After ten years of working on the Euclid space telescope Will Percival has gotten used to thinking long term. But when he met with European colleagues to talk about the project earlier this month, things suddenly felt much more immediate.
But unlike Webb, which is busy making the most distant stars and galaxies in the universe visible to us, Euclid is built to explore something that will never be visible to anyone, at least not directly. In 1998 astronomers announced a second startling discovery. By measuring the motion of still more distant galaxies, they found that the expansion of the universe has been speeding up. The term “dark energy” was coined to put a label on the effect, but understanding exactly what dark energy is has proved far more challenging.Theorists have speculated about the nature of dark energy and what it means for the fate of the universe.