What’s special about the number 12? If you spend much time with small children the answer may already be obvious to you. Children don’t always like to share, so when goodies are portioned they must be distributed EXACTLY evenly, or furious protests will ensue. The number 12 is the lowest number that can be divided into equal halves, thirds AND quarters. It’s perfect for keeping the peace in small groups of varying size.One dozen is such a handy number for divvying up, that it’s also a natural for dividing time—much more versatile than a number like 10 which, despite it’s roundness, can only be cut in half, no more. Once you look at it that way, a day with 12 hours (or, practically speaking, a sundial divided into 12 partitions) suddenly makes a lot of sense.
Surprisingly, it also bears on the question of whether our universe is just one among countless others. Here’s why:
To the astronomer-priests of ancient Egypt and Babylon, 12 was not just an easy number to work with but one that arose naturally in the cosmos. There are usually 12 full moons per year, with each successive full moon advancing into a new constellation—hence the 12 astrological signs of the zodiac. Clearly, the gods who designed the heavens are hip to the convenience of 12 as well.
You can continue playing this numbers game and you’ll find more signs of intelligent design in the heavens. What’s the lowest number that is divisible into halves, thirds, fifths AND sixths (though not quarters)? The answer is 30, the apparent number of days in a lunar cycle. A far more versatile number is 360, which can be evenly divided by 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 24, 30, 36, 40, 45, 60, 72, 90, 120, 180. Amazingly, to a first approximation it is also the number of days in a year.
What does it all mean? To our ancestors, the appearance of numbers like 12 and 360 in time keeping would have seemed like evidence for design. To us, it simply means that nature is full of numerical coincidences. The fact that we have nearly, but not quite 360 days in the year is not because of a divine plan or a law of nature. It just happens to be that way. Ditto for the number of lunar months in the year (which is closer to 12.5). On other worlds, with different days and different moons these numbers would work out quite differently.
This is not unlike a debate raging in cosmological circles about whether the fundamental parameters of our universe are mere coincidences or the products of deep natural laws. The prime example is the cosmological constant, which represents the energy density of empty space. In our universe, this number is so close to zero that it was long assumed to be so. Then, along came “dark energy”, discovered in 1998. Now cosmologists are faced with something that looks like a cosmological constant that is not zero, but still very small for no apparent reason other than this small number apparently permits stars, galaxies and life to exist. Could the universe be designed just for us?
To avoid the notion that we live in a universe mathematically designed for life, one can assume there are many universes, with many values of the cosmological constant. Leonard Susskind, one proponent of this idea, calls it the “cosmic landscape”. Others find this idea rather hard to swallow because, they say, it amounts to giving up on science explaining reality.
Thousands of years ago our predecessors must have pondered the number 12 and its place in nature. To some extent they were deceived. To many scientists it feels like nature is pulling a fast one on us all over again. It’s just not clear which way.
Ivan Semeniuk is host of The Universe in Mind podcast, and science journalist in residence at the Dunlap Institute for Astronomy and Astrophysics, University of Toronto.