On 9/15/2011 3:30 PM, Stephen P. King 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. AFAIK the only way to fix the singularity problem of GR is to
introduce a cut-off scale/energy at which curvature (or the source) can exist. I am
aware of a few ideas that do this but none that are widely studied.
String theory is widely studied and the string duality scale provides a cutoff, but I
don't think anybody has been able to work out the details. It would provide an updated
version of gravity as an emergent QFT phenomenon as first proposed by Sakaharov.
Brent
It is my suspicion that GR is a theory that need to be examined as to its tacit
assumptions. While it is beautiful and amazingly predictive, the singularity problem
(and the hole problem, to mention some others) point to a need for reconsideration of
its fundamental ontological assumptions. It seems to me that GR might be better
considered as a theory that relates the observations of multiple observers with each
other and not a theory of space-time per se.
Onward!
Stephen
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