[net.space] Unified Field Theory - Time dil

carroll@uiucdcsb.CS.UIUC.EDU (11/13/85)

Not strictly true. You can travel at the speed of light, if you have
no "rest mass", e.g. a photon. As to traveling faster than light, your
time dilation becomes imaginary, and no one knows what that means.
The main argument against faster than light (FTL) is causality violations.
If you could get from place to place faster than light, you could send
messages back in time, because what is "now" is different for people who
are moving at different speeds. It is easy to create a situation with
three people, one saying "A happened before B", "B happened before A",
and "A and B were simultaneous".