Black Holes & Firewalls: Recent Papers

[Demystifier]

Because the result would not be reproducible since you cannot even compare results. It wouldn't be science.

Would it be science if 100 physicists jumped into the black hole to compare their results?

 

[friend]

Would it be science if 100 physicists jumped into the black hole to compare their results?

They would have to come back to life to tell us about it. We might as well figure out the physics of heaven and the resurrection.

 

[Nano-Passion]

Would it be science if 100 physicists jumped into the black hole to compare their results?

It isn't real physics if they cannot escape the event horizon to verify their results with us, then its just philosophy. :tongue2:

 

[Demystifier]

It isn't real physics if they cannot escape the event horizon to verify their results with us, then its just philosophy. :tongue2:

I think WE, not THEM, are doing philosophy, because we can't see what happens inside the horizon, while they can see what happens outside of the horizon. :tongue:

 

[audioloop]

Lenny's back!


Singularities, Firewalls, and Complementarity

Susskind
( on 16 Aug 2012)
Almheiri, Marolf, Polchinski, and Sully, recently claimed that once a black has radiated more than half its initial entropy (the Page time), the horizon is replaced by a "firewall" at which infalling observers burn up, in apparent violation of the equivalence principle and the postulates of black complementarity. In this paper I review the arguments for firewalls, and give a slightly different interpretation of them. According to this interpretation the horizon has standard properties, but the singularity is non-standard. The growing entanglement of the black with Hawking radiation causes the singularity to migrate toward the horizon, and eventually intersect it at the page time. The resulting collision of the singularity with the horizon leads to the firewall. Complementarity applies to the horizon and not to the singular firewall.
Almheiri, Marolf, Polchinski, and Sully conjecture that firewalls form much earlier then the Page time; namely at the scrambling time. I argue that there is no reason to believe this generalization, and good reason to think it is wrong.
For most of this paper I will assume that the firewall argument is correct. In the last section before the conclusion I will describe reasons for having reservations.

and polchinski repost
We have not changed our minds. Various arguments are expanded and sharpened

Black Holes: Complementarity or Firewalls?
http://arxiv.org/pdf/1207.3123.pdf

We argue that the following three statements cannot all be true: (i) Hawking
radiation is in a pure state, (ii) the information carried by the radiation is emitted
from the region near the horizon, with low energy eective eld theory valid beyond
some microscopic distance from the horizon, and (iii) the infalling observer encounters
nothing unusual at the horizon. Perhaps the most conservative resolution is that
the infalling observer burns up at the horizon. Alternatives would seem to require
novel dynamics that nevertheless cause notable violations of semiclassical physics at
macroscopic distances from the horizon.

-----
read also

Why doesn't hawking radiation prevent a space-like singularity
https://www.physicsforums.com/showthread.php?t=632543

 

[Nano-Passion]

I think WE, not THEM, are doing philosophy, because we can't see what happens inside the horizon, while they can see what happens outside of the horizon. :tongue:

Can an observer in the horizon really see what is going on outside the horizon?

 

[Demystifier]

Can an observer in the horizon really see what is going on outside the horizon?

Yes he can, really.

 

[PAllen]

It doesn't seem to have been pointed out that you can say that this new physics at the horizon does not apply to our universe until heat death. All existing black holes (stellar or galactic) are 'new' in the sense of the firewall papers until CMB radiation has fallen far closer to absolute zero; only then do the BH's even start losing mass to Hawking radiation. Then they must lose some significant amount of mass before proposed firewalls occur. This would be orders of magnitude times the age where all stars have burned out.

 

[friend]

Black Holes: Complementarity or Firewalls?
http://arxiv.org/pdf/1207.3123.pdf

... Perhaps the most conservative resolution is that the infalling observer burns up at the horizon. ...

Just had a thought about that. An infalling observer to outsiders appears to slow down and "freeze" at the horizon. But compared to the Hawking radiation at the horizon, this may seem like a burning fire. Or am I missing something?

 

[MTd2]

Just had a thought about that. An infalling observer to outsiders appears to slow down and "freeze" at the horizon. But compared to the Hawking radiation at the horizon, this may seem like a burning fire. Or am I missing something?

This is what I thought. To compensate for the time compression in relation to the infinity, the hawking radiation should go to infinite, that is, it would burn fast. So, isn't it an argument supporting fast scramble interpretation?

 

[Nano-Passion]

Yes he can, really.

I'm not quite convinced. Isn't there a lot that we don't know about how black holes exactly work?

Would you get a 360° view if you are in the horizon, just as you do now?

 

[PAllen]

I'm not quite convinced. Isn't there a lot that we don't know about how black holes exactly work?

Would you get a 360° view if you are in the horizon, just as you do now?

