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Could someone please explain to me Feynman and Wheeler's theory of waves acting forward and backward in time?

I have read about their idea of an antiparticle behaving as a particle travelling backward through time, but cannot see how no paradoxes emerge.


marked as duplicate by Qmechanic May 17 at 11:36

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  • $\begingroup$ Can you give an example of the paradox? There are certainly issues involving entropy/information loss, but in a simple particle system they may be different than we see in thermodynamics. $\endgroup$ – Digiproc May 17 at 11:28
  • $\begingroup$ @Digiproc Time travel always risks paradox because, for example, a time machine can go back and interfere with its own construction. But quantum mechanics avoids this because all the time loops and so forth occur "out of sight" between measurements. $\endgroup$ – Mitchell Porter May 17 at 11:32
  • $\begingroup$ Possible duplicates: physics.stackexchange.com/q/391/2451 and links therein. $\endgroup$ – Qmechanic May 17 at 11:36
  • $\begingroup$ @Digiproc For example, one could design a mechanism with a target that would shut a gate when struck by a pellet, such that the advanced field cause by the pellet closed the gate before the pellet arrived, in which case the pellet could not strike the target, in which case the advanced field would not close the gate after all...and so on. $\endgroup$ – Physics May 17 at 12:19
  • $\begingroup$ @Physics This is not a paradox, just a confusion that unfortunately is too wide spread. There is no paradox in time travel (e.g. no silly "grandfather paradox"). The logical flaw in your description is in the "in which case" statement that wrongly assumes the events unfolding as a sequence along a non existent "time dimension" different from real time. The 4D spacetime is static. We move in it as a slice of 3D space along the real time dimension. In 4D, everything has already happened, including time travel, if any. No paradox. You can't kill your grandfather, because he already has lived. $\endgroup$ – safesphere May 18 at 1:08