Farewell to Reality (42 page)

*
Recall that Euclidean geometry, in which the angles of a triangle add up to precisely 180
⁰
, is based on the assumption of a ‘flat' spacetime.

11

Ego Sum Ergo Est

I Am Therefore It Is: the Anthropic Cosmological Principle

A theorist goes astray in two ways: 1. The devil leads him by the nose with a false hypothesis. (For this he deserves our pity.) 2. His arguments are erroneous and sloppy. (For this he deserves a beating.)

Albert Einstein
¹

In the last four chapters we have had an opportunity to review the various approaches that theorists have taken in their attempts to resolve some of the more stubborn problems with the current authorized version of reality.

We have seen how attempts to resolve the quantum measurement problem have led to many worlds. We have seen how attempts to push beyond the standard model of particle physics and find rhyme or reason for its twenty experimentally determined parameters have led to SUSY and superstring/M-theory. We have seen how SUSY and various braneworld scenarios in M-theory suggest solutions for the hierarchy problem. In search of potential dark matter candidates we examined the lightest supersymmetric particles predicted by SUSY and the lightest Kaluza—Klein particles, thought to be projected from M-theory's hidden dimensions. We saw how the multiverse resolves the problem of dark energy and the cosmological constant. In the cosmic landscape, ours is but an ordinary, if not rather mundane, universe among a vast multiplicity of universes.

Despite their speculative or metaphysical nature, in the context in which I've presented them so far these contemporary theories of physics still conform to the Copernican Principle. They do not assume an especially privileged role for us as human observers.

Perhaps you'll then be surprised to learn that one approach to resolving the fine-tuning problem, an approach growing in importance and gaining support within the theoretical physics community, puts human beings firmly back into the equation. It is called the anthropic cosmological principle, where ‘anthropic' means ‘pertaining to mankind or humans'.

I should say upfront that this is all rather controversial stuff. Many scientists have argued that the anthropic cosmological principle is neither anthropic nor a principle. Others have argued that it is either dangerous metaphysics or completely empty of insight. Either a false hypothesis, deserving of Einstein's pity, or erroneous and sloppy thinking, deserving of a beating.

I believe that the anthropic cosmological principle is symptomatic of the malaise that has overtaken contemporary theoretical physics. We'd better take a closer look.

The carbon coincidence

In his
Discourse on Method,
first published in 1637, the French classical modern philosopher René Descartes tried to establish an approach to acquiring knowledge of the world by first eschewing all the information delivered to his mind by his senses. He had decided that his senses couldn't be trusted. He cast around looking to fix on something about which he could be certain.

After some reflection, he decided that that something was his own mind. And, he reasoned, given that he possesses a mind, then in some form or another he must exist.
Cogito ergo sum,
he declared: I think therefore I am.

Human beings are carbon-based life forms that have evolved certain mental capacities. We are conscious and self-aware, and, like Descartes, we are able to reflect intelligently on the nature of the physical universe we find around us. It seems a statement of the blindingly obvious that, whatever it is and wherever it comes from, the physical universe supports the possibility that we could (and, indeed, do) exist. We exist therefore the universe must be just so. We might adapt Descartes' famous saying thus:
ego sum ergo est —
I am therefore it is.

The problem is that as soon as we put human beings (or, at the very least, the possibility of cognitive biological entities) back into the
equation in this way, we acquire a perspective that makes the universe look like an extraordinary conspiracy.

One of the most notable examples of a ‘coincidence' of the kind that betrays conspiracy in the physical mechanics of the universe was identified by the physicist Fred Hoyle in the early 1950s. It concerns the process by which carbon nuclei are produced in the interiors of stars.

The primordial big bang universe (or the steady-state universe favoured at the time by Hoyle) contains only hydrogen and helium and trace amounts of slightly heavier elements such as lithium. In the early 1950s, the relative abundances of heavier elements were therefore something of a mystery. How are these elements formed?

Hoyle supposed that at the high temperatures and pressures that prevail in the centres of stars, the primordial hydrogen and helium would get further ‘cooked'. These light nuclei would fuse together in a series of reactions to form successively heavier nuclei, in a process now called
stellar nucleosynthesis.

When two hydrogen nuclei fuse together to form a helium nucleus, two of the four protons transform into neutrons, and energy is released. This energy holds the star up against further gravitational collapse, and the star settles down into a period of relative stability.

As the supply of hydrogen becomes depleted, however, the energy released from such fusion reactions is no longer sufficient to resist the force of gravity. A star with enough mass will blow off its outer layers and its core will shrink. The temperature and pressure in the core will rise, eventually triggering fusion reactions involving helium nuclei.

But at this point we hit a snag. Fusing hydrogen nuclei (one proton) and helium nuclei (two protons and two neutrons) together to make lithium is not energetically possible. A lithium nucleus with three protons and two neutrons is unstable: it needs one or two more neutrons to stabilize it. Fusing two helium nuclei together to make beryllium is similarly impossible — a beryllium nucleus with four protons and four neutrons is likewise unstable. It needs another neutron.

