(urth) Travelling North aka miscellaneous thoughts on Wolfe

[Paul Zinn-Justin]

That is incorrect. Some quantities might become imaginary but that is a 
mathematical artefact.
The real point is, if you combine faster than light travel and Lorentz 
invariance of the laws of physics (the invariance principle that is the 
basis of Einstein's theory of special relativity), then you can indeed 
have trajectories which connect two arbitrary points of spacetime i.e. 
in a given reference frame it will look like you can move freely forward 
or backwards in time (you're not going ``straight'' into the past -- 
you're making little loops, like travelling to a distant star faster 
than light and then coming back the same way).

On 06/10/2010 03:45 PM, Jack Smith wrote:
>
>
>     It is also not clear that moving faster than the speed of light
>     would allow you to go backward in time.   If the mathematics of
>     the relativity equations correctly describes reality, then a
>     velocity greater than the speed of light puts you not into
>     negative time but into imaginary time.
>
>

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