an underdog theory

Jemma Everyhope-Roser

At Solvay, de Broglie lost, but did physics win?

You’ve probably heard of string theory, standard quantum mechanics, and general relativity. But pilot wave? No, never heard of that. The reason why goes back to the theory’s history. Antony Valentini wrote about this (and other things) in the book he coauthored, Quantum Theory at the Crossroads: Reconsidering the 1927 Solvay Conference.

This story begins in the early twentieth century, a time of revolutionary advancements in physics, at the Solvay Confer­ences in Brussels, Belgium. Some of the best and brightest minds attended these conferences: Einstein, Marie Curie, Heisenberg, Schrödinger, and Planck, to name a few.

Louis de Broglie was also there. He was from Paris, then something of a backwater in theoretical physics. His theory, pre­sented at the 1927 conference, was well regarded by figures like Einstein and Schrödinger (who adapted it but threw out the particle aspect in his famous equation).

But de Broglie’s theory wasn’t widely read. That’s because it was in French. Louis de Broglie was an isolated francophone in a world of high-powered Germanic physicists. In the end, Bohr and Heisenberg won the day. At the Fifth Solvay Conference in 1927, physicists met and debated quan­tum theory. It wasn’t exactly a popularity contest.

But what ended up happening was a “victory” for standard quantum mechanics, also known as Copenhagen quantum mechanics. After that, all other approaches were just seen as, well, wrong.

For all that, de Broglie went on to win the Nobel Prize in physics in 1929.

Sparking new thought

Now, fast forward. It was after World War II and de Broglie’s work had fallen into obscurity. A young assistant professor named David Bohm started employment at Princeton Univer­sity’s Institute of Advanced Study. Coincidentally, that was also where Albert Einstein worked. So, when Bohm published a book in 1951 defending standard quantum mechanics, Einstein criticized it. Apparently that sparked a new line of thought in Bohm, because he ended up developing de Broglie’s partial proof and demonstrating that pilot-wave theory was completely equivalent to standard quantum mechanics. But the story doesn’t end here.

Around this time, McCarthyism was burning across the country. And David Bohm, when working on his Ph.D. thesis at Berkeley under Oppenheimer, had dabbled in communism. He was recommended for and then denied access to the Manhattan Project. He was brought up to hearings again and again. When he received an invitation to work at the University of São Paulo in Brazil, he took it and got out of the country. His work was further discredited when he later turned to mysticism. For years, most physicists didn’t know about the theory or thought, vaguely, that it had been proven wrong. The few scien­tific papers that were written about pilot-wave theory dismissed de Broglie’s approach as just plain wrong and Bohm as a kooky communist.

But in the ‘80s, many physicists began to question standard quantum mechanics. The theory had problems, unanswerable questions, and just didn’t make sense. In those days, Valentini says, people were defending quantum mechanics by saying things like: “It’s meaningless to ask such questions,” and “I don’t believe any other theory can be true.” But in the last fifteen years, major­ity opinion began to change as pilot-wave theory became accepted as a legitimate theory. The criticism changed to: “Well, if it is equivalent experimentally, what’s the point in studying it then?” John Bell, after spending a year’s leave from CERN at Stanford, wrote a paper that arguably came out in favor of the de Broglie-Bohm pilot-wave theory. This paper was what prompted Antony Valentini to look for real answers to the big questions in physics.