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30
votes
2answers
939 views

Are modified theories of gravity credible?

I'm a statistician with a little training in physics and would just like to know the general consensus on a few things. I'm reading a book by John Moffat which basically tries to state how GR makes ...
7
votes
3answers
2k views

Do the laws of physics evolve?

Hubble's constant $a(t)$ appears to be changing over time. The fine stucture constant $\alpha$, like many others in QFT, is a running constant that varies, proportional to energy being used to measure ...
8
votes
1answer
772 views

On Flatness problem, Inflation etc

I have a couple of naive questions from the topic of the title. We know \begin{eqnarray} \Omega-1=\frac{k}{a^2H^2}-\frac{\Lambda}{3H^2} \end{eqnarray} Now I read that from the standard big bang ...
4
votes
3answers
711 views

Vacuum and repulsive gravity

How can one show from General Relativity that gravity is attractive force, and under which conditions it becomes repulsive, also why positive energy vacuum drives repulsive gravity?
2
votes
1answer
138 views

extracting energy from cosmological expansion

This question is a more concrete reincarnation of an old question about energy conservation in GR. Are there mechanisms to extract energy from the cosmic rate of expansion? putting some extremely ...
11
votes
4answers
626 views

Why didn't Newton have a cosmological constant

Einstein initially added the Cosmological Constant because (if I get this right) it seemed to him that the universe should be static. I agree that back then this would have been an obvious assumption. ...
4
votes
1answer
170 views

Vacuum energy extraction: What happens to the cosmological constant?

If the vacuum energy is extracted, then what will happen to the cosmological constant? Will it remain the same? .