An extract from ‘Quarks, Chaos and Christianity’
by John Polkinghorne

Suppose God were to lend you the use of his Universe-Creating Machine. As you approached this no doubt impressive piece of machinery, you would find that there are a large number of knobs for you to adjust. For example, there would be a set of knobs relating to gravity. One would be an on/off switch: do you want gravity in your world at all, and, if you do, what kind? Inverse square law (like Newton discovered in our universe) or some other form? Once you’ve decided this, there’s another knob to adjust to determine how strong you want gravity to be. It may surprise you to learn that, in the way scientists measure these things, gravity is actually a very weak force in our world (it may got seem so if you’ve ever fallen out of an upstairs window, but this is due to the fact that gravity always adds up; nothing cancels it out). Perhaps you would like it stronger in your universe, or even weaker? You decide, and twiddle the knobs accordingly. Then all of the other forces of nature await your attention.There’s electromagnetism, the force that holds matter (and us) together. In our universe it is much stronger than gravity. How would you like it to be in yours? So it would be for the other forces of nature. Finally, there are some knobs to determine size and such like qualities. Do you want a vast universe, like ours with trillions of stars, or something a bit smaller and more domestic?

Right! All the knobs are set, you pull the handle and out comes the universe God has allowed you to create. You wait to see what happens. You’ll have to be patient, it may take billions of years. I suppose my guess would be that, in the end, most universes would do something interesting if you waited long enough. Changing the forces would have effects.For example, if you made gravity stronger, ‘people’ would be shorter because it would be harder to grow tall. Whatever happened, some sort of fruitful outcome would surely result. Not necessarily human beings, of course, but little green men. I would have been completely wrong!

We now understand that unless you had set these knobs very precisely, fine tuned them to specifications extremely close to your own universe, the world you had decided to create would have had a very dull and sterile history. It would not have produced anything like such interesting consequences as you and me. We live in a very special universe — one in a trillion you might say.

This is a very surprising conclusion and I’d like to sketch some of the reasons we have for reaching it. First, you’ve got to be careful to get off to a good start. If your universe expands too quickly from its initial Big Bang, it will rapidly become too dilute for anything interesting to happen in it. On the other hand, if it expands too slowly, it will recollapse before anything interesting happens. Your universe had also be pretty smooth, otherwise large irregularities in its early history will generate catastrophically destructive turbulence. However, it mustn’t be too smooth either as, if there is no graininess at all, then stars and galaxies will be unable to form.

You need stars because they have two indispensable rolled to play in making life possible. One role, of course, is as reliable sources of energy. Life has been able to evolve on Earth because the Sun has been a steadily burning source of energy for the billions of years during which evolution has been happening. We know that stars burn uniformly for very long periods: it is a delicate balance between gravity and electromagnetism. Disturb this balance, and stars either become too cool to act as effective energy sources, or so hot that they burn away in a better of a few million years — far too short a time to bring about life. So, you had better set those gravity and electromagnetic control knobs pretty carefully.

However, this won’t be enough by itself, for stars have a second vital role to play. They are the nuclear furnaces in which are made the elements that are the raw materials of life. For the first three minutes of its history, the whole universe was hot enough to be the arena of nuclear reactions. It was like a cosmic hydrogen bomb. However, the very early universe was also very simple, and so it could only do very simple things. It made only the two simplest elements, hydrogen and helium. They don’t have an interesting enough chemistry to provide the the basis for life. For this you need the richer possibilities provided by the heavier elements. In particular, you need the very fertile chemistry of carbon. Every atom of carbon inside our bodies was once inside a star. We are all made from the ashes of dead stars.

To make carbon in a star, three helium nuclei have to be made to stick together. This is tricky to achieve and only possible because of a special effect (technically, a resonance) is present just in the right place. This delicate positioning depends upon the strong nuclear force  that holds nuclei together.Change this force a little, and you loose the resonant effect. Also, carbon is not enough; for life one needs lots more elements. Oxygen for instance. You make it by sticking another helium nucleus on to a carbon one. This must be possible to do, but not too readily, otherwise all of your hard-won carbon will turn into oxygen and you’ve lost it. This is another constraint on the nuclear forces.This delicately balanced chain of reactions can continue, if the knobs are set just right, up to iron. Inside a star, you can’t get any further that this for iron is the most stable nucleus and it won’t easily change into anything bigger. So, two tasks remain. One is to make elements beyond iron, some of which, like zinc and iodine, are essential for life.The other is to ensure that the other elements you’ve already made are actually available for the coming-into-being of life. There’s no point in being locked up, unless, inside the cooling core of a dying star. So, some stars will have to explode as supernovae, scattering their life-generating elements into space, where they can form the chemical environment second-generation stars and planets as these condense out of the debris of the explosion. If we are made of stardust, there must be some dust from stars around. If you’re very clever, you can adjust the knobs so that the heavier elements (zinc, iodine and so on) are made in the course of these supernovae explosions. Doing this places a constraint on the weak nuclear force, responsible for certain types of radioactive decay.

You may not have followed all of the details of the foregoing discussion, but I’m sure you will see that making the raw materials for life is no trivial matter. It is only possible at all in a very special universe.

Asking and answering the questions, ‘Why can we do science at all?’, and ‘Why is the universe so special?’ have given us a nudge in the direction of religious belief.