Gravity and fine-tuning

But something else was needed to establish the actual strength (or weakness) of the force of gravity itself. It was about 70 years after Newton’s death that James Cavendish carried out the first experiment to measure what is now known as the ‘gravitational constant’ – the big G as some would call it (as opposed to little g which is something else).

What is the big G?

It is a unique number which defines the strength of the force of gravity. It is called a constant because it never changes, and it is the same throughout the universe as far as we know.

It is a very small number indeed, because the force of gravity is a very weak force – the weakest of the fundamental forces of the natural world.  Because it is so small it is very difficult to measure accurately; so far from being big, the big G is in fact almost unbelievably small. It takes trillions and trillions of atoms, like a planet for example, to create a significent force.

So where did this number come from?

It is built into the structure of our universe; all we can do is measure it to the best of our ability. If you believe that all space and time and our universe began in a huge explosion known as ‘the Big Bang’, then this number is just an unplanned, accidental product of a massive uncontrolled explosion and it has no special meaning whatever.

But the value of this number is critical to the whole fabric of the universe as we know it. If this gravitational constant was just the slightest bit different, a tiny fraction larger or smaller, the universe would be very different and we would not be here at all. On the face of it, it looks as if this number has been carefully calculated to ensure we are here, living on an earth and in a solar system which is friendly to our existence.

It is not the only important number that gives this impression, this appearance of being ‘tweaked’ or ‘finely tuned’, to make life possible. 

Gravity is just one of the four fundamental forces in our universe. Two of the others operate within the atom: the ‘strong’ nuclear force and the ’weak’ nuclear force. The fourth is the electrical force that drives all chemical and biological actions and reactions.  All these forces are defined by numbers set to specific values (constants) that make all matter and life possible.

There are many others – up to 30 or so ‘constants’ of this sort. This appearance of ‘fine-tuning’ is inescapable and scientists in general have had to accept it, no matter how reluctantly. Sir Fred Hoyle, one time Astronomer Royal in the UK, said:

"A commonsense interpretation of the facts suggest that a super-intellect has monkeyed with physics, as well as with chemistry and biology, and that there are no blind forces worth speaking about in nature. The numbers one calculates from the facts seem to me so overwhelming as to put this conclusion almost beyond question."

Stephen Hawking took over a position which had once been occupied by Newton himself,  Lucasian Professor of Mathematics at Cambridge, England. He makes the same comment: 

"The laws of science, as we know them at present, contain many fundamental numbers, like the size of the electric charge of the electron and the ratio of the masses of the proton and the electron… The remarkable fact is that the values of these numbers seem to have been very finely adjusted to make possible the development of life."