“We… are what happens when a primordial mixture of hydrogen and helium evolves for so long that it begins to ask where it came from.” –Jill Tarter
But that doesn’t mean we can’t also look to the hydrogen itself, and use its information to learn about where other things may have come from!
An extraordinary example of this — including what’s possible, if not yet practical — comes from looking at the 21-cm emission line of hydrogen, a forbidden transition with the smallest inherent line width of all!
In principle, what could we learn? Come find out!