Why do objects such as quarks, which are smaller than the wavelength of visible light, have no color? If the color of an object is simply the color of the light that is reflected off it, then why cannot extremely small objects reflect wavelengths of light that are larger than themselves?
On the macro-scopic scale, small objects can “reflect” larger ones. For example, if one had very good aim, one could theoretically bounce a tennis ball off a pinhead.
Why is the same thing not possible on the microscopic scale?
My WAG is that the odds of any particular wavelength actually managing to ricochet off such a small target (more of a probability function than a physical target anyway) are so small that that the length of the wave that gets reflected is essentially irrelevant.
Anyone who actually knows anything about physics is encouraged to correct me.
For what it’s worth, here’s my WAG:
I don’t know anything about quarks, but I see no reason, in principle, why an atom could not be said to have “color” in the sense that it has a tendency to reflect certain wavelengths of radiation and absorb others.
For example, let’s suppose you shine full-spectrum light on a bar of gold, set up a device to capture and measure one photon that is reflected off the the bar of gold. It seems to me that (1) the photon you capture is likely to be of a wavelength associated with gold; and (2) that photon was reflected, a split-second earlier by a single gold atom. Thus, you can now guess at the color of a particular atom (even though the atom itself would be difficult to locate).
(disclaimer: i’m not a physicist)
When we look at a gold coin, we know what color it is. So we really know what color a single gold atom is. But bouncing a single photon off a gold atom isn’t going to work. We can not detect a single photon. We need lots of photons to “see” stuff. At least this is my WAG.
atoms (as opposed to molecules) do not have colors - they are clear except under special conditions…
molecules have colors
you could not see the color of one atom or molecule - not because it is too small - but because the color of one atom would be too faint. How could you check the color of an atom or a molecule? Get a large number of them and shine light on them.
Explanation:
First of all how do we see things? We see things because they reflect light into our eyes.
Next what is the color of something? The color of something is the color of light that it reflects most when light of all colors shines on it. A green leaf is green because when the sun shines its light on the leaf, the color that the leaf reflects best to our eyes is the green. The sun’s light contains all the colors of the rainbow (red orange yellow green blue indigo) but the color that is reflected most to your eye is the green.
The part of an atom or molecule that “reflects” the light is the electrons on the outside of the atom. Now…the color comes in two steps…
Step 1: The electrons first absorb some of the light that hits the atom or molecule.
Step 2: The electrons which absorbed the light then emit (give out) some light
If the electrons give out exactly the same light as they absorb, the substance is “colorless”…however if the color of the light emitted is different from the color absorbed, then the substance has a color. In the case of the leaf, the leaf absorbs all the colors but only reflects green.
For atoms and regular lighting - whatever the atom - the absorbed light and the emitted light are the same. That is because for a single atom the electrons have to absorb and emit the same light.
In molecules, where two or more atoms share some of their electrons, the molecules can absorb light of one color and emit another color. This works whether the atoms are the same (eg two Nitrogen atoms) or different elements. Paints and dyes (the chemicals used to color clothes) are complicated molecules where the arrangement of the electrons make the molecules reflect specific colors very well.
http://www.fnal.gov/pub/inquiring/questions/colorofatoms.html
First of all, “color” is simply the way that your brain interprets certain information. Things don’t really have “color.” We perceive them to be a certain color because the object interacts with light in a certain way. Things can be different “colors” depending on a whole bunch of complex variables including such things as lighting conditions.
This might sound really picky but it’s an important point when your talking about the “color” of an atom. Atoms don’t have colors as we would perceive them. They have spectra. What this means is that atoms will absorb and emit radiation only at certain discrete wavelengths. We sometimes assign “colors” to these wavelengths but we’re really talking about a much more precise concept than what we see as, say, “blue.” We’re talking about a single frequency of electromagnetic radiation (light).
Therefore, in answer to your question, atom of different elements do indeed have several precise “colors” associated with them depending on the frequencies at which they emit and absorb light.
As for quarks they do have “color” but, uhmm, Oh, never mind! Suffice to say that they don’t have “color” in the sense that it was referred to by the OP.
And if a tree falls in the forest…
Likewise we have the problem of deciding if something that reflects so little (if any) light would reflect enough that it would strike the rods & cones of the human eye at all. Forgetting about color altogether for the moment, subatomic particles are invisible, in the strictest sense of the word because they can’t be seen.
I see several others beat me to it. That’s because I had to meditate on the enormity of the mystery.
Ohmmmmmmmmmm…
Ahh, but what is the sound of a single grain of wheat, falling onto a feather bed? The sound of a whole sack of wheat?
