Chronology Protection Conjecture: Where are They?
September 8, 2010 4 Comments
“Where are they?” It becomes necessary to ponder about time travellers if you are going to discuss time travel. Well, if time travel is possible, where are the time travellers from future? What if a time machine is handled over you? Where would you like to go first in time dimension? Of course, your answer would be ‘in the past’!! As you know quantum physics allows time travel with given circumstances.[See, Time Travel]
I have already peer reviewed a lot of research paper in regards to time travel. Consider, if our civilization might have been survived for next six centuries and fore, we would have reached to the stage of post singularity and tending to become a typeII civilization. Since every time travelling trick acquire highly risky and pesky technologies like traversable wormholes, tipler cylinder, closed time like curve,macroscopic casimir effect(filled with high negative energy densities) so it is fairly reasonable to assume that building a time machine is just a engineering problem. I bet if we have ensured our survival to the next ten centuries, we would have all such technologies which are today viewed as the challenge. So I’ll assume that our future descendents have such technology which would allow them to travel back and forth in time. Now, a obvious question which knock down our brain is-“where are they?”
Well explanation can be offered in two ways:
1.Chronology Protection Conjecture(CPC):This was first proposed by Pro. Hawking in 1992. Well CPC is nothing but a metaphorical device which prevents the macroscopic time travel. The idea of chronology protection gained considerable currency during the 1990’s when it became clear that traversable wormholes,which are not too objectionable in their own right seem almost generically to lead to the creation of time machines. Why CPC is a key issue? In Newtonian physics, and even in special relativity or flat-space quantum field theory, notions of chronology and causality are so fundamental that they are simply built into the theory ab initio. Violation of normal chronology (for instance, an eect preceding its cause)is so objectionable an occurrence that any such theory would immediately be rejected as unphysical. Unfortunately, in general relativity one can’t simply assert that chronology is preserved, and causality respected, without doing considerable ad-ditional work. The essence of the problem lies in the fact that the Einstein equations of general relativity are local equations, relating some aspects of the spacetime curvature at a point to the presence of stress-energy at that point. Additionally, one also has local chronology protection, inherited from the fact that the spacetime is locally Minkowskian(the Einstein Equivalence Principle), and so in the small general relativity respects all of the causality constraints of special relativity. There is quantum like thingy known as Cauchy horizon problem which prevent the formation of closed time like curve but that could be easily overrun by Casimir effect(exception of Cauchy horizon problem). One side of the horizon contains closed space-like geodesics and the other side contains closed time-like geodesics. When waves traveling in Misner space pass through the identification world line. As this happens infinitely many times while approaching the horizon, the stress-energy tensor diverges at the horizon. Presumably, this prevents space time from developing closed time-like curve ts that would otherwise be feasible. Thus, CPC is protected.
2.Multiverse Theory: This could also be proposed as a possible strategy to explain the paradox. There are infinite universes having every single possibility. So, it is possible that indeed, time travellers from future might be lurking into the past enjoying dinosaur riding but in a different parallel universe. Thusly, it resolves the paradox.
3.No Time Machine can be engineered: Probably this is the simplest solution to the paradox. The parody with time travel is that it always involves something that is way beyond our technology or even rhetorical ideas. General requirements of a time machine are tipler cylinders, black holes, warp drives, wormholes, Kerr Neumann black holes, BPS black holes etc. which won’t seem feasible by any means of technology. Perhaps, which is why there are no time traveller intruding into the past to get better resources, appaling Homo Sapiens.