If you are asking classically, there are no doubts. If you are asking in the context of quantum gravity, nobody knows for sure.

As for 360 view, when you stand on the Earth do you have 360 view of the heavens? What can be said (classically) is that until you reach the singularity, null paths reach you from all spatial directions, and an angular region of these include light from outside the horizon.

The horizon is strictly a one way phenomenon: outgoing light doesn't escape it (or reach it, if emitted from inside the horizon). There is no obstacle at all to incoming light passing it and overtaking timelike trajectories of infaller's who have not reached a singularity.

 

[Nano-Passion]

If you are asking classically, there are no doubts. If you are asking in the context of quantum gravity, nobody knows for sure.

As for 360 view, when you stand on the Earth do you have 360 view of the heavens? What can be said (classically) is that until you reach the singularity, null paths reach you from all spatial directions, and an angular region of these include light from outside the horizon.

The horizon is strictly a one way phenomenon: outgoing light doesn't escape it (or reach it, if emitted from inside the horizon). There is no obstacle at all to incoming light passing it and overtaking timelike trajectories of infaller's who have not reached a singularity.

The Earth isn't a good analogy for this, imagine yourself looking around your room instead, that is a 360 degree view that I am talking about. Let's just start with a circle on the z plane, what would the observer inside the black hole see? Let us say that the observer just reached the horizon and is on the edge per say. Why would the observer be able to see all around him? Light from the other side of the horizon would not reach him.

 

[PAllen]

The Earth isn't a good analogy for this, imagine yourself looking around your room instead, that is a 360 degree view that I am talking about. Let's just start with a circle on the z plane, what would the observer inside the black hole see? Let us say that the observer just reached the horizon and is on the edge per say. Why would the observer be able to see all around him? Light from the other side of the horizon would not reach him.

I think the Earth is a perfect analogy. You can't see part of the sky because you see the ground instead. You get light from 360 degrees - part from the sky, part from the ground. Inside the horizon, the singularity and its affects on light prevent you from seeing outside the horizon in some directions; in directions away from the singularity, you get light unimpeded from outside the horizon. In directions toward the singularity, you get light from earlier infallers, if any (if none, you would see black for a growing range of directions as you approach the singularity). There is nothing mysterious going on here.

 

[friend]

As I understand it, the time dimension inside a black hole is alway pointed directly to the singularity. So objects that fall inside a BH can only travel with some component of their velocity pointing towards the center. In other words, you can non travel in any direction with a component pointing outwards, you must always have some component inward. I think this means that no object can travel tangentially to the center. So you will ever see objects coming from the side, only from the rear.

 

[PAllen]

As I understand it, the time dimension inside a black hole is alway pointed directly to the singularity. So objects that fall inside a BH can only travel with some component of their velocity pointing towards the center. In other words, you can non travel in any direction with a component pointing outwards, you must always have some component inward. I think this means that no object can travel tangentially to the center. So you will ever see objects coming from the side, only from the rear.

Some of this is just peculiarities of the way Schwarzschild coordinates label things. Geometrically, you can say that all forward going timelike curves reach the singularity (in more complex black holes than the spherically symmetric, this is not necessarily true - some can escape to other 'sheets' of the manifold). It is true that you cannot have a time like path remaining on a 2-sphere of constant area around the singularity [ take this a definition of pure tangential motion]. However, you can have tangential components, such that infallers can collide before reaching the singularity.

As for seeing, if you have luminous dust falling in from all radial directions, an ifnaller will see light from all spatial directions until they reach the singularity. What is unusual is that light seen from toward the singularity was actually emitted from a dust particle as of when it was further from the singularity than you are now. You receive it from the direction of the singularity because you 'bump' into the light as it slowly moves inwards, though emitted in an outward direction. Despite this, all looks normal (sufficiently locally). A key point to keep in mind: no matter how extreme the near singular region, a sufficiently small chunk of spacetime behaves just like Minkowski spacetime - this is part of the fundamental definition of a pseudo-riemannian manifold.

 

[audioloop]

Just had a thought about that. An infalling observer to outsiders appears to and "" at the . But compared to the radiation at the , this may seem like a burning fire. Or am I missing something?

Hence the term...


-----
Guest Post: Joe Polchinski on Black Holes, Complementarity, and Firewalls
http://blogs.discovermagazine.com/c...on-black-holes-complementarity-and-firewalls/
...The idea is that an observer falling into a black hole, contrary to everything you would read in a general relativity textbook, really would notice something when they crossed the event horizon. In fact, they would notice that they are being incinerated by a blast of Hawking radiation: the firewall...



