All Questions
4
questions
2
votes
2
answers
151
views
Negative Temperature and bounded Energy of the Universe
I have just learned about the pretty cool idea about negative temperature (although it is "hotter" then positive temperature...) of a two level system. The condition for having negative ...
- 2,794
2
votes
1
answer
91
views
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
12
votes
1
answer
10k
views
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
4
votes
3
answers
3k
views
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