For a long time, people believe that all possible states of matter are
described by Landau symmetry-breaking theory. Recently we find that string-net
condensation provide a mechanism to produce states of matter beyond the
symmetry-breaking description. The collective excitations of the string-net
condensed states turn out to be our old friends, photons and electrons (and
other gauge bosons and fermions). This suggests that our vacuum is a string-net
condensed state. Light and electrons in our vacuum have a unified origin --
string-net condensation.Comment: 14 pages, to appear in YKIS2004 proceedings, homepage
http://dao.mit.edu/~we