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From: bbowen@megatest.UUCP (Bruce Bowen)
Newsgroups: sci.space
Subject: Re: Black holes (was Re: Comparing c and speed of sound)
Message-ID: <1927@costello.megatest.UUCP>
Date: 14 Feb 89 04:40:03 GMT
References: <8902080259.AA04715@cmr.icst.nbs.gov> <210@v7fs1.UUCP>
Reply-To: bbowen@costello.UUCP (Bruce Bowen)
Distribution: usa
Organization: Megatest Corporation, San Jose, Ca
Lines: 23

In article <210@v7fs1.UUCP> mvp@v7fs1.UUCP (Mike Van Pelt) writes:
>In article <8902080259.AA04715@cmr.icst.nbs.gov> roberts@CMR.ICST.NBS.GOV (John Roberts) writes:
>>My own area of skepticism: I'm not convinced that it's possible for a 
>>black hole to come into existence in a finite period of time, from the
>>viewpoint of an outside observer.
>
>I'm convinced you're right.
>
>Since time slows down, asymptotically approaching 'stopped' at the
>event horizon, the closest there can be is a "black hole in progress".
>-- 

   This is not true.  The total time for a black hole to form for an
outside observer is the integral of the ratio of outside time to local
time integrated over the local time for the black hole to form.  The
ratio goes to infinity as the edge gets close to the event horizon so
one has an improper integral, but the value of this integral is finite.

As an example the integral from 0 to 1 of 1/sqrt(1-x)   = 2
even though 1/sqrt(1-x) goes to infinity as x -> 1


Bruce