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Talk about the problems of time travel and causality loops.
This brings another objection. According to special relativity, traveling faster than light is equivalent to traveling backwards in time, according to some observers. In particular, if faster than light travel is possible without too many arbitrary restrictions, it is possible to have events in the future cause events in the past. This is called a causality loop.
In relativity there are two kinds of intervals, time-like and space-like, the former corresponding to sublight speeds and that latter to supralight speeds. The two are non-equivalent so faster than light objects won't have a rest frame. This is not the same thing as traveling backwards through time, but I'm not really sure how this paragraph should be edited, without trying to explain the whole theory here.