Welcome to Cosmology and Thermodynamics

Experimental evidence that a freely expanding gas does not cool down.

I invite readers to think about this practical example of an expanding gas. 

A scuba diver has on his back a cylinder of high pressure air for breathing.  The air expands from 150 atmospheres to one atmosphere.  What is the temperature of the expanded air which the scuba diver breaths?

Cosmologists such as P.C.W. Davies and Sciama give the following equation for the cooling of such a gas,

TV ϒ - 1 = constant , , , which is equivalent to (T1/T2) = (P1/P2)1 - 1/ϒ

And for air  ϒ = 1.40 .

If we substitute into that equation 

 P1 = 150 atmospheres, P2 = 1 atm. ,  T1 = 293 K,  then T2  is the temperature of the expanded air and  we find that T2 = 70 K ,  i.e. an extremely low temperature.

Does a scuba diver get frost bite round his mouth and nose ?

Not in the slightest !  

In fact the expanded air is at ambient temperature and this proves that expanding a gas like air does not cool down and cosmologists are wrong to apply such an equation to the cooling of the Universe.

To ram home the point even further, consider letting down hydrogen from a high pressure of 150 atmosphere and room temperature to one atmosphere. The hydrogen actually warms up by 50C because of Joule-Thomson Effect; this is quite contrary to the theories of cosmologists!

An essential point in this discussion is that matter has properties;  these include pressure, temperature, density, specific capacity, enthalpy, internal energy, entropy, ionization energy and many more.  These properties must be taken into account in Cosmology and Astrophysics. The Hot Big Bang Theory which ignores these properties is fallacious.

References, , Davies, P.C.W. (1974) "The Physics of Time Asymmetry", p. 89.

Sciama, D.W. "Modern Cosmology".