I want to make a point of clarification about something I wrote above. I wrote: > any FTL drive can be used to make "closed time-like loops", which would allow

I want to make a point of clarification about something I wrote above. I wrote: > any FTL drive can be used to make "closed time-like loops", which would allow travelers to meet up with their own past selves. That should have read "closed causal curves", or perhaps "closed space-like curves". I made the same typo on another occasion or two in this thread. "Closed time-like curves" do also exist, at least theoretically, and they also let you visit your our own past history, but they do not involve FTL travel. Instead, they are artifacts of General Relativity, in which causality is violated without traveling faster than the speed of light. They typically involve traveling around certain kinds of very massive objects. Another kind involves traveling in a very very large circle at close to the speed of light.