-----
...or the information is lost
(or the unitarity is lost, option gaining attention now)

This is what I thought. To for the time compression in relation to the infinity, the hawking radiation should go to infinite, that is, it would burn fast. So, isn't it an argument supporting fast scramble interpretation?

right

Almheiri, Marolf, Polchinski, Sully, arXiv:1207.3123: You hit
a firewall at the horizon if t > O(R log R) (scrambling time)

 

[PAllen]

It doesn't seem to have been pointed out that you can say that this new physics at the horizon does not apply to our universe until heat death. All existing black holes (stellar or galactic) are 'new' in the sense of the firewall papers until CMB radiation has fallen far closer to absolute zero; only then do the BH's even start losing mass to Hawking radiation. Then they must lose some significant amount of mass before proposed firewalls occur. This would be orders of magnitude times the age where all stars have burned out.

Note, this observation is related to 'old' being the Page time. This is what is most strongly argued in the Polchinski et.al. paper. However, they argue that very likely the criterion is the scrambling time. The above observation does not apply if this is true.

 

[sshai45]

Note, this observation is related to 'old' being the Page time. This is what is most strongly argued in the Polchinski et.al. paper. However, they argue that very likely the criterion is the scrambling time. The above observation does not apply if this is true.

So does this mean that any black hole existing now would have a firewall? I find this intriguing, since it seems to be suggesting that general relativity starts to fail even sooner than one may think, in that it starts to fail right at the event horizon, well before the singularity.

 

[PAllen]

So does this mean that any black hole existing now would have a firewall? I find this intriguing, since it seems to be suggesting that general relativity starts to fail even sooner than one may think, in that it starts to fail right at the event horizon, well before the singularity.

Yes, that would be the consequence if Polchinski et.al. are right about firewalls forming in scramble time.

 

[S.Daedalus]

Actually I prefer Bousso's statement that the cloning paradox and entanglement paradox don't exist at all(http://arxiv.org/abs/1207.5192). No observer can see both of the qubits, so it does not contradict no cloning principle. This is the 'observer complementarity'.

Continuing what is apparently en vogue for this topic, Bousso has 'completely rewritten' his paper, from "Observer Complementarity Upholds the Equivalence Principle" to now "Complementarity Is Not Enough", apparently now considering his earlier argument 'naive'.

 

[S.Daedalus]

Hm, there's a new paper by Andrew Hamilton -- "Illusory horizons, thermodynamics, and holography inside black holes" -- which does not address the firewall issue directly, but might nevertheless be relevant: he argues for an 'illusory horizon', which is the horizon an infalling observer continues to see 'below' himself, even after crossing the 'true' horizon. This horizon is the one where the infalling observer sees the Hawking radiation being emitted. He only 'reaches' this horizon upon reaching the singularity. This seems to suggest that either there is no necessity for a firewall, or, if there still is, the infalling observer only encounters it at the singularity. But I haven't really thought about this much (and it's not my field at any rate).

 

[Sourabh N]

It seems a popular assumption -- "Consider a black hole that forms from collapse of some pure state" (quoted from the AMPS paper). I don't see an obvious reason for this though. Can someone explain this or direct me to one?

 

[audioloop]

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

"Polchinski admits that he thought they could have made a silly mistake. So he turned to Susskind, one of the fathers of holography, to find it. “My first reaction was that they were wrong,” says Susskind. He posted a paper stating as much8, before quickly retracting it, after further thought. “My second reaction was that they were right, my third was that they were wrong again, my fourth was that they were right,” he laughs. “It’s earned me the nickname, ‘the yo-yo,’ but my reaction is pretty much the same as most physicists’.”

Since then, more than 40 papers have been posted on the topic in arXiv, but as yet, nobody has found a flaw in the team’s logic. “It’s a really beautiful argument proving that there’s something inconsistent in our thinking about black holes,” says Don Page, a collaborator of Hawking’s during the 1970s who is now at the University of Alberta in Edmonton, Canada."

"here is another option that would save the equivalence principle, but it is so controversial that few dare to champion it: maybe Hawking was right all those years ago and information is lost in black holes. Ironically, it is Preskill, the man who bet against Hawking’s claim, who raised this alternative, at a workshop on firewalls at Stanford at the end of last year. “It’s surprising that people are not seriously thinking about this possibility because it doesn’t seem any crazier than firewalls,” he says"

 

[Ben Niehoff]

As someone who works on fuzzballs, I have to point out that being incinerated at the horizon does NOT necessarily violate unitarity. It just means that one's degrees of freedom are being violently reorganized.

