Re: No comments on "An Exceptionally Simple Theory of Everything" ?

Hello:

My one question has to do with group theory. I recall reading on John
Baez's web site that gravity can be viewed as the result of the group
Diff(M) of all continuous diffeomorphisms of a manifold M. That is
jargon folks may be unfamiliar with so let me explain as best I can.

What we need to be able to do is to in a smooth way, go from one
metric to another without changing the physical Universe. In
Newtonian physics, one cannot rotate time into space, so it cannot
describe gravity. In special relativity, the constraint of working
with inertial observers does not allow one to change the metric once
it is set. Under the action of the group Diff(M), one can transform
from empty flat Minkowski spacetime to one with a mass and the
Schwarzschild metric. With a mass M in the Universe, the metric
changes locally: get closer to the source mass, the metric curves
spacetime more.

In the paper, Garrett Lisi uses the group so(3,1), a spin connection.
I would appreciate comments by people in the know about the
differences in the group theory approach.

Thanks,
doug

.

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