It’s a fundamental property of the universe, and one that continues to blow people’s minds: photons behave as both particles and waves, matter and energy. Photons aren’t alone in this—every elemental particle is thought to act the same way—but they are perhaps the most well-known example.
Light’s split personality was first theorized back in the early 1900s, we’ve been growing more adept at detecting different aspects of wave-particle duality. Now, for the first time, physicists have captured light acting as both a wave and a particle in the same snapshot.
Fabrizio Carbone, a physicist at the École Polytechnique Fédérale de Lausanne in Switzerland, and his collaborators beamed photons into a 40-nanometer silver wire and observed what happened to a stream of electrons running along the surface of the wire. As the electrons traveled along the photon-filled wire, they were influenced by the photons directly and indirectly. When a photon hit an electron, it transferred some energy, speeding up or slowing down the electron depending on the angle of the strike. The electrons were also excited by the light’s wave-like nature, though not through direct contact.
What resulted is the stunning image of both light’s waves—which you can see along the top left-bottom right axis in the image—and its discrete particle nature—the stepped transitions running perpendicular to the waves.
Here’s Marcus Woo, reporting for Wired:
“It does appear to me as fantastic work,” says Frank Koppens, a physicist at the Institute of Photonic Sciences in Spain who wasn’t involved in the experiment. “You could indeed argue that this is showing wave-particle duality.”
This image doesn’t change known physics—if anything, it reinforces it. But by measuring how quantum forces exert their pull on electrons, it does show a way to observe quantum behaviors, which are impossible to directly monitor without disruption. And that could help us better understand what, exactly, is happening at the quantum scale.