The Science of Discworld IV Judgement Da - By Terry Pratchett, Ian Stewart Page 0,128
much smaller.
With more than two constants, this effect becomes more pronounced, not less. Numerous examples are analysed at length in Stenger’s book. You can compensate for a change to several constants by making suitable changes to several others. It’s just like the car example. Changing any one feature of a car, even by a small amount, stops it working – but the mistake is to change just that one feature. There are thousands of makes of car, all different. When the engineers change the size of the nuts, they also change the size of the bolts. When they change the diameter of the wheel, they use a different tyre.
Cars are not finely tuned to a single design, and neither are universes.
Of course, the equations for universes might run contrary to everything that mathematicians have ever seen before. If anyone believes that, we’ve got a lot of money tied up in an offshore bank and we’d be delighted to share it with them if they will just send us their credit card details and PIN. But there are more specific reasons to think that the equations for universes are entirely normal in this respect.
About twenty years ago, Stenger wrote some computer software, which he called MonkeyGod. It lets you choose a few fundamental constants and discover what the resulting universe is capable of. Simulations show that combinations of parameters that would in principle permit life forms not too different from our own are extremely common, and there is absolutely no evidence that fine-tuning is needed. The values of fundamental constants do not have to agree with those in our current universe to one part in 1030. In fact, they can differ by one part in ten without having any significant effect on the universe’s suitability for life.
More recently, Fred Adams wrote a paper for the Journal of Cosmology and Astroparticle Physics in 2008, which focuses on a more limited version of the question.fn3 He worked with just three constants – those that are particularly significant for the formation of stars: the gravitational constant, the fine structure constant, and a constant that governs nuclear reaction rates. The others, far from requiring fine-tuning, are irrelevant to star formation.
Adams defines ‘star’ to mean a self-gravitating object that is stable, long-lived, and generates energy by nuclear reactions. His calculations reveal no sign of fine-tuning. Instead, stars exist for a huge range of constants. Choosing these ‘at random’, in the sense usually employed in fine-tuning arguments, the probability of getting a universe that can make stars is about 25%. It seems reasonable to allow more exotic objects to be treated as ‘stars’ too, such as black holes generating energy by quantum processes, and dark matter stars that get their energy by annihilating matter. The figure then increases to around 50%.
As far as stars go, our universe is not improbably balanced on an incredibly fine knife edge, battling odds of billions to one against. It just called ‘heads’, and the cosmic coin happened to land that way up.
Stars are only part of the process that equips a universe with intelligent life forms, and Adams intends to look at other aspects, notably planet formation. It seems likely that the results will be similar, debunking the almost infinitesimal chances alleged by advocates of fine-tuning, and replacing them by something that might actually happen.
What, then, went wrong with the fine-tuning arguments? Failures of imagination and blinkered interpretations. For the sake of argument, let us accept that most values of the constants make atoms unstable. Does this prove that ‘matter’ cannot exist? No, it just proves that matter identical to that in our universe can’t exist. What counts is what would happen instead, but advocates of fine-tuning ignore this vital question.
We can ask the same question for the belief that the only viable aliens will be just like us, as many astrobiologists still maintain – though fewer of them than there used to be. The word ‘astrobiology’ is a compound of astronomy and biology, and what it mostly does is put the two sciences together and see how they affect each other. To analyse the possibility of alien life, especially intelligent alien life, conventional astrobiology starts with the existence of humans, as the pinnacle of life on Earth. Then it places them in the context of the rest of biology: genes, DNA, carbon. It then examines our evolutionary history, and that of our planet, to find environmental features that helped bring life, and us, into existence.