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Photon Exchange in Atoms

by Lazernugget
Tags: atoms, exchange, photon
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Lazernugget
#1
Feb12-13, 09:36 AM
P: 54
Sorry if this post seems short, I had to write it in a hurry.

I'm currently reading Leonard Susskind's 'The Cosmic Landscape'. In it, he describes how electrons and protons both emit photons, which is what gives them their charge. The explanation is really awesome, but I have one thing I can't figure out. Electrons have negative charge and protons have positive, but their photons are the same type, right? So wouldn't they repel even though they are opposite charges? What property of the photon makes positive and negative things attract instead of repel, and why don't they electrons spiral into the nucleus if the protons attract the electrons?

Thanks,

-Lazer
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Naty1
#2
Feb12-13, 12:15 PM
P: 5,632
I wish my answers were as good as your questions!

Electrons have negative charge and protons have positive, but their photons are the same type, right?
yes, they are gauge bosons, a mathematical entity in quantum mechanics. I don't think there
is any fundamental 'intuitive logic' beyond the mathematical description which has been found to work. But maybe someone can astound us!!


So wouldn't they repel even though they are opposite charges?
What property of the photon makes positive and negative things attract instead of repel
well, I can't answer this question within QM in an intuitive way, but I can say the logic stated is incorrect: you could equally posit 'same charges attract'..and that would also be incorrect. A simple/superficial answer is 'we ascribe different mathematical symbols/values related to different charge.' [If we observed three types of electric charge, we'd use a different model with three values!!]

For example, in classical electromagnetism the Coulomb force between particles is simply assigned a plus or minus depending on charge type...If the two charges have the same sign, the electrostatic force between them is repulsive; if they have different sign, attractive....Not especially intuitive...and the electromagnetic field is the same in either case.

Again, I think the best 'final' explanation within QM will be mathematical along the lines of charge being associated with conserved quantum numbers and the electric charge being the generator of the U(1) symmetry of electromagnetism....

Who ordered THAT?? well, it works in QED. That is; it very accurately describes what we observe.


and why don't they electrons spiral into the nucleus if the protons attract the electrons?...
again, I don't know of a logical/intuitive explanation. One 'simple' answer is the Pauli exclusion principle...It is based on spin statistics and mathematical symmetry considerations
which result in bound particles exhibiting quantized behavior: Electrons cannot occupy the same quantum state, so electrons have to "stack" within an atom, that is, have different quantum numbers [mathematical characteristics]. A related viewpoint is that all bound particles become quantized, and this is described via standing waves...like resonant vibrations of a violin string....or confining a particle in a potential 'box'. String theory ascribes such behavior based on tension and energy of the vibrating modes of the string....

yeah, a bit 'hand-wavy' I guess.


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