Ohmmmmmm
These subatomic particles are also so small that when they are hit by a photon (particle of light) they move. They bounce around. This is a bit of a problem in that we change their momentum by trying to detect them by shining a light on them.
In terms of reflection lets consider a shiny object in a dark room. When we shine a flashlight onto the object the light is reflected and we see the object. If that object were teeny, when the light hit it the object would get pushed around by the light and the light would not be reflected. We can tell where the little object is (or was) at the time of the collision. We can also change the amount of energy the photon (light) has bumping into the object to determine the momentum of the little object. However, we can’t determine it’s momentum and where it is at the same time, since determining it’s momentum requires bumping it with a photon thereby changing where it is.
I’m not sure if this is Heisenberg’s principle. 
Bumper sticker: Heisenberg may have slept here.
So…
After photons strike the back of my eye…they are reflected back?
Here is a related question which has bugged me for decades:
For a given object, is it possible to determine its color without looking at it?
In other words, can color be determined purely on the basis of laboratory data, such as atomic weights, numbers of protons, or whatever?
I’d be surprised if color is a purely sensory phenomenon. Rather, it is based on the wavelengths reflected from the object, and there’s gotta be some mathematical way of figuring that out.
Some of them are. Those are the ones that are wasted because your eyes aren’t 100% efficient. The ones that you actually see are absorbed by special molecules in your retinal cells and converted into another form of energy.
Without going deeply into “How vision works”, the short answer is “No”, they aren’t reflected back. The energy of the photons excites electrons in nerve cells which cause them to fire, sending messages to the brain. Once out of energy, the photons cease to be.
Now, if you go to your opthomolololomotometrist and he or she shines a bright light into your eye, he or she can see the back of your eyeball because some of that light is reflected. This is mostly due to overloading and the light hitting areas that are not covered by lots of nerve cells.
Are photons reflected back after striking the back of the eye? Some certainly do. Have you ever seen a flash photo of someone who’s got “red-eye”?
Anything which can interact with photons can have color.
To add a little detail to that - the reason why “overloading” and red-eye occurs is that the molecules in your receptors can only accept a certain amount of energy (light) and need to convert that light to other energy (chemical) and release that energy out towards your brain before it is able to accept more energy. This whole reaction takes time - a relatively small amount, but enough so that when there’s a lot of light available, and a lot of energy, then some will definitely not be used, and so reflected.
As for determination of the “colour” of something without physically looking at it, there are certainly equations for this. None of which I know, of course, but I am supposed to be learning them :). Actually, I’ll look at it, and if no one gets back to it before I do, then I’ll try my hand at answering.
Some people on the boards are actually specroscopists, and so would probably know more (I don’t take the Structure and Spec. class till next year) but this is what I know right now.
There is a way to determine the wavelength, lambda, of what a particle gives off, and associate that with a colour.
NOTE: what I am about to talk about applies to hydrogen in particular, but gives acceptable but not accurate results for other molecules with many electrons also. Blame Schrodinger for it. And I have no idea if any of this can be said for large items.
Here we go:
We can calculate the energy of an electron at certain energy levels by using the equation(bare with me, I dont know the neat math font) :
E= ( n[sub]x[/sub] + n[sub]y[/sub] + n[sub]z[/sub] )h[sup]2[/sup] / 8mL[sup]2[/sup]
Where n is an energy level determined by the principle quantum number
h is Planck’s constant = 6.626x10[sup]-34[/sup]
m = mass of an electron = 9.109x10[sup]-31[/sup]
and L = size of the space in which the electron is found.
To determine n - light is quantized, so it can only have specific energies and nothing in between them, so through theoretical calculations you can determine how much energy you need to give to an electron to get it from n=1 to n=2 and so on. So give that much energy, and excite the electon.
So of we ecxite the electron from it’s ground state (E1) to the next state (E2), we can determine the difference in Energy levels, delta E.
When the electron returns to it’s ground state, it will give off the energy you gave it earlier in the form of light (i.e. a photon).
Since we also know that delta E = hc/lambda, we can now solve for lambda, since we know h and c (speed of light in a vacuum).
And all this without looking at the electron.
I think absorption spectra work oppositely to this - you can get the electron excited, and measure the wavelength given off, and can thus determine the size of the space containing the electron. I’m not 100% sure what you’d apply this to.
This is why we need one of those spectroscopists here!
[sub]So, did I get it right? Will I pass my final?[/sub]
I feel like such a nerd.
I’m gonna stop posting to this thread now. At least til someone else does.
thanx, all