Re: Two Schwarzschild radii

On Jun 13, 5:15 pm, mluttgens <mluttg...@xxxxxxxxx> wrote:
On 11 juin, 16:39, Tom Roberts <tjroberts...@xxxxxxxxxxxxx> wrote:



mluttgens wrote:
On 10 juin, 18:54, carlip-nos...@xxxxxxxxxxxxxxxxxxx wrote:
Indeed, if there *were* a "surface" just outside the Schwarzschild
radius, rather than an event horizon, then relative to that surface,
infalling matter and light would, certainly have a very large energy..
[...]

So, you agree that "if there *were* a "surface" just outside the
Schwarzschild radius, rather than an event horizon, then relative
to that surface, infalling matter and light would, certainly
have a very large energy". Why don't you say 'an infinite energy'?

Because it IS NOT infinite for such a surface outside the horizon. Note
also that a massive object (such as a real surface) cannot remain at the
horizon.

Moreover, observations don't confirm such very high emissions of
energy. Could it be that black holes simply don't exist?

You got it BACKWARDS -- because the emissions from matter impinging on
such a real surface are not observed, such a real surface is presumably
not present, implying a horizon is present. That's why these objects are
considered to be back holes. Yes, such objects are not unique to GR, and
other theories have similar objects, but GR is mainstream and those
other theories are not, so the GR description is generally used.

I presume that you will disagree with the following quote,
as it doesn't come from a textbook, but from wikipedia:
http://en.wikipedia.org/wiki/Event_horizon
"The description of black holes given by general relativity
is known to be an approximation, and it is expected that
quantum gravity effects become significant in the vicinity
of the event horizon. This allows observations of matter
in the vicinity of a black hole's event horizon to be used
to indirectly study general relativity and proposed extensions to it."

This is NOT the generally-accepted guess. The standard expectation is
that GR breaks down near the singularity, not at or near the horizon of
a large black hole (> 1,000 solar masses or so). That's because at the
horizon of such a large black hole gravity is not much stronger than in
places where GR has been well tested. For small black holes (< 1 solar
mass or so), gravity at the horizon is indeed much larger than in
regimes where GR has been well tested, so it is not known whether or not
GR is a good model there.

        Note the difference between an expectation and something
        that is not known.

If the author is right, one has to conclude that general
relativity is an incomplete theory. An "extended" GR theory
would perhaps exclude a "gravitational singularity" at the event
horizon.

Most physicists think GR is incomplete, because of its incompatibility
with quantum phenomena. A theory of quantum gravity is expected to look
considerably different from GR near any singularity. But there is no
general expectation of any sort of true singularity at an event horizon,
and GR is expected to be reasonably close to a quantum gravity model
there (there is a coordinate singularity for some coordinates, but
that's not physical).

Tom Roberts

http://www.mathpages.com/rr/s7-03/7-03.htm

Thus we are not surprised to find him (Einstein) writing in “The
Meaning
of Relativity”:

"For large densities of field and matter, the field equations
and even the field variables which enter into them have no real
significance.
One may not therefore assume the validity of the equations for very
high density of field and matter… The present relativistic theory of
gravitation is based on a separation of the concepts of “gravitational
field” and of “matter”. It may be plausible that
the theory is for this reason inadequate for very high density of
matter…"

It's worthy to read the full article.

Marcel Luttgens

It has calculus. Are you sure you understood the article?
.

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