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Humans sitting at Blombos Cave

Origins
As the Gemini North Telescope peers into the heart of the globular cluster M13, it is seeing some of the oldest stars in the universe--and almost seems to be looking back to the big bang itself.
Credit: Gemini Observatory

Title: Where Did It All Come From?
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]