That it leads to paradoxes like “two people kill each other, each one being killed by the other before he pulls the trigger” in the case of a tachyon duel. And that kind of paradoxes (unlike the “I killed my grandfather” paradox) can’t even be explained by alternative histories/Everett branches.
Existence of tachyons doesn’t necessarily imply that paradoxes would be instantiated. Of course, even if there were tachyons, the world would still be consistent with itself. In the tachyon duel, perhaps the classification of the state of duellists (whether alive or dead) could depend on the reference frame, or perhaps the duel could not happen for some specific reason. Once you can write consistent equations of motion for elementary particles that allow for tachyons—and I think this is possible (although I don’t know much about tachyons, maybe there are some problems which I am unaware of) - complex stories about killing grandfathers and shooting people with neutrinos must add up to normality, even if they seem weird at the beginning.
Well, what’s so bad with “time travel” after all?
That it leads to paradoxes like “two people kill each other, each one being killed by the other before he pulls the trigger” in the case of a tachyon duel. And that kind of paradoxes (unlike the “I killed my grandfather” paradox) can’t even be explained by alternative histories/Everett branches.
Existence of tachyons doesn’t necessarily imply that paradoxes would be instantiated. Of course, even if there were tachyons, the world would still be consistent with itself. In the tachyon duel, perhaps the classification of the state of duellists (whether alive or dead) could depend on the reference frame, or perhaps the duel could not happen for some specific reason. Once you can write consistent equations of motion for elementary particles that allow for tachyons—and I think this is possible (although I don’t know much about tachyons, maybe there are some problems which I am unaware of) - complex stories about killing grandfathers and shooting people with neutrinos must add up to normality, even if they seem weird at the beginning.