All Questions
5
questions
4
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What kind of matter's energy density scales as the inverse of the scale factor
We know that radiation energy density scales as $a^{-4}$ with EoS parameter ($w=\frac{1}{3}$), matter as $a^{-3}$ with ($w=0$), curvature as $a^{-2}$ with ($w=-\frac{1}{3}$).
Then which kind of matter ...
- 682
15
votes
4
answers
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If dark matter can't lose kinetic energy, then why is it not traveling at relativistic speeds?
I have read this question:
The only way you can do this is to remove kinetic energy from the system.
With normal matter this is done through electromagnetic interactions, which turn the kinetic ...
- 29k
2
votes
0
answers
158
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How could the universe's expansion "remove the mean gravitational potential"?
I'm citing W. C. Saslaw's The Distribution of the Galaxies: Gravitational Clustering in Cosmology, chapter 25, where he adresses (what seems to be a Newtonian approximation of) the thermodynamic ...
- 2,463
2
votes
1
answer
91
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No Temperature in an Expanding Universe?
The statistical definition of temperature as $\bigg(\dfrac{\partial \ln \Omega}{\partial E}\bigg)^{-1}$ inherently assumes the existence of a well-defined energy. To my understanding, a well-defined ...
user87745
4
votes
3
answers
3k
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Why the temperature is getting lower when the universe is expanding
As we know, if an ideal gas expands in vacuum, as its energy is unchanged, the temperature remains the same. An ideal gas's energy does not depend on volume. In general, the energy is $kT$ times the ...
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