This is the question of questions, the ultimate mystery--and
astronomy has given us at least one big piece of the answer.
Some 13.7 billion years ago, according to the best available evidence,
the universe sprang to life in a single, vast eruption known as
the big bang. Everything was born in that instant--matter,
energy, space and even time itself, all ballooning outward from
an infinitesimal point. The universe has been expanding and cooling
ever since. And slowly, over those billions of years, the primordial
matter that emerged from the big bang has been organizing itself
into galaxies, stars, planets and most recently, us.
Astronomers have also been able to fill in this cosmic
story with quite a few details.
(University of California, Los Angeles (UCLA), cosmologist Ned Wright offers an advanced online tutorial.)
Within the first few minutes after the big bang, for example,
the expanding universe had cooled enough for simple atomic nuclei
to form, rather like water droplets condensing out of a fog.
This was the origin of light elements such as hydrogen and helium.
(Heavier elements such as carbon, iron and uranium would form
much later, inside of stars.)
Then, after another 380,000 years of expansion, temperatures fell
to the point where those nuclei could combine with free-floating
electrons. The result was a thin haze of stable atoms, mostly hydrogen
and helium gas, plus a kind of afterglow that’s been streaming
through the universe ever since. This microwave
background radiation, as it’s known, has provided astronomers
with an immense amount of information about conditions in the very
early universe. Indeed, they continue to study it with every
instrument at their command. One prime example is the NSF-funded BOOMERANG experiment,
in which high-altitude balloons have been carrying a series of
microwave telescopes aloft over Antarctica since 1998. Another
is NASA’s WMAP satellite,
which has been mapping the microwave background in unprecedented
detail since its launch in 2001.
Ironically enough, however, astronomers’ very success at filling
in the details of the big bang story has forced them to confront
a new mystery: a profound gap in our understanding of matter and
energy.
What Is the Universe
Made of, and How Does It Work? [Next]
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