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Self force on an accelerating electron 
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#1
Apr2212, 11:15 PM

P: 31

In Feynman lectures vol 2, chap 28, it is given that for an electron at rest, the net self force exerted on itself is zero(due to repulsions etc.). But when accelerated, owing to the retardation of the electromagnetic fields, there would be a net self force. A series expansion(with unknown coefficients )has been provided. Can we actually calculate the self force? Does it ever exist?



#2
Apr2312, 06:02 AM

Sci Advisor
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P: 2,497

Yes, it exists. This is a major problem for highenergy accelerators for electrons. There you need to use linear accelerators since in ring accelerators you loose too much energy in synchrotron radiation. On the other hand synchrotron radiation itself is also an interesting light source that can be used for many applications in material sciences, chemestry, and biology.
The theoretical issue is not completely solved, even today. For a very detailed recent review on this matter, have a look at Fritz Rohrlich, Classical Charged Particles, World Scientific 2007 


#3
Apr2312, 07:59 AM

P: 31

Does that mean the electromagnetism is not complete? Or is this outside the domain?



#4
Apr2312, 03:17 PM

P: 617

Self force on an accelerating electron
Since the selfforce only arises under accelerations, it is not a selfforce in an absolute sense. Visualizing it as a "selfforce" may even be misleading. An accelerating charge emits radiation and loses some energy in the process, just like a gun recoils when it shoots off a bullet, to satisfy conservation of momentum and energy (traveling electromagnetic waves carry both momentum and energy). So it is more of an interaction of a charge with the fields than with itself. 


#5
Apr2312, 08:23 PM

P: 31

Thank you chrisbaird. How is, exactly, an electron imagined to be? Is it a charged sphere or what is its geometry? If we have to discuss about theself force then we have to assume the electron to be a spherical surface distribution of charge. But another question, doesn't the electron undergo Lorentz contraction while accelerating?



#6
Apr2312, 08:59 PM

P: 3,014




#7
Apr2412, 08:45 AM

Mentor
P: 11,917




#8
Apr2412, 12:46 PM

P: 617

Thank you for helping to clarify. I meant that Maxwell's equations are complete on the macroscopic level. Asking "What is the shape of an electron according to classical electromagnetics?" is a nonsensical question because classical electromagnetics only describes macroscopic charges (it's like asking what is the shape of the cheese contained in rainbows). An electron is too small to be addressed by Maxwell's equations. You have to go to quantum theory to talk about elementary particles. When we talk about "point particles" in classical electromagnetic, we mean spheres of charge that are small enough compared to the rest of the system that they look like points, but big enough and containing enough charges (millions) to be considered classical.



#9
Apr2512, 08:28 PM

P: 31

To compute the self force, i assume we must take the electron to be a charged sphere.



#10
Apr2512, 08:46 PM

P: 3,014

No, you can still use a point particle, and use AbrahamLorentz force.



#11
Apr2612, 03:46 AM

P: 31

Is this one of the reformulations of electrodynamics? Like Feynmanwheeler and bopp?
Thanks for the link and reply. Boltzmann 


#12
Apr2612, 04:26 AM

P: 3,014

You may look up WheelerFeynman absorber theory. As for bopp, I don't know what it stands for.



#13
Apr2612, 08:47 AM

P: 31

By Bopp I mean the field theory developed by him , which is in a way a modification of maxwell electromagnetism.It was also mentioned briefly in Feynman vol2
Can you suggest any references for an introduction to Qft? Boltzmann. 


#14
Apr2612, 08:49 AM

P: 3,014

A. Zee, QFT in a nutshell



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