`Thus when the universe was 1 second old, 1 year old, and 1 million years
old, its temperature were 15 billion, 3 million, and 3 thousand degrees
absolute, respectively. Inserting the present age of the universe (t=10^17
sec) [...] we find
T present = 50 degrees absolute'
but perhaps should have noted that the calculation using this elided formula
1.5 by 10^10
temperature = -------------------------
[time]^1/2
used an age since BB of only 3.2 billion years (if I'm adding on my fingers
correctly), which gives 21 degrees K (ditto) for what is currently regarded
as a more plausible 16 billion years.
Damien Broderick