 

[audioloop]

Black hole horizons and Quantum information
21-29 March 2013. CERN.
http://indico.cern.ch/conferenceOtherViews.py?view=standard&confId=222307

An Apology for Firewalls
Speaker: Joseph Polchinski (KITP)
http://indico.cern.ch/getFile.py/access?contribId=10&resId=1&materialId=slides&confId=222307

Comments on black hole interiors
Speaker: Juan Maldacena (IAS Princeton)
http://indico.cern.ch/getFile.py/access?contribId=11&resId=0&materialId=slides&confId=222307

Quantum Mechanics vs. the Equivalence Principle
Speaker: Raphael Bousso (LBL Berkeley)

...

 

[jacophile]

Hi, can someone help me understand the firewall idea?

I have a heuristic understanding that the firewall is created due to breaking entanglement between particles (virtual particles?) inside the EH and old Hawking radiation that emanated from the BH previously.

I don't understand how the entanglement problem arises. They seem to be saying that all particles "in" the BH are entangled with previous Hawking radiation. They then say that a recent Hawking radiated particle must be entangled with its anti-pair that falls inside the EH.

So far so good...

The problem seems to be that the new particle is also entangled with previous radiation. Why?

The new particle is generated outside the EH not inside it where the previously entangled particles are.

So why is the newly created particle entangled with old radiation?

I know that the particle pair explanation is a heuristic analogy but whatever is going on, it's outside the EH and therefore not associated with previous radiation surely?

Judging from the previous post this is a very trivial and huristic view of the postulated system but can someone explain it to me in these terms?

 

[tade]

I believe the answer lies in entanglement.

 

[jacophile]

Care to elaborate?
My question is about entanglement so yep, I'm sure the answer is too...

 

[tade]

Care to elaborate?
My question is about entanglement so yep, I'm sure the answer is too...

At first I thought the photons due to Hawking radiation were entangling with one another through some kind of holographic manifestation. Though now that I think about it, it sounds highly unlikely.

 

[audioloop]

http://www.scientificamerican.com/article.cfm?id=black-hole-firewall-paradox

“To me it’s the best thing that’s happened in awhile,” says University of California, Berkeley, physicist Raphael Bousso of the so-called “black hole firewall paradox,”

Polchinski and his colleagues conclude that not only is space not smooth at a black hole horizon—at that point the laws of physics completely break down. Instead of an unobtrusive boundary, the scientists argue that there must actually be a sharp division they call a firewall. “The firewall is kind of a wall of energy—it could be the end of spacetime itself,” Polchinski says. “Anything hitting it would break up into its fundamental bits and effectively dissolve.”

But physicists have also assumed that information can never be destroyed. The new work says those two ideas are mutually incompatible. “It’s a paradox because several things we believed were true can’t all be true,” -----
SPOTLIGHT LIVE: FALLING INTO A BLACK HOLE
http://www.kavlifoundation.org/science-spotlights/spotlight-live-falling-into-black-holes.

 

[PAllen]

We should note in this thread the latest two papers by a pair of (string) theorists who have been consistently arguing against BH firewalls:

http://arxiv.org/abs/1310.6334
http://arxiv.org/abs/1310.6335

Not sure why this line of papers (these are latest in a series going back to shortly after the AMPS paper) has gotten little attention. These arguments seem broadly consistent with the recent Maldacena/Susskind questioning of firewalls.

 

[atyy]

Andreas Karch's What’s Inside a Black Hole’s Horizon (which I came across via Lubos Motl's blog post) includes favourable comments on the first in the series of papers by Papadodimas and Raju which PAllen linked to.

 

[Haelfix]

We should note in this thread the latest two papers by a pair of (string) theorists who have been consistently arguing against BH firewalls:

http://arxiv.org/abs/1310.6334
http://arxiv.org/abs/1310.6335

Not sure why this line of papers (these are latest in a series going back to shortly after the AMPS paper) has gotten little attention. These arguments seem broadly consistent with the recent Maldacena/Susskind questioning of firewalls.

They are well known in the field, and are taken very seriously. The current state of confusion involves dissecting exactly what is or is not generic. Currently ER=EPR and the A in Rb ideas (like the above) seem to involve special counterexamples, but whether the situation always holds in general is still murky.

 

[bcrowell]

Andreas Karch's What’s Inside a Black Hole’s Horizon (which I came across via Lubos Motl's blog post) includes favourable comments on the first in the series of papers by Papadodimas and Raju which PAllen linked to.

Can anyone explain more about the content of this article? It seems to be an attempt to water down Marolf and Polchinski's recent paper http://arxiv.org/abs/1307.4706 for nonspecialists, but it doesn't seem watered down enough for me to understand. He loses me in the first paragraph:

Marolf and Polchinski presented arguments, now reported in Physical Review Letters [1], suggesting that there is no well-defined quantum mechanical calculation that could predict the outcome of the in-falling observer’s measurement.

Why would we expect to have a calculation that could predict the outcome of this measurement? Don't we expect it to be random?