Originally Posted By: Bill S.
Richard Gott (Time Travel in Einstein’s Universe). ...provides an excellent description of cosmic strings, and the geometry of spacetime around a string. He also explains how cosmic strings might be detected because their enormously compacted mass – some “…10 million billion tons per centimetre,” – would give rise to gravitational lensing

Btw, thanks for the info, this is the first I've heard of R. Gott's 1991 time machine model based on cosmic strings. I just read about it in 'A User's Guide to the Universe', p.158 (by Dave Golberg and Jeff Blomquist, 2010). It seems that what you'd have to do is:

(1) find an infinitely long cosmic string
(2) accelerate it to close to the speed of light

That would take forever, eh? Is there no getting away from infinity, Bill grin

"Time is what prevents everything from happening at once" - John Wheeler