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. 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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