/sci/ - Science & Math

>>5937824
>Certain matter has a certain colour because its atoms reflect a certain wavelength instead of absorbing it.

You just answered your own question. If it doesn't reflect, scatter, or generate visible light, it doesn't have a color.

>>5937833

But electrons absorb photons

By the way, do nucleons and other particles absorb photons? If not, why?

but color is just what you perceive. there is no official color. we only see like 10 percent of all wavelangths, its what we perceive as color.

>>5937847
>But electrons absorb photons

No, atoms absorb photons.

>>5937868

Yeah, but all the other wavelengths, if we could see them, have different colours.

>>5937875

But the electron is what's affected

>>5937876

i guess we'll never know what it will look like

>>5937852
They can absorb X-rays and gamma rays. Less energetic photons no, since they reach nowhere near the energy to move nucleons through energy levels.

Also, an electron can absorb a photon bringing it to a higher energy level, meaning that we can't see that photon, since it's absorbed. But don't excited electrons spontaneously emit photons equal to the energy difference, meaning they randomly emit the same photon, so we would see the photon anyway?

>>5937877
An excited electron moving to lower energy orbitals produces photons.

Given the energy associated with subatomic particles, my best guess is that if they do emit energy in the form of photons, their wavelengths are very likely far outside of the visible spectrum. (eg, gamma radiation)

>>5937896
Energy can be lost if the energy of the incident photon is slightly higher than the energy difference.

Also, electrons may be falling down several levels, and there are many potential routes which result in emitting different energy photons.

>>5937900
That's correct. Hence why excited nuclei in radioactive isotopes release gamma rays; excited nucleons are dropping down to a more stable state.

When an electron randomly emits a photon, will the direction of the photon also be random? If not, why?

>>5937986
Yes, except in a laser.

are you asking about Colour Force? and gluons?

>>5938003

Nope, just plain colour. Light wavelengths. Red, blue, etc.

>>5937986
>When an electron randomly emits a photon

Electrons don't emit photons. Stop saying that.

So, if gamma rays were in our visible spectrum, and our eyesight was such that we could see down to a quantum level, we would see electrons as colour gamma? Does colour stop existing at some quantum point?

>>5938132

How not?

>>5938139

I'm guessing that it doesn't, I can't see why it would.

>>5938139
If a gamma ray hits an electron, it knocks it out of the atom completely. That is why it is ionising radiation. So no, gamma rays would not be reflected from them and your sensor would only pick up background

>>5938144
>How not?

What do you mean how not? They don't.

>>5938155

I'm asking how they don't, when I'm always told the contrary.

The first post in this thread answered your question. The concept of color is not applicable to subatomic particles.

>>5938159
>when I'm always told the contrary.

I'm sure you're not.

>>5938159

What is it about what I'm being told that's wrong?

>>5938154

If any photon is absorbed by an electron and then emitted again, could you not see it?

>>5937824
prolly clit flavour

>>5938168
The energy of the gamma ray will become the kinetic energy of the free electron, which will then be released as a number of high-energy (UV and X-ray) photons when it collides with stuff.

>>5938161

I'm told they drop energy levels and thereby emit a photon. I've been told that in lots of places. Why is that wrong?

>>5938176
>I'm told they drop energy levels and thereby emit a photon. I've been told that in lots of places. Why is that wrong?

That's not wrong, you just misunderstood what it meant. That's not just an electron, it's an atom. One of the atom's electrons drops an energy level, and the atom emits a photon. You need the whole atom. A free floating electron doesn't have an "energy level."

You may as well ask what it smells like.

>>5938186

Oh yeah, well I knew that.

>>5937824
atoms are too small.

the visible light range is 390 to 700 nanometers.

single atoms are way too small.

>>5937875
Electrons do absorb photons, in the process of scattering them. They then re-emit the photon to conserve energy and momentum. They also both emit and absorb photons as a method of mediating the electrostatic force. Here is a Feynman diagram of two electrons exchanging a photon. One emits, one absorbs a photon. (You cannot tell which one because both orders of emission/absorption contribute equally).

