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The two black holes pass each other in such a way that at the point of closest approach the edges of the two discs pass through each other.
Now, if we have a photon moving perpendicular to that action (you should visualise this as moving straight upwards) such that it passes through the edge of both discs exactly at the moment when they pass through each other,...
Can a photon escape from inside the event horizon of two black holes?
Picture a situation where two black holes are moving in opposite directions at just a fraction under the speed of light. Their event horizons are length contracted so much that they practically become discs rather than spheres.
Picture one moving towards you and the other moving away, and imagine them side by side as they pass each other - both should be deflected sideways by each other's pull, and the amount of that deflection will be related to how fast they're moving.
The first problem is that conventional Black Hole solutions (e.g. Schwarzschild or Kerr–Newman Solutions) just won't continue to apply (they won't even hold as a rough approximation) when two black holes come into such close proximity. As such it's not obvious that there would be two separate event horizons, or that they would pass through each other. As the Black Holes approach each other, a different solution to the Einstein Field Equations would be exhibited. I can barely guess what that might look like but our best models are going to be those used for orbiting black holes that eventually merge (e.g. the sort of thing that LIGO has observed).
You're using special relativity concepts to describe something gravitational, which isn't the way to go about it.
Translation, two black holes with high relative velocity and similar Schwarzschild radius r pass at perhaps less than 2r of each other (coordinate separation?)
Event horizons can't 'pass through each other'. Either there could be events between them from which light could escape or the event horizons merge, and it must become one black hole.
There will be a sort of coordinate distance between them at closest approach, and we assume that they're far enough apart that they don't merge. You're at that midpoint, and by symmetry, you go nowhere. You live to see the day and tell others about it, so light has escaped from you, and thus you've never been within either event horizon.
Quote from: David Cooper on 17/07/2022 01:05:56There may be room for an argument about whether the event horizons join up for a moment or not in a case where the black holes don't merge and go their separate ways afterwardsNo there isn't. An event horizon isn't a location in space. It's a null surface, and there's no way for two null surfaces to touch and then separate. For example, it's not possible for the future light cones of two spatially separated events can intersect and then later on not intersect.
There may be room for an argument about whether the event horizons join up for a moment or not in a case where the black holes don't merge and go their separate ways afterwards
the edges of the two discs pass through each other.
If you have overlapping event horizons, how would anything "know" which hole to fall into?
It wouldn't fall towards either singularity, but it would be inside the event horizon of both.
tiny manufactured black holes which can be guided by moving masses near them while those masses can be held apart such that their locations can be controlled at all times with precision.
Clearly if it's possible for the two black holes to pass each other at very high speed without merging if their event horizons touch.....
Hi.Sorry, this is going several posts back....Quote from: David Cooper on 17/07/2022 00:45:20Clearly if it's possible for the two black holes to pass each other at very high speed without merging if their event horizons touch..... I'm not sure what this sentence or group os sentences was saying. There's an "IF" in it. Are you asking if this is possible, or is the IF an accident and you are telling us it is possible and then the rest of the stuff described in the sentence does happen? Best Wishes.
I don't really need to worry about the "If".
Quote from: David Cooper on 17/07/2022 18:23:47It wouldn't fall towards either singularity, but it would be inside the event horizon of both.In which case it must remain in both because it can't leave the event horizon of either.That means they can not separate.And that means they must merge.
Firstly the black holes aren't intrinsically changed into discs. At best that's only how it will be for a distant observer that is not moving with the black hole.
That's an assertion which may be correct,
If you are observing these and see the black holes approaching each other at these high relative speeds which you measure as a fraction less than c in opposite directions, you will also measure the event horizons to be contracted so strongly that they are almost turned into flat discs, exactly as a spherical planet would be when observed to be moving at such a speed.
You can certainly calculate under both LET and GTR that the black holes look spherical to observers moving at the same speed and in the same direction as them
Quote from: David Cooper on 18/07/2022 18:25:34That's an assertion which may be correct,It's not an assertion, it's a deduction.Which bit do you disagree with?
There is a difference between how things "look" and how they are. You might be mixing the two.I agree that a Black hole looks like a sphere to a distant observer moving with the Black Hole. However, it is not actually a sphere as you would imagine one in 3-D Euclidean space.
.... I've now found a situation where you can play with the strength of dark energy to change the size of a universe such that you can create an infinite line of black holes separated by vast distances, ....... You then have all these black holes moving along parallel paths throughout the rest of the experiment....
If anyone has simulation software capable of checking it, they should be able to provide a definitive answer
If we have two long lines of black holes running into each other (with each black hole aimed at the open spaces between black holes in the opposite line, all the event horizons would link up into one with lots of singularities within it
so can they really be halted quickly enough to stop them separating again?
If the two singularities move further apart by continuing in the direction they were moving in at the start, the depth of that photon in the gravity well will reduce and it can end up outside the event horizon.
it can end up outside the event horizon.