In our online poll to find out what Plus readers would most like to know about the Universe you told us that you'd like to find out if time travel is allowed. We took the question to Kip Thorne, Feynmann Professor of Theoretical Physics, Emeritus, at the California Institute of Technology, and here is his answer.
Labels: IYA2009
posted by Plus @ 11:05 AM
4 Comments:
 At 2:00 PM, Ray said...

I know a little GR; but no Quantum Gravity and very little QM.
I interpret the article as saying that the consensus is: Quantum Gravity can not be fit into Godel's timeclosed solution to GR. Is that correct? In that case the global topology would constrain the deeper theories. Put another way Quantum Mechanics can not be embedded/formulated on an arbitrary manifold.
These are questions; not statements.
Ray  At 9:25 PM, Quantum_Flux said...

It is the same thing for observer 1 to rapidly travel into the past as it is for observer 2 to rapidly travel into the future.
 At 3:38 PM, Ray said...

I read references 2,3
3 is quite readable.
2 is tougher and I am not through.
The idea that some local properties can't be extended globally in some topologies is not as strange as it might seem at first glance; there are other examples.
I do have doubts about some of the reasoning; but that doesn't fault the reasoning just the presumptions.
I think its possible that the "energy conditions" are not the right analysis tool. Something along the lines of Entropy (Maxwell's daemon ) might be sharper in the mathematical sense.
Ray  At 5:32 PM, The Grin Reaper said...

Th relation to Casimir vacuums was fascinating. So is the solidarity of Hawking's argument.
Although the possibilities of time travel would lead to the age old grandfather paradox, and I am not sure as to what would be a right explanation. Maybe the Copenhagen interpretation of splitting states to maintain Quantum decoherence.
Cannot say anything conclusively.