All Questions
3
questions
1
vote
2
answers
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Lagrangian density for flat space time
The lagrangian density of a classical scalar field is given as $$\mathcal{L}=\frac{1}{2}\partial_{\mu}\phi \partial^{\mu}\phi -V(\phi).$$
For a flat and homogenous space time the FRW metric is $g_{\...
- 31
1
vote
2
answers
601
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Expanding universe and Time-translation invariance
My understanding is that there are 5 implicit assumptions when introducing the Lagrangian formulation.
Assumptions:
We appear to know that the principle of stationary action is true for the universe
...
- 143
0
votes
0
answers
149
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Reparametrization invariance in FRW
It is usually pointed out that FRW metric is invariant under time reparametrization. Consider the flat case for simplicity
$$ds^2=N(t)^2dt^2-a(t)^2dr^2-a(t)^2r^2d\Omega^2$$
The choice of function $N(...
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