The sounds of the Little and Big Bangs

TL;DR

This paper explores the analogy between the quark-gluon plasma in heavy ion collisions and the early universe's Big Bang, focusing on sound waves generated during phase transitions and their potential detection as gravity waves.

Contribution

It introduces the concept of sound modes in the quark-gluon plasma and hypothesizes their amplification and possible detection as gravity waves from cosmological phase transitions.

Findings

Sound waves in QGP can be described by hydrodynamics.

Inverse acoustic cascade may amplify sound wave amplitudes.

Collision of sound waves could produce detectable gravity waves.

Abstract

Studies of heavy ion collisions have discovered that tiny fireballs of new phase of matter -- quark gluon plasma (QGP) -- undergoes explosion, called the Little Bang. In spite of its small size, it is not only well described by hydrodynamics, but even small perturbations on top of the explosion turned to be well described by hydrodynamical sound modes. The cosmological Big Bang also went through phase transitions, the QCD and electroweak ones, which are expected to produce sounds as well. We discuss their subsequent evolution and hypothetical inverse acoustic cascade, amplifying the amplitude. Ultimately, collision of two sound waves leads to formation of gravity waves, with the smallest wavelength. We briefly discuss how those can be detected.