Natalie Wolchover in Quanta:
To look back in time at the cosmos’s infancy and witness the first stars flicker on, you must first grind a mirror as big as a house. Its surface must be so smooth that, if the mirror were the scale of a continent, it would feature no hill or valley greater than ankle height. Only a mirror so huge and smooth can collect and focus the faint light coming from the farthest galaxies in the sky — light that left its source long ago and therefore shows the galaxies as they appeared in the ancient past, when the universe was young. The very faintest, farthest galaxies we would see still in the process of being born, when mysterious forces conspired in the dark and the first crops of stars started to shine.
But to read that early chapter in the universe’s history — to learn the nature of those first, probably gargantuan stars, to learn about the invisible matter whose gravity coaxed them into being, and about the roles of magnetism and turbulence, and how enormous black holes grew and worked their way into galaxies’ centers — an exceptional mirror is not nearly enough.