Large Hardon Collider

[Eliseos]

I don't know much about how we process color, but one interesting fact is that if you were to take a green light and a non-green light at the same intensity, humans would perceive the green one as being much brighter. Our brains adapted to growing up in green environments by getting better at seeing green things specifically (as opposed to an overall increase in vision).



My teachers told me that too, now that I think about it. When I go back in time to punch the teachers who taught me the structure of an atom, I'm going to give these teachers a visit too.

Edit (I don't want to double post): An interesting thing I read earlier today is that Pauli didn't come up with the exclusion principle. He summarized someone else' work and got published. When he originally got published, he was eager to give credit to the appropriate person. But when he got his Nobel Prize, he decided to take all of the credit for himself. I'm kind of glad he got the credit, because otherwise it would have been called the "Stoner Principle", and professors everywhere would have to deal with lame marijuana jokes from their undergrads.

Double posting for ease of me being able to write this post without editing in with quotations. Now that you mention the thing about green colors, I do remember that from my high school teacher. This is also the reason why tennis balls are the green that they are, and why emergency vehicles (well, really the only emergency vehicles I've seen that are that green are the ones at airports) are green as well. It's much easier for us to pick it out amongst an overload of colors.

And yeah, I rage every time I think of something profound I had learned during my childhood, only to find out it was completely wrong.

EDIT: Or not double posting! And yeah leroy, I think (hope) all of my friends could/do know why that is lol. Some of the people I've met (not my friends!) I would wonder about though.

[Tristam]

As i understand it, there are three photopigments that absorb visible light, so as it was mentioned earlier, we can't see some lights because energy is too high, and i believe (correct me on this) we can't see others because we do not have the photopigments that absorb slight lower or higher wavelengths.

Yeah exactly, we only have cells that are specific to a certain range of wavelengths. And they are less sensitive at the extremes. And somehow those three types of cells and the varying sensitivities allow a brain to distinguish however many colors we can see.

[Eliseos]

Yellow, Magenta, and Cyan are the three colors, right? Like how a computer screen uses red, green, and blue to make all other colors?

EDIT: Well, apparently not lol, disregard this post

http://en.wikipedia.org/wiki/CMYK_color_model is what I was thinking of.

[Kuya]

Thanks for the explanations and links, Tristam and SilentRoy.



So true.



Well technically, the term still wouldn't apply. My specific interest would be particle physics if the job market wasn't a problem. The only person (to my knowledge) who's sticking to anything specifically space related is Miz.





The same guy I talked to about biology made a good point about engineers.

I don't care about applications to my research, I learn it just for fun. However, the funding I get from my research are going to be from people who do care about applications. So, technically, we rely on engineers for us to be able to continue our own research.

I still say we get rid them though.



I'm on my sleeping pills while typing this and I'm not going to proof read. So there's bound to be lots of mistakes, and some of the stuff I say may not even make sense.

I'm going to use frequency in my explanation instead of wavelengths. When it comes to color, it makes no difference since every specific wavelength corresponds to some specific frequency. So you could say color depends on wavelength, or equivalently that it depends on frequency. Since frequency is easier to work with mathematically, it's what I'm used to using. As you probably already know, lower frequency means higher wavelength and vice versa.

Our perception of color is pretty much something our brain makes up to distinguish wavelengths, kind of like how we can distinguish pitch. SciAm had an article once about how they could make people see strange or unusual color perceptions by tricking the brain to interpret signals differently somehow.

You are correct in that objects don't have color, they simply absorb and reflect different wavelengths. The reason there are differences between what's absorbed and reflected is related to the quantum nature of light.

First note that the energy of a photon is directly related to it's frequency (the constant of proportionality is planks constant). So red light, which is the lower frequency of the visible spectrum, is simply light composed of photons with lower energy. Blue is light composed of photons with higher energy. So the color we perceive is simply a matter of how energetic the photons in the light are.

For simplicity, suppose we have a hydrogen atom. The electron on the atom will have a certain amount of energy at any given point in time. Quantum theory puts a limit on how low the energy can possibly be. So in other words, you can't make the energy of the electron zero (or arbitrarily close to zero). You're eventually going to reach what's called the ground state, where the electron's energy cannot drop any further under any circumstance.

The electron can become more energetic though. But not by arbitrary amounts. The electron is going to have a "next highest" state. In other words, the electron will either have the ground state energy, or the energy of the next highest state (which we call the first excited state). The electron cannot have any energy between these two states or under the first state. It's either in the first or the second.

So what if I attempt to give the electron an energy between the two states? Suppose, for example, I bombard the atom with photons who's energy is exactly half the amount required to jump from the ground state to the first excited state. Will the electron go halfway up?

