Wave Particle Duality

  • #1
hey guys i was wondering if you knew any thing that helped to prove the wave-particle duality theory of light. any help would be greatly appreciated:smile:
 

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  • #2
mathman
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Basic "proof" is experimental.

Particle behavior is shown by the photoelectric effect (Einstein, 1905 - this is what got him the Nobel prize).

Wave behavior is shown by the double slit experiment - the effect shows up even when the source is emitting one photon at a time!
 
  • #3
ZapperZ
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tennis freak said:
hey guys i was wondering if you knew any thing that helped to prove the wave-particle duality theory of light. any help would be greatly appreciated:smile:
You may also want to read our FAQ in the General Physics forum.

Zz.
 
  • #5
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So a followup question, in the double slit, since diffraction takes place, how does the photon know that the slit is there, considering it does not touch it?
 
  • #6
selfAdjoint
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pmerrill said:
So a followup question, in the double slit, since diffraction takes place, how does the photon know that the slit is there, considering it does not touch it?
Some photons go through one slit, some through the other; that is, there are two eigenstates and the collapse goes to one or the other randomly. The interference pattern comes when you look at a whole series of photons, where classical physics would produce two spots, one behind each slit, what actually happens is the diffraction pattern showing that overall, the photons interfered with each other.

If the photon was a wave, this would be a natural phenomenon; see Huygen's construction. In the photon case of course you can frequently think of it as an EM wave; the problem comes with matter particles like electrons, which act the same way.
 
  • #8
selfAdjoint
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Farsight said:
I thought this looked like a good depiction of the dual slit experiment:

http://www.joot.com/dave/writings/articles/entanglement/spookiness.shtml

Lower down is the Bell State Quantum Eraser which seems particularly mysterious to me.
Good catch, Farsight. Why don't you start a thread on the Bell State Quantum Eraser and explain what you think happens and why it confuses you?
 
  • #9
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Quite right, PF, mentor. But a more fundamental question is how, with a system in which a quantum can travel two paths, does the introduction in one path AFTER the time allowble for the quantum to pass affect the results? I don't recall the reference, but it is at least five years old.

Ernies
 
  • #10
mathman
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One point that should be stressed concerning the double slit experiment is that the diffraction pattern shows up when the source is emitting one photon at a time, so you don't have interference between phtons, only interference of a photon with itself. Similar results can be seen with an electron source, one at a time through the double slit.
 
  • #11
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mathman said:
One point that should be stressed concerning the double slit experiment is that the diffraction pattern shows up when the source is emitting one photon at a time, so you don't have interference between phtons, only interference of a photon with itself. Similar results can be seen with an electron source, one at a time through the double slit.
So that implies that a photon is a non localised entity. The double slit implies that the photon goes through both slits at the same time. Correct? Does this mean that a photon is non localised all the time or that it "magically" splits when it goes through the double slit and recombines after?

If it is so non localised why wouldn't it interact with other photons all the time? Would it be pointless to say "one photon", when in reality it's a probability distribution that is spread over the entire universe but happens to collapse to a point when it "interacts" with the environment?

Quantum physics $%$#@#$!!!
 
  • #12
selfAdjoint
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mathman said:
One point that should be stressed concerning the double slit experiment is that the diffraction pattern shows up when the source is emitting one photon at a time, so you don't have interference between phtons, only interference of a photon with itself. Similar results can be seen with an electron source, one at a time through the double slit.

If you send just one photon through, you do not see the interference pattern on the screen, just a tiny spot. And that photon is then gone. When the second photon comes along it makes another spot, and is also absorbed. After a great many photons have behaved this way you see the interference pattern, made by the spots produced by the individual photons. Thus rather than "the photon interfering with itself" it's more like each photon interfering with particles that either aren't there any more or that haven't got there yet.
 
  • #13
dlgoff
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Since some of the spots aren't directly behind the slits, doesn't it mean the photon interfered with itself to cause this displacement?
 

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