Rob Spekkens: a detective descrambling reality

Rob Spekkens describes his job, at times, as unscrambling an omelet.

He’s borrowing the phrase from another physicist, E.T. Jaynes, who applied the term to the challenge of truly understanding quantum theory and its implications.

For Spekkens, the omelet is made of two thoroughly scrambled facets of quantum theory: claims about what actually exists in the world, and claims about what we are able to know about it.

“A lot of what I’ve been trying to do,” Spekkens explains, “is sort of unscramble the omelet.”

He wants to understand the constituent ingredients of reality, which requires both the the precision of a physicist and the perspective of a philosopher; thankfully, Spekkens is both.

Long before he was devising equations on quantum states or causal models, Spekkens was drawn to what he calls the “why questions.” He discovered philosophy before physics, when he was still in high school, and he was drawn to its focus on rational argumentation.

As an undergrad at McGill University, Spekkens pursued a joint degree in physics and philosophy — a five-year program he describes as “perfect for me.”

“In philosophy,” he says, “you learn how to make a really bulletproof argument. You learn how to figure out what are the key assumptions in an argument.”

Spekkens specializes in the field of Quantum Foundations, which aims to refine and reformulate quantum theory in ways that express its true nature and structure. More than a century after its formulation, scientists around the world — Spekkens among them — are still making sense of its meaning and implications.

“It’s a bit surprising,” says Spekkens, “that still, scientists don’t agree on what quantum theory says about the nature of reality.”

These are deep questions, perhaps the deepest, about how the universe really works. Spekkens isn’t the “shut up and calculate” type of physicist who can happily accept that quantum theory simply “works.” Spekkens wants to explain how and why it works. 

“I might be able to drive a car really well,” he says, “but I might not be able to tell you exactly how it works.” Quantum theory, in his view, is a technology that scientists have learned to operate fluently without actually understanding what’s happening under the hood.

“Typically,” he says, “if you understand some technology and how it works, it allows you to use it better.” 

Understanding how something works often requires taking it apart and putting it back together again. Sometimes you have to really examine all the component parts to know how they contribute to the whole.

The universe is complicated, so physicists often create simple, stripped-down versions of it called toy models. Early in his career, Spekkens developed one that now bears his name. The Spekkens toy model is a simplified framework that reproduces quantum features using classical systems that are constrained by limits on what observers can know. The toy model shows that some of the bizarreness of the quantum realm may emerge from limits on what we know, not necessarily from reality itself being bizarre.

Demystifying quantum theory requires a deep understanding of cause and effect, which led Spekkens to take up – and in fact help jumpstart – the emerging field of quantum causal inference.

“The field of causal inference tries to disentangle causation and correlation,” he explains. The rules of cause-and-effect that we experience in the everyday world can get messy when applied to complex systems, or to fundamental physics, and require careful detective work.

Many quantum paradoxes, Spekkens realized, have the same logical structure as classical causal puzzles and philosophical conundrums, where mistaken assumptions about influence and inference create apparent contradictions.

A faculty member at Perimeter since 2008, Spekkens launched and leads the institute’s Quantum Causal Inference Initiative, which brings together physicists, statisticians, and AI experts to rethink quantum theory with causal tools.

For Spekkens, physics is a state-of-the-art, ever-evolving toolset for disassembling ancient philosophical questions and looking for clues like Sherlock Holmes. Fittingly, Spekkens described himself as a “causal detective” in a 2020 public lecture he co-delivered with Perimeter colleague Elie Wolfe. And now he’s got his hands on one of the biggest scientific ‘whodunits’ of all time: the case of the scrambled quantum omelet.

Like Holmes, Spekkens and his team look for hidden connections, separate cause from coincidence, and resist jumping to conclusions that don’t fit the facts. The stakes are high:  the reward for probing this mystery might be a new understanding of quantum theory, one that has remained out of reach for a century.