DARK ENERGY MIGHT BE ABOUT TO THROW A SPANNER IN THE WORKS

The most mysterious phenomenon in the Universe could be about to spring another surprise on us

- DR KATIE MACK

It takes some hubris to name a new project the Dark Energy Spectroscopic Instrument (DESI). After all, dark energy is completely invisible - it gives off no light to be collected and analysed with a spectrograph. In fact, it's never been seen at all it has evaded every attempt we've made to image or capture it with even our most advanced telescopes and detector experiments.

As far as we can tell, dark energy is something that is indiscernible, perfectly uniform throughout space and has no interaction at all with matter or light. Its only function, through some as-yet-undetermined mechanism, is to make space expand ever faster.

So how is it, then, that DESI's just-announced first data release is, as promised, shaking up our understanding of dark energy? There are only a few observational handles we can get on something as frustratingly elusive as dark energy. Since all dark energy does is stretch spacetime, testing different theories of dark energy's nature involves learning how that stretching has occurred across cosmic time. One method is charting the expansion history of the Universe; a related method is to look at how quickly matter built up into galaxies and clusters at different points in our cosmic past.