BH question

[Alan Grayson]

According to QM, does time stop at the event horizon of a BH? TIA, AG 

[Alan Grayson]

On Monday, November 4, 2019 at 6:56:55 PM UTC-7, Alan Grayson wrote:

According to QM, does time stop at the event horizon of a BH? TIA, AG 

Sorry; I meant according to GR. AG 

[Lawrence Crowell]

On Monday, November 4, 2019 at 7:56:55 PM UTC-6, Alan Grayson wrote:

According to QM, does time stop at the event horizon of a BH? TIA, AG 

There is no time on the horizon for particle geodesics on the horizon. These can only be photons, which as null geodesic particles have zero proper time.

LC 

[Alan Grayson]

Isn't that a singularity of sorts; not one involving infinity, but still a baffling result that time stops? What happens to time when one crosses the horizon? AG 

[Lawrence Crowell]

Crossing the horizon is a nonevent for the most part. If you try to accelerate so you hover just above it the time dilation and that you are in an extreme Rindler wedge will mean you are subjected to a torrent of radiation. In principle a probe could accelerate to 10^{53}m/s^2 and hover a Planck unit distance above the horizon. You would be at the stretched horizon. This would be almost a sort of singular event. On the other hand if you fall on an inertial frame inwards there is nothing unusual at the horizon.

LC

[Alan Grayson]

Do you mean that clock rates continue to slow as an observer approaches the event horizon; then the clock stops when crossing, or on the event horizon; and after crossing the clock resumes its forward rate? AG 

[Brent Meeker]

On 11/5/2019 9:09 PM, Alan Grayson wrote:

Crossing the horizon is a nonevent for the most part. If you try to accelerate so you hover just above it the time dilation and that you are in an extreme Rindler wedge will mean you are subjected to a torrent of radiation. In principle a probe could accelerate to 10^{53}m/s^2 and hover a Planck unit distance above the horizon. You would be at the stretched horizon. This would be almost a sort of singular event. On the other hand if you fall on an inertial frame inwards there is nothing unusual at the horizon.

LC

Do you mean that clock rates continue to slow as an observer approaches the event horizon; then the clock stops when crossing, or on the event horizon; and after crossing the clock resumes its forward rate? AG 

He means the infalling clock doesn't slow down at all.   Whenever you see the word "clock" in a discussion of relativity it refers to an ideal clock.  It runs perfectly and never speeds up or slows down.  It's called relativity theory because observers moving relative to the clock measure it to run slower or faster than their (ideal) clock.

Brent

[Alan Grayson]

I see. So if for the infalling observer, his clock seems to be running "normally", but for some stationary observer, say above the event horizon, the infalling clock appears to running progressively slower as it falls below the EH, even if it can't be observed or measured. According to GR, is there any depth below the event horizon where the infalling clock theoretically stops? I say "theoretically" since the clock below the EH cannot be seen from above the EH. AG

 

[John Clark]

On Tue, Nov 5, 2019 at 8:03 PM Lawrence Crowell <goldenfield...@gmail.com> wrote:

>if you fall on an inertial frame inwards there is nothing unusual at the horizon [of a Black Hole]

That's what everybody thought until 2012 when a paper appeared that through some doubt on that assumption:

Black Holes: Complementarity or Firewalls?

They say a inertial observer would encounter a firewall and burn up as soon as he passed the Event Horizon, do you disagree? 

John K Clark

 

[Brent Meeker]

I just explained that clocks never slow in relativity examples.  So now you ask if there's a place they stop??

Brent

I say "theoretically" since the clock below the EH cannot be seen from above the EH. AG

 

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[Brent Meeker]

I disagree.

Brent

[John Clark]

On Wed, Nov 6, 2019 at 6:12 PM 'Brent Meeker' v<everyth...@googlegroups.com> wrote:

Black Holes: Complementarity or Firewalls?
They say a inertial observer would encounter a firewall and burn up as soon as he passed the Event Horizon, do you disagree? 

>I disagree.

Where did they go wrong?

John K Clark

[Brent Meeker]

A Note on (No) Firewalls: The Entropy Argument
Yasunori Nomura, Jaime Varela
(Submitted on 29 Nov 2012 (v1), last revised 8 Jul 2013 (this version, v4))
An argument for firewalls based on entropy relations is refuted.
https://arxiv.org/pdf/1211.7033.pdf

