# Time travel to the past in binary black hole system

I just saw this YouTube video (only 3 mins long) of Neil deGrasse Tyson explaining what happens when two black holes collide. He says that when the black holes are rotating around each other, there exists a path that you could follow that would cause you to travel back in time. Any chance that someone could explain this in an intuïtive way to me? I just finished my 1st bachelor physics, to give you an idea of my knowledge. I also understand the basics of special relativity.

• This is a general relativity issue and it would be more helpful if you could find the research that Tyson references in the video. – user6972 May 18 '14 at 19:10

There is a solution to Einstein's equations due to Kramer and Neugebauer$^1$ that describes two black holes rotating around each other. Well, sort of. I confess I don't really understand the details, but the two black holes have to be separated by a massless rod, so at best it would only be an approximation to a real binary black hole.
$^1$ Kramer D. and Neugebauer G., "The Superposition of Two Kerr Solutions," 1980, Phys. Lett. A, 75, 259 - I don't think this is available online.