In a state of rising panic, we skip over lithium and beryllium and look to the next element in the periodic table. What about carbon? A carbon nucleus has six protons and six neutrons. This would seem to require fusing together three helium nuclei. This is energetically
possible, but the chances of getting three helium nuclei to come together in a simultaneous ‘three-body' collision are extremely remote. It's much more feasible to suppose that two helium nuclei first fuse to form an unstable beryllium nucleus, which then in turn fuses with another helium nucleus before it can fall apart. This sounds plausible on energy grounds but the odds don't look good. The beryllium nucleus tends to fall apart rather too quickly.

Yet here we are, intelligent beings evolved from a rich carbon-based biochemistry. Given that we exist, carbon must somehow be formed in higher abundance, despite the seemingly poor odds.

Hoyle reasoned that the odds
must
somehow get tipped in favour of carbon formation. He therefore suggested that the carbon nucleus must possess an energetic state that helps greatly to enhance the rate of the reaction between the unstable beryllium nucleus and another helium nucleus, thereby producing carbon faster than the beryllium nucleus can disintegrate. Such an energetic state is called a ‘resonance'. Hoyle estimated that the carbon nucleus must have a resonance at an energy of around 7.7 MeV. It was subsequently discovered at 7.68 MeV. The reaction is called the triple-alpha process.
*

This struck Hoyle as remarkable. If the carbon resonance were slightly higher or lower in energy, then carbon would not be formed in sufficient abundance in the interiors of stars. There would therefore be insufficient carbon in the debris flung from those stars that are ultimately destined to explode in spectacular supernovae. The second-generation star systems that formed from this debris would then hold planets with insufficient carbon to allow intelligent, carbon-based life forms to evolve.

Change the energy of the carbon resonance by the slightest amount, and we could not exist. Hoyle wrote:

Would you not say to yourself, ‘Some super-calculating intellect must have designed the properties of the carbon atom, otherwise the chance of my finding such an atom through the blind forces of
nature would be utterly minuscule.' Of course you would … A common sense interpretation of the facts suggests that a superintellect 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.
²

The Goldilocks enigma

The carbon coincidence is just the beginning. It occurs because of a delicate balance between the strength of the strong force and the energetics of nuclear reactions involving protons. In
just Six Numbers,
British astrophysicist Martin Rees identified a series of six dimensionless physical constants and combinations of constants that determine the nature and structure of the universe we inhabit. Change any one of these numbers by just 1 per cent and, Rees argued, the universe that resulted would be inhospitable to life. If the constants were not so fine-tuned, we could not exist to observe the universe and ponder on its remarkable cosmic coincidences.

These six numbers include
ɛ
, the fraction of the mass of the four protons that is released as energy when these fuse together to form a helium nucleus inside a star.
ɛ
determines the amount of energy released by a star like our own sun and the subsequent chain of nuclear reactions responsible for the production of other chemical elements. Like the carbon coincidence, it depends on the strength of the strong force. If too little energy is released, the planetary system orbiting the star remains cold and lifeless. Too much, and the planetary system is hot and lifeless.

The set of numbers also includes
, the ratio of the strength of the electromagnetic force to the strength of the force of gravity. This is a large number (10
³⁶
), and says that the mechanics of the atom are dominated by electromagnetic forces — gravity is irrelevant. But gravity is cumulative. Gather lots of atoms together and it adds up.
determines the relationship between the behaviour of matter at atomic and subatomic levels and matter at the levels of planets, stars, galaxies and clusters of galaxies. Make the force of gravity just a little bit larger in relation to the force of electromagnetism and the universe would be smaller and would
evolve much faster. There would be no time for biology to develop. Make gravity a little weaker and there would be no stars.

The density parameter, Ω, is the ratio of the density of mass-energy to the critical value required of a flat universe. It depends on the balance between gravity and the rate of expansion of the universe. Too much mass-energy and the result is a closed universe which expands a little but then contracts rather quickly: too quickly for life to gain a foothold. Too little mass-energy and the result is an open universe which expands too quickly to support the evolution of galaxies.

Likewise, the cosmological constant, Λ, seems similarly fine-tuned for life. Although it was something of a shock to cosmologists in the late 1990s to discover that A isn't precisely zero and that the expansion of the universe is accelerating, the value of the constant is still extremely small. Ridiculously small according to quantum theory. But if it was any larger, the universe would be open and there would be no stars, no galaxies and no life.

Of course, we can trace the large-scale structure of the visible universe — galaxies and clusters of galaxies — right back to the quantum fluctuations that prevailed during the inflationary epoch. These ripples are slight — about one part in 100,000. This variation is captured in the ratio
, derived from the energy required to break up large galactic clusters or superclusters and the energy of the rest mass of such structures. If
were smaller, there would be no large-scale structures. Make it larger and the universe would consist only of supermassive black holes.