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Given two equally massive black holes moving at 99% of light speed, it seems there would clearly be enough energy for most (99%?) of the mass of both to be ejected and / or radiated well beyond the event horizon of their combined mass.

This got me to thinking about a different possible past and future of the universe than the idea that the Big Bang just randomly happened to start out if a singularity, etc., and compared to the idea of an eternal "heat death".

I imagine a scenario where the universe expands until all the expanding energy runs out, and all the mass has coalesced into a few extremely massive black holes, and at this point they're accelerating toward each other. When they reach each other, they're moving at near light speed. When they collide, wouldn't the mass be redistributed as equally as it was during the last Big Bang? After all, there wouldn't be any more or less energy at that point than there is now, so what's to say this couldn't happen over and over again?

orokusaki
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If two black holes hit head on at 99% the speed of light, the result would be one black hole sitting stationary in the center of mass frame with roughly twice the mass and some fraction of the energy expended as gravitational radiation.

Base
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  • You can't beat the event horizon. Anything you throw into an event horizon just makes it bigger. Even other event horizons (For rotating black holes the rotational energy is not stored inside the event horizon but in the ergosphere, so it is possible to extract this energy via the Penrose process for example). – Base Aug 28 '15 at 04:22
  • Would this also happen, if two planets free-fell into each other? – orokusaki Aug 28 '15 at 04:24
  • No, for anything planet sized you would get a spectacular explosion :) If you let two neutron stars free fall onto one another however, it is very likely you would create a black hole. – Base Aug 28 '15 at 04:26
  • That is to say, a black hole doesn't follow the rules of physics? I don't see why there is any reason that 2 equally massive (homogenous and symmetrical for simplicity's sake) objects shouldn't carry their momentum right through each other, like any other object would. – orokusaki Aug 28 '15 at 04:32
  • General relativity is complicated and quite non intuitive. A black hole is a region of spacetime that has become causally disconnected from the rest of the universe. Anything that goes in will never come back out and there is nothing that can be done to get matter out. That is why they are called black: Nothing that goes in ever comes out. – Base Aug 28 '15 at 04:35
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    Also, if you accelerated an ordinary particle to relativistic speeds and collided it head on with another particle (classically at least) the result would be the two particles bouncing off each other in opposite directions. For a black hole, its more like an inelastic collision where both particles just sit there with all their energy expended as heat (except in the black hole case it becomes part of the mass energy of the black hole). – Base Aug 28 '15 at 04:39
  • How could the Big Bang have ever happened. If the universe was a singularity just before the Big Bang, it would have necessarily been the most massive black hole possible. Could it be possible that space is created when matter expands, rather than matter expanding into space? If this were the case, wouldn't that also imply that a new universe could come from any given black hole, perhaps in a different dimension (re: "disconnected from the universe"? – orokusaki Aug 28 '15 at 04:40
  • I have a hard time accepting this. It would seem that black holes couldn't move, if it were also the case that matter entering them at a vector has no effect on their position or inertia. I believe that black holes are not in fact as small as they're currently believed to be. P.S. Thanks for the discussion. I just realized it's nearly 1am and I have to work early in the morning. Cheers and have a good night. – orokusaki Aug 28 '15 at 04:43
  • @orokusaki Remember that mass is energy and vice-versa, maybe that will help clear things up for you. – Sponge Bob Aug 28 '15 at 08:39