[ExI] Time Travel and FTL flight

[Adrian Tymes]

On Thu, Sep 2, 2021 at 2:26 PM Ben Zaiboc via extropy-chat <
extropy-chat at lists.extropy.org> wrote:

> On Thu, 2 Sept 2021 at 18:02, Adrian Tymes via extropy-chat
> <extropy-chat at lists.extropy.org> wrote:
> >
> <snip>
> > But clearly it is not time travel
>
> So Adrian, are you saying that FTL flight wouldn't involve time-travel?
>
I am saying that it doesn't necessarily involve time travel.  There may be
certain versions that might involve it, but there exists at least one
version that does not.

> I thought that under certain circumstances it would (specifically FTL
> travel to a location that was accelerating away at a significant rate
> relative to the point of departure, then FTL return. I think). Or is there
> no problem, and it's just the simple fact that nothing with mass can travel
> at, or faster than, light-speed that stops us being able to do it? (and
> tricks like Acubierre Drive, if it could exist, would work without causing
> paradoxes)?
>
The latter.  Normal acceleration beyond light speed might cause it, but is
impossible, so it doesn't matter what the math says if it were - and even
if it were possible, it would not be the only way.  As you note, there
exist tricks to get around the limit, and said tricks also (so far as we
currently know) cut off the potential for time travel.

Thus: not all forms of FTL that are possible, cause time travel.  It may be
that no forms of FTL that are possible, cause time travel, but I have not
yet done that analysis.

The matter at hand was the objection that FTL always causes time travel,
which I believe is not a true claim.
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