"Among the many intriguing concepts in Einstein’s relativity theories is the idea of closed timelike curves (CTCs), which are paths in spacetime that return to their starting points. As such, CTCs offer the possibility of traveling back in time. But, as many science fiction films have addressed, time travel is full of potential paradoxes. Perhaps the most notable of these is the grandfather paradox, in which a time traveler goes back in time and kills her grandfather, preventing her own birth.
In a new study, a team of researchers has proposed a new theory of CTCs that can resolve the grandfather paradox, and they also perform an experiment showing how such a scheme works. The researchers, led by Seth Lloyd from MIT, along with scientists from the Scuola Normale Superiore in Pisa, Italy; the University of Pavia in Pavia, Italy; the Tokyo Institute of Technology; and the University of Toronto, have published their study in a recent issue of Physical Review Letters. The concepts in the study are similar to an earlier study by some of the same authors that was posted at arXiv.org last year.
“Einstein's theory of general relativity supports closed timelike curves,” Lloyd [explained]. “For decades researchers have argued over how to treat such objects quantum mechanically. We believe that our theory is the correct theory of such objects. Moreover, our theory shows how time travel might be accomplished even in the absence of general relativistic closed timelike curves...”
(for complete article including illustrative graph of "quantum gun" experiment, see PhysOrg.com)
More information: Seth Lloyd, et al. “Closed Timelike Curves via Postselection: Theory and Experimental Test of Consistency.” Physical Review Letters 106, 040403 (2011). DOI:10.1103/PhysRevLett.106.040403 (abstract only, subscription required for complete access)
Addendum- PDF of the original incarnation of the Lloyd Team paper prior to 1/11 revision: "Closed Timelike Curves Via Post-Selection: Theory and Experimental Demonstration" Download Lloyd Team Paper 5:12:10.
Further thoughts re: resolution of the grandfather paradox based on Richard Feynman's multiple histories theory: http://www.physicsforums.com/archive/index.php/t-162.html
-Maureen Lang
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