After seeing the first few minutes of [Veritasium’s](https://www.youtube.com/watch?v=Kp_kqamkYpw) video on how half of the baryonic matter was yet unobserved until recently, he mentions how the ratio of deuterium and helium and other elements were all formed within the first 20-ish minutes after the big bang but also how with around 10 seconds the universe had cooled significantly.
How is that sort of timescale measured accurately when the big bang happened so long ago, especially when even some modern history events cant be traced down to hapening within an exact year sometimes?
In: Physics
I dont think they really can, they just reconstruct through models. Like if you know all the matter was crammed into an area the size of the sun, it would have to behave like xyz, if it was the size of a basketball, it would be abc, etc.
Remember, what scientists are trying to do is the equivalent of coming on a massive smoking crater and trying to reconstruct what was there before the explosion by looking at the pieces they can find.
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