Basic assumptions of cosmology:


With Lambda not equal 0

Currently prefered model (from Supernova distances)

So, future is uncertain (implies expansion forever).

What about past, which above shows is the same for many models?


When T was high enough, all H atoms in U were ionized ...

So, earlier U was opaque, later U (including today) is transparent to CBR photons ...



What does opaque mean?

What happens to wavelength hence Planck Curve & temperature?