Probing Cosmic Expansion and Early Universe with Einstein Telescope
Abstract
Over the next two decades, gravitational-wave (GW) observations are expected to evolve from a discovery-driven endeavour into a precision tool for astrophysics, cosmology, and fundamental physics. Current second-generation ground-based detectors have established the existence of compact-binary mergers and enabled GW multi-messenger astronomy, but they remain limited in sensitivity, redshift reach, frequency coverage, and duty cycle. These limitations prevent them from addressing many fundamental open questions in cosmology. By the 2040s, wide-field electromagnetic surveys will have mapped the luminous Universe with unprecedented depth and accuracy. Nevertheless, key problems including the nature of dark matter, the physical origin of cosmic acceleration, the properties of gravity on cosmological scales, and the physical conditions of the earliest moments after the Big Bang will remain only partially constrained by electromagnetic observations alone. Progress on these fronts requires access to physical processes and epochs that do not emit light. Gravitational waves provide a unique and complementary observational channel: they propagate over cosmological distances largely unaffected by intervening matter, probe extreme astrophysical environments, and respond directly to the geometry of spacetime. In this context, next-generation GW observatories such as the Einstein Telescope (ET) will be transformative for European astronomy. Operating at sensitivities and frequencies beyond existing detectors, ET will observe binary black holes and neutron stars out to previously inaccessible redshifts, enable continuous high signal-to-noise monitoring of compact sources, and detect gravitational-wave backgrounds of astrophysical and cosmological origin. Together with space-based detectors, ET will play a central role in advancing our understanding of cosmic evolution and fundamental physics.
Keywords
Cite
@article{arxiv.2601.06017,
title = {Probing Cosmic Expansion and Early Universe with Einstein Telescope},
author = {Angelo Ricciardone and Mairi Sakellariadou and Archisman Ghosh and Alessandro Agapito and M. Celeste Artale and Michael Bacchi and Tessa Baker and Marco Baldi and Nicola Bartolo and Andrea Begnoni and Enis Belgacem and Marek Biesiada and Jose J. Blanco-Pillado and Tomasz Bulik and Marica Branchesi and Gianluca Calcagni and Giulia Capurri and Carmelita Carbone and Roberto Casadio and J. A. R. Cembranos and Andrea Cozzumbo and Ivan De Martino and Jose M. Diego and Emanuela Dimastrogiovanni and Guillem Domènech and Ulyana Dupletsa and Hannah Duval and Gabriele Franciolini and Andrea Giusti and Giuseppe Greco and Lavinia Heisenberg and Alexander C. Jenkins and Sumit Kumar and Gaetano Lambiase and Michele Maggiore and Michele Mancarella and Federico Marulli and Sabino Matarrese and Isabela Santiago de Matos and Michele Moresco and Riccardo Murgia and Ilia Musco and Gabriele Perna and Michele Punturo and Diego Rubiera-Garcia and Javier Rubio and Alexander Sevrin and Riccardo Sturani and Matteo Tagliazucchi and Nicola Tamanini and Alessandro Tronconi and Ville Vaskonen and Daniele Vernieri and Stoytcho Yazadjiev and Ivonne Zavala},
journal= {arXiv preprint arXiv:2601.06017},
year = {2026}
}
Comments
4 pages. White paper submitted to the ESO Expanding Horizons Call on behalf of ET OSB Div2 - Cosmology