Time Machines

All the talk about OPERA and time travel made me interested again in Time Machines - is there some real physics that gives some hope that one could be developed some day?

Prof Ronald Mallett at Connecticut University is working on a technique. Mallett published a paper describing how a circulating beam of laser light would create a vortex in space within its circle (Physics Letters A, vol 269, p 214).

Then he had a eureka moment. "I realised that time, as well as space, might be twisted by circulating light beams," Mallett says.

To twist time into a loop, Mallett worked out that he would have to add a second light beam, circulating in the opposite direction. Then if you increase the intensity of the light enough, space and time swap roles: inside the circulating light beam, time runs round and round, while what to an outsider looks like time becomes like an ordinary dimension of space.

A person walking along in the right direction could actually be walking backwards in time -- as measured outside the circle. So after walking for a while, you could leave the circle and meet yourself before you have entered it.
Link: Mallett

Kip Thorne of CalTech has a nice discussion of the possibilities here: Thorne

In it he postulates that perhaps the Casimir Effect, by providing a source of negative energy, may be used to prevent space-time wormholes from collapsing. It just needs rather a lot of energy...