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Itoero

The many definitions of a black hole

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Although black holes are objects of central importance across many fields of physics, there is no agreed upon definition for them, a fact that does not seem to be widely recognized. Physicists in different fields conceive of and reason about them in radically different, and often conflicting, ways. All those ways, however, seem sound in the relevant contexts. After examining and comparing many of the definitions used in practice, I consider the problems that the lack of a universally accepted definition leads to, and discuss whether one is in fact needed for progress in the physics of black holes. I conclude that, within reasonable bounds, the profusion of different definitions is in fact a virtue, making the investigation of black holes possible and fruitful in all the many different kinds of problems about them that physicists consider, although one must take care in trying to translate results between fields.https://www.nature.com/articles/s41550-018-0602-1

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1 hour ago, Itoero said:

Although black holes are objects of central importance across many fields of physics, there is no agreed upon definition for them, a fact that does not seem to be widely recognized. Physicists in different fields conceive of and reason about them in radically different, and often conflicting, ways. All those ways, however, seem sound in the relevant contexts. After examining and comparing many of the definitions used in practice, I consider the problems that the lack of a universally accepted definition leads to, and discuss whether one is in fact needed for progress in the physics of black holes. I conclude that, within reasonable bounds, the profusion of different definitions is in fact a virtue, making the investigation of black holes possible and fruitful in all the many different kinds of problems about them that physicists consider, although one must take care in trying to translate results between fields.https://www.nature.com/articles/s41550-018-0602-1

Don't know if I accept that. The basic definition of a BH, is simply a mass of density, such that the escape velocity is "c"......most of the conflict is with the aspect of the EH, and information paradox, and attempting GR and quantum data together. 

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Actually the 'Black Hole' is defined by the Event Horizon.
It's black and a hole because things, including light, fall in but cannot come back out of the Event Horizon.
The EH ( where as you say, Vescape = c ) is the only physical manifestation.
 

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32 minutes ago, MigL said:

Actually the 'Black Hole' is defined by the Event Horizon.
It's black and a hole because things, including light, fall in but cannot come back out of the Event Horizon.
The EH ( where as you say, Vescape = c ) is the only physical manifestation.
 

According to S Hawking it's rather an apparent horizon.https://arxiv.org/pdf/1601.00921.pdf

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8 hours ago, Gowright said:

I think black holes are interesting 

Correct way of thinking!

Edited by Itoero
adjusting reply

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6 hours ago, Strange said:

Although the title is different, this seems to be the same: https://arxiv.org/abs/1808.01507

It looks interesting but will take some time to read

Stephan Hawking (and Perry, and Strominger) suggests  that black holes might have 'soft hair' , low-energy quantum excitations that release information when the black hole evaporates.

This is a paper about Black hole entropy and soft hair:

"We are deeply saddened to lose our much-loved friend and collaborator Stephen Hawking whose contributions to black hole physics remained vitally stimulating to the very end. This paper summarizes the status of our long-term project on large diffeomorphisms, soft hair and the quantum structure of black holes until the end of our time together."https://arxiv.org/pdf/1810.01847.pdf

 

I think this 'denies' the no-hair theorem which postulates that all black hole solutions of the Einstein-Maxwell equations of gravitation and electromagnetism in general relativity can be completely characterized by only three externally observable classical parameters: mass, electric charge, and angular momentum.

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The EH might be 'apparent', since it is only a mathematical construct, Itoero.
But it is also where all physical information regarding the BH is stored.

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16 hours ago, MigL said:

The EH might be 'apparent', since it is only a mathematical construct, Itoero.
But it is also where all physical information regarding the BH is stored.

The EH and AH (apparent horizon) are both mathematical constructs. The 'soft hair' which can be stored on the AH can't be stored on the EH...according to the theories...

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