All Questions
Tagged with cosmology statistical-mechanics
77
questions
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307
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Boltzmann equation collisional operator in thermal equilibrium
Edited after Thomas' answer
http://jila.colorado.edu/~ajsh/astr5770_14/grbook.pdf#section.30.5
Question 30.6. "Detailed balance":
System is in thermal equilibrium, and the physics of the system is ...
- 848
12
votes
1
answer
748
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Integrated Boltzmann equation for dark matter
In Dodelson's book, the equation for a scattering process $ a + b \Leftrightarrow c + d $ is given as
\begin{align}
a^{-3} \frac{\mathrm d (n_a a^3)}{\mathrm d t}&=-n^{\text{eq}}_a n^{\text{eq}}...
- 301
4
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1k
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Boltzmann equation in cosmology
I have a question about the Boltzmann equation in cosmology.
Im trying to understand how this can hold? Where does the logarithmic terms come from?
It is explained quite well here http://www.damtp....
- 41
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1
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158
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Cosmological Boltzmann equation [closed]
Consider the Boltzmann equation:
$$\frac{d \ln{n^c(T)}}{d \ln{T}} = \frac{\Gamma}{H}(1 - \frac{n^c_{eq}(T)}{n^c(T)})$$
We know that the ratio $\Gamma/H$ can be considered constant, let us put it ...
- 319
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1
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10k
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Number $g(T)$ of relativistic degrees of freedom as a function of temperature $T$
Let us consider the total number of relativistic degrees of freedom $g(T)$ for particle species in our universe:
$$g(T)=\left(\sum_Bg_B\right)+\frac{7}{8}\left(\sum_Fg_F\right)$$
Where the sums are ...
- 1,517
10
votes
7
answers
2k
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Mathematically possible vs physically probable outcomes
A good buddy of mine and I have had a friendly debate about the origins of the current state of our universe (namely; Earth and life on Earth) and have fundamentally disagreed in our stances with ...
- 201
2
votes
1
answer
266
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Usefulness of SUSY models when it cannot exist at any non-zero temperature
Unlike other symmetries (like electroweak symmetry), SUSY is spontaneously broken at any non-zero temperature due to some variation of the fact that the boundary conditions on bosons and fermions in ...
- 847
3
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126
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Evolution of black holes ensemble
Background:
I’ve read many times that arrow of time can be explained from extremely low entropy of the Universe at the Big Bang (http://preposterousuniverse.com/eternitytohere/faq.html). The argument ...
- 69
8
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245
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Does quark color contribute to "spin degeneracy" for QGP calculations?
Like the title say, does quark color matter in counting contributions in a early universe plasma (QGP), as when adding up the total plasma energy density, or is it just spin? The book I have (Pathria) ...
- 397
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145
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Does the Standard Model plasma develop a spontaneous magnetisation at finite temperature?
Reference: arXiv:1204.3604v1 [hep-ph] Long-range magnetic fields in the ground state of the Standard Model plasma.
Alexey Boyarsky, Oleg Ruchayskiy, Mikhail Shaposhnikov.
The authors of this paper ...
- 16.6k
4
votes
3
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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 ...
- 553
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4
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3k
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Why aren't we Boltzmann brains in an infinite universe?
Either space is finite or it is infinite.
a) - If space is infinite in extent, either it is thermal over an infinite volume, or it is in the vacuum state for most of it. If it is thermal, infinity ...
- 109
13
votes
2
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580
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Can $10^{23}$ stars be treated with methods of statistical mechanics?
Statistical mechanics is used to describe systems with large number of particles ~$10^{23}$.
The observable universe contains between $10^{22}$ to $10^{24}$ stars. Can we treat those many stars as a ...
- 17.1k
3
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3
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2k
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Black body and cosmic microwave background radiation
Why is the sprectrum of the cosmic microwave background radiation (or seems to be) that of a black body?
- 2,890
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7
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Why was the universe in an extraordinarily low-entropy state right after the big bang?
Let me start by saying that I have no scientific background whatsoever. I am very interested in science though and I'm currently enjoying Brian Greene's The Fabric of the Cosmos. I'm at chapter 7 and ...
Kristof Claes