Jonathan Reeves wrote:
> Anders Sandberg replied:
> >> If something can move FTL, then relativity is obviously not correct
> >> the first place. The reason FTL is dismissed in relativity (besides
> >> the impossibility of accelerating beyond c)
> FTL does not depend on _accelerating_ beyond c. A constant
> acceleration of less than c would result in travel at faster than the
> speed of light relative to your start point.
no it would not. You would approach c, but never pass it, even to any outside observers. You can have two objects moving just below c in opposite directions as outside observers see it, but they will still appear to each other as separating at just under c.
> >> However, "time travel" in various forms can be done without FTL.
> >> example would be wormholes, which are allowable solutions to
> >> relativity (even if their physical possibility remains unknown).
> >> wormholes you can move to a distant time and/or space without going
> >> FTL in your local frame. The same problems with causality might
> >> emerge, but again quantum effects such as the Visser build up of
> >> virtual particle or Novikov's principle might keep physics sane.
> Problems with causality/wormholes are due to the 'space/time
> continuum' - an artifact of relativity theory.
I am increasingly of the opinion that even though time travel is
theoretically possible through wormholes, in practice I think that the
amount of time it takes to make use of such travel will waste any time
gained in traveling into the past, then back to your original locality
in space. I doubt that it will ever be more than a laboratory curiosity.
It does not matter whether you travel from the other side of the
wormhole back through normal space, or wait until the wormhole can be
spun down to travel back to the original local frame at an earlier time.
The time gained will be lost again....in this way causality can be
conserved while allowing specific FTL loopholes like that....