Causality in GR Does General relativity allow for violation for causality ever?
I know that the Lorentz boosts in SR do preserve causality (since \gamma >0). But is this always true in presence of curvature also?
The movie interstellar did show the protagonist communicating with his past. Is it more of a fantasy or is it allowed by scientific theories?
 A: GR does allow for the possibility of closed timeline curves, which are paths in spacetime that return to an earlier time. Whether they violate causality depends upon one's model of time.
If you take the view that particles are points in spacetime, then the protagonist in Interstellar could not possibly communicate with his past self, since the particles that comprised him in the past have all moved on to exist in the present. Likewise, if you followed a closed timeline curve to return to 1950, say, you would not be able to influence your grandfather because the particles that comprised him then no longer exist in that area of spacetime.
If you take the view, as some do, that particles are in fact worm-like objects in space-time (ie with a point-like spatial extent but a wormlike time extent), then potentially a closed timelike curve could result in the head of the worm curving back to meet its body somewhere.
If you google presentism v eternalism you will find many results that describe these contrasting views. Note, however, that they are differing philosophical attitudes towards the meaning of time- they are not physics.
