I understand that theoretically no particle that has nonzero resting mass can travel at the speed of light, as the mass increases to infinity the closer to c it achieves. Therefore no particle with mass can go through the speed of light and then travel faster than the speed of light back in time. I also understand that serious physicists have speculated that a consistent physics could be created in which there are particles that can only travel faster than the speed of light. The particles would have pure imaginary mass and it would take additional energy to slow them down rather than to speed them up.
So far I think I understand. From here I show my ignorance I think …
What would the tachyon universe look like, both from a vantage point within it and from our vantage point? Would Black-Holes be White Holes repelling photons in that universe? What sort of effects in our universe would we look for as evidence of tachyons?
Is there any basis in quantum physics for particles changing from one sort to another as they flit in and out of existence in a vacuum? And, theoretically (assuming as a thought experiment that tachyons do exist in reality), as particles approach c at an event horizon, could they flit into photons, and flit back as tachyons?
Any sources to offer which review what speculations serious physicists have come up with (rather than the crazies that I can find myself all across the internets).
Thanks to any with knowledge for indulging me!