Time travel and cosmic strings

[Hercule Poirot]

In his book "the universe in a nutshell", stephen hawkings is discussing the possiblity of time travel to the past (ch. 5 How to protect the past). He introducted the concept of cosmic strings to explain that. would anyone here could explain this concept and it's relation to time travel?

Thanks,

 

[gijsbert2002]

What cosmic strings exactly are I don't know, but the tension on them is huge and the energy is because of that. They are strings, so that means that their energy and mass are distributed along a line, apparently that does something to the space curvature opening possibilities if they were to slide along each other creating other types of energy that way (like heat). They are apparently predicted to having been caused by the big bang.

Cosmic strings are *very* theoretical, but they seem to be allowed to exist by quantummechanics and relativity. In everything that we've seen before (like all predicted particles for example) everything that was predicted by a (for now assumed) valid theory really exists.
So we might conclude that because they are allowed to exist, they must. Argument comes also from Hawking.

 

[JesseM]

The relation to time travel is that it's been shown that a hypothetical dense, rotating cylinder of infinite length would allow a traveler moving near it to go backwards in time--google "van stokum cylinder" to find more info on this. But I don't think cosmic strings would actually be infinite in length.

 

[hellfire]

You can read about cosmic strings and other topological defects here:
http://www.damtp.cam.ac.uk/user/gr/public/cs_top.html