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If I understand this right the Ricci flow on a compact manifold given by

$\partial g_{\mu \nu} = - 2R_{\mu \nu} + \frac{2}{n}\!R_{\alpha}^{\alpha} \,g_{\mu \nu}$

tends to expand negatively curved regions and to shrink positively curved regions.

Looking at the above definition I`m wondering if the parameter n can be used to achieve $\partial g_{\mu \nu} = 0 $ even if the Ricci tensor is not zero such that the validity of physics, that depends on the metric to be constant (as a precondition), could be extrapolated to curved manifolds to describe an expanding universe with a positive cosmological constant?

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I`ve just seen that at theoretical physics SE a related question is asked: theoreticalphysics.stackexchange.com/questions/675/… So I`ll observe both places for answers. –  Dilaton Dec 11 '11 at 23:45
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1 Answer 1

up vote 3 down vote accepted

I get the impression that OP is referring to Normalized Ricci Flow (NRF):

$$ \frac{1}{2} \partial_t g_{\mu\nu} ~=~ -R_{\mu\nu} + \frac{\langle R \rangle}{n} g_{\mu\nu}~. $$

Here $\langle R \rangle$ is the average scalar curvature over the full space-time $M$. The average procedure is often weighted with an Einstein-Hilbert Boltzmann factor. It is just a number (as opposed to a space-time dependent scalar quantity).

Also $n$ is the space-time dimension, which is fixed, and hence cannot be easily varied as OP suggests.

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Thanks @Qmechanics You are right ... –  Dilaton Dec 17 '11 at 11:26
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