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byron178
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Is the electron-positron interpretation traveling backwards in time really time travel backwards or is it a trick or an aid?
mathman said:To me it is an aid or a mathematical trick.
Bill_K said:The short answer is, That's right - nothing ever travels backwards in time. The long answer combines an unfortunate historical misunderstanding with what is a really deep property of quantum fields.
When quantum field theory was first being developed, the description anticipated was in terms of a wavefunction ψ(x,t) a relativistic generalization of the Schrodinger wavefunction. But as the Klein-Gordon equation and the Dirac equation made clear, relativistic invariance implied the existence of negative energy (or at least negative frequency) solutions. And these solutions seemed to represent particles traveling backwards in time.
Second quantization put things in an entirely different light. ψ was not a wavefunction after all, but an operator. And furthermore, what that operator stood for hinged on the choice of Hilbert space. Resolution: the Hilbert space we had been assuming all along was the wrong one. The 'negative energy states' needed to be replaced by positive energy states of a second particle, the antiparticle. And the interpretation required of the field operator ψ was a hybrid. Part of ψ created particles, while the other part destroyed antiparticles.
Now here's what's deep about the thing. In any interaction, it's the combination ψ that always appears. That means the amplitude for the creation of a particle is closely tied to the destruction of an antiparticle. An antiparticle interacts "as if" it was a particle that had been twisted around to point into the past. The fact that this works consistently may seem like a trick, but it is much more than that!
clem said:Feynman diagrams are in 4-momentum space,so there is not even any time to speak about.
Feynman just liked to be whimsical in his descriptions.
An electron-positron question refers to the phenomenon of the creation and annihilation of an electron-positron pair. This occurs when a high-energy photon interacts with a nucleus or another high-energy particle, resulting in the conversion of the photon into an electron and a positron. Similarly, when an electron and positron collide, they can annihilate each other and produce a high-energy photon.
Electron-positron pairs are important in understanding the behavior of particles at the subatomic level. They also play a crucial role in many physical processes, such as particle accelerators and nuclear reactions.
Electron-positron pairs can be created through various processes, such as pair production, where a high-energy photon interacts with a nucleus and produces an electron-positron pair, or through the decay of other particles, such as mesons.
An electron is a matter particle, while a positron is its antimatter counterpart. When an electron and positron collide, they annihilate each other, releasing energy in the form of gamma rays. This process is used in medical imaging techniques such as PET scans.
The annihilation of an electron-positron pair produces two or more gamma rays, which can be detected and analyzed to gain insights into the properties of the particles involved. It is also used in experimental studies of fundamental particles and their interactions.