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than 140 trillion Earth oceans.
1
It is spread thinly, to be sure, being
some 300 trillion times less dense than the Earth's atmosphere. And
it is cold, at −53 degrees Celsius, all this being worked out by the
extraordinarily precise measuring capabilities of modern spectro-
metric arrays. But that is still much hotter and denser than the water
that is scattered, say, across the Milky Way. It shows that water—the
stuff of our oceans—has been virtually everywhere, from close to the
beginning of time itself. It is not some kind of cosmic rarity that our
Earth, by some quirk, happens to have in abundance.
How is that water made, though, in the depths of the universe?
2
It
is, of course, made up of two atoms of hydrogen conjoined with an
atom of oxygen: H
2
O, the first chemical compound that any child
learns at school. That does not mean it is simple. There are deceptive
subtleties in that three-atom molecule, as we will see, which make
possible all kinds of things, such as oceans, icecaps—and life itself.
Nevertheless, one can start with the basic ingredients and go on from
there.
With hydrogen it is straightforward. Or straightforward, at least, if
we close our eyes to the mysteries that surround the origin of the
universe, in the Big Bang, some 13.8 billion years ago. Hydrogen was
the main material product of the Big Bang. More precisely, it is the
main material product that we can currently observe. There is out
there a very great amount of 'dark matter', which must exist, for it
holds the galaxies together. Dark matter dwarfs the total amount of
normal matter in the universe, but otherwise it remains quite
mysterious.
3
The Big Bang, at its very beginning, was far too hot (at many tril-
lions of degrees Celsius) for hydrogen—or any other kind of atom—to
exist. But, when the primordial mass of subatomic particles had
stretched and cooled sufficiently, when the universe had grown from
nothing to the size of our solar system now, about a millionth of a
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