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# Astrophysics/Temperature of the cosmic radiation

Question
Hello,
the temperature of the cosmic radiation to date, is about 2.7 degrees Kelvin.
I was wondering:
1) E 'possible to calculate how much time will it take to come down from 2.7 to 1.7?
2) I do not think will ever go down to zero, but what do you think the minimum limit at which this temperature will go down?

Andrea

Well, perhaps you can get some guidance from http://www.cv.nrao.edu/course/astr534/CMB.html for starters to help understand the thermodynamics behind the derivation.  Basically, I'm going to estimate, since decoupling happened only a few hundred thousand years after the Big Bang (to the best knowledge of current models) and you're asking about something billions of years in the future.  With the CMB currently at 2.725 K and the best known age of the universe at 13.8*10^9 years, if the universe closely fits Hubble's law for the next few billion years then the temperature of the universe will be inversely proportional to its size scale...and hence roughly behave in such a manner to its age.  That means that the universe has to expand until it is 21.9 billion years old to reach 1.7 K.  Roughly.  Models of the universe that contain dark energy, which seems to be causing the universe to accelerate as it expands, could shorten this time.  That's an advanced topic, and no one is perfectly sure exactly what dark energy is, so it's a little beyond the scope of this forum.

Astrophysics

Volunteer

#### Dr. Stephen O. Nelson

##### Expertise

Fusion, solar flares, cosmic rays, radiation in space, and stellar physics questions. Generally, nuclear-related astrophysics, but I can usually point you in the right direction if it's not nuclear-related or if it's nuclear but not astrophysics.

##### Experience

Just moved from being a physics professor at the University of Texas of the Permian Basin into government work. Doctoral dissertation was on a reaction in CNO-cycle fusion, worked in gamma-ray astronomy in the space science division of the naval research laboratory in the high-energy space environment branch.

Organizations
Government work as a physical scientist with a nuclear focus.

Education/Credentials
Ph.D. in physics, research was on nuclear fusion reactions important in stellar fusion, further work on space telescope technology.