Black Hole Firewalls: Explaining to John K Clark

[johnkclark]

I've heard some explanations of the Black Hole firewall involving broken entanglement releasing energy that frankly I don't understand, but I have another way to think about it and I'd like to know if its even approximately correct. As I'm getting closer and closer to the Event Horizon time would slow down for me, and that means if I'm looking at you far from the Black Hole you would seem to be moving faster and faster, when I hit the Event Horizon itself I would see the entire future history of the universe up until the point the Black Hole evaporated away. You would only very very rarely see a photon of Hawking Radiation coming from the Black Hole but I would see them much more often and the photons would have more energy too because they didn't have to clime out of such a steep gravity well. The closer I got to the Event Horizon the hotter I would get until I got to the Planck temperature which I think is about 10^32 K.

Am I on the wrong track or is any if this right?

John K Clark

 

[PAllen]

Almost all of it is wrong. Falling through the horizon, all the way to the singularity, looking back, you:

1) do not see the whole future history, you only see a small part of it.
2) you do not see see the outside moving faster. In fact, if you free fall from far away, you see the outside red shifted by a factor of 2 on horizon crossing, meaning seeing clocks two twice as slow as yours.
3) Hawking radiation has nothing to do with the firewall hypothesis.

 

[johnkclark]

Red Shifted?? Maybe I'm missing something but it seems to me if I'm at the bottom of a deep gravity well and you're at the top and you shine a light down to me the light should gain energy when it reached me and I would see it blue shifted, that is to say the electromagnetic field of the light should oscillate faster from my point of view than it does from your point of view, in other words when I look up at you things look like they're happening faster for you than they are to me. I also don't know where got that factor of 2 at the Event Horizon, I would think it would be shifted a lot larger than that at the Event Horizen and toward the blue not the red end of the spectrum.

John K Clark

 

[PAllen]

Red Shifted?? Maybe I'm missing something but it seems to me if I'm at the bottom of a deep gravity well and you're at the top and you shine a light down to me the light should gain energy when it reached me and I would see it blue shifted, that is to say the electromagnetic field of the light should oscillate faster from my point of view than it does from your point of view, in other words when I look up at you things look like they're happening faster for you than they are to me. I also don't know where got that factor of 2 at the Event Horizon, I would think it would be shifted a lot larger than that at the Event Horizen and toward the blue not the red end of the spectrum.

John K Clark

You are missing something. The infaller approaches the speed of light relative to stationary observers on approach to the horizon (and the stationary observers need proper acceleration approaching infinite to remain stationary). The result is that if the stationary observer sees extreme blue shift, the passing infaller nearing the speed of light sees small redshift instead, due to Doppler.

The data I gave (red shift factor 2 for infall from far away) is a standard calculation people do in a first course in GR. You can't reason from popsci concepts. You have to understand the math if you want to explore the physics in a sensible way.

 

[PeterDonis]

I've heard some explanations of the Black Hole firewall involving broken entanglement releasing energy

Please give a specific reference.

 

[johnkclark]

http://www.nature.com/news/astrophysics-fire-in-the-hole-1.12726

By the way, I be interested to know if you agree with Pallen that just before I fall through the Event Horizon I will see light from the outside red shifted not blue shifted.

John K Ckark

 

[PeterDonis]

I be interested to know if you agree with Pallen that just before I fall through the Event Horizon I will see light from the outside red shifted not blue shifted.

Yes, @PAllen is correct. As he says, this is a standard calculation that people do in a first course in GR.

Many pop science discussions of this do not draw the crucial distinction between what an observer at rest just above the horizon would see, and what an observer free-falling into the hole would see. The observer at rest just above the horizon would indeed see light coming in from the rest of the universe highly blueshifted. Your intuitive reasoning in post #3 is more or less correct for this observer (though there are still plenty of complications that you have not delved into). But that's not the observer you were talking about in your OP.

 

[PAllen]

http://www.nature.com/news/astrophysics-fire-in-the-hole-1.12726

By the way, I be interested to know if you agree with Pallen that just before I fall through the Event Horizon I will see light from the outside red shifted not blue shifted.

