiment on to it's logical conclusion by adding paint of all the other colors, we wind up with black. No light is being reflected because all the colors (full spectrum) is now being absorbed by the paint.

So, let's follow this with a simple exercise. Take a brightly colored red rose into a totally darkened room, cover a flashlight (or torch, if you're British) with a transparent blue plastic film, and then shine the light onto the rose. What color would you expect to see?

 

You have me pegged right as a beginner but alas, I am too old to be a student. I've reached an age in my life where I've decided to learn more about the universe I live in. I wish I had started earlier. I never knew I would like cosmology and related subjects until I started reading about it. I appreciate your's and eveyone else's help here. Thanks for going easy. I'll have more questions soon and I hope I get the same co-operation then.

 

I'm sure you will.

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Despite a lot of what you see going on here, there are actually several nice people on board.

Also, don't forget that no one is ever too old to be a student. I learn new things every single day. I never plan to stop - and I'm 60+.

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I'm not quite that far but I'm gaining on ya. As you know I've been trying to learn as much as I can in a short time and am grateful for the answers to my queries. I have another one.

I hope I can word this properly. Light from the moon takes 1.5 seconds to get here. Pretend I have a spacecraft that can make the trip in whatever time it takes. Will the spacecraft because it has mass travel fewer miles than the light. Does light follow a geodesic thru spacetime whereas mass in motion is able to carve itself a shorter route thru spacetime? Mass will take longer but travel a shorter distance. Is this true or am I misunderstanding some principle?

 

OK....forget that one.

Do you think there is more than the spectrum of light that we know? Could there be light that actually has mass & can't be detected? Anything?

 

I lean towards gas, any particle that travels that fast has to be a gaseous like state. Besides anywhere there is high entropy or energy there is light.



Dedicated to light

 

I would ask if anyone can clear up this little aspect of light that is bothering me. Since an object with mass cannot travel faster than c can it travel at exactly c?

 

To address your earlier point, Light travels in a straight line unless it is either reflected, or bent by a gravitational field. The spacecraft, if it coudl travel at the speed of light, woudl take the same amount of time.
Theoretically an object with mass could travel at C, I suppose (I'm no physicist) but the fact of the matter is that it would take an infinite amount of energy to get to that speed, ergo it would be impossible.

 

The short answer is "no, that would require an infinite amount of energy". Thus, massive particles always travel at some v < c (higher energies -> higher v for a given particle) and massless particles always travel at c (higher energies -> higher frequency).

By the way, with respect to your initial question, of course it is none of the 3 since solid, liquid, gas, and plasma phases are all phases of matter. Having said that, I would say that light is most similar to an ideal gas. Photons have momentum so they can exert pressure like a gas. Photons do not interact with each other, one of the hallmark characteristics of an ideal gas. If you had a perfectly reflective container you could even "weigh" your photons just like you can weigh a gas and they would have inertia just like a gas would.

-Dale

 

I realize that darkness pervades the cosmos but is there anywhere one can go in space and not observe a photon? It doesn't seem likely that such a place exists. It would appear that photons dominate the space landscape, yet it is dark.

The stars of the night sky as I understand it are from our own galaxy. The view from a position between galaxies would be quite darker I suppose but even so we should be able to observe other galaxies from any position. Now if photons are awash in space, do they need room to move around in? Also light waves must be intersecting other light waves but with no noticeable affect on the observer, so do photons collide? Do photons occupy space, have volume? Could the production and abundance of photons require or force the expansion of the universe?

 

If our eyes were sensitive to microwave range radiation (we would need huge eyes!) then we would see all of space glow with the cosmic microwave background radiation. Space would not appear dark.

Remember, you can think of light as both a wave and a particle. As particles, photons do not interact with each other, only with charged matter. E.g. you cannot collide two photons and have them bounce off in different directions. As waves, however, you can get interference patterns etc. An interference pattern is more like the sum of two waves rather than a collision. In other words, the waves don't "collide" to get an interference pattern, rather they just add themselves together.

-Dale

 

Photons do collide, IIRC, but not very often and they woudl have to be able to interact by virtue of having the same wavelengths.
As for volume, they dont have volume, just length, I think. And the expansion of the universe probably doesnt have anything to dow ith photons, seeing as they are massless, but you need to go and read up some cosmology to make sure.

 

We are able to see the universe when it was approximately 300,000 years old when light finally escaped the cosmic cloud of the infant universe. Why can't we train our telescopes to look 4.5 billion years back and see the solar system forming? or can we?

 

Just to add to this, I read in a recent Scientific American article that there is also a kind of light-analog of the CMB, I believe was termed the extra-galactic background light (EBL), that iirc was identified by measuring high-energy radiation from quasars as sort of a reference point. Anyway, the point is that space is not a void - there is energy permeating through it everywhere. I, however, am no physicist, so you might want to take that with a grain of salt and check for yourself.

What I originally came here to ask is, I think, a bit more in line with the OP's question. First (but not my main question), perhaps light would better fit a more general classification as a "fluid", since that can cover both gasses and liquids (and plasma and maybe particulate solids)?

My main question though requires a very hypothetical example because it's slightly outside the scope of known physics. I have a sort of interest in what happens when you push relativity to the limit and beyond - concerning faster than light travel, time dilation and travel, etc. I had been thinking about FTL travel, and wondering what kinds of forces a body would experience if doing so. Just for the sake of my curiosity, I am of course ignoring the huge hurdles that are required to do this, infinite energy, time dilation, possibilities of warp drives, etc. Still, if one were to imagine a body where v > c, let's say a perfectly spherical starship (for simplicity), the way the body would move through space changes from sub-light speeds. When we come to any really very high speed, some v >> c, eventually light would appear to stand still relative to the ship. At this point, how would light behave? I'm imagining it would look something like the plasma front that builds in front of a vehicle reentering the atmosphere, except that relies on the friction of the gas to adopt that behavior, which I'm guessing light doesn't experience (or only in minimal amounts)? I also imagine what it would look like for the observer in the ship, maybe pure white light in front and pure black from the void behind that the ship leaves in its wake? It is certainly true that in passing c the discerning observer could witness past events (would look like backwards time travel) from the light that he is catching up with, but would that just fade to unintelligible white as you speed up? Presumably the amount of energy of light striking the eye of the observer could become immense, beyond what energies normal matter could withstand.

I recognize this is not really in the realm of stuff you learn from physics class, but it's something I was curious about and I thought these forums would have a higher likelihood of expert response, so I'm giving it a shot.

 

good thread. I have some questions about light also.

1. how light is emitted? i know/read electron changes energy level and releases photon. but i don't understand the mechanism.

2. photon is a particle, move in straight line at light speed. does it vibrate along the way? does it carriy em force?

3. how exactly photon knocks out electron in photoelectric effect? point impact? force field interact?

4. what's difference between a red photon and a blue photon? is blue photon heavier or vibrates faster?

is light still around? seems he knows a lot about light. Thanks!

 

So how many times has jcc asked the same question and ignored the answers?

 

You have asked the same questions many times and received answers. Do you remember the answers? You either said the answers were bull shit or ignored them.
You're welcome!