Well, as I said, quantum theory wont allow this. So these photons will simply bounce off of the atom instead of being absorbed. We call this "scattering". So whatever energy these photons are, if we divide it by planks constant, we get the frequency (the color) of that light. Since this light is being scattered, we see the object as being that color.

What would happen if we shined a light at exactly the frequency we need to jump from ground to the first excited state (or some other excited state)? The photon would be absorbed. So the object would appear black.

If instead of shining light of one energy on it, we were to shine white light on it, the color we perceive would be the combination of all of the frequencies that are scattered.

For objects other than the hydrogen atom, it works basically the same way. Certain energies are allowed, and certain energies aren't. So certain photons are scattered, and certain photons are not.

Actually, I guess my post has been somewhat misleading so far. There are a bunch of different types of scattering that occur for different reasons. I can't get into those without a bunch of math, so I wont. Just note that the color of an object depends on what frequencies are scattered more easily for any reason. Most of the scattering isn't really the process I described above.

But I did describe the process above for a good reason. Scattering only determines the color of objects that don't emit their own light. In the example above, the frequencies that the hydrogen absorbed are the "absorption spectra" (see Eli's post). When the electron gets excited, it wants to go back to it's ground state. In order to do so, it has to emit a photon. The photon energies it can emit are the same as those it can absorb.

As Eli explained, this is what gives neon its color. The neon is excited by electricity, falls back to a less excited state, and emits light of the frequencies corresponding to changes in energy level. We see the frequencies associated with these energies. In Eli's picture, we see that the emission spectra is simply a bunch of stripes. In most everyday materials, the emission spectrum will be broad bands instead of stripes, or the entire spectrum will be the emission spectrum. In other words, most objects can emit light at any wavelength. However, they do not emit all frequencies equally. Some frequencies will be emitted a lot more than others. The amount of each wavelength emitted depends on the temperature of the object.

If you were to look at a piece of metal, it doesn't appear to emit any light. It actually does, but it emits a very small amount, and at wavelengths that we can't see. The human body emits it in the infrared frequencies, which is why we can track people down with infrared vision technologies. If our eyes could naturally see infrared, everybody would look as if they were gave off their own light (because they do, but we just can't see the infrared frequencies). If we heat up a piece of metal, it eventually starts to emit much more radiation at the red frequencies, so the light appears red. This is essentially where the color of objects who give off their own light come from.

By the way, you misspelled color. For some reason you put a "u" in it, but everyone knows color has no u.

This clarified a lot; you have a real knack for being able to convey information. You also answered my question about perception which i assume others agree with too: colour is merely the perceptual experience an organism goes through, and if we take the organism out of the equation, the only thing that exists is a frequency.

I had two questions, but i forgot one, so i will ask this instead even though i can just check wikipedia: what is white light in the context of your explanation, what makes it different?

[Chun Liroy]

I assume it means light that contains every color in the electromagnetic spectrum.

[Eliseos]

White light is just our brain combining all of the frequencies that are being emitted together. It's kind of like how TV just show pictures really fast, and our eyes fill in the rest to make it appear like it's actually moving.

[Cyn]

I assume it means light that contains every color in the electromagnetic spectrum.

Merely the visible electromagnetic spectrum. What we perceive as light.

Edit: comes back to why white things remain cooler. Less energy is being absorbed because the entire visible spectrum is being reflected.

[Chun Liroy]

That's what I meant since any light outside the visible spectrum doesn't have a definable color, but I'm just arguing semantics here.

[Cyn]

Well from the human perspective yes, but organisms that can see wider ranges of the spectrum would be viewing some of the things we perceive as white slightly differently.

[Cyn]

I don't even normally check this thread, I'm really glad I did though, I studied art all through school and have been doing lighting design for the past 10 years. The difference in perspective of the two ways of thinking about light and color are kind of amazing.

[Kuya]

Thanks to eli, tristam and woozie for the good answers, but i think i remember my question:

I got confused on something, are the frequencies we detect the ones that get reflected because the electron won't absorb the energies bouncing off it? Or are the frequencies we see the energy that gets absorbed and then re-emited because the electron goes back to the ground state? This makes it sound to me like we really see all the energy bouncing off the molecules except the energye lost due to energy conservation.

1- Is the energy that is absorded and then re-emited the one we don't see because this is the one that suffers from energy conservation?

2- the scattering explanation made it sound like all energy that bounces off a molecule is "weakened" much like in #1

3- is the energy we see the one that loses the least energy?

4- is the absorbtion and re-emision of energy only characteristic of some matter?

