Light: Wave or Particle?

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  • #26
ZapperZ
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MonstersFromTheId said:
When you say "ALL" the atoms in the solid, do you mean "ALL" the atoms as in all *types* of atoms in a structure (i.e. you need a representative minimum number of atoms to determine the collective behavior of the rest of the solid)?
Or by "ALL" atoms in the solid, do you mean literally ALL the atoms that are part of the solid.
The reason I ask.
I could see where it wouldn't take very much time at all for the effects of a photon hitting a solid to spread out through a representative minimum number of atoms, so that the collective properties of the rest of the solid could be established (i.e. the photon is reflected, absorbed, and/or transmitted on the basis of the behavior of that representative minimum number of atoms that's typical of the rest of the solid).
But if ALL the atoms that are part of the solid are required to determine whether or not the photon is reflected, absorbed, and/or transmitted, then I could see where the overall size of the solid would start to effect how long it takes before the photon actually IS reflected, absorbed, and/or transmitted.
Second question:
When talking about transparent solids, it would be a bit misleading to think of photons as traveling *through* the solid? It's more like photons hit one side of a piece of glass, the energy can't be absorbed, so the energy bleeds back out the other side of the glass as essentially new photons?
If you take the atoms (all kinds of them) apart, you will not have any phonons. It is the reason why phonons are called "collective" excitation. The lattice ions and the way they are arranged determine what kind of phonon spectrum is available for that particular solid.

Now the confusion comes in as in the SIZE of such domain. Note that for something the order of microns is already large when compared to the individual size of atoms and ions in the solid. This is sufficient for many-body physics to kick in.

There is no definite transition between when the number is too small for phonons to be present. The study in the mesoscopic regime is still an ongoing research area.

As for transparency, if you don't care about the details, then it is perfectly fine to think about the SAME photon emerging on the other side. But if "god is in the details", then that picture will have problems, not the least of which is the indistinguishable statistics of bosons.

Zz.
 
  • #27
daniel_i_l
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light as particle

I find this problem easier to swallow when I think about the fact that really, photons arn't so special. All matter (electrons , humans , planets...) also has wavelike properties! But in the macroscopic world these properties aren't as noticable.
It helps if you think about photons (and all matter) as particles that move according to their "wave function". In the quantum world, it is impossible to predict were a particle will be in a certain time. Rather you can predict the probibiliy of a particle to be at a certain spot.
This is were the wave comes in. Where there is more chance for the particle to be found in a certain place, the value of the wave there is bigger, were there is less chance the value of the wave is smaller. You can think about the "wave" part of a particle as a probibility wave that "says" how much chance you have of finding the particle at a certain location. But really the photon is only a particle. You get interferance when the probibility wave cancels out at certain places and goes to zero. That means that no photons have a chance of going there, and you get black lines.
 

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