Why is the Universe expanding more and more rapidly? The Dark Energy
Spectroscopic Instrument (DESI) is being designed to try to find out.
Is the acceleration due to a cosmological constant? a dynamical
dark energy field? a failure of General Relativity? New
instrumentation of the 4-meter telescope Mayall telescope will enable
us to measure more than 20 million galaxy redshifts and find the
imprint of waves that propagated in the cosmic plasma for the first
380,000 years. That imprint will map the expansion history of the
Universe with unprecedented accuracy and may answer the biggest
question in physical science.