I am adding this image and ask that while listening to this video you occasionally look at it.
CTC's
In mathematical physics, a closed timelike curve (CTC) is a world line in a Lorentzian manifold, of a material particle in spacetime that is "closed", returning to its starting point.
Source: https://www.youtube.com/watch?v=mCSDwxJXgEI
https://en.wikipedia.org/wiki/Closed_timelike_curve
Time travel experiment demonstrates how to avoid the grandfather paradox (Update)
http://phys.org/news/2011-03-grandfather-paradox.html