First I would like to say that I'm sorry if this question has been asked before- I'm new here. I was reading QED by Richard Feynman, and he mentioned that any given antiparticle is just it's regular particle counterpart moving backwards in time. How is this possible? I thought that it was only possible to go backward in time moving faster than the speed of light. Does this mean that antiparticles are moving faster than the speed of light and therefore have negative mass? Or is this idea of particles moving backward in time no longer accepted, as QED was published in the 80's. I'm sorry if these are stupid questions; I'm new to quantum theory, and I don't have the necessary mathematical background to fully grasp most of the theories.