Lucien Hardy: A quarter-century exploring physics frontiers

Lucien Hardy stepped out of an airport terminal into a Canadian winter and a scene that felt a bit surreal.

A limousine was waiting at the curb; Hardy was surprised to learn it was waiting for him. It had been sent to take him to a brand-new physics institute in a Canadian city he had barely heard of.

He climbed into the limo and was whisked off into his future.

Twenty-five years later, he describes his introduction to Perimeter Institute as if recalling snippets of a dream. It began with strange voicemails from a Canadian named Howard Burton, inviting Hardy to visit a nascent physics institute being built in a place called Waterloo. Burton’s voicemails described a sort of scientific sanctuary where Hardy could pursue his research into general relativity and quantum mechanics with total academic freedom.

Hardy was, at the time, happily ensconced in the physics department of Oxford and had no intention of moving to Canada. He tried to ignore the persistent calls from this Perimeter place.

But then Michele Mosca, a Canadian mathematician working alongside Hardy at Oxford, started talking about the new Perimeter Institute for Theoretical Physics taking shape in Waterloo, Ontario. Mosca didn’t beat around the bush: he handed Hardy an airplane ticket to Canada and urged him to use it. 

So Hardy relented, partly out of curiosity, partly to get people from Canada to stop pestering him.
 
When he stepped out of the limousine in Waterloo he did not find a gleaming new physics institute. That hadn’t been built yet. What he found was a small group of renegade deep thinkers who believed breakthroughs in fundamental physics would only come from people working together in the fuzzy regions between subdisciplines.
 

Hardy and his fellow physicists established the first incarnation of Perimeter Institute in the remnants of a post office with a stone clock tower, with Burton serving as the institute’s director. They used old hockey sticks as pointers in lectures (they still do, 25 years hence).

“I sort of think of that building, on King Street, the old post office, as the sort of spiritual home of Perimeter Institute,” says Hardy. “Because that’s where we established who we were and the atmosphere, the environment.”

Hardy and the founding researchers of Perimeter were charged with bringing to reality the audacious goal of Perimeter founder Mike Lazaridis — to build the world’s premiere fundamental physics research centre in Waterloo. 

Hardy was hooked. 

“I realized that this was a really serious endeavour and there was a lot of backing behind it,” he says. “I kind of caught the bug and I agreed to come to Canada.”

He didn’t just change countries; he also changed trajectory.

Hardy had already built a reputation in quantum foundations (the study of what quantum theory actually means, not just how to use it). His early work exploring correlations of entangled quantum particles resulted in what is now widely known as Hardy’s Paradox.

Hardy is always quick to point out that Hardy’s Paradox isn’t really a paradox at all, but rather a sign we’re “not thinking about the situation right.” 

But the name stuck, and so did the broader theme of his career: using rational, almost philosophical reasoning to understand quantum ttheory. Over his 25 years as a Perimeter faculty member, he has explored dozens of facets of the theory, and has been increasingly drawn to an axiomatic approach. 

Instead of taking the standard mathematical machinery of quantum theory for granted, Hardy has tried to rebuild it from the ground up. He looks for simple statements — axioms — that single out quantum theory from all the other ways the universe could behave.

When he arrived in Waterloo, the question became whether this axiomatic, operational way of thinking could help with the biggest open question in physics: quantum gravity.

“One of the great things about being in an environment like this is it influences you and you change your research direction,” he says. “When I came here I had some interest in quantum gravity… that’s now increasingly the main thing I’m interested in, because of people around thinking about this too. There’s never a shortage of people to talk to and ideas to think about.”

Quantum gravity aims to unify the two most foundational ideas in physics: Einstein’s general relativity and quantum theory. Each is extremely successful on its own, but they “don’t fit together… mathematically [or] conceptually,” Hardy says. 

He believes the key to that unification is to embrace, not avoid, the most radical features of each theory. General relativity treats the causal structure of spacetime as something that can curve and change. Quantum theory allows systems to be in indefinite states, neither here nor there. 

Combine those radical elements, and you’re led to a startling idea: perhaps in quantum gravity, even the causal order between events can be indefinite. For example, Event A might be before event B and after it, at least in a quantum sense. 

It’s such a counterintuitive notion that it requires a new mathematical language, which Hardy has spent more than two decades constructing. His general probabilistic frameworks can handle indefinite causal structure through a “quantum frame of reference.”

If you don’t get it, that’s normal. Hardy’s research explores some of the most mind-bending ideas in science, and he happily confesses he is befuddled much of the time. 

Hardy’s willingness to tackle the most challenging ideas is what first made him such a sought-after recruit when Perimeter was being created a quarter-century ago. 

“It’s a fun place to be,” he says of Perimeter. “There’s an acceptance, I think, that there are different ways of pursuing theoretical physics. And we do tend to work together to help each other achieve what we need to achieve.”

The old post office is no longer Perimeter’s home, though its clock tower is still visible from the fourth floor of Perimeter’s custom-built headquarters a few blocks away. 

“It feels really shocking that it’s been 25 years,” he says. “It does seem like yesterday in some ways. We’ve become the largest theoretical physics institute in the world. And certainly, to my way of thinking, the best one.”