From: max@west.darkside.com (Erik Max Francis)
Newsgroups: rec.arts.sf.written,rec.arts.sf.science,sci.physics,sci.skeptic
Subject: Re: Davis Mechanics (was Re: John Woods Campbell)
Date: 12 Jan 93 19:19:24 GMT
Organization: The Dark Side of the Moon +1 408 245 SPAM

jasonr@syma.sussex.ac.uk (Jason F Ralph) writes:

> I really DO hate to spoil the party, but if you want to argue the toss
> about black holes I thought that you might like to know that according
> to Einstein's Theory of General Relativity... they don't exist. (Or,
> more precisely, they cannot form... stuff/matter falling into a black
> hole NEVER reaches it... time dilation and so forth.)

Sorry, no.  From an external frame of reference -- that is, from someone 
outside the influence of the black hole -- a particle never reaches the 
event horizon.  But from the point of view of someone actually falling 
into the black hole, the particle passes through the event horizon 
without trouble; it's the _singularity_ that the particle never reaches.

Take a spaceman falling into a black hole.  His friends in the space 
station orbiting safely out of the static limit and accretion disk are 
watching.  He sends a signal back to the station to let them know what's 
going on; he sends a regular pulse of coherent light every second.

He starts falling.  As he gets closer to the event horizon, his 
colleagues note that his signals are getting farther and farther apart, 
weaker and weaker, and the frequency of the light he's sending is getting 
more and more redshifted.  They notice that the limit is the event 
horizon -- as the spaceman's position approaches the event horizon, the 
length of time between pulses approaches infinity.

But that's only from the station's point of view.  From the spaceman's 
point of view, things are rather different.  We'll assume that the tides 
from the black hole are not too severe, so the spaceman can actually 
experience what's going on.  (This isn't too unreasonable an assumption 
near the event horizon if the black hole is sufficiently large.)

He starts falling.  He sends his pulse every second.  Since it's being 
sent every second from his frame of reference, he never notices anything 
strange about the time between pulses (until the tides wreck him and his 
beacon).

If the black hole is large enough, the spaceman won't notice anything 
strange _at all_ as he passes the event horizon.  Now he is inside the 
black hole, and can never get out.  As he falls further and further, the 
gravitational pull increases and the tidal forces increase.  Note that he 
can still watch what's going on _outside_ of the black hole; the black 
hole is only a one-way membrane, pointing toward him.  Nothing 
spectacular (neglecting tidal forces which would have killed him long 
ago) seems to be happening, but as he looks up (out of the black hole), 
he notices that strange things are happening.  He sees the Universe sped 
up.  He sees all the stars die one by one, he sees the galaxies disappear 
beyond the edge of visibility . . . and then he dies as the black hole 
spits him out, particle by particle, as Hawking radiation.

This of course assumes that the Universe is open.  If it isn't, then he'd 
see the galaxies get closer and closer, the stars boil, and the Big 
Crunch.


  ____  Erik Max Francis -- ..!apple!uuwest!max -- max@west.darkside.com   __
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