Merging black holes / wormholes

[JOLEON]

OK, so black holes are dimensionless, being a singular point in space, right? So if this is the case, then doesn't that mean a black hole must lead to another, because it is a hole in space-time? (wormhole)
So my question is, what if two black holes, (which have infinite gravitational pull, and for arguments' sake obey the wormhole theory, come together and combine in some way? I mean, is that even possible, for them to combine, and if so, what would that do to the quantum tunnelling?

Sorry if I sound like an idiot, I'm only sixteen. Basically, I just want to watch clever people discuss.

[gmalivuk]

Without a theory of quantum gravity, we don't really have a way of answering.

[JOLEON]

So are you saying that we have no idea what happens when black holes come together? Not even a loose theory?

[Sizik]

The current theory is that they will combine into a bigger black hole.

[Scyrus]

The current theory is that they will combine into a bigger black hole.

It would also release a lot of energy, correct?

[gmalivuk]

So are you saying that we have no idea what happens when black holes come together? Not even a loose theory?

GR will tell what happens to spacetime curvature when two collide (which, yes, "simply" results in a single, larger black hole). But we have no theory of what this will do to quantum things like tunneling, because we have no theory of quantum gravity. (Which also means we don't know what happens at the center, since quantum uncertainty says you *can't* have all that mass confined to a single point, but without quantum gravity we don't really know what happens there instead.)

So if this is the case, then doesn't that mean a black hole must lead to another, because it is a hole in space-time? (wormhole)

Incidentally, this definitely doesn't follow. There is no reason to believe that black holes are always connected. After all, a hole in a piece of paper doesn't always connect to another piece of paper.

[eSOANEM]

OK, so black holes are dimensionless, being a singular point in space, right?

That would be a classical singularity, not the black hole (which would usually refer to the event horizon, at least in terms of size), and almost everyone believes that a theory of quantum gravity will show that black holes don't actually contain a singularity and that there'll be some sort of degeneracy pressure preventing that final collapse.

So if this is the case, then doesn't that mean a black hole must lead to another, because it is a hole in space-time? (wormhole)

No. Even if there is a true singularity inside the black hole, it doesn't have to lead anywhere and, in order for it to do so, you'd have to introduce some pretty big and unsupported assumptions about the topology of the universe. The "hole" in the name "black hole" doesn't refer to a hole in the "sheet" of spacetime, but rather is metaphorical and refers to the fact that, like a big hole, things that fall in don't come out (although this analogy is poor for obvious reasons).

So my question is, what if two black holes, (which have infinite gravitational pull, and for arguments' sake obey the wormhole theory, come together and combine in some way?

The black hole (if there is a singularity at all) would only have infinite gravitational pull at the singularity itself, outside of that, you get a roughly Newtonian gravitational field. In fact, if the sun were to collapse into a black hole right now, assuming it didn't lose any mass doing so, our orbit would be unchanged.

Also, singularities acting as wormholes is a problematic notion (or at least, one which probably isn't particularly helpful). If something were to fall through one singularity and out the other, it would immediately be pulled back through by the exit-singularity's infinite pull (unless quantum gravity allows for finite-pull singularities). Even if we assume we can get around this, the fact remains that, without allowing transitions to FTL (which are generally a bad thing) or naked singularities (singularities without an event horizon), the object which fell through will still be trapped by the exit's event horizon and so the fact that it fell through one singularity and out the other will not be observable to the outside universe.

Non-wormholey black holes merging is a perfectly reasonable albeit tricky problem to compute. There's a simulation on youtube of a simple case of this where you can see what happens to the event horizons.

If you start introducing wormholes into the idea, the horizons will behave similarly but inside things are going to get weird although, looking at some of the simulations of schwarzchild wormholes, I suspect you'd get some sort of hall-of-mirrors effect going on (if wormholes are even possible).

The current theory is that they will combine into a bigger black hole.

It would also release a lot of energy, correct?

Yup, if you look at the simulation I linked, the combined black hole starts off with bulges moving quickly which rapidly even out and, at the end they show some numbers showing that the spin has decreased. This is because it loses energy.

[gmalivuk]

The black hole (if there is a singularity at all) would only have infinite gravitational pull at the singularity itself, outside of that, you get a roughly Newtonian gravitational field. In fact, if the sun were to collapse into a black hole right now, assuming it didn't lose any mass doing so, our orbit would be unchanged.

It's true that far from the event horizon, the force is roughly Newtonian, and it's also true that the collapse of a static spherically symmetric mass into a black hole won't have any effect on the force of gravity outside the surface of the object. However, gravitational pull becomes infinite at the event horizon itself, in the sense that at this point infinite force would be necessary to prevent something from falling in.

[eSOANEM]

The black hole (if there is a singularity at all) would only have infinite gravitational pull at the singularity itself, outside of that, you get a roughly Newtonian gravitational field. In fact, if the sun were to collapse into a black hole right now, assuming it didn't lose any mass doing so, our orbit would be unchanged.

It's true that far from the event horizon, the force is roughly Newtonian, and it's also true that the collapse of a static spherically symmetric mass into a black hole won't have any effect on the force of gravity outside the surface of the object. However, gravitational pull becomes infinite at the event horizon itself, in the sense that at this point infinite force would be necessary to prevent something from falling in.

Yeah, I messed up there. Thanks.