Could we expect that temperature of CMB decreases or increases?

[Ignition]

Could we expect that temperature of CMB decreases or increases?
Could we suppose that we are in a contracting universe?

 

[marcus]

Could we expect that temperature of CMB decreases or increases?
Could we suppose that we are in a contracting universe?

It is pretty clear we are in an expanding universe. The expansion of space (shorthand for a regular pattern of increasing distances between stationary observers) causes the CMB temperature to decrease.

For the sake of discussion we can make the unrealistic assumption that we are in a contracting universe----space is contracting (meaning a regular pattern of decreasing distances between stationary observers.) OK, that would cause a BLUESHIFT of all light, including the CMB. this would cause an INCREASE in temperature, by the same factor as the wavelengths are decreased.

The CMB light was emitted when the universe expansion was about 400,000 years old and the temperature of the light at that time was about 3000 kelvin.
Since that time, distances have increased by a factor of about 1100, and the temperature of the CMB light has decreased by the same factor----from about 3000 kelvin down to about 3000/1100 kelvin.

We can expect the CMB temp to gradually decrease in the future at exactly the same percentage rate that distances are increasing-----currently about 1/140 of a percent every million years.

to me this seems like a very slow rate of decrease of temperature, almost too slow to pay any attention to it, but you asked about---so that's what it is!

 

[Chronos]

The universe was hotter in the past, which is consistent with the expansion model. See http://www.spaceflightnow.com/news/n0012/24vlthot/