A 100-year-old theory might explain what’s wrong with quantum mechanics

March 16, 2026

6 min read

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A 100-year-old theory might explain what’s wrong with quantum mechanics

One physicist is on a mission to get scientists to look into Louis de Broglie’s pilot wave theory

By Tim Folger edited by Clara Moskowitz

Yuichiro Chino/Getty Images

Quantum mechanics is both the most powerful theory physicists have ever devised and the most baffling. On the one hand, countless experiments have confirmed its predictions; the theory undergirds modern technology and enables the electronic devices we use every day. On the other hand, quantum mechanics describes an underlying reality that is utterly at odds with the world we perceive. In the quantum realm, a single particle exists in many places at once—at least while no one is looking at it. The theory also allows for inexplicable connectedness: a pair of atoms, no matter how widely separated, can be “entangled,” such that whatever happens to one atom instantaneously affects the other. Albert Einstein called the phenomenon “spooky action at a distance.”

These paradoxes have defined—or plagued—the theory since its inception more than a century ago. To this day, physicists still don’t agree on what quantum mechanics is telling us about the nature of reality. Are there multiple universes? Do things come into existence only when they’re observed? Is consciousness somehow central to the laws of physics? And what if all these mysteries could have been resolved right at the birth of quantum mechanics?

. That’s the case that physicist Antony Valentini, a physicist at Imperial College London, makes in his new book Beyond the Quantum: A Quest for the Origin and Hidden Meaning of Quantum Mechanics (Oxford University Press, 2026).

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Valentini argues that Louis de Broglie, a French physicist and Nobel laureate, developed a framework for quantum mechanics that eliminated its paradoxes around 100 years ago. In pilot wave theory, as de Broglie’s brainchild is known, particles are guided by attendant waves. The particles themselves are always in one position and one position only; it is the spatially extended pilot wave that creates the impression that a particle is at once here and there. There’s no need for an observer to conjure that particle into being. Even though de Broglie’s conjecture in 1924 about the wavelike nature of matter was quickly confirmed by experiment and became integral to quantum theory, the physics community discounted or misrepresented the larger ideas from which he derived his key insights.

Valentini has spent his entire career championing and extending de Broglie’s views. He recently spoke to Scientific American about his lonely path and why de Broglie might have been on to something.

[An edited transcript of the interview follows.]

In the history of science, has there ever been another situation like this, where there have been such wildly divergent views about what a theory means?

I’m not sure there has. If you go back to the time of [Isaac] Newton, he thought that space was empty and that there was a direct gravitational action at a distance. And on the continent, there were the Cartesians [followers of mathematician and philosopher René Descartes], who thought, “Oh no, space is full of this material medium, and that explains gravitational attraction.” But [the debate] didn’t last all that long. Certainly in the quantum case, the sheer variety of interpretations that say such completely different things about the world—I think it’s a pretty safe bet that there’s no analogue in the history of science.

One of the most striking things about modern physics is the stark divide between the macroscopic and quantum worlds, each of which seems to be governed by entirely different physical laws. You liken this to the way medieval astronomers split the cosmos into earthly and celestial regions.

I think it’s a useful and valid parallel, this idea that there was a heavenly realm that we couldn’t understand; anything above the moon and beyond was eternal and unchanging, completely different from the sublunar world, which was made of ordinary, imperfect matter that was always changing. It’s a distinction that goes back to Aristotle. The parallel with quantum mechanics is extraordinary, that the quantum system is something that our mind can’t understand. We can only understand the macroscopic one.

Austrian physicist Erwin Schrödinger developed quantum theory’s wave equation, which describes quantum systems as waves that evolve with time. What role did this equation play inthe