Guys.. if light is reflected through absorption and re-emission by electrons.. how do mirrors work?
Why are all the photons reflected the same amount?
And there's glass in front of the mirrory part of the mirror, how does that work?
Why are things transparent?

How does it work, /sci/?
Why doesn't mirrors reflect UV light? ( why is glass opaque to certain spectrums, but transparent to others? )
At first i thought it was because "oh but dey atoms just dun absorb da wavelenghts"
but it's an entire SPECTRUM of wavelengths, it can't work like that.

And how/why the fuck do lenses work.
I can't.
Just tell me it's going to be alright.

>>5938245
What do you mean, atoms are too small? You can totally see light emitted from individual atoms. Not 20 seconds ago, i looked at the light emitted from a diffuse cloud of lithium atoms held in a magneto-optical trap inside a vacuum. Each atom is emitting separately, since they're too far apart to interact. They scatter 671nm light, so they are a brilliant red color.

With appropriate optics, you could even resolve a single atom. In fact, you can see single ions held in an ion trap with your naked eye. (You see a spot much bigger than the ion, of course, since you can't resolve an object the size of an atom with your eyeball, or with the wavelength of light they emit).

>>5937875
If electrons don't absorb photons, I'm literally out of a job.
>>5937824
There's something called the "lambda over 2" effect, which basically states that the smallest thing that you can observe with light of a certain energy is roughly half that wavelength's err... wavelength. So, the highest energy light we can easily create with a laser is around 200 nm (this is subjective), most molecules are around 2 or 3 angstroms, so 100nm is much larger than .2nm (regardless of how small the wavelength is, making light with a wavelength of even 100 angstroms would require absurd amounts of energy).
But it's a bit more complicated. When we look at something we don't actually see an object, we see light emitted from that object. Your eyes only sense photons that excite light-sensitive molecules in the back of your eyes, so you can't actually "see" anything directly. So what color are particles? They don't have one.

>>5937824
quarks are up and down
maybe not the color you're thinking of though

So let's say an object is green when white light is shone on it. This means it reflects green light, but it does that by absorbing it first, and then reflecting it via random drop in energy level? Doesn't this mean that for every object, there is a split second that it is black, since it has absorbed all wavelengths?

Right, but that's just to do with our biology, isn't it? The mantis shrimp can see 16 primary colours.
I want to know the actual physical limit.

>>5938355
was directed to
>>5938305

Also, another question, if you shine light onto a black object, like a red laser, you will see that red colour against the blackness. What's going on there? Black objects are supposed to absorb all light.

>>5938355
>colour
>physical
here we goooOOO

>>5938365
Well obviously it's not black enough.

>>5938355

>>5938365

Unless that's because all the electrons are already excited, in which case, why doesn't shining white light on it turn it white?

>>5938282
>Why are all the photons reflected the same amount?

They're not.

>>5938282
>but it's an entire SPECTRUM of wavelengths, it can't work like that.
Why not? Solid objects can have very wide spectra of absorption. This is due to the very complicated way the atoms in the crystal structure interact, and the way electrons fill the resulting Fermi sea. There are on the order of 10^23 electrons, each at a different energy level, each capable of making around 10^23 different transitions to absorb a photon at the corresponding frequency (or at nearby frequencies, since you don't have to be perfectly on resonance to absorb a photon).

>>5938374
I meant degree amount, like all photons (that hits my retina) are reflected at the same angle on the mirror ( kinda, you know what I mean, see shitty picture )

>>5938355
The physical limit to what? If you want to know the limit to the precision with which you can resolve two colors(i.e., two frequencies of light), that depends on the time over which you measure them. If you measure for a time you can resolve light of frequencies that differ by at least delta-omega = 1/(2 t). That's just from applying the energy-time form of the Heisenberg uncertainty principle.

>>5938393
In real mirrors, it's not perfect (surfaces don't reflect perfectly, etc.). But for an ideal mirror, it can be explained using Feynman path integrals. See, for example, http://lesswrong.com/lw/pk/feynman_paths/..

