Why the universe wasn't fine-tuned for life

IF THE force of gravity were a few per cent weaker, it would not squeeze and heat the centre of the sun enough to ignite the nuclear reactions that generate the sunlight necessary for life on Earth. But if it were a few per cent stronger, the temperature of the solar core would have been boosted so much the sun would have burned out in less than a billion years - not enough time for the evolution of complex life like us.

In recent years many such examples of how the laws of physics have been "fine-tuned" for us to be here have been reported. Some religious people claim these "cosmic coincidences" are evidence of a grand design by a Supreme Being. In The Fallacy of Fine-tuning, physicist Victor Stenger makes a devastating demolition of such arguments.

A general mistake made in search of fine-tuning, he points out, is to vary just one physical parameter while keeping all the others constant. Yet a "theory of everything" - which alas we do not yet have - is bound to reveal intimate links between physical parameters. A change in one may be compensated by a change in another, says Stenger.

In addition to general mistakes, Stenger deals with specifics. For instance, British astronomer Fred Hoyle discovered that vital heavy elements can be built inside stars only because a carbon-12 nucleus can be made from the fusion of three helium nuclei. For the reaction to proceed, carbon-12 must have an energy level equal to the combined energy of the three helium nuclei, at the typical temperature inside a red giant. This has been touted as an example of fine-tuning. But, as Stenger points out, in 1989, astrophysicist Mario Livio showed that the carbon-12 energy level could actually have been significantly different and still resulted in a universe with the heavy elements needed for life.

The most striking example of fine-tuning appears to be the dark energy - or energy of the vacuum - that is speeding up the expansion of the universe. Calculations show it to be 10¹²⁰ bigger than quantum theory predicts. But Stenger stresses that this prediction is made in the absence of a quantum theory of gravity, when gravity is known to orchestrate the universe.
Even if some parameters turn out to be fine-tuned, Stenger argues this could be explained if ours is just one universe in a "multiverse" - an infinite number of universes, each with different physical parameters. We would then have ended up in the one where the laws of physics are fine-tuned to life because, well, how could we not have? (For a related philosophical discussion read this article.)

Religious people say that, by invoking a multiverse, physicists are going to extraordinary lengths to avoid God. But physicists have to go where the data lead them. And, currently, there are strong hints from string theory, the standard picture of cosmology and fine-tuning itself to suggest that the universe we can see with our biggest telescopes is only a small part of all that is there.

Source New Scientist