Under an Iron Sky: On the Entropy at the Start of the Universe
  Curiously, our Universe was born in a low entropy state, with abundant free
energy to power stars and life. The form that this free energy takes is usually
thought to be gravitational: the Universe is almost perfectly smooth, and so
can produce sources of energy as matter collapses under gravity. It has
recently been argued that a more important source of low-entropy energy is
nuclear: the Universe expands too fast to remain in nuclear statistical
equilibrium (NSE), effectively shutting off nucleosynthesis in the first few
minutes, providing leftover hydrogen as fuel for stars. Here, we fill in the
astrophysical details of this scenario, and seek the conditions under which a
Universe will emerge from early nucleosynthesis as almost-purely iron. In so
doing, we identify a hitherto-overlooked character in the story of the origin
of the second law: matter-antimatter asymmetry.
