Einstein predicted that gravity bends spacetime such that travelling through time is possible; but only forward in time. According to General Relativity we can travel in the future, but not backwards in past. Closed timelike curves are possible, i.e. we can travel in future and than come back to our origin.
Can we also travel backwards in time according to some physical theory? I have heard that antiparticles move backwards and not forward in time. Also I know about Tachyons (they have imaginary mass and travel backwards in time), but I think Tachyons are still not observed in experiments.
My question: Is there a physical theory that predicts also that particles can travel backwards in time? Or are such things still impossible due to natural laws?
Every answer would be greatly appreciated!
