The implications for hadron physics of astrophysical observations relating to primordial black holes are discussed. If one assumes that fluctuations in the space-time metric at very early times were scale invariant then the speed of sound in the primordial fireball must exceed $0.01c$ at times earlier than ${10}^{-12\mathrm{}}$ sec, as a consequence of observational limits on primordial black holes. This suggests that superbaryons probably do not exist. It is further shown that black holes with masses < ${10}^{25}$ g are unlikely to exist in nature unless either the spectrum of density fluctuations or the equation of state of dense hadronic matter behave in a rather special way.

• Received 19 May 1975

DOI:https://doi.org/10.1103/PhysRevD.12.2949