Where is the matter in a black hole?

[phinds]

Does an event horizon form at "full size" instantaneously? For some reason I thought it would start at the very center of the object (singularity or whatever one calls it) and propagate out at the speed of gravity, c, and stop at the diameter determined by the mass of the singularity plus, I suppose, whatever other matter ended up inside it as it expanded. If it forms at full size all at once, how does it "know" about the matter it will have swallowed once it exists? Space time curvature changes at the speed of gravity, doesn't it?

When the gravity in a region becomes strong enough that light can't get out there is, by definition, an event horizon. It does not form at a center and move out.

 

[anorlunda]

Maybe, maybe not but there is no evidence for it or theory that suggests it so this is personal speculation which is not allowed here.

That's true, but we do know that the BH gravitates, so something exists inside there. Leonard Susskind also asserts that things inside the EH can be entangled with things outside which also argues for the existence of things inside the EH. Isn't it also true that if the BH has a net charge, that we could detect that from outside the EH? So it is tantalizing. Some properties of the BH's content are observable, but the identity of such content is not observable.

 

[phinds]

That's true, but we do know that the BH gravitates, so something exists inside there. Leonard Susskind also asserts that things inside the EH can be entangled with things outside which also argues for the existence of things inside the EH. Isn't it also true that if the BH has a net charge, that we could detect that from outside the EH? So it is tantalizing. Some properties of the BH's content are observable, but the identity of such content is not observable.

No argument with any of that, I was just letting him know (as you recognize) that what HE was saying is personal speculation and that it's not suitable for this forum.

 

[Grinkle]

When the gravity in a region becomes strong enough that light can't get out there is, by definition, an event horizon. It does not form at a center and move out.

Trying to come up with something observable to ask about. If sufficient mass to cause an event horizon 1 light minute in radius were to collapse, and I am far enough away to watch safely through a telescope, and I am looking at the star field behind the object as it is collapsing, would I see an instant occlusion that is 1 LM in radius instead of an occlusion that grows at light speed for one minute and then stabilizes?

 

[DaveC426913]

Trying to come up with something observable to ask about. If sufficient mass to cause an event horizon 1 light minute in radius were to collapse, and I am far enough away to watch safely through a telescope, and I am looking at the star field behind the object as it is collapsing, would I see an instant occlusion that is 1 LM in radius instead of an occlusion that grows at light speed for one minute and then stabilizes?

The "sufficient mass" occupying that space is already sufficient to bend the light so you can't see it, before it collapses into a black hole.

Remember, the star field is only affected by the amount of mass present. And the mass has not changed.

So, nothing will change in the star field upon collapse - it will already be distorted/missing.

 

[Grinkle]

The "sufficient mass" occupying that space is already sufficient to bend the light

Of course - thanks.

 

[newjerseyrunner]

Actually, bending space does not require any additional dimensions. It's easier to picture in 1D. Think of a meter stick made of rubber. You can stretch parts of it and manipulate it all you want along it's axis, no need to invoke any height or width. I like to envision it more like stretching space. The reason the term bending is used is obvious when you move to a higher dimension: take that meter stick and pull it out into a sheet. Now there is no way to stretch any part of it without causing a bend to the rest of it.

On a semi-related note, I thought you might find it interesting that we do actually know a bit about what happens to neutrons and protons under that pressure: they become a quark-gluon plasma, and then quark degenerate matter. As far as I'm aware, the former we've made in the LHC and the other is based on QMs math. Beyond that is where the mystery lies.

 

[anorlunda]

The video below is pretty entertaining, and it touches on the subject of this thread. Susskind posits a scenario where 100% of the contents of two black holes could be entangled with the contents of the other BH, and how a wormhole between them could exist. Alice could enter the EH of BH1, while Bob enters the EH of BH2 and they meet each other in the middle in a wormhole. But alas, neither of them can tell anyone outside the EHs about their experience.

Of course the serious science behind this whimsy is an attempt to unite the quantum and GR views, via information theory.

 

[EugeneBird]

Thank you Anorlunda, I didn't think anyone was going to mentions the newest discovery: the AMPS argument. Joe Polchinski and three others discovered violations of Quantum Mechanics in the view that everything at the event horizon of a black hole is 'nothing special' and that you just slide on through not noticing anything is there. This is what Leonard Susskind is speculating about in the video above. Most of what you have read in this thread has been called into question two years ago! Black holes might not even have an 'inside' to their event horizons ... decades of talk from kip Thorne and Steven hawking turned on their heads with this new info ... so exiciting ... Watch this video to get it straight from the scientist himself!

 

[PeterDonis]

Thread closed for moderation.

 

[PeterDonis]

Does an event horizon form at "full size" instantaneously?

No. See below.

When the gravity in a region becomes strong enough that light can't get out there is, by definition, an event horizon. It does not form at a center and move out.

The first sentence is true, but the second sentence does not follow from it. Here is what actually happens (according to the GR model of gravitational collapse to a black hole):

The event horizon is the boundary between the region of spacetime that can send light signals to infinity and the region that can't. Suppose we have a spherically symmetric object that is collapsing, and light rays are being emitted radially outward from a point at the center of the collapsing object. One of these light rays (more precisely, outgoing spherical wave fronts) will intersect the surface of the object at the exact instant that that surface is at $r = 2M$, i.e., at the radius where the surface of the object is just passing the event horizon. That light ray (outgoing spherical wavefront) will then stay at $r = 2M$ forever (we are assuming nothing else falls in in the future). The entire history of that spherical wave front marks out the event horizon, not just the portion after it reaches $r = 2M$. (Can you see why?) So the event horizon does form at the center of the collapsing matter and move outward.

 

[PeterDonis]

If a sun collapses to a black hole, the matter does not cross the event horizon.

Yes, it does. See my previous post.

it seems that during the collapse gravitational forces have been so intense, that even protons and neutrons became squeezed to something we do not understand.

We don't really understand the equation of state of condensed matter at densities higher than nuclear densities (or neutron star densities). So we don't really have a good basis for discussion of this topic.

May be these squeezed particles together with electromagnetic radiation still exist inside the black hole.

According to GR, the matter that collapses to form the black hole continues to collapse down to the singularity, and then ceases to exist. I don't think any physicists believe that the GR model is correct all the way down to the singularity; but we don't have a good theory to replace it, and won't until we figure out how quantum gravity works. So again, we don't really have a good basis for discussion of this topic.

 

[PeterDonis]

Joe Polchinski and three others discovered violations of Quantum Mechanics in the view that everything at the event horizon of a black hole is 'nothing special' and that you just slide on through not noticing anything is there.

I think it would be more correct to say that Polchinski et al have claimed that they have discovered violations of QM in this case. This is an area of active research and speculation, and there is no settled answer yet.

 

[PeterDonis]

Some overly speculative posts have been deleted, and one subthread has been moved to a separate thread in the Quantum Physics forum. I have also added a few clarifying posts. This thread appears to have run its course and will remain closed.