John M:
>
>Cher Quentin,
>let me paraphrase (big):
>
>so someone had an assumption: BH. OK, everybody has the right to fantasize.
>Especially if it sounds helpful.
Well, the basic assumption was more broad than that: it was that general
relativity is a trustworthy theory of gravity. There's plenty of evidence
that supports various predictions of GR which differ from Newtonian gravity,
like the precession of the perihelion of Mercury's orbit, the gravitational
lensing of light near stars and galaxies, and gravitational time dilation
which can be measured at different altitudes on Earth (and it also needs to
be taken into account when programming the clocks on board the orbiting GPS
satellites). One of GR's predictions is that a sufficiently large collapsing
star will form a black hole (another is that the universe must be either
expanding or contracting, which lead to the Big Bang theory once redshift
was observed). Black holes were theorized for a while, then in the last two
decades they found observational evidence for a large number of likely black
holes with telescopes.
Most physicists believe general relativity's predictions will cease to be
accurate at the "Planck scale" of very short distances and times and very
high energy densities, and that at these scales it will need to be replaced
by a quantum theory of gravity. So although they are fairly confident that
GR is correct about large collapsing stars forming a black hole with an
"event horizon" and a size proportional to its mass (given by the
'Swarzschild radius'), they think that the prediction of a singularity of
infinite density at the center could be wrong, and that we'll need a theory
of quantum gravity to understand what's really going on there.
Jesse
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Received on Sat Mar 10 2007 - 13:25:14 PST