All Questions
Tagged with cosmology statistical-mechanics
77
questions
4
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353
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Pressure in Scott Dodelson's book Modern Cosmology
I am completely at a loss in deriving the equation 2.62 given in Scott Dodelson's Modern Cosmology book. That is the following expression for the pressure of Fermi-Dirac and Bose-Einstein ...
- 568
2
votes
1
answer
349
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Does ΛCDM imply infinitely many Boltzmann brains?
In this paper, Sean Carroll basically argues that the ΛCDM/'flat lambda' cosmological model has to be wrong since it implies that we're probably Boltzmann brains (and therefore shouldn't trust our ...
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-3
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1
answer
225
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Must the origin of the universe be non-physical? [duplicate]
Since the 2nd law of thermodynamics says the universe's entropy is constantly increasing, then its initial entropy must have been smaller than it is today.
However, no known physical law can reduce ...
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0
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73
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Statistical physics in cosmolgy
In https://ned.ipac.caltech.edu/level5/Sept03/Trodden/Trodden4_2.html and also in Mo et al. (Galaxy Formation and Evolution) the number density, energy density and pressure of the different particle ...
- 317
1
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2
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180
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Kolb and Turner's expresion for number density Eqn. (3.46) and pressure in Eqn. (3.48)
Having defined the phase space distribution function $f(\textbf{r},\textbf{p},t)$ in $\mu-$space, one can express the information that there are $N$ particles in the volume $V$ through the condition \...
- 26.8k
1
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Estimation of the entropy of the universe
I heard the following way to estimate the entropy of the universe:
using that the entropy is dominated by photons, in particular the cosmic microwave background radiation, which has a wavelength ...
- 9,304
-1
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1
answer
420
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Confusion on the concept of Boltzmann brain
I heard that a Boltzmann brain is a brain-like object that materialized from random fluctuations of particle fields, where particles randomly "pop into existence" and just so happened to form a brain.
...
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2
votes
2
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191
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Must the universe recur, be infinite, or be infinitely divisible?
When I was an undergraduate, I had this thought: Suppose that everything is made of atoms (I mean, pieces which cannot be separated further) and the universe has a finite amount of space.
Let $N$ be ...
9
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4
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Is heat death reversible by thermal or quantum fluctuations given an infinite time?
I'm new here, so apologies if the question doesn't sound meaningful considering what physics is supposed to answer. I don't have a physics or mathematics background, but I did learn a few things about ...
- 452
3
votes
1
answer
537
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Collision term in Boltzmann Equation
In Dodelson's Book, chapter 3, we have the collision term in Boltzmann equation is written as
$$\int\frac{d^3p_1}{(2\pi)^32E_1}\int\frac{d^3p_2}{(2\pi)^32E_2}\int\frac{d^3p_3}{(2\pi)^32E_3}\int\frac{...
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7
votes
2
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280
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Why is energy minimized over the string landscape?
As understand it, the 4D string landscape is a function that assigns an energy to every possible compactification of the 6 small spatial dimensions. We expect our universe to lie in a local energy ...
- 48.4k
2
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1
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962
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Two conflicting forms of equation of state of non-relativistic gas
I've run into two conflicting derivations of the equation of state of a non-relativistic gas. However, the derivations of the relativistic equation of state of both sources agree. I think maybe the ...
- 935
0
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1
answer
1k
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Poincare recurrence time of the Universe
I've read around a bit, and it seems to be universal that the notion of a Poincare recurrence time for the universe exists. And it seems to be debated that the universe can be given an entropy, as it ...
- 139
1
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0
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50
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Phase-space average equal to the quantum mechanical average in the early universe
I was reading Mukhanov's book of cosmology http://www.amazon.com/Physical-Foundations-Cosmology-Viatcheslav-Mukhanov/dp/0521563984 , specifically about symmetry restoration in the early universe ...
- 11
3
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1
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The fate of Poincaré recurrence with the Big Rip
Recently, there has been a lot of talk in the media about the "Big Rip". It most certainly resulted from the paper by Marcelo M. Disconzi and Thomas W. Kephart where they have figured out a ...
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