|MadSci Network: Physics|
The statement that anti-particles travel ``backwards in time'' is to be understood in a more mathematical sense. It helps to think that way when doing calculations in quantum field theory, but there is no physical implication: Anti-particles are as ``real'' as particles and they move forward in time. Actually it is quite arbitrary whether one calls e.g. the electron or the positron the ``anti-particle'' -- it is a matter of convention.
In my opinion, it is quite unfortunate that the idea of particles travelling `backwards in time'' made its way to popularizations of quantum field theory. It confuses more than it helps.
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