Gravitational-wave physics and astronomy in the 2020s and 2030s

The 100 years since the publication of Albert Einstein’s theory of general relativity saw significant development of the understanding of the theory, the identification of potential astrophysical sources of sufficiently strong gravitational waves and development of key technologies for gravitational-wave detectors. In 2015, the first gravitational-wave signals were detected by the two US Advanced LIGO instruments. In 2017, Advanced LIGO and the European Advanced Virgo detectors pinpointed a binary neutron star coalescence that was also seen across the electromagnetic spectrum. The field of gravitational-wave astronomy is just starting, and this Roadmap of future developments surveys the potential for growth in bandwidth and sensitivity of future gravitational-wave detectors, and discusses the science results anticipated to come from upcoming instruments. In the past few years, gravitational-wave observations provided stunning insights into some of the most cataclysmic events in the Universe, heralding a bright future for gravitational-wave physics and astronomy. This is a Roadmap for the field in the coming two decades. Gravitational-wave observations of binary black hole and neutron star mergers by LIGO and Virgo in the past five years have opened a completely new window on the Universe. The gravitational-wave spectrum, extending from attohertz to kilohertz frequencies, provides a fertile ground for exploring many fundamental questions in physics and astronomy. Pulsar timing arrays currently probe the nanohertz to microhertz frequency band to detect gravitational-wave remnants from past mergers of super-massive black holes. The space-based Laser Interferometer Space Antenna (LISA) will target gravitational-wave sources from microhertz up to hundreds of millihertz and trace the evolution of black holes from the early Universe through the peak of the star formation era. Einstein Telescope and Cosmic Explorer, two future ground-based observatories now under development for the 2030s, are pursuing new technologies to achieve a tenfold increase increase in sensitivity to study compact object evolution to the beginning of the star formation era. Gravitational-wave observations of binary black hole and neutron star mergers by LIGO and Virgo in the past five years have opened a completely new window on the Universe. The gravitational-wave spectrum, extending from attohertz to kilohertz frequencies, provides a fertile ground for exploring many fundamental questions in physics and astronomy. Pulsar timing arrays currently probe the nanohertz to microhertz frequency band to detect gravitational-wave remnants from past mergers of super-massive black holes. The space-based Laser Interferometer Space Antenna (LISA) will target gravitational-wave sources from microhertz up to hundreds of millihertz and trace the evolution of black holes from the early Universe through the peak of the star formation era. Einstein Telescope and Cosmic Explorer, two future ground-based observatories now under development for the 2030s, are pursuing new technologies to achieve a tenfold increase increase in sensitivity to study compact object evolution to the beginning of the star formation era.