Religion in an Age of Science by Ian Barbour
Chapter 5: Astronomy and Creation
I. The Big Bang
1. Theories in Astrophysics
Physical cosmology is the study of the physical structure of the cosmos as a whole.1 In 1917, Willem de Sitter, working with Einstein’s general relativity equations, found a solution that predicted an expanding
universe, In 1929, Edwin Hubble, examining the "red shift" of light from distant nebulae, formulated Hubble’s Law: the velocity of
recession of a nebula is proportional to its distance from us. Space itself, not just objects in space, is everywhere expanding. Extrapolating
backward in time, the universe seems to be expanding from a common origin about fifteen billion years ago. In 1965, Arno Penzias and Robert Wilson discovered a faint background of microwaves coming from all directions in space. The spectrum of those waves corresponded very closely to the 3 K residual radiation, which had been predicted from relativity theory. The radiation is the cosmic fireball’s afterglow, cooled by its subsequent expansion.
Indirect evidence concerning the very early moments of the Big Bang have come from both theoretical and experimental work in high-energy physics. Einstein himself spent his later years in an unsuccessful search for a unified theory that would integrate gravity with other physical forces. More recent research has moved closer to this goal. There are four basic physical forces: (1) the electromagnetic force responsible for light and the behavior of charged particles; (2) the weak nuclear force responsible for radioactive decay; (3) the strong nuclear force that binds protons and neutrons into nuclei; and (4) the gravitational force evident in the long-distance attraction between masses. Recent attempts to develop a theory that would integrate these forces have moved through several stages.
In 1967, Steven Weinberg and Abdus Salam showed that the electromagnetic and weak forces could be unified within an
Electroweak Theory. The theory predicted the existence of two massive particles, the W and Z bosons, which mediate between the two kinds of force. In 1983, Carlo Rubbia and coworkers found particles with the predicted properties of W bosons among the products of high-energy
collisions in the CERN accelerator in Geneva.
There has been some progress in attempts to unite the electro-weak and strong forces in a Grand Unified Theory (GUT). The unification would be mediated by very massive X-particles, which could only exist at energies higher than those in any existing accelerator. However, the GUT theory implies that protons decay spontaneously, very slowly, rather than being stable, as previously supposed. Physicists are trying to detect this extremely low level of proton decay with experiments in deep mines, where other stray particles are screened Out. A GUT theory would help us understand the structure of matter today, and it would also contribute to our understanding of the very early moments of the Big Bang.
The unification of gravity with the other three forces within one
Supersymmetry Theory has appeared more difficult because we have no successful quantum theory of gravity. But there has been recent
excitement concerning Superstring Theory, which escapes the anomalies of previous attempts. The basic constituents would be incredibly
massive, tiny, one-dimensional strings which can split or loop. With differing patterns of vibration and rotation, they can represent all known particles from quarks to electrons. The theory requires ten dimensions;
six of these would somehow have to disappear to leave the four
dimensions of spacetime. There is no experimental evidence for strings;
the energy required for their existence would be far beyond those in the laboratory, but it would have been present at the very earliest instants of the Big Bang.2 Physicists have a strong commitment to simplicity, unity, and symmetry, which motivates the search for a unified theory even when direct experimentation is impossible.
Putting together the evidence from astronomy and high-energy physics, a plausible reconstruction of cosmic history can be made. Imagine a trip backward in time. Twelve billion years after the Big Bang, microscopic forms of life were beginning to appear on our planet. Ten billion years after the bang, the planet itself was formed. One billion years from the beginning, the galaxies and stars were coming into being. At t500,000 years, the constituent atoms appeared. A mere 3 minutes from the beginning, the nuclei were starting to form out of protons and neutrons.
Plausible theories concerning these events can account for the relative abundance of hydrogen and helium and for the formation of heavier chemical elements in the interior of stars (see fig. 3).3
TIME TEMP. TRANSITION 15 billion yrs. (today)
12 Microscopic life 10 Planets formed
1 Galaxies formed (heavy elements)
500,000 yrs. 2000_ Atoms formed (light elements) 3 mins. 109 Nuclei formed (hydrogen, helium) 10-4 sec. l012 Quarks to protons and neutrons
10-10 1015 Weak and electromagnetic forces separate 10-35 1028 Strong nuclear force separates
10-43 ‘ 1032 Gravitational force separates (0 Infinite Singularity)
Fig 3. Major Cosmological Transitions
The farther back we go before 3 minutes, the more tentative are the theories, because they deal with states of matter and energy further from anything we can duplicate in the laboratory. Protons and neutrons were probably forming from their constituent quarks at 10-4 seconds (a ten- thousandth of a second from the beginning), when the temperature had cooled to 1012 (a thousand billion) degrees. This fantastically dense sea of hot quarks had been formed at about 1010 seconds from an even smaller and hotter fireball -- which had expanded and cooled enough for the electro-weak forces to be distinguishable from the strong and
gravitational forces.4
Before 10-35 seconds, the temperature was so high that all the forces except gravity were of comparable strength. This is the period to which a Grand Unified Theory would apply. We have almost no idea of events before 10-43 seconds, when the temperature was 1032 degrees. The whole universe was the size of an atom today, and the density was an incredible 1096 times that of water. At these very small dimensions, the Heisenberg uncertainties of quantum theory were significant, and all four forces were united. This would have been the era of
Supersymmetry. I will return later to examine some remarkable features of these very early stages.
But what happened before that? At the time t=0, was there a
dimensionless point of pure radiation of infinite density? And how is that point to be accounted for? To the scientist, t=0 is inaccessible. It appears as a singularity, to which the laws of physics do not apply. It
represents a kind of ultimate limit to scientific inquiry, something that can only be treated as a given, though one can speculate about it.