IMAGINE PLAYING GOD, and tinkering with the properties of the universe.

 Before you is a machine crammed with knobs and dials — call it a ‘Designer Machine’. One knob controls the strength of gravity, a lever varies the masses of all electrons, yet another dial fixes the number of spatial dimensions, and so on. It turns out that to set the variables for the universe we see today, you need to adjust the position of about 30-something knobs, and everything else follows from them. And here’s the rub.
Change just a few of the settings (or ‘parameter values’, to use the jargon) even an infinitesimal amount, and there would be nobody around to witness the result. Unless the settings are unerringly close to their present values, we’d have no universe, no life and certainly no humans.
One of the best-known examples of this life-friendly ‘fine-tuning’ of the laws of physics concerns carbon, the element on which all known life is based. The Big Bang that kicked off the universe coughed out plenty of hydrogen and helium, but no carbon. So where did the carbon in our bodies come from? The answer was worked out in the 1950s: most of the chemical elements heavier than helium were manufactured in the cores of stars, as the product of nuclear fusion reactions. It is the energy released by these reactions that makes the Sun and stars shine.

However, while the details of stellar nuclear reactions are fairly straightforward, there is a notable exception: carbon. Most nuclear reactions in stars occur when two atomic nuclei, rushing around at tremendous speed care of the searing temperatures, collide and fuse, forming a heavier element. But carbon cannot be made this way because all the intermediate steps from helium to carbon involve highly unstable nuclei. The solution, spotted by University of Cambridge astronomer Fred Hoyle, is for carbon to form from the simultaneous collision of three helium nuclei.

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