Recipe for the Universe
Our whole Universe is governed by just six numbers, set at the time of the Big Bang. Alter
any one of them at your peril, for stars, planets and humans would then not exist.
by Sir Martin Rees, Astronomer Royal
Mathematical laws underpin the fabric of our Universe - not just atoms, but
galaxies, stars and people. The properties of atoms - their sizes and masses, how many different kinds there are, and the forces linking them together -
determine the chemistry of our everyday world. The very existence of atoms depends on forces and particles deep inside them. The objects that astronomers study - planets, stars and galaxies - are controlled by the force of gravity. And everything takes place in the arena of an expanding Universe, whose properties were imprinted into it at the time of the initial Big Bang.
Science advances by discerning patterns and regularities in nature, so that more and more phenomena can be subsumed into general categories and laws. Theorists aim to encapsulate the essence of the physical laws in a unified set of equations and a few numbers. There is still some way to go, but progress is remarkable.
Six numbers
As the start of the twenty-first century, we have identified six numbers that seem especially significant. Two of them relate to the basic forces; two fix the size and overall 'texture' of our Universe and determine whether it will continue for ever; and two more fix the properties of space itself:
The cosmic number omega measures the amount of material in our Universe - galaxies, diffuse gas, and 'dark matter'. Omega tells us the relative importance of gravity and expansion energy in the Universe. A universe within which omega was too high would have collapsed long ago; had omega been too low, no galaxies would have formed. The inflationary theory of the Big Bang says omega should be one; astronomers have yet to measure its exact value.
These six numbers constitute a 'recipe' for a universe. Moreover, the outcome is sensitive to their values: if any one of them were to be 'untuned', there would be no stars and no life. Is this tuning just a brute fact, a coincidence? Or is it the providence of a benign Creator? I take the view that it is neither. An infinity of other universes may well exist where the numbers are different. Most would be stillborn or sterile. We could only have emerged (and therefore we naturally now find ourselves) in a universe with the 'right' combination. This realisation offers a radically new perspective on our Universe, on our place in it, and on the nature of physical laws.
It is astonishing that an expanding universe, whose starting point is so 'simple' that it can be specified by just a few numbers, can evolve (if these numbers are suitable tuned) into our intricately structured cosmos.
Another number, epsilon, defines how firmly atomic nuclei bind together and how all the atoms on Earth were made. The value of epsilon controls the power from the Sun and, more sensitively, how stars transmute hydrogen into all the atoms of the periodic table. Carbon and oxygen are common, and gold and uranium are rare, because of what happens in the stars. If epsilon were 0.006 or 0.008, we could not exist.
Perhaps there are some connections between these numbers. At the moment, however, we cannot predict any one of them from the values of the others. Nor do we know whether some 'theory of everything' will eventually yield a formula that interrelates them, or that specifies them uniquely. I have highlighted these six because each plays a crucial and dis-tinctive role in our Universe, and together they determine how the Universe evolves and what its internal potentialities are; moreover, three of them (those that pertain to the large-scale Universe) are only now being measured with any precision.
What distinguishes our Universe from all those others may be just six numbers.