With constructor theory, the physicist, Chiara Marletto, invokes the impossible

By | May 3, 2021

Amanda Gefter writes:

They say that in art, constraints lead to creativity. The same seems to be true of the universe. By placing limits on nature, the laws of physics squeeze out reality’s most fantastical creations. Limit light’s speed, and suddenly space can shrink, time can slow. Limit the ability to divide energy into infinitely small units, and the full weirdness of quantum mechanics blossoms. “Declaring something impossible leads to more things being possible,” writes the physicist Chiara Marletto. “Bizarre as it may seem, it is commonplace in quantum physics.”

Marletto grew up in Turin, in northern Italy, and studied physical engineering and theoretical physics before completing her doctorate at the University of Oxford, where she became interested in quantum information and theoretical biology. But her life changed when she attended a talk by David Deutsch, another Oxford physicist and a pioneer in the field of quantum computation. It was about what he claimed was a radical new theory of explanations. It was called constructor theory, and according to Deutsch it would serve as a kind of meta-theory more fundamental than even our most foundational physics — deeper than general relativity, subtler than quantum mechanics. To call it ambitious would be a massive understatement.

Marletto, then 22, was hooked. In 2011, she joined forces with Deutsch, and together they have spent the last decade transforming constructor theory into a full-fledged research program.

The goal of constructor theory is to rewrite the laws of physics in terms of general principles that take the form of counterfactuals — statements, that is, about what’s possible and what’s impossible. It is the approach that led Albert Einstein to his theories of relativity. He too started with counterfactual principles: It’s impossible to exceed the speed of light; it’s impossible to tell the difference between gravity and acceleration.

Constructor theory aims for more. It hopes to provide the principles behind a vast class of theories of physics, including the ones we don’t even have yet, like the theory of quantum gravity that would unite quantum mechanics with general relativity. Constructor theory seeks, that is, to provide the mother of all theories — a complete “Science of Can and Can’t,” the title of Marletto’s new book.

Whether constructor theory can really deliver, and how much it truly differs from physics as usual, remains to be seen. For now, Quanta Magazine caught up with Marletto via Zoom and by email to find out how the theory works and what it might mean for our understanding of the universe, technology, and even life itself. [Continue reading…]

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