>>5938127
yeah, i miss read what the OPs post said

>>5937876
Nigga, u high as fuck. Are you asserting that things we cannot see should have colors?

>>5938282
This is a really good set of videos for physics. He has other channels that deal with chemistry and amth, too. Check em out.

http://www.youtube.com/watch?v=Omr0JNyDBI0

>>5938573

Yes.

>>5938410

Nah, I want to know at what point a photon can stop representing matter with colour.

I guess if we were tiny, able to see down to a quantum level and could see the whole spectrum, we wouldn't see the electron being represented at all when our eyes receive the photon, but just see the colour, filling our vision.

>>5938368

So if you had a perfectly black object, you wouldn't be able to shine any colours on it and see it? How does that work? If all the electrons are already excited, do the new photons just pass through it?

Also, >>5938343 I'd still like to hear thoughts about that.

Also, how do mirror reflect? Why does angle of incidence equal angle of reflection?

Also, what's the difference between a white object and a transparent object, if neither absorb photons?

>>5938596

Yeah, I watch the sixtysymbols videos, they are good, but I still have many uncertainties about how electrons and photons work, because it isn't explained in great enough depth.

>>5939591
Color is basically a colloquialism we have for the familiar wavelengths we can see. If we can't see something, it doesn't have a color. The question simply doesn't make sense

>>5939604
what kind of uncertainties

>>5939867

The last three lines I typed in >>5939591

>thinking waves of probability can have color

>>5938168
No, you're fundamentally misunderstanding what a photon "is".

Remember, it has properties of both particles and waves. In this case, being "emitted" is more of a wavelike properties. It is the change in energy states that creates a certain wavelength of energy(which is what we refer to for simplicity as "emitting a photon")

You don't see photons because they aren't things - they are the results of changes in electromagnetic fields. Your eyes simply interpret a small subset of these wavelengths as visible light (ie, colors).

As for your original question, I think statistical mechanics would address this. To my understanding, a large collection of photons conform conform to a spherical distribution. Photons travelling in a particular direction conform to a cone shape. I don't think there is really any meaning to the "direction" a photon is emitted - I think of it more like the propagation of energy fluctuations.

>>5939893

>So if you had a perfectly black object, you wouldn't be able to shine any colours on it and see it? How does that work? If all the electrons are already excited, do the new photons just pass through it?

If you had a perfectly black object, as you describe, with a color that absorbed all wavelengths of visible light and a texture that didn't let any reflect off, it would just appear as a black mass. Incidentally, it would also become very hot if you shine enough light on it for long enough. But no, photons wouldn't pass through it. The way it works is that the energy levels from one electron energy state to another are very well defined and rigid (quantum theory), so when a photon is released, it's a very specific wavelength. That's where we get the spectrum line series, and it's what we use to tell if a star is red or blueshifted. However, an atom has many more than just one energy level, and electrons can jump down from more than one level at a time. Each different combination of "jumps" will give you a different wavelength. The radiation given off by such bodies is called blackbody radiation.

>>5940698

>So let's say an object is green when white light is shone on it. This means it reflects green light, but it does that by absorbing it first, and then reflecting it via random drop in energy level? Doesn't this mean that for every object, there is a split second that it is black, since it has absorbed all wavelengths?

I guess it wouldn't be "green" for however long it take the atom to absorb the photon, raise the electron to the energy level, and spit it back out (electrons don't absorb photons, btw. The atom, as a whole, absorbs photons, and raises electrons to higher energy states.), but the idea of "being green" would have to be more rigidly defined. "being green" for me just means it reflects green light. It's a property of the matter, itself.

>>5940739

>Also, how do mirror reflect? Why does angle of incidence equal angle of reflection?

This is difficult to explain if you haven't taken first year chemistry. I don't know if it was in this thread or another, but there was a link explaining why mirrors only seem to absorb and emit photons at a certain specific angle of incidence, when physically, photons are absorbed and emitted at every point along the surface of the mirror. I don't even really understand it, tbh. Feynman diagrams confuse the fuck out of me.

>>5939893
I hope
>>5940751
>>5940739
>>5940698
answered your questions, somewhat.