Ten years ago, cosmologists discovered they were living a lie. The expansion of the universe was not slowing down as a result of gravity, as they had long believed: it was speeding up. The working explanation is that everything we know is only about 1 per cent of what’s out there. Another 3 per cent or so is hot interstellar gas we can see because it radiates X-rays and radio waves. An invisible substance called dark matter, possibly phenomena such as giant black holes and unseen particles, is thought to compose 22 per cent of the cosmos. Everything else, almost three-quarters of the total, is dark energy, a force that is apparently driving the universe apart.

“Your whole life as an astronomer, you learn that the universe is expanding, but it should be slowing down,” said Tod Lauer, an associate astronomer at the National Optical Astronomy Observatory who is investigating dark energy. “But we find out it’s speeding up. That’s the most incredible shock we’ve had in cosmology in the last 40 years.”

Gary Hinshaw, an astrophysicist at the NASA Goddard Space Flight Center, went even further. “It’s the biggest surprise in cosmology in 100 years,” he said.

Figuring out the nature of dark matter and dark energy is now the biggest question in the universe. NASA and the Department of Energy plan to spend billions of dollars to find the answers on Earth and in space. They’ll use giant particle colliders and new telescopes that will look at exploding stars, ancient sound waves and gravity-induced distortions of light.

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