The Hubble Space Telescope observed the universe in visible light; but as the universe expands, the light of the most distant objects shifts into the infrared and escapes visible telescopes. To overcome this, NASA, ESA, and CSA built, over thirty years of effort, a vast telescope working entirely in the infrared: a 6.5-metre gold-coated mirror of eighteen hexagonal segments. Launched in December 2021, the James Webb Space Telescope settled at the L2 point 1.5 million kilometres from Earth, unfolding a tennis-court-sized sunshield to keep the extreme cold that infrared observation requires.

The first scientific image, released in July 2022 — "Webb's First Deep Field" — showed the telescope's power. In a patch of sky as small as a grain of sand held at arm's length, thousands of galaxies appeared. The mass of a foreground galaxy cluster had bent and magnified, like a lens, the light of far more distant galaxies behind it (gravitational lensing). The light from some objects in this image had set out just a few hundred million years after the Big Bang — that is, we were seeing the infancy of the universe.

In its first months Webb exceeded expectations: it found more mature, larger galaxies than expected in the very early universe; it distinguished molecules such as water vapour and carbon dioxide in the atmospheres of exoplanets; it showed clearly, for the first time, inside the dust clouds where stars are born.

Every telescope is a time machine: to look far is to look into the past. About a century after Hubble showed that the universe is expanding, Webb looks toward the earliest moments of that expansion — drawing a little closer to the moment where this timeline begins.