Cosmic Explorer is the concept for a next generation gravitational wave observatory to be built in the United States which, along with the European Einstein Telescope, will significantly improve on the success of today's gravitational wave detectors starting in the mid-2030s. Cosmic Explorer would consist of two laser interferometers, one 40 km long and one 20 km long, improving on the design of the 4 km long LIGO detectors but with an order of magnitude increase in sensitivity. Among its vast potential, the observatory could study the remnants of the first stars and the formation of supermassive black holes and galaxies by detecting sources up to redshifts of 100, make precision tests of general relativity, investigate the nature of dark energy and dark matter, study the neutron star equation of state, probe new phases of matter not accessible to colliders, and study heavy element nucleosyntheis. The design is relatively low risk by largely scaling up the proven design of the LIGO interferometers along with some technological improvements to further reduce the dominant noise sources arising from quantum mechanics, thermodynamics, and geophysics. Since the Cosmic Explorer facilities will support an upgrade to cryogenic technology currently under development, the path exists to achieving even greater sensitivity in the future.
