Invisible force

At the South Pole, the harshest environment on Earth, astronomers try to unravel the mystery of dark matter, a force greater than gravity that will determine the fate of the cosmos.

For thousands of years our species has studied the night sky and wondered if anything else is out there. In 2009, we celebrated the 400th anniversary of Galileo’s answer: Yes. Galileo trained a new instrument, the telescope, on the heavens and saw what no other person had seen before: hundreds of extra stars, mountains on the Moon, satellites of Jupiter.

Since then, we have found more than 400 planets around other stars, 100 billion stars in our galaxy, over 100 billion galaxies beyond our own, even the faint radiation that is the echo of the Big Bang.

"Now scientists think that even this extravagant census of the universe might be as out-of-date as the five-planet cosmos that Galileo inherited from the ancients. Astronomers have compiled evidence that what we’ve always thought of as the actual universe – me, you, this magazine, planets, stars, galaxies, all the matter in space – represents a mere 4% of what’s actually out there.

The rest they call, for want of a better word, dark: 23% is something they call dark matter, and 73% is something even more mysterious, which they call dark energy.

“We have a complete inventory of the universe,” Sean Carroll, a California Institute of Technology cosmologist, has said, “and it makes no sense.”

Scientists have some ideas about what dark matter might be – exotic and still hypothetical particles – but they have hardly a clue about dark energy. In 2003, the U.S. National Research Council listed “What Is the Nature of Dark Energy?” as one of the most pressing scientific problems of the coming decades.

The head of the committee that wrote the report, University of Chicago cosmologist Michael S Turner, goes further and ranks dark energy as “the most profound mystery in all of science.”

The effort to solve it has mobilised a generation of astronomers in a rethinking of physics and cosmology to rival and perhaps surpass the revolution Galileo inaugurated on an autumn evening in Padua. They are coming to terms with a deep irony: it is sight itself that has blinded us to nearly the entire universe.