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Age of a dark energy dominated universe

In non-dark-energy-dominated phases, $a\propto (t-t_1)^\gamma$ for some $\gamma>0$ and some reference time $t_1$. This means that $a=0$ when $t=t_1$, so that time $t_1$ is the beginning of the ...
Sten's user avatar
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0 votes

How do we account for the 'one way' drag of moving space?

In FLRW spacetime, there is a drag-like contribution to the equation of motion of a test particle, $$\frac{\mathrm{d}\vec p}{\mathrm{d}t}=-H\vec p.$$ Here $\vec p$ is the momentum with respect to the ...
Sten's user avatar
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1 vote

How do we account for the 'one way' drag of moving space?

In the body of the paper The river model of black holes, the authors do not use the term "drag" anywhere to describe the model. They describe it as a flow, but not a flow of a viscous ...
Dale's user avatar
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1 vote
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How to find critical density?

The Friedmann eqn is: $$H^2+\frac{k}{a^2}=\frac{\rho}{3M_p^2}$$ where $M_p^2=1/8\pi G$ is the Planck mass. In this eqn we take cosmology constant as dark energy, which becomes a part of $\rho$ above. (...
Albert Zhao's user avatar
0 votes
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How to understand critical density?

1: The critical density is the required density for a flat universe, so it requires only $\Omega_{\rm K}$ to be $0$, but not $\Omega_{\Lambda}$, so it also holds with dark energy if you include its ...
Yukterez's user avatar
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1 vote

Are modified theories of gravity credible?

Although the existing answers aren't wrong, I feel like this part has not been emphasized enough. NB: I'm interpreting your question as "are modified gravity theories that eliminate the need for ...
Allure's user avatar
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2 votes

If space has a positive curvature, is the expansion of the universe caused by time, not "dark energy"?

General relativity doesn't work like that. Space doesn't need a place to put itself. It is the place. In many cosmologies with positive spatial curvature, the universe recollapses, so it passes ...
benrg's user avatar
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