If the universe was hot, what should be left over?

That time, that place

By 1948 Hubble's observations had established that the universe expands. Run it backwards and everything converges.

Many disliked the conclusion — a beginning sounded religious — and the steady-state model was a strong alternative.

Why this question

Gamow's approach was different. He asked what would have been made if the early universe was very hot.

In the first hot minutes, fusion turns hydrogen into helium. The calculation said about a quarter of the matter in the universe should be helium — which matched observation.

And it made one more prediction. Where did that heat go? Expansion cooled it, so it should still be there as very cold radio waves filling the whole sky.

What was found

The prediction was largely forgotten. When Penzias and Wilson found it in 1965 while trying to eliminate noise from an antenna, they did not know what they had.

Only after asking theorists at a nearby university did they learn: the afterglow of a hot early universe.

Steady-state ends here. Gamow also wrote popular books — the Mr Tompkins series, turning relativity and quantum mechanics into stories. He thought making hard things enjoyable mattered.