Michael Lorrey (
Fri, 20 Dec 1996 18:54:16 -0500

Anders Sandberg wrote:
> On Sun, 15 Dec 1996, John K Clark wrote:
> > Well OK, Tipler found a solution in General Relativity that shows that an
> > infinitely long, extremely dense cylinder made of Neutronium (the stuff of
> > Neutron Stars) and spinning at almost the speed of light would be able to tip
> > a light cone enough to act as a time machine, but there are two very important
> > problems.
> >
> > 1) Nobody knows if a cylinder of finite length would work also, the math is
> > too difficult to figure out.
> This is true, but there are other FTL or time travel (CTC) solutions of
> GR, such as the Alcubierre warp drive, passing cosmic strings or
> traversable wormholes.

Yes I read an article a few years ago on such theories. One being that
entering a wormhole, orbiting around its other end in a certain way, and
returning would induce such travel into the past. As for travel into the
future, that's the easy part, all you need is near-relativistic
capability to dilate time. One should also be able to travel into the
past with a simple black hole, according to the latest from Hawking.

Of the allowable manifolds, a quite sizeable subset
> have such beasties (anybody who knows if the measure of CTC manifolds in
> the space of all possible GR manifolds is zero, one or somewhere
> between?).
> > 2) The very rapid rotation would cause the cylinder to fly apart.

Neutronium has such a high gravity gradient that it is self supporting,
as evidenced by black holes that spin nearly at the speed of light.

> On the other hand, I think "tame" FTL and time travel is possible, as
> constrained by the results of Khatsymovsky (you can do FTL, but only
> inside your future light-cone). I.e. you can build wormhole empires and do
> apparent FTL, but not violate causality or build generalized time
> machines.


Michael Lorrey --------------------------------------------------------- President Northstar Technologies Agent Inventor of the Lorrey Drive --------------------------------------------------------- Inventor, Webmaster, Ski Guide, Entrepreneur, Artist, Outdoorsman, Libertarian, Certified Genius.