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Rigged in favour of life

Posted by iKnowHOW on October 31, 2006

The universe seems to be “just right” for life.

Albert Einstein is famous for remarking that what most interested him was whether God had any choice in the nature of his creation. By this, Einstein was asking in characteristically quaint language whether the universe could have been otherwise. Two generations later, Einstein’s rhetorical question has resurfaced with a vengeance, and sparked a controversy that has split the physics community.

At the heart of the row lies the deep problem of the laws of physics: where do they come from and why do they have the form that they do? These are not questions that scientists normally ask. But they have been thrown into this by the work of a band of theorists struggling to merge all known laws into a unified mathematical scheme.

A fashionable contender is string theory, which replaces the notion of a world built from particles with the claim that little loops of writhing string can explain everything from electrons to the force of gravity. It’s a compelling idea that has attracted the world’s top brains, but has yet to convince sceptics. Meanwhile, dramatic progress in cosmology has enabled astronomers to piece together the story of the universe back to the first split seconds after the Big Bang.

Given these sweeping advances, it isn’t surprising that some scientists are tempted to move beyond technicalities and tackle the big foundational questions: how the universe came into being, and why its laws are mathematical in nature. One question above all has received a lot of attention. Scientists have long known that the existence of life depends rather delicately on a number of felicitous coincidences and special factors in fundamental physics and cosmology. Like Baby Bear’s porridge in the story of Goldilocks, the universe seems to be “just right” for life.

Getting it right

Imagine playing God. In front of you is a machine complete with a row of knobs. Twiddle this knob and you make all electrons a bit heavier; twiddle that knob and you slightly strengthen the force that binds protons and neutrons in atomic nuclei. According to the standard models of particle physics and cosmology, there are thirty-something such adjustable quantities needed to describe the physical world.

Simple calculations then suggest that meddling with some of the knob settings, even by a tiny amount, would prove lethal, wrecking any hope that life could emerge in the universe. If protons were just a tad heavier, all else being equal, they would decay into neutrons, and atoms would fall apart. If the nuclear force were a few per cent different then carbon, the life-giving element, would never have formed in abundance by nuclear reactions inside stars. In each case, life would be impossible. Taking into account many such “fine-tunings” in physics and cosmology, it looks as if the universe is a fix — a big fix.

This is where the knives come out. Some cosmologists, most notably Lord Rees, president of The Royal Society, believe there is a very natural explanation for the uncanny bio-friendliness of the universe.

What we have all along been calling “the universe” is, it seems, nothing of the sort. Rather, it is but an infinitesimal fragment of a vast and elaborate system of many universes, or distinct cosmic regions, collectively dubbed “the multiverse”.

Crucially, claims Rees, the laws of physics we observe in our universe are not the same everywhere but are more akin to local by-laws. Other universes within the multiverse will have different laws. Thus a universe over there may be expanding faster than ours and contain electrons with stronger charges, while in the universe next door gravity may be a bit weaker or protons a bit heavier.

These cosmic-scale variations might be completely random. The occasional universe would then fall in the “Goldilocks zone” like a winner in a cosmic jackpot, and possess by pure chance laws and properties just right for life. It would then be no surprise that we perceive a universe so weirdly suited to our own presence.

The multiverse idea isn’t just idle speculation, but is bolstered by discoveries in subatomic particle physics. As the energy of physical processes is raised, in particle collisions, so the laws describing the particles’ behaviour tend to become simpler and mesh neatly together. The greatest particle physics experiment in history was the Big Bang that gave birth to the universe 13.7 billion years ago, so it makes sense to expect the universe to have started out with simple laws.

Then, as the universe expanded and cooled, so the effective, relatively low-energy “by-laws” we observe in the lab emerged from the fiery maelstrom. If there are many alternative low-energy laws, as theory suggests, then it is likely that a sort of cosmic patchwork quilt arose, in which each patch acquired its distinctive set of laws. Our universe is buried deep in such a patch.

Sceptics speak

If all this seems hard to swallow, some particle physicists — especially string theorists such as Nobel prizewinner David Gross of the University of California at Santa Barbara — will heartily agree with you. They have slammed the multiverse explanation of the Goldilocks enigma, calling it sloppy science and quasi-religious mumbo-jumbo.

The holy grail of particle physics is to produce a final theory of everything. It will nail down completely every aspect of physical law: all particle masses, the strength of every force, the details of the Big Bang — each will be precisely determined in a welter of breathtaking mathematics.

According to this ambitious vision, God would have no choice in the matter (to paraphrase Einstein), because the laws of physics would be uniquely specified by the theory, with no lassitude to vary from one universe to the next. The fact that this unique set of laws just happens to permit life would be shrugged aside as an incidental quirk of no significance.

The multiverse proponents have hit back, in turn accusing the string theorists of promissory triumphalism. So far, string theory, or for that matter any other contender for a final theory of everything, has yet to predict correctly a single particle mass or force strength.

Some cynics have denounced putative theories of everything as in reality theories of nothing. Amid this acrimonious bickering, it is worth asking whether there might be another explanation for why the universe appears to have been ingeniously rigged in favour of life.


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