Astrophysical Factors

Abstract

We must review some aspects of the current understanding of the history of the universe. Evidence arising from observations of the rate at which stars and galaxies are receding from the earth indicates that, approximately 14 billion years ago (the exact time remains in some dispute) the universe as we observe it was confined to a very small region of space and has been expanding from that confined space ever since (the ‘Big Bang’) (More precisely, the space itself has been expanding, but this distinction need not concern us.) Some details of the very early history of that expansion remain in some dispute. However, there is strong evidence that, roughly one second after the expansion began, the initial material cooled sufficiently to leave mainly electromagnetic radiation, two kinds helium nuclear isotopes, two kinds of hydrogen nuclei (protons and deuterons) and electrons.