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

Jonathan Reeves (JonathanR@mail.iclshelpdesks.com)
Wed, 17 Feb 1999 11:56:48 -0000

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I wrote: 

> Correct me if I'm wrong (I'm sure someone will), but all the 'time
> travel' phenomena that I've heard about are to do with
> things(information) apparently moving faster than the speed of light.
> The interpretation that they are moving backwards in time is solely
due
> to a refusal to believe that something can travel at FTL speeds, as this
> suggests the currently accepted view of relativity may not be entirely > correct.

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.

>> is that it would
>> completely mess up causality, which generally is/was regarded as a bad
>> thing. If you buy Novikov's principle of self-consistency or something
>> similar, then this might not be a serious problem after all - >> causality gets weird and loopy, but not inconsistent. 

>> 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.

Jon Reeves


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I wrote:

> Correct me if I'm wrong (I'm sure someone = will), but all the 'time
> travel' phenomena that I've heard about are to = do with
> things(information) apparently moving faster = than the speed of light.
> The interpretation that they are moving = backwards in time is solely due
> to a refusal to believe that something can = travel at FTL speeds, as this
> suggests the currently accepted view of = relativity may not be entirely
> correct.

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.


>> is that it would
>> completely mess up causality, which = generally is/was regarded as a bad
>> thing. If you buy Novikov's principle of = self-consistency or something
>> similar, then this might not be a serious = problem after all -
>> causality gets weird and loopy, but not = inconsistent.

>> 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.

Jon Reeves