# Re: CMB Redshift Question (Visible Wavelengths)

1. May 2, 2012

### JArnold

The earlier thread was closed for some reason.

It prompted this question: Given the formula for CMB temperature Tobs = Tem/(1+z) (analogous to the formula for z) it seems the age of the universe at the emission of the CMB would have been about 12.5 Myr (if 13.75 Gyr presently), not 380,000 years:

1101 = 13750/12.5

If 380,000 is correct, then for z to be 1100 the current age would have to be about 420 Myr:

1100 ~ 420/.38

I understand that calculating for z is complicated for large distances, but the same should hold for CMB. So why the inconsistency?

2. May 2, 2012

3. May 2, 2012

### JArnold

That thread wasn't helpful. I had specific questions, and I believe my calculations were correct. Here's another strange calculation: The spatial expansion between 13,750 Myr and .38 Myr would be 36,184 -- not 1100.

4. May 3, 2012

### Ich

You'll find these numbers also in the other thread, and you'll find what they mean.
Your calculations are not correct, as redshift doesn't scale linearly with age.

5. May 4, 2012

### JArnold

That's fine. But if redshift doesn't scale linearly, neither does CMB "temperature", given by Tobs = Tem/(1+z) in the original thread.

6. May 4, 2012

### Ich

Right. Inconsistency solved.