Under the Microscope Prof William RevilleCosmology is the branch of physics that studies the origin and evolution of the universe, and its discoveries and speculations are fascinating.
Most people are familiar with the theory that the universe was born about 13.7 billion years ago in a gigantic explosion - the Big Bang. But probably only relatively few people know of the now respectable idea that the Big Bang spawned not only the universe in which we live, but an infinite number of parallel universes. This scenario explains several difficult questions, including why our universe happens to be so perfectly suited to life. Expanded details can be consulted in 25 Big Ideas by Robert Matthews (One World, 2005).
It seems that the Big Bang was not the start of everything but was itself the result of events already under way in a newborn universe. Observations made since 1992 indicate that the universe erupted from nowhere 13.7 billion years ago. It was filled with energy, called a scalar field, that has anti-gravitational effects. These caused inflation, the process by which the baby universe suddenly expanded from a billion times smaller than a proton to grapefruit size in 10-32 seconds - one second divided by 10-multiplied-by-itself-32-times! Then the scalar field collapsed releasing energy and matter in the familiar Big Bang.
How could many universes come out of a single origin? Well, there were many kinds of scalar fields, all with different properties.
Andrei Linde, a Russian cosmologist, proposed in the 1980s that our universe may just be one in an infinitely large number of parallel universes in which all the different variations of scalar field are manifest - the "chaotic inflation" model. Most of these universes would not be suitable for life, but many would.
Many scientists have long been fascinated by the observation that the properties of the world are so perfectly suited to life. The nature of the physical laws that govern the world and the values of many physical constants in nature are precisely right to allow life to arise and to flourish. If the values of many of the constants in nature were just the tiniest bit different, life would either never have arisen or if, it arose, would never have evolved.
For example, if the ratio of the force of gravity to the force of electromagnetism were slightly different than it is, stars would either burn out much more quickly and wouldn't support life on orbiting planets long enough to allow complex life forms to develop, or the stars would burn too dimly to support life on orbiting planets.
Science has formalised the observation that the universe seems uniquely fitted to support life into a principle called the anthropic principle. There are two forms of the principle, a weak form accepted by most scientists and a strong form that few scientists support. The weak form simply states that the fact the universe contains observers puts constraints on what the whole universe can be like. For example, it must be at least as old as it is because of the necessity for carbon on which life is based, to be forged in stars, for life to begin on earth and to slowly evolve to its present state.
The strong form of the principle states that the universe must have properties that allow life to emerge at some time during its history. This resembles a religious statement too closely for most scientists to support it as a scientific principle.
Nevertheless, the observations behind the anthropic principle provide a very dilute form of scientific evidence that the world was designed to support life, because of the seeming great improbability that accidental developments would produce the very many conditions necessary for life to emerge and prosper. This is illustrated by the amusing parable of the fly on the wall.
Imagine an enormous wall on which a fly is crawling. A single rifle shot rings out and hits the fly dead centre. What do you conclude? Either the rifle-man aimed the shot very carefully or else he was extremely lucky. Now imagine the fly on the wall again. A prolonged burst of machine gun fire sprays the wall with bullets and one of the bullets hits the fly. This is unsurprising because of the great number of bullets involved.
These two scenarios (single shot or machine gun burst) are analogous to the two possibilities of life arising in a single universe or in one (or several) universe(s) out of an infinite number of universes. In the latter case, since the universes all have different properties, it would not be at all surprising that, by chance, at least one of them would be hospitable for life. However, in the former case it is legitimate to ask the question - is something special going on here?
At the moment the idea of multi-universes is just that - an idea. Indeed I am not even sure that it qualifies as a scientific idea. A scientific hypothesis is legitimate only if it is testable. If universes exist in addition to our own we may never be able to communicate with them or physically detect them.
However, if we can confirm that there is an infinite number of universes out there, this would explain how at least one of them, ours, is uniquely fitted for life. Of course this would not then rule out the possibility of a Designer, it would simply explain the method of design - an infinite number of throws of the dice!
William Reville is associate professor of biochemistry and public awareness of science officer at UCC -