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What are neutrinos and why do they matter?

WATCH ABOVE: Canadian scientist Arthur McDonald discusses his groundbreaking work on neutrinos which won him the 2015 Nobel Prize for Physics

After a Canadian scientist was named one of the winners of the Nobel Prize in Physics Tuesday morning, you might wonder for what exactly he won the prestigious prize.

It’s all about the universe.

Arthur McDonald, a professor emeritus at Queen’s University and the director of the Sudbury Neutrino Observatory (SNOLAB), shared the prize with Japanese scientist Takaaki Kajita for their groundbreaking work on neutrinos.

Our universe is comprised of many particles: protons, neutrons, electrons, photons and neutrinos are five of the most common.

Aside from the photon, neutrinos are the most abundant particle in the universe. And when we say neutrinos are abundant, they are everywhere.

These incredibly small, almost massless particles that travel at almost the speed of light, are part of the building blocks of our universe. Which is why physicists are want to figure them out.

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“The universe is kind of lumpy. There are stars, planets and galaxies and empty space in between,” said Clarence Virtue, a physics professor at Laurentian University who has worked on experiments at SNOLAB. “If you smeared all that out uniformly, the average density of the universe is about 1 proton per cubic metre. That’s very, very thinly spaced. So there’s a lot of empty space out there. And the number of neutrinos per cubic metre is somewhere  about 300 million.”

WATCH: Queen’s professor awarded Nobel Prize in Physics

“If you really want to understand the universe, its evolution, you probably have to understand neutrinos as well.”

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The experiments conducted by McDonald and Kajita show that neutrinos change identities as they travel — changing from muon, tau or electron — something that can only happen if they definitively possesses mass. This didn’t fit with particle physic’s Standard Model, which explains and predicts how matter interacts in our universe.

The Nobel-winning experiments are an important breakthrough, with the implication that the Standard Model needs to be revised to account for neutrinos having mass.

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McDonald observed the neutrinos as they travelled from the sun down to SNOLAB, a facility that lies two kilometres underground. The experiments are conducted so far underground as a way of reducing the signal-to-noise ratio. In particular, there is a need to reduce cosmic rays, a form of high-energy radiation that penetrates our atmosphere, with some eventually reaching the ground — and me and you. Because neutrinos are so weak, it’s especially important to reduce that signal-to-noise ratio.

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SUDBURY NEUTRINO OBSERVATORY

“By going two kilometres underground you get rid of almost all of the cosmic rays; you knock them down by a factor of a million or so,” Virtue said.

“Sitting here on the surface, you and I are traversed by comic rays several times per second. And if you go underground, you can spend an entire 40-hour work week and not be hit by a single one.”

Fundamentally, the research is helping us understand the inner workings of our universe and the attempt to answer the question: How did we get here?

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