““Where carbon comes from in the universe is also a deep function of quantum physics. Like all the heavier elements, it us produced via nucleosynthesis (from nuclear fusion) in stars. But the high abundance of carbon (it comes in fourth in the count of atoms in today's universe, after hydrogen, helium, and oxygen) relies on several key properties of the cosmos. Most carbon forms through the triple-alpha process: the fusion of two helium nuclei into a beryllium-8 nucleus, followed by the fusion of the beryllium nucleus and another helium nucleus into carbon. This would be a horribly inefficient way to make carbon, except for some subtle coincidences. These coincidences are pretty technical, and may only be truly relished by nuclear physicists, but they're worth knowing about because they can help you grasp the connections between fundamental physics and us. The first coincidence is that in a star's interior, the combined energy of a beryllium-8 nucleus and a helium nucleus can closely match that of an energized carbon-12 atomic nucleus. This "resonance" in energies is key; it greatly enhances the rate of the next fusion step-making carbon-12. The second coincidence is that the nuclei of beryllium-8 just happen to be stable for long enough for them to have a good chance of catching one of those helium nuclei as they buzz around. And finally, the new carbon-12 nucleus is not efficient about immediately fusing with any spare helium nuclei to make a heavier oxygen nucleus-the carbon doesn't get gobbled up into oxygen, and lives to build your DNA a few billion years later.””