Branches of the Black Hole Wave Function
Need Not Contain Firewalls
Ning Bao,1 Sean M. Carroll,2 Aidan Chatwin-Davies,2
Jason Pollack,3
and Grant N. Remmen1
We discuss the branching structure of the quantum-gravitational wave function that describes the evaporation of a black hole. A global wave function which initially describes a
classical Schwarzschild geometry is continually decohered into distinct semiclassical branches
by the emission of Hawking radiation. The laws of quantum mechanics dictate that the
wave function evolves unitarily, but this unitary evolution is only manifest when considering
the global description of the wave function; it is not implemented by time evolution on a
single semiclassical branch. Conversely, geometric notions like the position or smoothness of
a horizon only make sense on the level of individual branches. We consider the implications
of this picture for probes of black holes by classical observers in definite geometries, like
those involved in the AMPS construction. We argue that individual branches can describe
semiclassical geometries free of firewalls, even as the global wave function evolves unitarily.
We show that the pointer states of infalling detectors that are robust under Hamiltonian
evolution are distinct from, and incompatible with, those of exterior detectors stationary
with respect to the black hole horizon, in the sense that the pointer bases are related to
each other via nontrivial transformations that mix the system, apparatus, and environment.
This result describes a Hilbert-space version of black hole complementarity.
https://arxiv.org/pdf/1712.04955.pdf


Cool horizons for entangled black holes
Juan Maldacena, Leonard Susskind
General relativity contains solutions in which two distant black holes are connected through the interior via a wormhole, or Einstein-Rosen bridge. These solutions can be interpreted as maximally entangled states of two black holes that form a complex EPR pair. We suggest that similar bridges might be present for more general entangled states.
In the case of entangled black holes one can formulate versions of the AMPS(S) paradoxes and resolve them. This suggests possible resolutions of the firewall paradoxes for more general situations.
https://arxiv.org/abs/1306.0533

Brent

[Alan Grayson]

On Wednesday, November 6, 2019 at 3:46:54 PM UTC-7, Brent wrote:

On 11/6/2019 12:05 AM, Alan Grayson wrote:

On Tuesday, November 5, 2019 at 10:23:58 PM UTC-7, Brent wrote:

On 11/5/2019 9:09 PM, Alan Grayson wrote:

Crossing the horizon is a nonevent for the most part. If you try to accelerate so you hover just above it the time dilation and that you are in an extreme Rindler wedge will mean you are subjected to a torrent of radiation. In principle a probe could accelerate to 10^{53}m/s^2 and hover a Planck unit distance above the horizon. You would be at the stretched horizon. This would be almost a sort of singular event. On the other hand if you fall on an inertial frame inwards there is nothing unusual at the horizon.

LC

Do you mean that clock rates continue to slow as an observer approaches the event horizon; then the clock stops when crossing, or on the event horizon; and after crossing the clock resumes its forward rate? AG 

He means the infalling clock doesn't slow down at all.   Whenever you see the word "clock" in a discussion of relativity it refers to an ideal clock.  It runs perfectly and never speeds up or slows down.  It's called relativity theory because observers moving relative to the clock measure it to run slower or faster than their (ideal) clock.

Brent

I see. So if for the infalling observer, his clock seems to be running "normally", but for some stationary observer, say above the event horizon, the infalling clock appears to running progressively slower as it falls below the EH, even if it can't be observed or measured. According to GR, is there any depth below the event horizon where the infalling clock theoretically stops?

I just explained that clocks never slow in relativity examples.  So now you ask if there's a place they stop??

Brent

I know, but that's not what I asked. Again, the infalling clock is measured as running slower than a stationary clock above the EH. As the infalling clock goes deeper into the BH, won't its theoretical rate continue to decrease as compared to the reference clock above the EH? How slow can it get? AG 

I say "theoretically" since the clock below the EH cannot be seen from above the EH. AG

 

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[Brent Meeker]

On 11/6/2019 4:44 PM, Alan Grayson wrote:

On Wednesday, November 6, 2019 at 3:46:54 PM UTC-7, Brent wrote:

On 11/6/2019 12:05 AM, Alan Grayson wrote:

On Tuesday, November 5, 2019 at 10:23:58 PM UTC-7, Brent wrote:

On 11/5/2019 9:09 PM, Alan Grayson wrote:

Crossing the horizon is a nonevent for the most part. If you try to accelerate so you hover just above it the time dilation and that you are in an extreme Rindler wedge will mean you are subjected to a torrent of radiation. In principle a probe could accelerate to 10^{53}m/s^2 and hover a Planck unit distance above the horizon. You would be at the stretched horizon. This would be almost a sort of singular event. On the other hand if you fall on an inertial frame inwards there is nothing unusual at the horizon.

LC

Do you mean that clock rates continue to slow as an observer approaches the event horizon; then the clock stops when crossing, or on the event horizon; and after crossing the clock resumes its forward rate? AG 

He means the infalling clock doesn't slow down at all.   Whenever you see the word "clock" in a discussion of relativity it refers to an ideal clock.  It runs perfectly and never speeds up or slows down.  It's called relativity theory because observers moving relative to the clock measure it to run slower or faster than their (ideal) clock.

Brent

I see. So if for the infalling observer, his clock seems to be running "normally", but for some stationary observer, say above the event horizon, the infalling clock appears to running progressively slower as it falls below the EH, even if it can't be observed or measured. According to GR, is there any depth below the event horizon where the infalling clock theoretically stops?

