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Re: Hey Zephram....

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Posted by Zephram Cochrane/">Zephram Cochrane on November 5, 1999 20:39:17 UTC

: ...on time travel...do you think there is any way possible?

If a black hole forms with enouph charge or spin, it has been shown that there are then no real event horizons(they are complexified) and closed time-like loops form near the hole. The problem is that much charge or rotation may prevent such a hole to form under the normal process of collapse due to gravitation. In other words if there exhists such a hole we would be able to use it to travel back in time as far back as the event at which it was formed.

: ... do you know what I'd be talking about if I mentioned those equations that allow for a light cone to tip in such away that your local future becomes your global past...

Such equations can be derived from the geodesic equation for a number of space-time geometries. One I worked out for the case of a neutral object falling along the polar axis of a charged and rotating black hole is:

In between the two event horizons that this kind of hole has, this is exactly what happens.

:... the universe must be curved and closed,...

Time, as well as any spacial dimention could be closed curved for all valid frames in the universe, and so of course this presents one such form of time travel that is not incompatable with modern cosmology, but this one particular form of time travel is not the only form to be considered.

As a side note there are different paradigms being used to understand whats really the same principle of relativity. This leads to differences in definitions which is really no big deal except that a few layman self appointing themselves expert complain about it thinking there are contradictions because of it where they aren't. But, more to the point, one definition of the state of curvature is a space-time with a zero Reiman tensor. The relavence here is that the state of a closed "looped" universe does not require curvature as given by this definition. From this point of view a cylindrical tube for instance is a case of a surface with closed spacial loops but is a flat(uncurved) space according to that definition. So the universe could be closed along a spacial dimention and uncurved. The other definition, I preferr, is the state of having a non-special relativistic metric tensor for an otherwise cartesian coordinate system. By this definition curvature is not invariant and the Reiman tensor is irrelevant and saying there is curvature is nothing more or less than saying that there is gravitation in the frame you chose.

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