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?


closed as off-topic by user10851, John Rennie, Martin, ACuriousMind, Danu Aug 28 '15 at 19:36

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    $\begingroup$ No, because the Big Bang didn't happen at a point. $\endgroup$ – John Rennie Aug 28 '15 at 5:26
  • $\begingroup$ Also, note that relativity implies that one cannot talk about objects having some fixed speed at all, in an absolute sense. $\endgroup$ – Danu Aug 28 '15 at 19:36

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.

  • $\begingroup$ 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). $\endgroup$ – Graham Reid Aug 28 '15 at 4:22
  • $\begingroup$ Would this also happen, if two planets free-fell into each other? $\endgroup$ – orokusaki Aug 28 '15 at 4:24
  • $\begingroup$ 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. $\endgroup$ – Graham Reid Aug 28 '15 at 4:26
  • $\begingroup$ 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. $\endgroup$ – orokusaki Aug 28 '15 at 4:32
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    $\begingroup$ 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). $\endgroup$ – Graham Reid Aug 28 '15 at 4:39

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