Flying in deep space away from the reflected light of the sun and the Earth, Euclid will spend six years seeking evidence of the “dark universe” that shapes the movements of galaxies and stars. 

“The science driving Euclid is understanding dark energy,” says Will Percival, director of the University of Waterloo’s Centre for Astrophysics and primary science coordinator for the Euclid mission. “Euclid is going after the big prize of understanding that.”

For decades, physicists have been puzzled by something almost unexplainable: the universe is accelerating in its expansion. That’s “one of the big problems in physics” because gravity and visible matter can’t explain the acceleration, says Percival. 

Since Isaac Newton formulated the gravitational theory in 1665, we’ve known how gravity shapes the movements of the planets, stars, and moons. Then, Albert Einstein taught us about the strange behaviours of physics at the speed of light a century ago. Yet math can’t quite account for how fast the universe is expanding, nor all the movements of big objects. We use the terms “dark energy” and “dark matter” to quickly explain each, but nuance escapes us.

Dark matter is unknown matter. It’s the stuff we can’t see with telescopes, which look at wavelengths of light from slow, heat-emitting infrared to frantic, high-energy X-rays. We best glimpse dark matter as it affects other objects – such as when a galaxy passes in front of a distant star, bending and magnifying the stellar light into a sharper view.

Dark energy describes how the universe is getting bigger, a discovery so monumental its huge team received a Nobel Prize for the work. But while we first saw the expansion through NASA’s Hubble Space Telescope and a team of other observatories, charting it with precision will require a sharper view. That’s where Euclid’s new mission comes in.

The new spacecraft will look at “weak lensing,” Percival explains, “which is the small distortions of galaxies because the light is travelling through them.” Euclid will also look for ripples in the normal matter telescopes can pick up, known as “baryonic acoustic oscillations.” You can think of these oscillations as space-time vibrating on the quantum scale, and those ripples all are influenced by how the universe rapidly grew in its infancy some 13.8 billion years ago.

More government support is available with the National Research Council’s Herzberg Astronomy and Astrophysics Research Center. The community was so impressed by the NRC’s work on the Canada France Hawaii Telescope – especially with how they managed petabytes of data flow from the scientific facility – that NRC will now do similar work for Euclid.

“Our job is to recycle photons,” explains Stephen Gwyn, who leads NRC science in Victoria, B.C. Photons are parcels of light that are crucial to understanding how space behaves. We can precisely chart their movements by mapping photons from galaxies and stars.

Getting Euclid’s data from deep space will take a long time. First, the telescope must find room in the European Space Agency’s busy ground stations to ferry its precious haul back to our planet from deep space. Like a zip file, the data must be compressed for the long journey.

Upon arrival, the data will then be parsed and parcelled by scientists, much of it through long-established techniques like removing small distortions from the instruments. The ultimate aim is to make the data crisp and clean for scientists to map exactly how many photons came from distant space objects, to “measure the shapes of the galaxies to extremely high accuracy,” says Gwyn.

Machine learning will also kick in as the data gets parsed. An algorithm will be trained on a catalogue of billions of objects to look for anomalies. As Euclid has yet to start observing, Gwyn says we can’t predict what the mission may find. But one example of an “anomaly” could be a redshift – a galaxy moving away from us – at a speed different than the models predict.

Through spying on shifting redshift, Euclid will likely provide “an astonishing data set for understanding how galaxies evolve over most of the history of the universe,” says Douglas Scott, a cosmologist at the University of British Columbia employing two doctoral students looking at Euclid.

“There will be literally billions of galaxies in the Euclid survey, seen from the earliest times until today,” says Scott. “For a large fraction of these, we will have good redshifts, meaning that we know how far away they are and how long ago we are observing their light.”