Cosmic Explorer

Cosmic Explorer is a proposed third-generation ground-based gravitational wave observatory in the United States, designed to be approximately ten times more sensitive than current facilities like LIGO and Virgo. Unlike the incremental upgrades planned for LIGO (A+ and Voyager), Cosmic Explorer represents a clean-sheet design: a single L-shaped interferometer with 40-kilometer arms, roughly ten times the length of LIGO's 4-kilometer arms, situated in a seismically quiet location to minimize low-frequency noise.

The sensitivity improvement is not merely linear in arm length. Longer arms reduce the strain noise because the same gravitational wave signal produces a larger differential displacement over a longer baseline. But the gain also comes from the ability to use more powerful lasers and heavier test masses without encountering the same radiation pressure and thermal noise limits that constrain shorter instruments. The result is a detector that could observe the entire observable universe for compact binary mergers, detecting events at redshifts where the universe was a fraction of its current age.

Cosmic Explorer is designed to operate as part of a global network alongside the Einstein Telescope in Europe and space-based detectors like LISA. The network would be capable of resolving the stochastic gravitational wave background from unresolved sources, detecting core-collapse supernovae throughout the Milky Way, and observing the continuous gravitational wave emission from rapidly rotating neutron stars. These sources are beyond the reach of current detectors not because they are fundamentally different but because they are farther away or weaker.

The proposal raises a question about the sociology of big science. Cosmic Explorer would cost billions of dollars and require decades of development. The gravitational wave community must justify this investment not merely by the number of detections but by the kinds of physics that only a third-generation detector can access: tests of general relativity in the strong-field regime, constraints on the neutron star equation of state, and the search for physics beyond the standard model through precision gravitational wave measurements. The argument is that gravitational wave astronomy has already proven its value, and the next step is to scale the infrastructure to match the ambition of the science.