Science Musings Blog

"If the number controlling the growth of the universe since the Big Bang is just slightly too high, the universe expands so rapidly that protons and neutrons never come close enough to bond into atoms. If it is just ever-so-slightly too small, it never expands enough, and everything remains too hot for even a single nucleus to form. Similar problems afflict the observed masses of elementary particles and the strengths of fundamental forces." (Nature, Jan. 5, 2006)

For several decades now, cosmologists have been puzzled by how finally tuned the universe is. As Leonard Susskind, a string theorist based at Stanford University in California, says: "It's like you're throwing darts, and the bullseye is just one part in 10¹²⁰ of the dart board."

So finely tuned is our universe for life, that many cosmologists have imagined a kind of Intelligent Design, a world made just for us, although instead of calling it God, they call it the strong anthropic principle.

Now, however, string theorists are coming around to the idea that our universe is just one of 10⁵⁰⁰ universes -- a number vastly larger than the number of particles in our universe -- with every conceivable combination of values for the fundamental constants. Our universe appears particularly suited to us because this is the one (or one of the many) that made us possible. There are other universes exactly like this one (including a person exactly like me), some that are slightly different, and many, many more in which human life would be impossible. This has melancholy implications: As I said once in a Globe column, for every parallel universe where I'm trapped in an elevator with Cameron Diaz, there's another parallel universe where I'm trapped in an elevator with Dick Cheney.