The discussion centers on the relationship between bremsstrahlung and pair creation as described in Chapter 6 of M. Kaku's book on Quantum Field Theory (QFT). It is established that bremsstrahlung, which involves high-energy interactions with atoms, can lead to pair creation (electron and positron) when the energy exceeds 1.2 MeV. The key point is that while the Feynman diagrams (FDs) for bremsstrahlung and pair production share similar topological structures, they represent fundamentally different physical processes. In bremsstrahlung, an electron interacts with a proton to produce a photon, whereas in pair production, a photon interacts with a proton to create an electron-positron pair.
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Kaku meant that the FDs for brem and for pair prod have the same topology. What he meant by "rotate" is to change the physics of which particles come in and go out. Physically, brem and pp are very different.Buckeye said:In Chapter 6 of M. Kaku's book (QFT), he wrote (p184) "...by rotating the diagram around, we can convert bremsstrahlung into pair creation." Bremsstrahlung, as far as I know, involves atoms. Does this mean that when bremsstrahlung with >1.2 MeV strikes an atom we will get an electron and a positron?