Re: Do they or don't they exist? Is anyone familiar with this paper?

Fri, 26 Sep 2014 16:50:34 -0700 



________________________________
 From: meekerdb <[email protected]>
To: [email protected] 
Sent: Friday, September 26, 2014 3:11 PM
Subject: Re: Do they or don't they exist? Is anyone familiar with this paper?
 


On 9/26/2014 10:55 AM, 'Chris de Morsella' via Everything List wrote:


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> From: John Clark <[email protected]>
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>Before anybody gets too excited there are 2 things to keep in mind:
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1) There is overwhelming empirical evidence that Black Holes DO exist, so if a 
theoretician says they don't then that's the theoretician's problem not the 
Black Hole's.
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>We have overwhelming astronomical evidence that  entities exist which are 
>gravitationally massive and compact, by how things we can measure are affected 
>by their gravitational force. I know there is a big search on to actually see 
>a black hole -- or at least its accretion disk, but I am unaware that any have 
>actually been detected. What we do detect is that there are entities with 
>massive gravitational forces at the centers of most spiral galaxies, as well 
>as unseen companions that are exerting smaller scale yet still massive 
>gravitational influence on their visible counterparts.
>I agree with you that this is pretty strong and convincing evidence for the 
>existence of black holes, by the way... and that the onus is on the 
>theoretician who makes the radical claim to back that claim up with not only 
>mathematical internal consistency, but some prediction or falsifiable 
>statement about what observable reality should look like as a result.
>My point is that I am not as certain as you seem to be that we actually 
>understand these massive gravitational entities and that black holes actually 
>ever do form. As, I think Brent pointed out the time dilation at the location 
>of formation of a black hole would slow time down in a relativistic manner to 
>an almost pure standstill... so the burning up and process by which a black 
>hole never quite is able to form but burns its mass off in Hawking radiation 
>would be smeared over periods of many billions of years from our own 
>relativistic perspective... and so from our own point of view they would seem 
>to exist. 
>Not asserting that this is so.... just pointing out that the formation (or 
>never-quite-formation) of a black hole is a highly relativistic phenomena and 
>that in fact someone falling through the event horizon of a black hole would 
>experience time coming to a relativistic equivalent of a full stop (as Leonard 
>Susskind for example has argued).
>>That last doesn't follow.  A person falling into a large black hole
    would not necessarily notice anything.  Susskind has argued that
    they would encounter a "firewall" of trapped radiation within a few
    Planck lengths of the event horizon based on his sting-theory
    analysis.  But that's still very controversial.

Oops -- I should have read that before I hit the send button. I had the 
perspectives flipped... it is the outside observer seeing their colleague who 
has volunteered to jump into the blackhole, who would see them appear to freeze 
in time... you are correct -- to the person falling in through the event 
horizon everything would probably seem somewhat uneventful -- that is until 
their bodies where spaghettified by the intense tidal forces. 


I am not clear that in practice we would necessarily observe anything different 
-- at great astronomical remove -- whether or not a black hole ever actually 
forms. The process of formation occurs within such a relativistically extremely 
distorted region of spacetime, precisely due to its massive density and gravity 
that billions of years would pass for the outside observer, viewing the 
(possible almost instantaneous) process unfold from relatively flat spacetime.
>>Yes, that's the idea of the paper.  It will still *look* like a
    black hole while it's waiting for that radiation to get out.
Brent


Kind of reminds me of the adage that a watched pot never boils.... an exploding 
black hole (the release of Hawking radiation would be very large)... like that 
watched pot never boils.





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2) The most interesting sentence in the article was "The paper, which was 
recently submitted to ArXiv, an online repository of physics papers that is NOT 
PEER-REVIEWED". 
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>Yes, sure... this hypothesis is speculative, but the author is also an 
>associate professor of physics at a major American university and is a pretty 
>well known cosmologist. Not that easy to dismiss her as a fringe loon, if that 
>is what you are suggesting.
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>  John K Clark
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