The strength of gravity. The mass of the electron. The force that holds an atomic nucleus together. The energy of empty space. No theory says what these numbers have to be. Physicists simply measured them and wrote them down.
In particle physics and in cosmology there are about thirty such free numbers. Picture a panel, with each number set on its own knob.
People often think: turn a knob, and life will simply be different, silicon-based, for example. Let us check. Next come six knobs. Turn each one and see what remains of the Universe.
On every screen you can turn the scene with a finger or with the mouse.
Empty space has an energy of its own: the cosmological constant Λ. It pushes everything apart, in every direction. Gravity does the opposite: it gathers gas into galaxies and stars.
A calculation from quantum theory makes Λ 10120 times larger than the value we observe. On this scale that value would stand 117 divisions past the right-hand edge. The threshold “galaxies never gather”: Steven Weinberg, 1987.
In the first moments, particles and antiparticles are born. When they meet they destroy each other and turn into light. If the numbers had been equal, nothing would have been left.
It is measured from the cosmic microwave background: for every particle of matter today there are more than a billion particles of light. On the screen the pairs are counted in thousands, not billions, or the remainder could not be seen. Physics still does not know where the imbalance came from.
Atomic nuclei are built of protons and neutrons. The neutron is a little heavier. In front of you is a carbon atom, and everything alive is built of carbon. Shift the difference in mass.
The thresholds are worked out from masses that have been measured: the electron 0.511 MeV, the binding energy of deuterium 2.22 MeV. The whole scale on the screen is half a percent of the mass of the neutron.
When hydrogen in a star fuses into helium, 0.007 of the mass turns into energy. This number sets the strength of the strong nuclear force. Which elements can exist at all depends on it.
Marked in gold are the six chief elements of life. The calculation is by Martin Rees, Astronomer Royal, in Just Six Numbers.
Carbon is born in the stars, when three helium nuclei fuse almost at the same moment. That is possible only because the carbon nucleus has an energy level in exactly the right place: 7.65 MeV.
Fred Hoyle predicted this level in 1953, ahead of the measurement: if carbon exists, the level has to be there. They found it in the laboratory, where he had said it would be. The thresholds are calculated by Oberhummer et al., Science, 2000.
The Universe began in a state of almost perfect order. Only for that reason do stars burn in it, and time flow one way. Roger Penrose, a Nobel laureate in physics, worked out how precisely one would have had to “aim” to get a beginning like that:
That is a 1 followed by 10123 zeros. The whole visible Universe holds about 1080 atoms. Write one zero on every atom, and the atoms run out while the number has barely begun.
R. Penrose, The Emperor’s New Mind, 1989. Penrose himself calls himself a nonbeliever.
Any life at all, even a silicon one, needs three things: different atoms, so that something can be built, a source of energy, and time. Stars make silicon too. What these universes lack is not “our kind of life”. They have no chemistry and no stars, and some of them have no matter at all.
“A common sense interpretation of the facts suggests that a superintellect has monkeyed with physics, as well as with chemistry and biology.”
“The remarkable fact is that the values of these numbers seem to have been very finely adjusted to make possible the development of life.”
“The more I examine the universe and the details of its architecture, the more evidence I find that the universe in some sense must have known we were coming.”
Fifty marksmen are firing at you, and every one of them misses. “If they had hit me, I would not be surprised” is true. But it does not explain why all fifty missed.
Nobody has ever observed a single other universe, and there is no way to check. And a mechanism that stamps out universes with different numbers would itself have to be built very precisely. The question simply moves one floor up.
Perhaps. Then it will turn out that the only laws that were possible were exactly the ones under which life is possible. That is no smaller a wonder.
The knobs were set by the One who knew what He was building. He was before the Universe, outside it, and stronger than it. The Bible calls Him by name: God.
“For thus says the LORD, who created the heavens (he is God!), who formed the earth and made it (he established it; he did not create it empty, he formed it to be inhabited).”
Isaiah 45:18
The Universe was prepared so that you could be in it. The One who tuned it knows you, and He wants you to know Him.
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