  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.
