- #1
latentcorpse
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My notes for a particular course say that [itex]G_{ab} - \Lambda g_{ab}= x T_{ab}[/itex] where [itex]x=\frac{8 \pi G}{c^4}[/itex]
Then they say that the trace of this is [itex]-R+4 \Lambda=xT[/itex]
What?
Surely that's only possible if we have [itex]+\Lambda g_{ab}[/itex] as I have seen in every other text I've ever read?
However, when we derive the Freidmann equations from this we get a [itex]( \frac{\dot{a}}{a})^2=\frac{8 \pi G}{3} \rho -\frac{k}{a^2}+\frac{\Lambda}{3}[/itex]
So if we had [itex]-\Lambda[/itex] on the LHS as suggested in the notes then this will come over to the RHS and give a + as required by the Freidmann equations but now it is all inconsistent with the trace.
This is so confusing! Can anyone clear this up? Thanks.
Then they say that the trace of this is [itex]-R+4 \Lambda=xT[/itex]
What?
Surely that's only possible if we have [itex]+\Lambda g_{ab}[/itex] as I have seen in every other text I've ever read?
However, when we derive the Freidmann equations from this we get a [itex]( \frac{\dot{a}}{a})^2=\frac{8 \pi G}{3} \rho -\frac{k}{a^2}+\frac{\Lambda}{3}[/itex]
So if we had [itex]-\Lambda[/itex] on the LHS as suggested in the notes then this will come over to the RHS and give a + as required by the Freidmann equations but now it is all inconsistent with the trace.
This is so confusing! Can anyone clear this up? Thanks.