Re: BOOKS: Pournelle's *A Step Farther Out*

17 Feb 1999 13:39:08 +0100

Jonathan Reeves <JonathanR@mail.iclshelpdesks.com> writes:

> Anders Sandberg replied:
>
> >> If something can move FTL, then relativity is obviously not correct
> in
> >> 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.

I think you misunderstood me. If your spaceship accelerates at 1 G, a classical calculation would say that after one year you would travel faster than c. However, in relativity (and as evidenced in particle accelerators) even a constant acceleration doesn't lead to a velocity greater than c. What happens is that the mass of the accelerated object increases as 1/sqrt(1-(v/c)^2) and the energy needed to accelerate it to a few percent higher velocity diverges.

> >> However, "time travel" in various forms can be done without FTL. One
> >> example would be wormholes, which are allowable solutions to general
> >> relativity (even if their physical possibility remains unknown). With
> >> 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.

What do you mean by this? The same problem would occur in a discrete spacetime, such as a cellular automaton.

```--
-----------------------------------------------------------------------
Anders Sandberg                                      Towards Ascension!