Matt Dobbs, BSc’97, wants to solve the mystery of why the universe began to expand at an accelerated rate during its turbulent teens, a few billion years after the Big Bang 13.7 billion years ago.
Dobbs is one of the architects of CHIME (Canadian Hydrogen Mapping Intensity Experiment), a new kind of radio telescope that aims to build a 3-D map of the largely unobserved, adolescent universe when it was between about 2.5 and 7 billion years old, the largest volume of space surveyed to date.
Launched in early September at the National Research Council of Canada’s Radio Astrophysical Laboratory near Penticton, B.C., CHIME was built by a large team of scientists from McGill, the University of Toronto and the University of British Columbia.
The telescope’s main goal is to learn more about a turning point in early cosmic history, when the expansion of the universe mysteriously began to speed up due to effects of dark energy, which scientists believe counteracts gravity’s attractive force and pushes matter apart.
“We’re on the frontier in cosmology, looking at a time when the universe grew to a size that you could first see the effects of dark energy. There are no good measurements of dark energy for that critical period. We want to trace the evolution of dark energy through cosmic time and follow its growth pattern,” says Dobbs, a professor of physics and computer engineering at McGill, and co-leader of the project with scientists from U of T and UBC.
Dobbs and his collaborators conceived, designed and built CHIME as a highly specialized radio telescope that could make precise measurements of the acceleration of the universe to better understand how dark energy behaves.
Instead of using optical light, the telescope consists of four large half-cylinder reflectors (resembling snowboard half-pipes), lined with 2,048 antennas that collect signals from the faint radio waves emitted by distant hydrogen gas clouds, which evolved into the clusters of galaxies we see in the universe today.
CHIME’s 3-D mapping of the distribution of hydrogen in the universe – a technique known as intensity mapping – will be used to measure how the size of the spaces between clumps of galaxies changed from 2.5 years billion to 7 billion years of age. This data can be used to determine the expansion rate of the universe and growth pattern of dark energy.
After the Big Bang, the universe’s expansion slowed. But sometime during the adolescent phase, dark energy turned the universe’s deceleration into acceleration. “We’re looking for a growth spurt that began when dark energy took control and started driving the expansion. We want to trace dark energy’s history to see if it’s constant or changing. If you don’t understand the evolution of dark energy, it’s guesswork to predict the future of the universe,” says Dobbs, who was awarded the 2014 Canadian Association of Physicists Association Herzberg Medal, recognizing his leadership in developing new instrumentation for millimetre wavelength telescopes.
CHIME is unlike any other radio telescope because it has no round, steerable dish, no moving parts and extraordinary digital processing power. While a standard telescope must be aimed at the object being studied, this one doesn’t move and relies on the Earth’s rotation to sweep it around the sky each day.
Dobbs played a key role in designing and building the telescope’s radio correlator, a custom-built digital network and processing brain that converts the massive amount of information from radio waves into a 3-D picture of the overhead sky.
The telescope’s electronics are relatively cheap because it deploys the low-cost, high-powered components at the heart of the booming cellphone and video game industries: signal amplifiers developed for cell phones, telecommunications network switches, and sophisticated graphics cards developed for video game processors.
“It’s the largest radio correlator in the world and processes as much data per second as all the cellphones in the world,” he says.
Dobb’s technical ingenuity and eagerness to innovate were given free reign in helping to design a unique telescope with the power and sensitivity to probe the secrets of the pubescent universe.
“The scientists on our team had never built a radio telescope, which was an advantage for us in designing a novel instrument. We didn’t design something safe and were skeptical about everything that had been done before. We designed a telescope that pushed the boundaries and I’m excited because we’re developing a whole new way to look at the sky,” he says.
