Mark Halpern and his team are in a race against time to study dark energy's role in the expansion of our universe.
Astronomer Mark Halpern doesn’t come into work every day thinking about the fact that he is leading a team that is creating the biggest map of the universe by volume ever made. But that ambition drives his research.
An professor at the University of British Columbia, Halpern is also the principal investigator of the Canadian Hydrogen Intensity Mapping Experiment, or CHIME for short, based at the Dominion Radio Astrophysical Observatory in Penticton, BC. The experiment is a collaboration between UBC, the University of Toronto, McGill, and the National Research Council of Canada. Its centerpiece is a massive halfpipe-shaped telescope that collects radio signals to detect hydrogen intensity, which is a measure of how much hydrogen is clustered in the universe, and if it has moved or spread out.
The researchers can then analyse the spread of hydrogen in the universe to determine how much—and how quickly—the universe is expanding.
“If I make a sound somewhere, it travels away from that sound in a spherical shell,” Halpern said. “So we're going to map these big spherical shells as a function of distance from us, and by comparing their present speed to how big they look, that comparison tells us the expansion history of the universe.”
The experiment officially began in September 2017, and Halpern says they should have a 3D map of the expansion of the universe viewable from Canada in about five years. “It looks like a blobby, noisy thing,” he said.
The universe hasn't stopped expanding since the Big Bang 13.8 billion years ago, and it’s happening at an increasingly accelerated rate. In the process of completing the experiment, Halpern and his team hope to learn more about the mysterious force, what they call dark energy, that is causing this expansion. Halpern said that there's twice as much dark energy as everything else in the entire universe combined, yet what it actually is remains unknown. One solid theory is that as dark energy expands, its density stays exactly constant.
“Sadly, that would be the most boring possible answer,” he said. “Sadly, it's the most likely. I'm open to surprises, but if you had to place a bet, you would bet on the boring answer.” He did emphasize that the boring answer would still mean a complete confirmation of the theory of general relativity.
Radio astronomy projects like these are important for our understanding of the universe (and potentially extraterrestrial life) but Halpern said that due to radio interference from cell phones and other frequency-emitting devices like car key fobs, it might just be a matter of time before the radio waves are so clogged up that we can’t process any incoming signals. Communications satellites have already started to use some of CHIME’s radio frequencies and Halpern expects more to come in soon. “We have about a decade in which to try really hard to make these maps.”
But for now, the project is on track to be completed within that time frame . With the increasing demand for high-end computing hardware and communications devices, Halpern and his team were able to equip CHIME with commercially available low-noise radio frequency transistors that gather two terabytes of data every second that are then processed in five truckloads of computers, at a fraction of what they would cost years ago. Astronomy has effectively never been so accessible.
“If you like putting together a computer system or fixing your bicycle, you can channel that fun into measuring how the universe began,” Halpern said. “These are experiments done by people who love to do things.”
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