Starting with a Bang

Nobel laureate Arthur McDonald unravels mysteries that all started with a big bang

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Canadian astrophysicist and Nobel laureate Arthur McDonald, center, meets The Big Bang Theory cast (Credit: Queen’s University)

Nerdy genius Sheldon Cooper from the popular sitcom The Big Bang Theory would struggle to contain his jealousy if he got to meet Arthur McDonald – because McDonald won the Nobel prize and he hasn’t.

“And my high-school sweetheart, Janet, was hot. She still is after being my wife of 50 years,” joked McDonald, the astrophysicist whose work has earned the respect of many, including a former student, David Saltzberg, science consultant of The Big Bang Theory.

The real-life science whiz at Queen’s University in Canada was awarded the prestigious award in 2015 for solving a long-standing mystery in fundamental physics: the properties of neutrinos, known colloquially as the ghost particles.

Neutrinos are one of the basic building blocks of our world. Their origin can be traced back to the period immediately after the Big Bang.

They hold the key to define how our universe evolves, how we can better observe supernova and black holes, and how the sun burns.

But neutrinos have certain unusual properties that make them extremely difficult to detect. They don’t carry electric charges so they don’t behave the way electrons do. They do not experience the strong interaction which binds quarks and protons in a nucleus.

Before McDonald’s discovery, scientists knew little about neutrinos, except that they are produced in the core of the sun, passing through the Earth in enormous quantities. In fact, hundreds of billions of them are going through your body at this moment.

“We are oblivious to their existence,” said McDonald. “For the type of neutrino – electron neutrino – we were studying, five millions go through something the size of your thumbnail every second. Maybe once in your lifetime, they’ll stop in your body.”

In 1984, a group of 16 scientists came together when a physicist, Herbert Chen Hwa-sen, at the University of California at Irvine tried to borrow C$3 million (HK$18.05 million) worth of heavy water from the Canadian government to build a neutrino detector.

No scientist had tried constructing such a facility before. The required engineering was a technological challenge. To build an effective detector, one has to first make a hole deep enough to get rid of the interference from other particles coming from outer space.

McDonald was a tenured professor at Princeton University at the time. He recalled the long journey from conception of the experiment to design, construction, commission and data analysis that ultimately led to the evidence that won him a Nobel prize.

“The cavity that we excavated was in an active nickel mine where thousands of tons of ore moved out in a day. The facility is the size of a 10-story building. No one had ever been able to dig a cavity that size at that depth before,” he said.

“We had to construct an acrylic sphere 12 meters in diameter, and five centimeters thick. The company that built it had to develop new techniques to do something no one had done before. It took us 2.5 years just to build the sphere.”

The Sudbury Neutrino Observatory, located in Canada, did not start operating until 1999. The facility was where McDonald and his large international team discovered that neutrinos can change identities, known as “flavors,” transforming themselves between electron-, muon- and tau-type.

The metamorphosis requires neutrinos to have mass, dispelling the long-held notion that they were mass- less. McDonald’s data have altered how scientists understand the innermost workings of neutrinos.

His measurements also verify our understanding of how the sun burns, leaving open the possibility of reproducing on Earth the nuclear fusion that powers the sun, and thus, developing a new energy source that will benefit mankind.

Scientists from Hong Kong play a substantial role in some of the latest neutrino research. There is a group from the University of Hong Kong working at the Large Hadron Collider at CERN in Geneva, McDonald said.

Another physicist at Queen’s University, named Mak Hay-boon, worked with McDonald to develop the Sudbury Neutrino Observatory. McDonald is building a new facility nearby, which will open next year, to work on neutrino double beta decay.

“A physicist named Wang Yifang, whom we shared another prize with last year, made his measurements at the Daya Bay reactor. He is doing another experiment at the Jiangmen Underground Neutrino Observatory in southern China,” he added.

McDonald has retired from teaching, but he is still active in neutrino research, including working on a paper about dark matter particles that will be published this summer. As life imitates art – or vice versa in his case – the astrophysicist is well on his way to unraveling a new mystery that all started with a big bang.

“This is what you do in basic physics. You keep track of the most important things internationally, look for opportunities where your skills and background can do something earth-shattering, and during the process, push the boundaries of technology,” he said.

The article first appeared in the Standard on July 11, 2017.