Canadian scientists try to shed light on dark energy

In a secluded valley near Penticton, B.C., a team of Canadian scientists is going after the big picture – no, make that the BIGGEST picture.

Using a radio telescope of novel design, the group aims to build a three-dimensional map of the universe ranging from 7 to 11 billion light years from Earth, the largest volume of space surveyed to date.

Their goal is to home in on a turning point in cosmic history, when the expansion of the universe mysteriously began to accelerate. Understanding what is causing the acceleration is considered one of the most pressing – and challenging – problems in physics.

"This really is the frontier," says Matt Dobbs a cosmologist at McGill University who is working on the electronics behind the new telescope. "We're looking at the place where a big discovery could be made."

Construction of the telescope began last week following confirmation on Jan. 15 from the Canadian Foundation for Innovation that it will underwrite 40 per cent of the project's estimated $11.5-million price tag – a modest sum relative to most large experiments in astronomy and physics. The remaining funding will come from provincial governments and other sources.

Dubbed the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, the telescope's objective is to map the clouds of hydrogen gas that are known to permeate the cosmos in a web-like structure. Although invisible to optical telescopes, the gas emits a telltale radio signal that astronomers can use to pinpoint position on the sky and distance in space, the information needed to build a 3D map.

But CHIME will also reveal the way the universe has changed over time, since the radio signals from the most distant portions of the map, travelling at light speed, will have taken longer to reach Earth than those from the nearest portions. Lying somewhere in between is the moment in cosmic time when the stately, outward expansion of space – a process under way since the universe began some 13.7 billion years ago – began to speed up.

"I think it's our best shot at gaining evidence that guides us to understanding how the universe can be this way," says Ue-Li Pen, a researcher at the Canadian Institute for Theoretical Astrophysics in Toronto whose work revealed the potential of the hydrogen mapping technique.

First detected in 1998, the acceleration of the universe is a Nobel-prize-winning discovery that has become a mystery of cosmic proportions. Dark energy is the leading explanation behind the acceleration: a weird form of energy that is embedded in the vacuum of space itself, subjecting the universe to a constant outward push that makes it expand ever faster. But some maintain the idea is a fiction and that the acceleration is a sign that physicists' understanding of how gravity works over cosmic distances is incorrect.

CHIME is not the first experiment looking to measure dark energy, but it is well positioned to observe the crucial period when the phenomenon began to take effect. That epoch lies beyond the reach of optical surveys that measure the acceleration by mapping the distribution of individual galaxies.

"That third dimension really makes it a powerful probe," says Josh Frieman, a cosmologist at the Fermi National Accelerator Laboratory near Chicago and director of the Dark Energy Survey, a U.S. effort to measure cosmic acceleration in two dimensions with an optical camera based in Chile.

Last week NASA announced it would partner with the European Space Agency on a telescope called Euclid, expected to launch no sooner than 2020, that will study the effect from space.

The CHIME telescope will be operating far more quickly and cheaply, in part because its simple design, made up of five 100-metre-long collectors, each curved like a skateboarder's half-pipe, has no moving parts. Instead it will rely on the rotation of the Earth to sweep the telescope around the sky, gradually building up its 3D map, which should be completed in four years.

The telescope is located at the Dominion Radio Astrophysical Observatory in the B.C. interior, where protection from man-made signals will allow it to pick up the faint radio whispers of hydrogen gas in deep space.