1
vote
2answers
56 views

Conservation of stress-energy and the fluid equation in cosmology

I'm trying to derive the equation for the cosmological fluid: $$\dot \rho + 3 \frac{\dot a}{a}(\rho +P)=0$$ by starting from the conservation of the stress-energy tensor: $$\nabla^\mu T_{\mu \nu} = ...
1
vote
0answers
81 views

Perturbed stress-energy tensor in a cosmological context?

In the theory of cosmological pertubations, we can write the metric of a null-curvature expanding Universe as : $ds^2 = -c^2\left(1+2\frac{\psi}{c^2}\right)dt^2 + a^2 ...
6
votes
2answers
273 views

Einstein tensor in Friedmann equations : where is the missing $c^2$?

I would like to demonstrate the several forms of the Friedmann equations WITH the $c^2$ factors. Everything is fine ... apart that I have a missing $c^2$ factor somewhere. In all the following $\rho$ ...