The separation distance between droplets of quark-gluon plasma (QGP) in the early Universe and in relativistic heavy-ion collisions is calculated in isothermal fluctuation theory. It is found that experimental information on the size of the QGP from relativistic heavy-ion collisions has the potential possibility of constraining the degrees of the inhomogeneous baryon-number density distribution and the formation of strange-quark matter at the epoch of the cosmic phase transition in quantum chromodynamics.