*to make sure my main question is clear: is the energy we see the energy that gets scattered or is it the energy that gets re-emitted? Or does this vary depending on whether the matter produces its own light or something?

edit: also thanks cyn

[Eliseos]

I don't even normally check this thread, I'm really glad I did though,

I think a lot of posters who would normally be interested in what goes on in this thread are put off by the size of it. I've seen a few posts saying they don't touch this thread because of that, even though it's usually us shooting the shit until someone posts a question, or an article. We would probably be able to get a lot more people involved in the discussion of whatever we're discussing (wat) if we made individual topics, but yeah.

[Kuya]

Now that i know we can post about biology, i might just use this thread to ask more questions about fisiological psychology and even have discussions about it!

[Chun Liroy]

I avoided this thread mostly because of Max and the bullshit I've seen that goes on in other scientific-y threads so I assume this was just the 46 page version. But then Miz pretty much made me post D:

[Eliseos]

Thanks to eli, tristam and woozie for the good answers, but i think i remember my question:

I got confused on something, are the frequencies we detect the ones that get reflected because the electron won't absorb the energies bouncing off it? Or are the frequencies we see the energy that gets absorbed and then re-emited because the electron goes back to the ground state? This makes it sound to me like we really see all the energy bouncing off the molecules except the energye lost due to energy conservation.

1- Is the energy that is absorded and then re-emited the one we don't see because this is the one that suffers from energy conservation?

2- the scattering explanation made it sound like all energy that bounces off a molecule is "weakened" much like in #1

3- is the energy we see the one that loses the least energy?

4- is the absorbtion and re-emision of energy only characteristic of some matter?

*to make sure my main question is clear: is the energy we see the energy that gets scattered or is it the energy that gets re-emitted? Or does this vary depending on whether the matter produces its own light or something?

edit: also thanks cyn

1) We see the energy that is re-emitted. The energy conservation is like sending electricity through a wire. The wire isn't a perfect conductor, and so some of the energy transferred is turned into heat and is lost. You can think of light we see as being on the other end of this circuit (yeah I know circuits make complete paths). Light is emitted from some object (our source of electricity in the circuit example), gets absorbed by some atom (resistance in our wire causing it to heat up), and gets reemitted, missing some frequencies that were absorbed previously (slightly less electricity gets to the other end of the circuit).

2) You can think of it that way, yeah. If an atom absorbs so much energy, an electron will absorb so much energy that it can simply just leave it's orbit and be ejected completely out of the atom, ionizing it.

3)No, not necessarily. It all depends on what kinds of frequencies the material/atom in question absorbs.

4)Not including dark-matter in the category of matter for the time being, all atoms have to absorb and emit light when light is incident on it.

*)This also depends on the situation. When you look in the sky, you see light being scattered. Blue light scatters the easiest, and so with the white light (you can consider a star as white light for the most part, even though some look orange, blue, green etc in the night sky), red doesn't get scattered as much and so it has a much much lower chance of reaching your eye. When you are looking at an object like a book, that would be the material absorbing and emitting light.

[Tristam]

Woozie that explanation was amazingly good, and kind of leads me into a question that might be simple, but bugs me from time to time, and is related (perhaps tangentially?) to your description of visible light.

In IR spectroscopy, the absorption and emission of energy is dependent on the vibrational frequencies of the molecules in question. And in protein tryptophan fluorescence spectroscopy, it isn't that the atoms in a tryptophan amino acid themselves are different from other amino acids, but the arrangement of the atoms leads to different absorption/emission spectra in the UV.

Sooo, I guess, is it that the electrons in chemical bonds are behaving the way you described for the hydrogen atoms, moving to different energy levels and such, when we do UV and IR spectroscopy. Or do the bonds absorb energy in a fundamentally different way to turn it into thermal motion and release it as another wavelength? Or am I way off base? I mean, CAN an IR wavelength that is absorbed into thermal motion of CO2 be used in another context to boost an electron into a different energy state?

Or is it too late and am I getting into crazy territory due to fatigue?

[Kuya]

So how does an organism perceive energy that isn't absorbed? (sorry that i don't seem to be getting it, but what i got was that we see the energy that is absorbed and then re-emitted, unless all energy is absorbed and only the energy that is re-emitted is seen)

[Kuya]

I seem to have gotten confused when i tried to equate what eli said with what woozie said.

[Cyn]

The spectrum we see is reflected, the waves we don't are absorbed as energy.

[Chun Liroy]

I assume that is just a mystery of the mind. Perhaps the wavelength hits certain cones and rods and activates them which produces a reaction that leads to the brain and it interprets it as color?