The Science of Discworld IV

MeV state [as] anthropic, or to use it as an example of the predictive power of the anthropic principle,’ Kragh wrote.
Pan narrans
has been at work again, and the human love of narrativium has rewritten the historical story.
    Next: it’s simply not true that ‘without that finely tuned resonance, we wouldn’t be here.’ The 7.65 MeV figure for the energy of the resonance is not what’s required for carbon-based life to exist. It is the energy needed to produce the amount of carbon actually observed. Change the energy, and carbon would still be produced … but in different quantities. Not as different as you might think: Mario Livio and co-workers calculate that any value between 7.596 MeV and 7.716 MeV would generate much the same amount of carbon. Anything
up to
7.933 MeV would generate enough carbon for carbon-based life to exist. Moreover, if the energy level dropped
below
7.596 MeV,
more
carbon would be produced, not less. The lowest energy that would produce enough carbon for life is the ground state of the carbon atom, the lowest possible energy it can have, which is 7.337 MeV. A finely tuned resonance is not necessary.
    In any case, resonances are ten a penny, because atomic nuclei have lots of energy levels. Finding one in the appropriate range isn’t really very surprising.
    A more serious objection arises from the calculation itself. When factors that Hoyle neglected are taken into account, the combined energies of helium and beryllium turn out to be significantly higher than the figure he used. What happens to this ‘extra’ energy?
    It helps to keep the red giant burning.
    The star burns at precisely the temperature required to compensate for the energy difference. This looks like an even more impressive coincidence. Forget carbon: something far deeper is going on. If the basic constants of the universe were different, then the precisely fine-tuned resonance would disappear, the red giant would fizzle out and there wouldn’t be enough carbon to make Fred Hoyle, Adam and Eve, you or the cat.
    However, this argument, too, is fallacious. Changing the fundamental constants affects the red giant star as well as the carbon resonance. In fact, because the star burns helium and beryllium fuel, the star’s nuclear reactions automatically home in on the temperature that makes the fuel burn. Isn’t it amazing that a coal fire burns at exactly the temperature that makes coal burn? No. If coal burns at all, then feedback ensures that the energy balance of the reaction automatically works out correctly. It may be amazing that our universe is so rich that coal can burn, or red giants shine, but that is a very different issue from fine-tuning. In a complex universe, however it may work, complex objects can arise, and they will be beautifully suited to the rules of that universe because that is how they came to be. But that does not imply that the universe was specially chosen or created to give rise to such objects. Or that those objects are improbable, or special.
    The carbon resonance of a red giant, and the energetics of burning coal, are feedback systems. Like a thermostat, they automatically adjust themselves to keep going. This sort of feedback is extremely common and not at all remarkable. No more remarkable, in fact, than the amazing way that our legs are just long enough for our feet to meet the ground. Gravity pulls us down, the ground pushes us up,and the combination perches us in just the place where our feet and the ground are in exquisite alignment.
    The issue of the physical constants is deeper. Today’s picture of fundamental physics depends on a series of mathematical equations, all fairly elegant and neat. However, these equations also involve about thirty special numbers: things like the speed of light; and the fine structure constant, which governs the forces holding atoms together. These numbers appear to be pretty much random, but they matter just as much as the equations. Different values of these fundamental constants lead to very different solutions of the equations – different kinds of universe.
    The differences are not just the obvious ones: gravity being stronger or weaker, light travelling faster or slower. They can be more dramatic. Change the fine structure constant even a little, and atoms become unstable and fall apart. Make the gravitational constant smaller, and stars blow up, galaxies disappear. Make it larger, and everything collapses into a single gigantic black