On 9/15/2011 6:59 PM, Jesse Mazer wrote:
On Thu, Sep 15, 2011 at 6:30 PM, Stephen P. King
<stephe...@charter.net <mailto:stephe...@charter.net>> wrote:
On 9/15/2011 5:17 PM, meekerdb wrote:
On 9/15/2011 1:42 PM, Stephen P. King wrote:
On 9/14/2011 9:49 PM, meekerdb wrote:
snip
On the contrary, the singularity is in the
description. Which is why no physicist believes the
description (General Relativity) is valid.
Brent
Ummm, really? Let me see if I understand this claim,
no physicist believes that General Relativity (GR) is
valid or no physicists believe that there are solutions to
the field equations of GR that are invalid? What about
Roger Penrose and Stephen Hawking? They wrote the paper
that showed a proof that the field equations of GR
generate singularities for relatively innocuous and
plausible conditions and yet they are still great
proponents of GR. So... what is the source of your opinion
re "no physicist believes ..."?
The importance of their paper was that it showed GR predicted
a singularity under very general conditions. Before that,it
had been widely assumed that the singularity prediction was
just an artifact of assuming perfectly spherical 3-geometry
with no rotation. Of course I can't really vouch for what
every physicist ever believed. But I was in graduate school
at the time studying GR and nobody I knew, including Penrose
whom I met and my fellow students, drew any conclusion except
that GR breaks down and does not apply in those circumstances.
And no one was surprised by this. There was already an
active search for a quantum theory of gravity, which it was
assumed would avoid singularities.
Brent
Hi Brent,
AH! I understand and agree with you then. But we have to deal
with the observational evidence that space-time is smooth down
below scales that most forms of quantum gravity theories, loop
quantum gravity for example, predict a granularity or foam or some
other form of discontinuity.
What observational evidence are you referring to? There was recently a
paper by Philippe Laurent that was widely misreported in the media as
giving evidence that ruled out "granularity" at the planck scale (see
http://www.esa.int/esaCP/SEM5B34TBPG_index_0.html for example), but in
fact if you look at the actual paper (at
http://arxiv.org/abs/1106.1068 ) it was specifically about ruling out
granular theories that predicted violations of the Lorentz-symmetry of
relativity. Most forms of string theory and loop quantum gravity
actually assume that Lorentz-symmetry is *not* violated (see
http://books.google.com/books?id=dWmZb3uQWbQC&lpg=PA320&dq=supersymmetric%20string%20theory%20lorentz%20invariant&pg=PA320#v=onepage&q=supersymmetric%20string%20theory%20lorentz%20invariant&f=false
<http://books.google.com/books?id=dWmZb3uQWbQC&lpg=PA320&dq=supersymmetric%20string%20theory%20lorentz%20invariant&pg=PA320#v=onepage&q=supersymmetric%20string%20theory%20lorentz%20invariant&f=false>
and http://arxiv.org/abs/1012.1739 for instance), so the new findings
wouldn't be a problem for them.
For a number of physical arguments that general relativity is likely
to break down at the Planck scale, see http://arxiv.org/abs/1001.1205
Jesse
--
See http://prl.aps.org/abstract/PRL/v97/i14/e140401
More soon..
Stephen
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