John K Ckark

Note that this article, aiming for accessibility, is not an accurate statement of what the referenced paper says. The referenced paper has no notion of energy from breaking entanglement, in the way the popular article does. However, I admit an overstatement. There is some connection between Hawking radiation and firewalls, in that what it is entangled with figures in the argument for why high energy modes must be encountered if a set of plausible assumptions holds.

 

[johnkclark]

If I were on the surface of a Neutron Star and looking through a telescope at your clock far away in zero g wouldn't I see your clock running much faster than my clock? And would't being of the surface on a Neutron Star be equivalent as far as Einstein is concerned to being in a spaceship in open space accelerating at a billion gravities or so?

John K Clark

 

[Ibix]

If I were on the surface of a Neutron Star and looking through a telescope at your clock far away in zero g wouldn't I see your clock running much faster than my clock?

Yes.

And would't being of the surface on a Neutron Star be equivalent as far as Einstein is concerned to being in a spaceship in open space accelerating at a billion gravities or so?

Dunno about the exact number, but yes. A clock infront of you would be similarly blueshifted. Not sure why you think this is relevant to anything in this thread, though.

 

[PAllen]

If I were on the surface of a Neutron Star and looking through a telescope at your clock far away in zero g wouldn't I see your clock running much faster than my clock? And would't being of the surface on a Neutron Star be equivalent as far as Einstein is concerned to being in a spaceship in open space accelerating at a billion gravities or so?

John K Clark

Yes for both but:

Someone free falling onto the neutron star would NOT see extreme blueshift due to Doppler relative to a surface observer for speed c/3 for typical neutron star. You keep ignoring that static observer is accelerating relative to free faller, and that they have high relative speed. In the case of a BH, a free faller’s speed relative to static observers approaches c as the horizon is approached.

 

[johnkclark]

Please correct me if I'm wrong, if I was hovering just outside the Event Horizon in a super powerful spaceship I could observe the Black Hole evaporating in just a few minutes even though for you who is far away that would take many trillions of years; the only problem is I would also observe many trillions of years worth of Hawking Radiation in just a few minutes, and that would cook me. However if I had no spaceship and was just freely falling through the Event Horizon the Hawking Radiation wouldn't bother me at all; or at least that was the idea before 5 or 6 years ago when this firewall/ entanglement business came up which seems to say the freely falling man may be cooked too at the Event Horizon, but I don't understand Black Hole Firewalls worth a damn.

John K Clark

 

[PAllen]

Please correct me if I'm wrong, if I was hovering just outside the Event Horizon in a super powerful spaceship I could observe the Black Hole evaporating in just a few minutes even though for you who is far away that would take many trillions of years; the only problem is I would also observe many trillions of years worth of Hawking Radiation in just a few minutes, and that would cook me. However if I had no spaceship and was just freely falling through the Event Horizon the Hawking Radiation wouldn't bother me at all; or at least that was the idea before 5 or 6 years ago when this firewall/ entanglement business came up which seems to say the freely falling man may be cooked too at the Event Horizon, but I don't understand Black Hole Firewalls worth a damn.

John K Clark

Yes, that is pretty much all correct. In fact before the firewall conjecture, technicalities of Hawking radiation implied it couldn’t even be detected by an infaller. Note, the form of energy at the proposed firewall is wholly unknown - the arguments are of the form ‘something must exist’. Some derivations don’t even involve Hawking radiation at all.

 

[PAllen]

I will try (at inherent risk of imprecision) to summarize the firewall issue.

There were a set of assumptions about the quantum picture of BH called “black hole complementarity”. The firewall argument shows these assumptions to be inconsistent. Many possible modifications of the assumptions remove the inconsistency. One such modification is to drop “no drama at the horizon”; that is what is called the firewall. However, so far, all alternative modifications are considered worse by most physicists, e.g. information loss or some violation of unitarity, or some other modification of quantum mechanics. Many physicists believe that ultimately, a “none of the above” option will be found, that preserves “no drama at the horizon”. For example, Juan Maldacena believes this, though not having any such complete proposal to put forth.