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The Origins of Quantum Physics 
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#1
Oct2712, 12:33 AM

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In the book "The Quantum Story", by Jim Baggott, we find the following:
"[...] Many physicists, including Planck and Bohr, dismissed the lightquantum. They preferred to think of quantization as having its origin in atomic structure, retaining Maxwell's classical wave description for electromagnetic radiation." I don't get this. How could they believe that light was emitted and absorbed in a discrete fashion, but that light itself wasn't discrete? If atoms were emitting quanta of light, how could light not be quantized? 


#2
Oct2712, 02:23 AM

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Welcome to PF;
Look up "semiclassical model". There were able to believe that because of how they worked their quantum theory in terms of small masses on a spring. Anyway: the math worked. 


#3
Oct2712, 03:00 AM

P: 21

Thanks for the warm welcome, Simon. I looked up what you suggested and found something relevant on Wikipedia:
"Even after Compton's experiment, Niels Bohr, Hendrik Kramers and John Slater made one last attempt to preserve the Maxwellian continuous electromagnetic field model of light, the socalled BKS model. To account for the data then available, two drastic hypotheses had to be made: 1. Energy and momentum are conserved only on the average in interactions between matter and radiation, not in elementary processes such as absorption and emission. This allows one to reconcile the discontinuously changing energy of the atom (jump between energy states) with the continuous release of energy into radiation." It seems like there's my answer right there, but I still don't understand it. Can someone elaborate on this? 


#4
Oct2712, 07:02 AM

P: 712

The Origins of Quantum Physics
It's quite interesting that Bohr disliked the photon idea so much that he was willing to give up energy conservation AND later on worked so constructively on the complete theory which included photons. Einstein never abandoned his view about how quantum mechanics should look like. It's also interesting that the final disproval of classical wave theories has not happened until the 70s. I'm no expert in this, but there's a review article by Thorn et al. which lies on my reading pile. ;) Maybe you're interested in it: http://people.whitman.edu/~beckmk/QM.../Thorn_ajp.pdf 


#5
Oct2712, 11:55 AM

P: 21

Kith, thanks a lot for your thorough answer, it was very helpful! But I think I would still have to take a look at the BKS theory to understand exactly how they managed to reconcile discrete emission/absorption with continuos radiation. As to the article you pointed out, I was really surprised to find out that the photoelectric effect can be explained without resorting to light quanta. I'll certainly be taking a better look at this. Thanks again!



#6
Oct2712, 08:09 PM

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It should not be surprising that even very bright people can hold to ideas that turn out to be incorrect. Everybody is wrong sometime and scientists have more opportunity to be wrong than most people: it's their job.
The semiclassical treatment in quantum optics is usually part of a postgraduate course. 


#7
Oct2812, 03:52 AM

P: 203

http://www.physicsforums.com/showthread.php?t=474537 The final "proof" came with the photon antibunching experiments not so long ago. I was so fascinated by this that I bought a book on quantum optics! 


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