Monday, May 11, 2009

In the smithy of the Sun


It is one of the wonders of science that we can tell exactly what distant galaxies, stars and nebulas are made of by a spectral analysis of their light. And the unsurprising answer is that they are made of exactly the same elements as the Earth.

I say "unsurprising," but that is only from our modern perspective. For most of human history it was assumed that the heavens were made of other stuff, less mundane, more ethereal. But no. It's hydrogen, helium, carbon, oxygen, and all the other familiar atoms that make up our terrestrial environment.

But not in uniform abundances. There is about ten times more of the heavier elements -- carbon and oxygen, say -- relative to hydrogen and helium in the shell of an exploded star (such as the Cat's Eye Nebula above) than in the surrounding gaseous medium. That's because heavy elements are forged in stars as they burn, fused from hydrogen and helium, and when a star dies explosively it sheds these elements to space -- to perhaps become in the fullness of time other stars and planets.

In the beginning, in the wake of the big bang, there was only hydrogen and helium. Stars, yes. Galaxies of stars. And big gassy planets like Jupiter. But no solid planets like Earth with cores of iron, shells of silicon and oxygen, and biospheres of carbon-based life. Many stars had to live and die in the arms of the Milky Way Galaxy to make the stuff of Earth and life. Starlight is the product. We are the ash.

There are about 1027 carbon atoms in a human body. That's 1000000000000000000000000000 carbon atoms, and every one was fused in a star that lived and died before the Sun and Earth were born. These atoms are passed around. I got mine from food, ultimately from the air and soil. I'm only using them temporarily. I'll give them back. Maybe some of my carbon atoms once resided in the body of Archimedes. Maybe some will eventually end up in my great-great-great-great-grandchildren's shoe polish or cucumbers.

You can never step in the same river twice, said Heraclitus. Everything flows. We are a river of atoms -- we coalesce, we effervesce, we disperse. A human soul is an eddy in a whirlwind. Enjoy it while you can.