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- Thread starter Royce
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chroot

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- Warren

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I understand that total momentum is conserved so if the photon carries momentum from or to the electron it changes the momentum of the electron thus its motion, direction and/or velocity?

I,m not yet fully grounded relativistcally yet. I feel like I have a split personally, one Newtonian and the other Einstienian and now I'm trying to learn about QED. I may shatter completely in a Quantum Relativistic way and enter a parallel universe.

Royce

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damgo

One thing to remember is that those Feynman diagrams lines

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Since he was so consistant in doing so I wondered if it was really significate and if so why if a photon has no mass. Thanks for clearing it up for me. I which I could say that now I understand but from what Feynman says nobody really does. We just have to except what is.

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drag

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Royce, I think it's worth noting that

Feynmann diagrams talk about "virtual

photons" - the virtual particles

"transferring" electromagnetic interactions.

They do not really exist.

You see, in QM there is no such thing as

a "continuing" wave or interaction. All

phenomena are quantified - seperated into

pieces - separate wave-particles. So the

virtual photons in these diagrams are actually

quantified interactions of the particles.

Live long and prosper.

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selfAdjoint

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You know the diagrams (the real ones, that is, not the ones in popularizations) are coded methods for determining the integrands of the integrals used in calculating such things as momenta, cross section, and such. Each kind of line and vertex corresponds to a particular expression, and they are all multiplied together under the integral sign. For this purpode it's only the connectivity of the diagram (bearing in mind there are different sorts of lines) that matters, not the slant of the in and out lines.

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as Feynman describes in his very good divulgatory book "QED", his diagrams have the horizontal axis indicating space, and the vertical that is time. Choosing the proper scales, a 45° line indicates a particle travelling at the speed of light in timespace. A line connecting two points indicates a contribution to the probability ampliture that the particle in the starting point in time-space can be found in the arrival point.

A "vertex" point, connecting two electron lines with a photon line (the "coupling" diagram) can be drawn in many possible different ways, each one indicating the probability amplitude to that initial-to-final state scattering. So, the electron lines are not shown either vertically, or horizontally, simply because vertical means being "steady" in one place, while horizontal means distributed over space.

Interestingly, a hydrogen atom is represented by Feynman as a straight vertical line (the proton) linked by many randomly drawn photons to an electron oscillating around another parallel vertical line. One more nice note - an electron line with the initial point higher in the diagram than the final one is not going "back in time" but it actually represents a positron going forward.

Hope it clarifies something...

bye

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umm... where could I find the written versions of his lecture?

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chroot

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Try a library or bookstore. They are called "The Feynman Lectures on Physics."Originally posted by wntr_75

umm... where could I find the written versions of his lecture?

- Warren

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