28 Mar 13
Originally posted by twhiteheadThe indistinguishability of identical particles is an important concept in quantum mechanics. Indeed, it's what's stopping you from falling to the center of the Earth.
Yes, I do realize that. It just that I have not heard of the two slit experiment with radio waves so I am having trouble reconciling the two.
[b]Why is it hard to reconcile this with quantum mechanics?
In quantum mechanics a particle is a probability wave of where it will be. But it will always be somewhere.
When you do the two slit experiment, a ...[text shortened]... the two beams are polarized in different directions then there will be no interference pattern.[/b]
28 Mar 13
Originally posted by KazetNagorraVery interesting.
The indistinguishability of identical particles is an important concept in quantum mechanics. Indeed, it's what's stopping you from falling to the center of the Earth.
Presumably photons with different energies are distinguishable, so can this interference happen if the energies are different? Is energy equivalent to wavelength with photons? Is there an infinite possible range of wavelength/energy in photons or is it quantized?
28 Mar 13
Originally posted by twhiteheadPhotons are not distinguishable.
Very interesting.
Presumably photons with different energies are distinguishable, so can this interference happen if the energies are different? Is energy equivalent to wavelength with photons? Is there an infinite possible range of wavelength/energy in photons or is it quantized?
The energy of a photon is proportional to its frequency (the proportionality constant is Planck's constant). However, due to Heisenberg's uncertaintly principle, the energy of a photon is never precisely determined (in a mathematical sense, a precisely defined wavelength corresponds to a photon being defined over an infinite time interval). The possible wavelengths are not quantized AFAIK, though this question may boil down to whether space and/or time are quantized or not.
29 Mar 13
Originally posted by KazetNagorraSo, if I understand you correctly, a radio wave photon could strike a screen as a light photon and vice versa in very rare circumstances?
Photons are not distinguishable.
The energy of a photon is proportional to its frequency (the proportionality constant is Planck's constant). However, due to Heisenberg's uncertaintly principle, the energy of a photon is never precisely determined (in a mathematical sense, a precisely defined wavelength corresponds to a photon being defined over an i ...[text shortened]... d AFAIK, though this question may boil down to whether space and/or time are quantized or not.
Would they also only interfere in very rare circumstances?
So for interference patterns we need light with very similar, but not necessarily exact wave lengths.
So when two photons from two sources strike a screen it may be impossible to tell which came from which source, and when that happens we get an interference pattern.
29 Mar 13
So back to refraction and the speed of light.
A photon is absorbed then by either an atom or the bonds between atoms (I don't think I have a definitive answer yet), and then moments later a new photon gets emitted in all directions.
However, the new photon interferes with other photons creating an interference pattern such that the photon appears to have been emitted in the direction of the original photon.
Does this seem right?
Now to crack reflection. I bet it too has to do with interference.
29 Mar 13
Originally posted by twhiteheadSo, if I understand you correctly, a radio wave photon could strike a screen as a light photon and vice versa in very rare circumstances?
So, if I understand you correctly, a radio wave photon could strike a screen as a light photon and vice versa in very rare circumstances?
Would they also only interfere in very rare circumstances?
So for interference patterns we need light with very similar, but not necessarily exact wave lengths.
So when two photons from two sources strike a screen it ...[text shortened]... ible to tell which came from which source, and when that happens we get an interference pattern.
Yes.
Would they also only interfere in very rare circumstances?
It's not a matter of interfering or not interfering, it's a matter of how much they interfere. A radio wave and a visible light wave interfere little.
So for interference patterns we need light with very similar, but not necessarily exact wave lengths.
Exactly. This is what is meant by coherence (and you can replace "light" by "any wave phenomenon" ).
So when two photons from two sources strike a screen it may be impossible to tell which came from which source, and when that happens we get an interference pattern.
Yeah, although the interference pattern does not depend on the screen, the screen is just a way of measuring it.
29 Mar 13
Originally posted by twhiteheadRefraction can be described quite easily using classical mechanics. The laws of refraction have been known for a very long time.
So back to refraction and the speed of light.
A photon is absorbed then by either an atom or the bonds between atoms (I don't think I have a definitive answer yet), and then moments later a new photon gets emitted in all directions.
However, the new photon interferes with other photons creating an interference pattern such that the photon appears to ha ...[text shortened]... n.
Does this seem right?
Now to crack reflection. I bet it too has to do with interference.
http://en.wikipedia.org/wiki/Snell%27s_law
For some info on reflection and the reason why the sky is blue:
http://en.wikipedia.org/wiki/Rayleigh_scattering
29 Mar 13
Originally posted by KazetNagorraI am talking about reflection not refraction. When light reflects off a mirror, are the photons absorbed and re-emitted, or do they 'bounce'? I am guessing the former, and that the angle that they are re-emitted is a function of their interference with incoming photons. This makes me wonder whether single photons can reflect off a silvered surface, and if so, are they interfering with themselves despite a tiny time delay.
Refraction ....
29 Mar 13
Originally posted by KazetNagorraAm I correct that when light goes through glass it is absorbed and reemitted causing it to apparently slow down, but no scattering occurs, whereas in a gas, the absorption and re-emission is so dispersed that only bits are slowed down which is what results in Rayleigh scattering? So the difference between shallower water (causing shorter wavelengths) and rocks poking up from the surface.
http://en.wikipedia.org/wiki/Rayleigh_scattering
29 Mar 13
Originally posted by twhiteheadAbsorption and (immediate) re-emission would be indistinguishable from "bouncing".
I am talking about reflection not refraction. When light reflects off a mirror, are the photons absorbed and re-emitted, or do they 'bounce'? I am guessing the former, and that the angle that they are re-emitted is a function of their interference with incoming photons. This makes me wonder whether single photons can reflect off a silvered surface, and if so, are they interfering with themselves despite a tiny time delay.
29 Mar 13
Originally posted by twhiteheadI'm not sure I understand your question.
Am I correct that when light goes through glass it is absorbed and reemitted causing it to apparently slow down, but no scattering occurs, whereas in a gas, the absorption and re-emission is so dispersed that only bits are slowed down which is what results in Rayleigh scattering? So the difference between shallower water (causing shorter wavelengths) and rocks poking up from the surface.
30 Mar 13
1 edit
Originally posted by KazetNagorraBut is it immediate? If light is slowed when going through glass, is it also slowed when bouncing off a mirror?
Absorption and (immediate) re-emission would be indistinguishable from "bouncing".
And if it is re-emitted, why is it only re-emitted on the 'air' side of each surface atom and not re-emitted further into the solid?
30 Mar 13
Originally posted by twhiteheadDoppler cooling works from the principle that in re-emission, the direction of emission is random.
But is it immediate? If light is slowed when going through glass, is it also slowed when bouncing off a mirror?
And if it is re-emitted, why is it only re-emitted on the 'air' side of each surface atom and not re-emitted further into the solid?
30 Mar 13
Originally posted by twhiteheadI don't know how far you want to delve into quantum mechanics, but as an undergrad we used Griffiths' book Introduction to Quantum Mechanics. If you really want to get some intuition into quantum mechanical concepts, it's a good place to start. You would need some basic calculus and knowledge of simple differential equations to handle it.
Thanks for all the info, its been quite an education. I think I need to get a book on the subject.