Abstract
At a time when the long-awaited images from the James-Webb Space Telescope are being analyzed, I'll summarize some of the discoveries made over the last few decades about the invisible Universe, as observed in the infrared. We'll discuss how this quest for the invisible Universe sheds light on open questions in our theories of galaxy formation : the low fraction of baryons in galaxies in apparent contradiction with the very high concentration of baryons in elliptical galaxies, the enigmatic universality of galaxy lifetimes around 600 million years, the origin of bimodality and downsizing, and the role of optically invisible galaxies.
