[ExI] Great sf writers: A.A. Attanasio
atymes at gmail.com
Thu Sep 2 16:56:27 UTC 2021
On Tue, Aug 31, 2021 at 11:44 AM Ben Zaiboc via extropy-chat <
extropy-chat at lists.extropy.org> wrote:
> On 30/08/2021 04:14, Adrian Tymes wrote:
> On Sun, Aug 29, 2021 at 10:49 AM Ben Zaiboc via extropy-chat <
> extropy-chat at lists.extropy.org> wrote:
>> At the very least, any writer who assumes that the speed of light can be
>> exceeded, should deal with the consequences that would ensue. I'm not
>> talking about being able to expand to other galaxies, etc., I'm talking
>> about the consequences that pretty much ensure that the speed of light
>> cannot be exceeded.
> Which consequences would those be?
> I'm thinking about time-travel paradoxes in particular, FTL travel leading
> to causality violation
Alas, this is a common misconception. People confuse "in (my/the origin's)
light cone" with "actually happened".
Let's take two points, A and B, some distance apart - say, in different
solar systems separated by a few light years. Someone teleports
(instantly, and thus FTL) from A to B, does something at B (big enough to
be noticed at A - say, causes B's star to go nova, with resultant radiation
input to neighboring solar systems), then teleports back.
The misconception says that this is time travel, because the action is done
at B before the light from B can reach A, but it doesn't "happen" to A
until the light from B reaches A.
But clearly it is not time travel. It just means it won't be seen at A -
or its consequences (travelling no faster than light) affect A - for a few
years. There may be an effect that might occur at A in a few years, and
whoever teleported to and from B will have foreknowledge of this. (In this
example, they might know to be on the far side of a planet from B when the
radiation arrives, and when that will be.)
"Time travel" would require going into the past of A itself, affecting
things that were already perceived at A. (Or going into the future - call
it A' - and then returning to the present, which would be going into the
past of A'.) People can and do change the future without time travel (or
FTL) all the time.
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