I just explained that clocks never slow in relativity examples.  So now you ask if there's a place they stop??

Brent

I know, but that's not what I asked. Again, the infalling clock is measured as running slower than a stationary clock above the EH. As the infalling clock goes deeper into the BH, won't its theoretical rate continue to decrease as compared to the reference clock above the EH? How slow can it get? AG

It appears (if the observer at infinity could see the extreme red shift) to asymptotically approach stopped as it approaches the event horizon.  This is because the photons take longer and longer to climb out because they have to traverse more and more spacetime.

Brent

[Alan Grayson]

I'm referring to two clocks; one at finite distance above the EH, and other infalling. Doesn't the infalling clock seem to run progressively slower from the POV of the other clock, as it falls lower and lower? AG 

[Brent Meeker]

I appears to run slower as seen by the distant observer.

Brent

[Alan Grayson]

As it goes deeper and deeper into the BH, does the clock ever appear to STOP? AG

[Brent Meeker]

It doesn't appear at all when it passes the event horizon.  It appears to stop as it approaches the event horizon.

Brent

[Alan Grayson]

I know it can't be observed as it falls through the EH. That's why I referred to clock "readings" after falling through as "theoretical". On the other hand, LC says falling through the EH is a non-event, as if the infalling clock behaves as we expect based on a clock entering a region of strong gravitational field. But let's say the clock appears to stop as it approaches the EH, which is what I thought. How do you reconcile this prediction, which is certainly weird? AG 

[Brent Meeker]

Well it doesn't make much sense to call observations theoretical when it's the theory that says they can't be observed.

On the other hand, LC says falling through the EH is a non-event, as if the infalling clock behaves as we expect based on a clock entering a region of strong gravitational field. But let's say the clock appears to stop as it approaches the EH, which is what I thought. How do you reconcile this prediction, which is certainly weird? AG

Reconcile it with what?  It's a consequence of the metric which is derived from Einstein's equations.  It's not as if it's some unexplained observation.  It's not an observation at all.  It's a theoretical prediction.

Brent

[Alan Grayson]

You don't see a problem with a theory that predicts a clock which stops as seen by an outside observer, when the observer using the clock, which measures proper time, must see it moving forward?  AG

[Brent Meeker]

No.  Why should it be a problem?  You're watching the clock approach the event horizon and the photons from it come further and further apart until you have to wait seconds between photons, and then hours, and then days, and years...why because they have to travel thru more spacetime.  If it's a rotating black hole, as most of them will be, each photon will have to orbit many times on it's way out.

Brent

[Alan Grayson]

If clock which is fixed some distance from the EH, and the BH isn't rotating, why must the photons traveling to the fixed observer have to travel progressively longer times? AG 

[Philip Thrift]

On Friday, November 8, 2019 at 12:42:40 AM UTC-6, Alan Grayson wrote:

You don't see a problem with a theory that predicts a clock which stops as seen by an outside observer, when the observer using the clock, which measures proper time, must see it moving forward?  AG

No.  Why should it be a problem?  You're watching the clock approach the event horizon and the photons from it come further and further apart until you have to wait seconds between photons, and then hours, and then days, and years...why because they have to travel thru more spacetime.  If it's a rotating black hole, as most of them will be, each photon will have to orbit many times on it's way out.

Brent

If clock which is fixed some distance from the EH, and the BH isn't rotating, why must the photons traveling to the fixed observer have to travel progressively longer times? AG 

Keep in mind that all this (deducing what happens in physical reality from the mathematics) all depends  on what mathematics one begins with.

Starting instead with a LQG-type mathematics, one might have a bouncing clock that slows until it bounces - going backwards in time.

Crossing the event horizon with Loop Quantum Gravity

Loosely speaking, the full phenomenon is analogous to the bouncing of a ball. A ball falls to the ground, bounces, and then moves up. The upward motion after the bounce is the time-reversed version of the falling ball. Similarly, a black hole “bounces” and emerges as its time-reversed version—the definition of a white hole.

https://resonancescience.org/crossing-the-event-horizon-with-loop-quantum-gravity/

@philipthrift

[Brent Meeker]

It's because there is more time to traverse.  It's a matter of the metric.

Brent

[Alan Grayson]

Doesn't this mean that the gravitational field of the BH becomes *infinite* at the EH? How else could the red shift become so large for photons leaving a clock at the EH, that from the pov of the fixed observer above the EH the clock approaching the EH seems to stop? AG

[Brent Meeker]

Look at Greg Egan's page on this: https://www.gregegan.net/SCIENCE/FiniteFall/FiniteFall.html#HOR

Brent

[Philip Thrift]

On Saturday, November 9, 2019 at 6:29:02 PM UTC-6, Brent wrote:

Look at Greg Egan's page on this: https://www.gregegan.net/SCIENCE/FiniteFall/FiniteFall.html#HOR

Brent

very strange

SF writer Greg Egan

@philipthrift