Time Travel: Is it Possible to return to an earlier time? (Please note: I've seen some other questions asked like the one I myself am asking, I realize that I am indeed late to the party, but I am genuinely curious and none of the previous answers have satiated me as of yet. Note that this is a highly hypothetical question, asked by somebody who isn't even a college student studying the idea of physics at this point in time, so go easy on me here. Sorry if this isn't worded well, but I still haven't studied much on the subject, nor am I used to typing up thesis papers. Excuse me please.) 
Theoretically, it is stated that if you were to travel through a Kerr Black Hole- a Black Hole with a rotating ring singularity- it would allow you to go back to an earlier point in time. Another says you can travel through time using a Wormhole and exotic matter. What I'm curious about is whether or not time travel is hypothetically feasible were one of these true, as in whether or not the sheer force would crush a human by attempting to use one of these routes.
 A: There are quite a large number of theoretical obstacles to the possibility of travelling back in time using general relativity : 
a) A lot of these solutions are unstable, making them rather benign. If you actually try to cross the Cauchy horizon (that's the point where spacetime ceases to be causal and allows you to travel back in time), it will collapse. This is among other things the case for the Kerr black hole.
b) Rather general theorems says that you cannot form a time machine (that is, make a time machine through human means, this does not concern the cases where the universe already contains time machine-like structures) without either violating the null energy condition (that the energy must always be positive) or producing singularities (cf for instance Tipler's "Causality violation in asymptotically flat spacetimes" or Hawking "Chronology protection conjecture")
c) Another even more restrictive theorem says that the energy of the quantum vacuum will diverge on the Cauchy horizon, which means that it will probably collapse on its own before forming. (cf Hawking "Chronology protection conjecture")
d) Some theorem also hints at the possibility that, if you try to form a time machine, the laws of physics as they stand cannot let you decide if what will form will be a time machine or another type of spacetime (loss of uniqueness of the solution). If the conditions are met for a time machine to form, it is possible that either a time machine will form or a spacetime with singularities. (cf Krasnikov's " Time machines with the compactly determined Cauchy horizon")
There are a lot of other problems associated with time machines, such as the difficulties of defining quantum fields on them, loss of quantum unitarity, breakdown of the Cauchy problem and such
