![]() ![]() The test masses are configured such that each is in near-perfect free fall (and, as such, approximate a local inertial frame) and are separated over very long baselines. GW detectors rely on a measurement of the variations in the light travel time between separated reference points - or ‘test masses’ - caused by a passing GW. GR predicts that the induced strain is perpendicular to the axis of GW propagation and is quadrupolar, that is, a wave travelling along the z-axis stretches (then compresses) the path along the x-axis while shrinking (then stretching) the y-axis (for one polarization in the orthogonal polarization, the elongation/compression occurs along axes rotated 45° relative to the x-axis and y-axis). GWs physically manifest themselves as time-dependent strains, h, in spacetime, or, more precisely, h = δ L/ L, where L is the distance between two reference points in space and δ L is the induced displacement over the baseline L. As predicted by general relativity (GR), GWs are transverse (oscillating perpendicular to the direction of propagation), travel at the speed of light and possess two polarizations. Finally, we highlight some of the technological challenges to be overcome to build future GW detectors before concluding.įundamentally different from and complementary to other astrophysical ‘messengers’ such as photons, neutrinos or cosmic rays, GWs provide unique information about the most energetic astrophysical processes in the Universe by carrying information about the dynamics of massive objects such as black holes and neutron stars moving at relativistic speeds. ![]() We then discuss the future prospects for synergistic observations using GW and EM observatories. Next, we provide a detailed survey of some of the outstanding scientific questions that can be answered with planned or envisioned future GW detectors. We first present an overview of GWs, the methods used to detect them and some scientific highlights from the past five years. The recent remarkable discoveries in GW astronomy have spurred the GWIC to re-examine and update the GWIC roadmap originally published a decade ago 7. Our intention in this Roadmap is to present a survey of the science opportunities and to highlight the future detectors that will be needed to realize those opportunities. Its primary goals are: to promote international cooperation in all phases of construction and scientific exploitation of GW detectors, to coordinate and support long-range planning for new instruments or existing instrument upgrades, and to promote the development of GW detection as an astronomical tool, exploiting especially the potential for multi-messenger astrophysics. The GWIC was formed in 1997 to facilitate international collaboration and cooperation in the construction, operation and use of the major GW detection facilities worldwide. ![]() In this Roadmap, we present the perspectives of the Gravitational Wave International Committee (GWIC, ) on the emerging field of GW astronomy and physics in the coming decades. 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.Įinstein 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. 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 gravitational-wave spectrum, extending from attohertz to kilohertz frequencies, provides a fertile ground for exploring many fundamental questions in physics and astronomy. 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. Nature Reviews Physics volume 3, pages 344–366 ( 2021) Cite this article Gravitational-wave physics and astronomy in the 2020s and 2030s
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