  We study the entanglement generated between Dirac modes in a 2-dimensional
conformally flat Robertson-Walker universe. We find radical qualitative
differences between the bosonic and fermionic entanglement generated by the
expansion. The particular way in which fermionic fields get entangled encodes
more information about the underlying space-time than the bosonic case, thereby
allowing us to reconstruct the parameters of the history of the expansion. This
highlights the importance of bosonic/fermionic statistics to account for
relativistic effects on the entanglement of quantum fields.
