Date: 31 January 2004
Subject: Dark Energy

The prevailing paradigm in astronomy (according to Astronomer-Royal Martin Rees) is that our universe has 5% ordinary matter, 25% dark matter and 70% dark energy. The evidence for this mysterious dark matter in spiral galaxies is from various sources. Spiral galaxies (like our own Milky Way) rotate, and the radial velocities of the various stars about the centre vary with the distance they are away. The observation is that there is a flat rotation curve as far out as we can trace stars, and this indicates that the gravitational mass of a galaxy is some 10x its visible mass.

A similar result obtains from looking at the behaviour of galaxies themselves within galaxy clusters. Gravitational effects of unseen matter have seemed the only way to explain what we observe.

The attempt to definitely identify cold dark matter has been an issue in astronomy for some 70 years. Intensive efforts were made from the 1980’s onwards to detect what were called WIMPs ie massive, but very weakly interacting, particles. At this moment there could be a billion or so WIMPs per second streaming through your body at a million kilometres per hour just as there are numerous neutrinos. Certainly neutrinos, and WIMPs if they exist, pass through matter with little hindrance – and this makes them difficult to detect. We are now pretty sure about neutrinos, but the jury still seems to be out on detection of WIMPs.

Since 1998 cold dark energy has been thought to be an alternative to a great percentage of the supposed cold dark matter. NASAs WMAP (Wilkinson Microwave Anisotropy Probe – launched June 30, 2001) seemed to confirm the existence of this in 2003 giving the current view of some 70% cold dark energy. The WMAP project, amazingly, gave a microwave light picture of the universe some 400,000 years after the Big Bang, some 13.7 billion years ago.

Later last year, however, a team led by Aastronphysicist Alan Blanchard at Toulouse, challenged this idea of dark energy, suggesting that a few adjustments to various estimated constants (eg the Hubble constant which says how fast the universe is expanding), and some alternative assumptions enable cold dark matter to better explain the WMAP results than dark energy (A&A 412, 35-44 (2003)). Their arguments are undogmatic, merelyclaiming that older models should not be so quickly written off.

How will the issues of cold dark energy/matter finally be resolved? Like all major problems in scientific paradigms this is impossible to say with foresight rather than hindsight. There could always be some major, as yet unimagined, shift of paradigm. Such large changes in the past have, however, never meant a total abandoning of everything previously believed. The figure of 13.7 billion is based on various assumptions, and it is conceivable that some future change in theory, as yet unimagined, could reduce significantly the age estimate of the universe. This possibility, however, should not be exaggerated. Presently, large numbers of different aspects in astrophysics come together to indicate that the universe is very old. Very precise physics of stellar evolution are known, and they well fits the types of stars we in fact observe.

Christians should be very wary of imagining that because paradigm change occurs in science, then literally any change is possible. We may, for example, find out some future things we did not previously know about the human body, but no one would imagine that (on the basis eg of Mark 7:21) one day we may discover that in fact thoughts occur in the heart not the brain.

Such a paradigm change would deny vast swathes of existing anatomical knowledge, and to teach it was never the purpose of our Lord. He was not teaching anatomy but theology.

To many of us, Scripture was no more intending to teach the age and structure of the universe than the anatomy of thought. Unfortunately, whilst there is (as far as I know at least) currently no Christian group opposed to heart transplants on the grounds that the heart is the seat of human thought, there are those who argue that science is mistaken because the universe is young. For any such to pin hopes on future paradigm change is to mistakenly pin the truth of Scripture to a forlorn hope. In astrophysics, there could eg be some change away from cold dark energy/matter to some other cosmology, but there are far too may pointers for a very old universe (ie in billions rather than thousands of years) to allow for some future change eg to a few thousand years. 70