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The anthropic principle is the idea that the physical laws that govern our Universe are precisely those that allow complex life like ours to emerge. Many scientists have wondered at the balance of these laws, arguing that any small change would alter the universe so radically that life would be impossible. Why is the Universe so finely tuned for life, they ask.

Nobody has come up with a reasonable answer to this question but today James MacDonald and Dermott Mullan at the University of Delaware argue that matters may be more robust than we thought.

Their argument is about the strong nuclear force. Various physicists have noted that if the strong force were just a little stronger, then protons would bind together more readily. That would mean that soon after the Big Bang, most protons would join together to form diprotons, leaving few if any single protons available to form hydrogen. Consequently, chemistry as we know it would be impossible.

But this reasoning fails to take other factors into account, say MacDonald and Mullan. The biggest factor is that protons and neutrons will always bind more strongly than protons and protons, regardless of the strength of the strong force. So although diprotons would form in this universe, they would also tend to decay into deuterons.

So hydrogen (and deuterium) chemistry would be just as likely in a Universe in which the strong force were stronger. (Of course, how the change would affect the the nucleosynthesis of other elements is another question.)

The work gives the lie to some of the more extraordinary claims regarding the anthropic principle. For example, some argue that since we are unable to find anything special about the combination of laws in our Universe, then maybe any permutation is possible. And if any permutation is possible, then perhaps these combinations exist in countless other universes. Of course, the only one we would experience is the one in which the laws are fine-tuned for our existence.

That’s an extraordinary line of argument. But the alternative–that organic chemistry is an emergent property of a wide range of the parameters governing the basic laws of physics–is even more jaw dropping.

MacDonald and Mullan’s work gives a tantalising hint that this idea might be worth pursuing a little more diligently.

Ref: arxiv.org/abs/0904.1807: Big Bang Nucleosynthesis: The Strong Force meets the Weak Anthropic Principle


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