[Groxx]

I thought special relativity also means that it is impossible to travel faster than light. So anything outside its range of what's possible can be calculated as utter nonsense without invalidating the theory within its range. Similar to how quantum effects seem to work by entirely different and contradictory rules, while still very clearly working.

[hugh3]

Yes and no. It predicts the impossibility of travelling faster than the speed of light and predicts which kinds of impossible you'd get if you did.

The first level of impossible is that you can't accelerate a body past c no matter how hard you try since continued acceleration will just get it arbitrarily close to c (in every reference frame). The second level of impossibility is that if you did find a magical way to do that then you'd wind up with time travel.