The concept behind tachyons is that whilst particles can't approach the speed of light they can be faster than the speed of light and not break relativistic equations (they couldn't then slow to the speed of light either). Similarly with time reversal.
Personally I think this is cool but probably also just difficult (if not impossible) to falsify and so hasn't yet been restricted. When you apply a mathematical model it's like applying a metaphor [so meta!], it has a limit at which it breaks down but that limit isn't always obvious and sometimes at the edges things look tantalisingly like they might work.
Personally I think this is cool but probably also just difficult (if not impossible) to falsify and so hasn't yet been restricted. When you apply a mathematical model it's like applying a metaphor [so meta!], it has a limit at which it breaks down but that limit isn't always obvious and sometimes at the edges things look tantalisingly like they might work.