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Whatever happened to the Particle Theory of Light?

by Mark
Tags: happened, light, particle, theory
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Mark
#1
May18-04, 09:10 PM
P: 59
Hello, I am a student in high schoool, and everywhere i look i see the obvious implications that light travels as a wave. I mean

-Rectilinear Propogation
-Refraction
-Reflection
-Diffraction

etc. all seem to point to wave theory, but what do the particle people say about these things..

just looking for a second opinion,

thanks
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russ_watters
#2
May18-04, 09:57 PM
Mentor
P: 22,244
Quote Quote by Mark
Hello, I am a student in high schoool, and everywhere i look i see the obvious implications that light travels as a wave. I mean

-Rectilinear Propogation
-Refraction
-Reflection
-Diffraction

etc. all seem to point to wave theory, but what do the particle people say about these things..

just looking for a second opinion,

thanks
Reflection and refraction are particle phenomena. The particle model is very much alive and well - in its domain of applicability: light is now well accepted to have a wave/particle duality.
quartodeciman
#3
May18-04, 10:18 PM
P: 383
You could do worse than read a book called "QED:The Strange Theory of Light and Matter" by Richard P. Feynman. He takes on versions of all these phenomena, analyzing with a conceptual setup consisting of a laser source, a block of glass and a photomultiplier as a counter. He considers reflection off the glass block in two stages: first, assuming for simplicity that the reflection all takes place off the surface of the glass; second, the reflection is layered throughout the glass. He constructs a diffraction grating by painting out certain positions along the surface of the glass. He handles refraction by considering the detector embedded in the glass (a bit of a far-fetch!). Rectilinear propagation is the most interesting thing of all. He denies that light particles are constrained to move along straight lines, then he shows how neighboring non-rectilinear paths effectively cancel each other, making the straight paths the only real contribution of the light energy at the end.

The one light phenomenon he apologizes about not covering is "polarization". It is a complicating factor for the rest of his presentation, so he elected to omit it.

I would have groused some about calling it a "particle" theory, but Feynman says it is in his first chapter. "We know that light is made of particles because we can take a very sensitive instrument that makes clicks when light shines on it, and if the light gets dimmer, the clicks remain just as loud-there are just fewer of them."

It might take multiple readings to get through this book, but it is worth it. Check out the drawings and their captions for a quick take on what is going on.

The theory of light is done in the first two chapters of QED. The rest of the book talks about electron/light interactions and quark/gluon interactions, so it is not strictly only about QED (Quantum Electrodynamics).

Amazon link to this book --->
http://www.amazon.com/exec/obidos/tg...glance&s=books

quartodeciman
#4
May19-04, 01:57 PM
P: 383
Whatever happened to the Particle Theory of Light?

Feynman QED lectures on video --->
http://www.vega.org.uk/series/lectures/feynman/


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