A Universe Fit For Intelligent Life - extract from 'Introduction to Astronomy and Cosmology,' by Ian Morison
This article is an extract about cosmic fine tuning from 'Introduction to Astronomy and Cosmology,' by Ian Morison. Copyright © 2008 John Wiley & Sons. Reproduced with permission of John Wiley & Sons ltd.
The very fact that you are reading this book tells us that our universe has just the right properties for intelligent life to have evolved. But why should this be so? As eloquently described in a book Just Six Numbers, by Martin Rees, there are a number of parameters that have a major influence on how universes can evolve and how stars produce elements that are needed for life. Two of these have already been covered in this chapter; the constants Ω and Λ If Ω had been higher the universe would have rapidly collapsed without allowing life a chance to evolve; if it had been smaller galaxies and stars would not have formed. In addition, if Λ, which is surprisingly small, had been larger, it would have prevented stars and galaxies forming.
You have also read in this chapter how the galaxies formed as a result of fluctuations in the density of the primeval universe – the so-called ‘ripples’ that are observed in the CMB. The parameter that defines the amplitude of these ripples has a value of ~10-5. If this parameter were smaller the condensations of dark matter that took place soon after the Big Bang (and were crucial to the formation of the galaxies) would have been both smaller and more spread out resulting in rather diffuse galaxy structures in which star formation would be very inefficient and planetary systems could not have formed. If the parameter had been less than 10-6, galaxies would not have formed at all! However, if this parameter were greater than 10-5 the scale of the ‘ripples’ would be greater and giant structures far greater in scale than galaxies would form and then collapse into super-massive black holes – a violent universe with no place for life!
One parameter of our universe is so well known that it is barely given a moment’s thought - the number of spatial dimensions, three. If this were either two or four, life could not exist.
Though we perceive gravity to be a ‘strong’ force (because we are close to a very massive body) it is actually incredibly weak in comparison with the electrostatic forces that control atomic structures and, for example, cause protons to repel each other. The factor is of order ~10-36. Let us suppose gravity was stronger by a factor of a million. On the small scale, that of atoms and molecules, there would be no difference, but it would be vastly easier to make a gravitationally bound object such as the Sun and planets but whose sizes would be about a billion times smaller. Any galaxies formed in the universe would be very small with tightly packed stars whose interactions would prevent the formation of stable planetary orbits. The tiny stars would burn up their fuel rapidly allowing no time for life to evolve even if there were suitable places for it to arise. Our intelligent life could not have arisen here on Earth if this ratio had been even slightly smaller than its observed value.
Einstein’s famous equation, E=mc2 relates the amount of energy that can be extracted from a given amount of mass, so the value of c is obviously fundamentally important. In practice only a small part of the energy bound up in matter can be released, as in the conversion of hydrogen to helium. This process releases 0.7% of the mass of the four protons that form helium – a percentage closely linked to the strength of the strong nuclear force. The parameter 0.007 has been called ‘nuclear efficiency’. However, if this value was too small, say 0.006, the sequence of reactions that build up helium could not take place. In the first of these reactions, two protons form a deuterium nucleus, but given a value of 0.006 for the nuclear efficiency, deuterium would be unstable, so preventing the further reactions that give rise to helium – stars would be inert. However, if this parameter was 0.008, meaning that nuclear forces were stronger relative to electrostatic forces, the electrostatic repulsion of two protons would be overcome and they could bind together so no hydrogen would have remained to fuel the stars. A critical reaction in the evolution of stars is the formation of carbon in the triple alpha process. As described earlier, Fred Hoyle played a key role in the understanding of this reaction and pointed out that even a change of a few percent from the observed value of 0.007 would have severe consequences on the amount of carbon that would be formed in stars – with obvious consequences for life as we understand it.
So how can it be that all the parameters described above are finely tuned so that we can exist? There are two possible reasons. The first is that our universe was ‘designed’ by its creator specifically so that it could contain intelligent beings, a view taken by some scientist-theologians. A second view is that there are many universes, each with different properties: the term ‘multiverse’ has been applied to this view. We have no knowledge of what lies in the cosmos beyond the horizon of our visible universe. Different regions could have different properties; these regions could be regarded as different universes within the overall cosmos. Our part of the cosmos is, like baby bear’s porridge, just right.’
From ‘Introduction to Astronomy and Cosmology’ pp. 326-328
by Ian Morison.
Copyright © 2008 John Wiley & Sons
Reproduced with permission of John Wiley & Sons ltd.