4 ms·
Bad news guys. Carroll, Farhi, and Guth along with 't Hooft already looked into this in the 1990s. The only way time travel is possible is if there is already a
by mattheww 16y ago
Bad news guys. Carroll, Farhi, and Guth along with 't Hooft already looked into this in the 1990s. The only way time travel is possible is if there is already a time machine in the universe. If there isn't one already, it's impossible to create one in an open universe, and in a closed universe, it's not possible to create one and then use it before the universe ends.
The proofs are in 2+1 dimensions, but they're generally believed to hold in 3+1.
http://preposterousuniverse.com/research/#ctcs http://preposterousuniverse.com/research/#ctcs for a brief summary with references by Carroll.
- Panoramix 16y agoAs I understood it, this pertains to a specific implementation of a time machine i.e., the Gott time machine. The jury is still out on other implementations, though of course everything seems to point towards them being impossible.
- mattheww 16y agoYou're right, but what other implementations have proven they can actually produce a closed time-like curve?
- Panoramix 16y agoWell, you have wormholes (but they require exotic matter) and anything with singularities in it; there is the Gödel solution of a "rotating Universe" (which could be true for a "parallel" universe), the van Stockum's solution and so on. I guess until closed time-like curves are proven to be unphysical (which seems likely), physicists will keep coming up with possible solutions to Einstein's equations which allow for CTCs (and refuting them). And who knows, maybe one of them can be implemented by humans. On the other hand, it would be very interesting to know what is the mechanism by which the Universe protects itself against CTCs.