# What is the rate at which the CMBR is cooling?

1. Nov 28, 2011

### PhoenixKnight

Hello everyone,

I have a question regarding the rate of cooling for the CMBR.

I understand that the rate of cooling is directly related to the rate of expansion of the universe, but I lack the mathematical prowess necessary to make any use of this.

I am specifically trying to determine an estimate of what the temperature of the CMBR would have been around 800 million years ago.

~PhoenixKnight

2. Nov 28, 2011

### Chronos

3. Nov 28, 2011

### PhoenixKnight

Can we assume that it has been cooling at a constant rate throughout those 11 billion years?

4. Nov 28, 2011

### marcus

No, but that paper Cronos cited is interesting and contains an elegant way of measuring temp.

5. Nov 28, 2011

### DrStupid

The current cooling rate is

$\dot T = H_0 \cdot T = 6.27 \cdot 10^{ - 18} {\textstyle{K \over s}}$

6. Nov 28, 2011

### marcus

Had a hard time waking up this morning. I originally wrote some nonsense, then deleted. Let's see if this is better.

You need to know the redshift corresponding to .8 billion years ago. That is a light travel time of .8 billion y.

So you google "ned light travel time"
and get the Ned Wright light travel time converter.
type in .8 in the box for LTT and press calculate
and you get z = 0.061

That means the CMB temp back then was 1.061 times what it is today.

Last edited: Nov 28, 2011
7. Dec 4, 2011

### boson18

is there known to be plasma excited and emitting in the gigahertz range in the near local system? this could explain the isotropic nature of the cmbr quite nicely outside the standard model.