Under an Iron Sky: On the Entropy at the Start of the Universe

Abstract

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.

22 pages, 6 figures. Published in Publications of the Astronomical Society of Australia

References in corpus (8)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Aspects of the cosmological "coincidence problem"
• SkyNet: A modular nuclear reaction network library
• Databases and tools for nuclear astrophysics applications BRUSsels Nuclear LIBrary (BRUSLIB), Nuclear Astrophysics Compilation of REactions II (NACRE II) and Nuclear NETwork GENerator (NETGEN)
• Asteroseismology and Exoplanets: Proceedings of the IVth Azores International Advanced School in Space Sciences
• Introduction to Big Bang Nucleosynthesis and Modern Cosmology
• Stellar evolution and modelling stars
• Proton-Rich Nuclear Statistical Equilibrium