Feynman Diagrams: Understanding Photon-Mediated Electromagnetic Force

In summary, the conversation discusses the confusion surrounding Feynman diagrams and the concept of photons mediating the electromagnetic force. The height difference in the vertices of the diagram is due to the convention of using time as the vertical axis. The important factor in calculating the amplitude is the reaction channel and the correct momentum and masses. Online sources can be helpful in understanding these concepts until a book is obtained.
  • #1
Moose352
166
0
I'm pretty new to the particle physics world, and modern physics in general, so bear with me. I also don't have a book yet, so it's kind of messed up I'm a bit confused by a few apsects of feynman diagrams, although my confusion actually lies much deeper. Looking at this diagram http://www.mov.vic.gov.au/scidiscovery/images/mn001708_w150.jpg which shows two electrons repelling, I don't understand why the vertex of the electron on the right is higher than that of the left. Actually, I don't think I even understand the concept of photons mediating the em force. I guess I don't really understand when a particle emits photons, and what implications that has. Can anyone point me to a good online source (until I get a book) or explain?

thanks
 
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  • #2
As far as the part of your question about one vertex being higher than the other, I believe it is conventional for particle physicists to let time be the vertical axis and a dimension of space be the horizontal axis when they draw Feynman diagrams. So you could interpret the diagram as meaning the particle on the left emits a virtual photon, and some time later the particle on the right absorbs it. When they calculate the associated amplitude, I don't think it really matters what the temporal ordering "really" was, and in fact if you tried to do something experimentally to detect which particle emitted the photon and which absorbed it, you would affect the process badly enough to create all sorts of mischief which would in turn have to be accounted for in your calculations.
 
  • #3
Janitor said:
As far as the part of your question about one vertex being higher than the other, I believe it is conventional for particle physicists to let time be the vertical axis and a dimension of space be the horizontal axis when they draw Feynman diagrams. So you could interpret the diagram as meaning the particle on the left emits a virtual photon, and some time later the particle on the right absorbs it. When they calculate the associated amplitude, I don't think it really matters what the temporal ordering "really" was, and in fact if you tried to do something experimentally to detect which particle emitted the photon and which absorbed it, you would affect the process badly enough to create all sorts of mischief which would in turn have to be accounted for in your calculations.

Janitor is exactly correct... the verticle axis is time, so the lower left hand particle emits a (virtual) photon and at some time later (up on the verticle axis) it is absorbed by another particle. All that matters when you calculate the amplitude, which in turn allows us to calculate the cross section, is what kinda of reaction channel it uses (in this case it is the t channel). When you know the channel and the correct momentum and masses you can calculate the amplitude using the rules for Feynman diagrams
 

What are Feynman diagrams?

Feynman diagrams are a visual representation of mathematical equations used in quantum field theory to describe the interactions between particles. They were developed by physicist Richard Feynman and are commonly used to understand the behavior of subatomic particles.

How do Feynman diagrams represent photon-mediated electromagnetic force?

Feynman diagrams use lines to represent particles and interactions between them. In the case of photon-mediated electromagnetic force, the lines represent the exchange of virtual photons between charged particles. The direction and shape of the lines indicate the direction and strength of the force.

Why are Feynman diagrams important in understanding photon-mediated electromagnetic force?

Feynman diagrams provide a visual representation of complex mathematical equations, making it easier to understand the behavior of subatomic particles and their interactions. They also allow scientists to make predictions about the outcomes of experiments and to test theories about the nature of photon-mediated electromagnetic force.

What are the limitations of using Feynman diagrams to study photon-mediated electromagnetic force?

Feynman diagrams are based on simplifications and assumptions, and may not accurately represent the complexity of interactions at the subatomic level. They also do not account for all the variables that may affect the behavior of particles, making them limited in their predictive abilities.

Are Feynman diagrams the only way to understand photon-mediated electromagnetic force?

No, Feynman diagrams are just one tool used to understand and study photon-mediated electromagnetic force. Other approaches, such as mathematical equations and experiments, are also used to gain a deeper understanding of this force.

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