"The event horizon is not made of any material substance it is merely a
particular hypersurface in spactime separating those places from which
signals can escape to external infinity to those places from which all
signals would be trapped ... Is there evidence for the existence of
black holes? Indeed there is. In the 1970's ... a number of double star
systems were known, where only one member of the pair would be luminous
.... The existence, mass, and the motion of the other was inferred from
the fine details of the motion of its visible partner ... from the
emission of X-ray signals, the invisible partner was deduced to be a
compact object, with a mass too great to be a ... white dwarf or a
neutron star ... X-ray emission was consistent with ... an 'accretion
disk' of gas and dust, spiralling gradually closer in towards the hole
at ever greater velocities becoming enormously heated as it gets nearer
the centre ... best known candidate ... Cygnus X-1 ... seven solar
masses, which certainly bars it from being a white dwarf or neutron star
...."
PV exponential metric would not predict the accretion disk I bet! Why
because from the outside there must be the infinite red shift of the
event horizon from g00(r = 2M) = 0 that is missing in PV and that
obviously affects the signature of signals from the matter in the disc
spiraling in toward the event horizon. One would see an anomalously
large redshift that obviously PV does not have because g00(PV) =/= 0 at
r = 2M.
"Now ... there is ... more directly impressive evidence for black holes
.... In some cases the material simply falls 'straight in' and this ...
appears now to have been observed If the attracting compact object were
to have a material surface of any kind, then the infalling material
would heat that surface up, and its glow would become visible .. But no
such glow is seen. ... There is also impressive evidence for very much
larger black holes ... "
27.8 The Road to Reality
On Apr 21, 2006, at 12:46 PM, Paul Zielinski wrote:
Might. But until that actually happens, as things now stand, Jack is
right that there is no viable alternative to GR as a fundamental theory
of gravitation.
Z.
Paul Zielinski wrote:
I think everyone, including Hal, agrees that the PV model is no
competition for GR as a theory of gravitation.
However, the question of the empirical accuracy of the exponential SSS
metric vs. the Schwarzschild metric can in principle be decided
independently of the PV model. If it turns out that the exponential SSS
metric is marginally more accurate than the Schwarzschild metric, then
that would enhance the relative accuracy of the PV model, but it still
wouldn't lead any competent physicist to take PV seriously as a
fundamental theory of gravitation.
My own position on PV is that it is an interesting toy model that may
give reasonable approximations to the predictions of GR for *certain
problems*, but given the existing data, it simply cannot compete with GR
for scope and accuracy, or as a fundamental theory.
If it should happen at some time in the future that a successor theory
to GR becomes available that is superior in accuracy and has a broader
domain of validity than GR, but which predicts an exponential SSS
metric, and this is confirmed by future observations, then we would have
a completely new ballgame. However, right now, Jack is completely
correct when he points out that GR is the best theory of gravitation
currently available.
Personally, even as contrary and argumentative as I tend to be, I see no
point in disputing this. I only question the *interpretation* of the
existing formal-empirical framework.
.
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