Cosmic strings and Gott's machine
Two hypothetical cosmic strings crossing at extreme speeds could tilt causality and produce time loops in the solution known as the Gott machine.
What would a cosmic rope be?
A cosmic rope is a hypothetical topological defect that could have formed during phase transitions of the early universe. It is neither a material string nor the fundamental string of string theory. It would be an extremely fine concentration of energy whose exterior geometry presents an angular deficit: a wedge of space is missing around it.
There is no confirmed detection of cosmic strings. Astronomical and gravitational wave searches set limits on their tension and abundance, but they remain useful theoretical objects for exploring cosmology and gravity.
Gott's proposal
J. Richard Gott studied two straight ropes passing past each other in opposite directions at very high speeds. The combination of their angular and motion deficits can warp the light cones in such a way that a path surrounding the pair closes in on its own past.
The traveler would not overtake the light locally. As in others closed time type curves, the anomaly is in the global structure created by the moving sources.
The obstacles
- Cosmic strings have not yet been observed.
- The setup requires extreme speeds and tensions.
- Total energy and causality analyzes indicate that physical sources cannot easily create the acausal region from ordinary conditions.
- The formation of a black hole or quantum feedback could prevent the loop.
A machine that may not be able to be built
The difference between "containing time curves" and "making them" is decisive. A geometry can be described with the acausal region already incorporated and yet be impossible to produce from a causal past with physically admissible matter. This tension connects the Gott machine with the the chronology protection.
The model remains important because it transforms a science fiction question into quantitative conditions: tension, speed, energy and global structure. Precisely these conditions reveal why the proposal is not a close technology.
Fuentes
Physical Review Letters: Gott's exact solution · Physical Review Letters: limits of physical cosmic strings
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