The Early Universe Odyssey With Gravitational Waves

TL;DR

This paper reviews recent advances in gravitational-wave astronomy, focusing on relic gravitational waves' quantum origin, detection prospects, and their cosmological significance, including their relation to density perturbations and CMBR observations.

Contribution

It provides a comprehensive overview of relic gravitational waves, emphasizing their quantum-mechanical origin, detection strategies, and their role in cosmology, contrasting with standard inflationary predictions.

Findings

Relic gravitational waves have a quantum-mechanical origin.

Detection of relic gravitational waves is feasible with upcoming interferometers.

Quantum squeezing manifests in metric spectra and CMBR multipoles.

Abstract

This contribution summarizes some recent work on gravitational-wave astronomy and, especially, on the generation and detection of relic gravitational waves. We begin with a brief discussion of astrophysical sources of gravitational waves that are likely to be detected first by the coming in operation laser interferometers, such as GEO, LIGO, VIRGO. Then, we proceed to relic gravitational waves emphasizing their quantum-mechanical origin and the inevitability of their existence. Combining the theory with available observations, we discuss the prospects of direct detection of relic gravitational waves. A considerable part of the paper is devoted to comparison of relic gravitational waves with the density perturbations of quantum-mechanical origin. It is shown how the phenomenon of squeezing of quantum-mechanically generated cosmological perturbations manifests itself in the periodic structures of the metric power spectra and in the oscillatory behaviour of the CMBR multipoles $C_l$ as a function of $l$. The cosmological importance of the theoretically calculated (statistical) dipole moment $C_1$ is stressed. The paper contains also some comments on the damage to gravitational-wave research inflicted by the "standard inflationary result". We conclude with the (now common) remarks on the great scientific importance of the continuing effort to observe relic gravitational waves, directly or indirectly.