RE: Interested in thoughts on this excerpt from Martin Rees

From: Stathis Papaioannou <stathispapaioannou.domain.name.hidden>
Date: Sat, 5 Aug 2006 21:15:18 +1000

CW writes:

> >c) Accepting "a)" and "b)" you assume "physical laws" making time travel
> >possible (which is of course controversial; this could be in principle
> >possible with very special assumption, which could also be false in
> >principle with other assumption).
>
> Time travel is as possible as teleportation of human beings.
>
> >If you do theoretical reasonings you have to make clear the assumptions
> >which are making things "possible in principle". Up to here, I can follow
> >you (I can imagine such fundamental assumptions).
>
> Of course, there are many details and assumptions to say PUA is possible.
> My point is that PUA is possible just like teleportation of human beings.
> I think they have similar possibility.

Not at all. There is a *huge* difference between what is possible in theory and
what is possible practically. A person wearing down a mountain with his fingers
is a practical impossibility, but there is nothing in the laws of physics making it a
theoretical impossibility. A person flying to Alpha Centauri in 5 minutes is logically
possible, but the laws of physics make it theoretically impossible. A person being
simultaneously taller than 180cm and shorter than 170cm is a logical impossibility.
These three examples for everyday purposes are equally unlikely to happen, but
they are fundamentally different from a philosophical standpoint. In the case of
classical teleportation, there is nothing in the laws of physics making it theoretically
impossible, and it is certainly not logically impossible. Time travel is much more
dubious: it may be a physical impossibility, and it may even be a logical impossibility.

Stathis Papaioannou
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Received on Sat Aug 05 2006 - 07:17:21 PDT

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