The Dark Energy Spectroscopic Instrument (DESI) has capped off the first seven months of its survey run by smashing through all previous records for three-dimensional galaxy surveys, creating the most extensive and most detailed map of the universe ever.
Yet the Dark Energy Spectroscopic Instrument is only about 10% of the way through its five-year mission. Once completed, that phenomenally detailed 3D map will yield a better understanding of dark energy, thereby giving physicists and astronomers a better understanding of the universe’s past and future. Understanding the expansion history is crucial, with nothing less than the entire universe’s fate at stake. Today, about 70% of the universe’s content is dark energy, a mysterious form of energy driving the expansion of the universe ever faster. As the universe expands, more dark energy pops into existence, which speeds up the expansion more, in a cycle that is driving the fraction of dark energy in the universe ever upwards.
Dark energy will ultimately determine the universe’s destiny: Will it expand forever? Will it collapse onto itself again, in a Big Bang in reverse? Or will it rip itself apart? Answering these questions means learning more about how dark energy has behaved in the past – and that’s precisely what Dark Energy Spectroscopic Instrument design aims to do. And by comparing the expansion history with the growth history, cosmologists can check whether Einstein’s theory of general relativity holds over these immense spans of space and time.