In the scientific cosmology that emerged during the twentieth century, ancient ideas of the emergence of cosmos from chaos were replaced by the idea of a universe that has expanded and evolved over the course of twelve billion to fifteen billion years from a tiny, dense, and hot state. The Big Bang theory of cosmology had its origins in models of the universe based on Albert Einstein’s theory of General Relativity. According to these theories, space-time itself emerges and stretches in the process of cosmic expansion. Over the last century a number of lines of evidence have supported Big Bang cosmology, particularly the discoveries of the red shifting of galaxies, the abundance of helium and deuterium in the universe, and background microwave radiation. According to standard Big Bang cosmology the universe is expanding and also decreasing in temperature and density, and this points back to a beginning of the universe of unthinkable smallness, density, and heat—to an original singularity. A singularity is a point at which the density and the curvature of space-time are infinite, a point at which the laws of physics no longer hold.
In 1948, physicists Fred Hoyle, Thomas Gold, and Hermann Bondi put forward an alternative to Big Bang cosmology with their steady-state idea of the universe. In this theory new matter and new galaxies are continuously brought into being, in a stable universe that has an infinite past. Although the steady-state theory was undermined by the discovery of background microwave radiation, some of its philosophical aims were incorporated into a Big Bang framework in what physicist Charles Misner called chaotic cosmology. Chaotic cosmology seeks to avoid attributing the order of the universe to initial conditions. It is committed to explaining the present nature of the universe without requiring knowledge of its initial state. It seeks to show that no matter how chaotic the state of the universe at the beginning of its expansion, there are processes that can smooth out irregularities and produce the isotropic and uniform universe that people can observe. But no known process could account for this smoothing out process until the rise of inflationary theories in the 1980s.
In the meantime cosmologists had begun to speculate about the beginning of the universe in terms of quantum theory. Quantum field theories differ from their classical predecessors in the way they understand a vacuum. Within quantum theory, a vacuum is not understood simply as nothing at all, but as a sea of continuously appearing and disappearing pairs of oppositely charged particles.
These processes are unobservable at the individual level and are called virtual, but are measurable at the collective level. The quantum vacuum is an infinite sea of virtual processes. Quantum theory allows for the spontaneous appearance of energy in the quantum vacuum for a very short time, as long as it is unobservable. Quantum cosmology involves a theory of the emergence of the universe from a fluctuation of the quantum vacuum. It thus, once again, suggests that an ordered universe appears from a chaotic initial state.
Chaos was to reenter the language of cosmology in the form of the theory of chaotic inflation. In order to solve some of the problems associated with the Big Bang, physicist Alan Guth in 1980 proposed that within a fraction of the first second the universe went through a period of extremely rapid expansion or inflation. Soon after, in 1983, physicist Andrei Linde put forward his theory of chaotic inflation, which dispenses with the idea of most initial conditions including the initial heat. The universe begins from chaos in the form of the seething ocean of different forms of scalar fields. The observable universe began from one such field, as one part of a process that may involve an unlimited ensemble of universes. In many recent models of the expanding universe, particularly those based on a period of rapid inflation, the observable universe would be a small domain within a much bigger universe, perhaps an infinite and eternal one.
In all of these theories, inflation provides the ordering principle, and chaos reappears in the initial conditions of the universe. As astronomer John Barrow has said: “Inflation does not explain the uniformity of the Visible Universe by eradicating primordial chaos, but by sweeping its effects out of sight beyond the boundary of the visible part of the Universe” (p. 239). It is worth keeping in mind that at this stage there is much more evidence for Big Bang cosmology in general than there is for the various forms of chaotic cosmology. In a recent evaluation of the major theories of cosmology, physicist P. James E. Peebles concludes that while there is compelling evidence that the universe has evolved from a hotter and denser state, the theory of inflation is “elegant, but lacks direct evidence and requires huge extrapolation of the laws of physics” (p. 45).