If we haven't figured out fusion by the time we could build a Dyson sphere-analog, and therefore have no need for such frippery, it will be our shame. Time trav

If we haven't figured out fusion by the time we could build a Dyson sphere-analog, and therefore have no need for such frippery, it will be our shame. Time travel is easy in the forward direction; we are all performing it at close to light-speed, in Minkowski space. FTL travel might turn out to be possible in the next millennium, even if not meaningfully useful. FTL travel and (backward) time travel are equivalent.