Haelfix said:
I've talked with Brian a lot, he is a big fan of geometry in physics in general. Much of his work in ST has been on the geometry side of things (b/c of dualities its often easier to switch perspectives).
He very much likes background independance (moreso than most), but I think he is like most string theorists in feeling that without matter fields it will be very hard to ultimately make sense of things.
Thanks, and great to have your comment, Haelfix! You earlier described the argument many String theorists give that background independence isn't needed ("Background Independence, who needs it? Just derive gravitons in a sufficient range of fixed geometries. The world is basically flat anyway, curvature is just a second or third order correction.") which I found enlightening and probably others here did too.
I want to amplify your comment here because it shows from your direct contact with him why Brian Greene may be more open to Loop's possibilities than are many of his String colleagues.
To repeat the obvious, 1915 Gen Rel is a geometric approach to gravity---gravity IS the changing geometry of the world----and as such it starts with no preconceived fixed geometry on which to build. It is "background independent"---having no fixed background geometry or framework of space and time---in that sense. A lot of people seem to think this is a mistake. But 1915 Gen Rel continues to be verified to high precision and so far has no competition for accuracy where it applicable. So this is a dilemma: Its dynamic geometry does not fit well with other physics, but there is currently no substitute.
LQG is distinguished by its attempt to quantize Gen Rel while keeping the fundamental principles intact---that gravity is geometry and that geometry is dynamic instead of being a fixed background.
So you are saying Brian Greene likes background independence and geometric-style physical models----which would tend to make him more understanding of LQG, other things things being equal. Potentially sympatico.
You are also saying that his main objection is that LQG does not include matter. That is also of interest because a number of recent LQG papers have begun exploring ways to include matter.
I should get some references.
There is one by Gambini and Pullin IIRC---Edgar1813, who I think is a grad student doing related research, would know about that.
There is a recent talk by Hanno Sahlmann at the end-October conference at perimeter. There is something by Laurent Freidel and David Louapre.
Also current work by Bojowald and Ashtekar has bearing on this---discussed by Ashtekar in his 20 September talk at Penn State.
This is not to say that I am aware of any progress being made, only that there are signs of people working about bringing matter into the picture.
Matter is already important in Loop Quantum Cosmology---in how LQC explains inflation. However LQC is different from the full LQG, so it
provides at best a guide for what may reasonably be expected in the full theory.
It's good to have a sense of where Brian Greene is on these basic issues
since he is such an opinion-leader.
