Astro2020 Science White Paper: Cosmology with a Space-Based Gravitational Wave Observatory

TL;DR

A space-based gravitational wave observatory operating in the mHz range could revolutionize cosmology by probing the universe's expansion history, origins, and exotic phenomena like primordial backgrounds, addressing fundamental questions about the universe's workings and destiny.

Contribution

This white paper advocates for a space-based gravitational wave detector with long interferometer arms to explore cosmological questions and discover new gravitational wave sources.

Findings

Potential to measure the universe's expansion up to redshift z ~ 10

Capability to detect primordial stochastic gravitational wave backgrounds

Ability to observe inspirals and mergers of massive black hole binaries

Abstract

There are two big questions cosmologists would like to answer -- How does the Universe work, and what are its origin and destiny? A long wavelength gravitational wave detector -- with million km interferometer arms, achievable only from space -- gives a unique opportunity to address both of these questions. A sensitive, mHz frequency observatory could use the inspiral and merger of massive black hole binaries as standard sirens, extending our ability to characterize the expansion history of the Universe from the onset of dark energy-domination out to a redshift z ~ 10. A low-frequency detector, furthermore, offers the best chance for discovery of exotic gravitational wave sources, including a primordial stochastic background, that could reveal clues to the origin of our Universe.