Large nucleation distances from impurities in the cosmological quark-hadron transition

We calculate the mean nucleation distance, $d_{nuc}$, in a first order cosmological quark-hadron phase transition. For homogeneous nucleation we find that self-consistent inclusion of curvature energy reduces $d_{nuc}$ to $\lesssim 2$cm. However, impurities can lead to heterogeneous nucleation with $d_{nuc}$ of several meters, a value high enough to change the outcome of Big Bang nucleosynthesis.