2025 Photon Tunnelling Experiment Measures Speeds Thousands of Times Faster Than Initial Bohmian Prediction

An experiment with photons published in the journal Nature in July 2025 has challenged a central element of Bohmian mechanics, the interpretation of quantum theory developed by David Bohm. Jan Klaers at the University of Twente in the Netherlands and his colleagues set out to study quantum tunnelling.

They found that the measured speeds of tunnelling photons reached thousands of kilometres per second while calculations using Bohm’s approach predicted a tunnelling speed of nearly zero kilometres per second.

The experiment used a laser shone into a thin layer of liquid filled with fluorescent dye molecules sandwiched between two mirrors, with the bottom mirror adorned with nano-sized patterns creating two parallel waveguides. Photons were created at the top of a designed "downward ramp" waveguide ending in a "bump" barrier.

Researchers tracked tunnelling and hopping between waveguides, using the hops as an internal clock to determine tunnelling speeds.

Klaers stated that the experiment points to issues with the guiding equation of Bohmian mechanics. "There are many guiding equations possible, and you can come up with additional models that actually produce the same particle density and are in agreement with our speed measurements," he said.

In a follow-up study, Klaers and his colleagues showed that tweaks to the guiding equation can make Bohm’s mathematics match their tunnelling experiment.

Bohm developed his interpretation of quantum mechanics, known as Bohmian mechanics, after deciding in the 1940s that the only way to understand the theory was to write a book about it. He published a pair of papers announcing Bohmian mechanics in 1952. In Bohmian mechanics, particles are always particles guided by a pilot wave and there is no wave function collapse.

The approach uses Schrödinger’s equation and a guiding equation that determines particle velocity from the configuration of all particles. It allows for non-local effects through quantum entanglement. Bohm was affiliated with several communist organisations during his doctoral studies.

He was unwilling to testify and provide evidence against his colleagues in front of the House Un-American Activities Committee. The political controversy added to resistance against his heterodox approach to quantum physics. In the 1990s, Bohm told New Scientist that he found Bohr’s idea that quantum mechanics could offer only formulae that make great predictions deeply unsatisfying.

"I said, that’s not enough. I don’t think I would be very interested in science if that were all there was," he said. Louis de Broglie formulated an idea similar to pilot waves in the 1920s but abandoned it.

In 1989, philosopher Renée Weber asked John Stewart Bell why Bohmian mechanics had been so easy to ignore. " He said that were it not for discrepancies with the mathematics of relativity, he would have adapted Bohm’s view as correct. Hui Wang at the University of Science and Technology of China stated that the velocity of tunnelling photons calculated from the team’s setup cannot be directly compared to predictions of Bohm’s theory.

"I think Bohmian mechanics is still a promising interpretation of quantum mechanics," Wang said. He stated that his own team is preparing a paper offering a resolution to Bohmian mechanics’ incompatibility with special relativity. @NewScientist reported that the 2025 Nature experiment was designed to study quantum tunnelling.

The current date is 2026-05-08 and the experiment occurred in 2025. Klaers disagrees with Wang on the interpretation of the team’s data and how they used it to calculate photons’ speeds but does not think the result rules out all ideas like Bohm’s. The follow-up study demonstrating that tweaks to the guiding equation can align the mathematics with the experiment leaves Bohmian mechanics with a new challenge while keeping it in contention.