In a striking display of quantum physics, a team of researchers has recreated one of science’s most legendary experiments—with unprecedented precision. At MIT, scientists cooled thousands of atoms to nearly absolute zero, arranged them in a neat lattice using laser light, and then used those atoms to scatter individual photons of light.
The experiment is a modern version of the double-slit experiment, designed to test whether light behaves like a wave or a particle. It’s an old question—but now answered in an impressively pure and direct way.
The results not only deepen understanding of quantum mechanics, they also prove that Albert Einstein’s explanation of the experiment fell short. His idea—that it might be possible to measure both the path of light and its interference pattern—turns out not to hold up when tested at the atomic level.
This modern approach to a classic quantum thought experiment shows what’s possible when technology meets the most abstract scientific ideas. It also clarifies one of the most famous disputes in physics, first argued between Einstein and Niels Bohr almost 100 years ago.
A Fresh Look at a Classic Experiment
The double-slit experiment is often introduced in high school classrooms to illustrate quantum weirdness. First performed by Thomas Young in 1801, it originally showed that light acts like a wave. Later, with the rise of quantum theory, it also became evidence that light behaves like a particle, or photon.
In the original setup, light shines through two slits and hits a screen. If photons acted only like particles, they would create two bright spots. Instead, they form a wave-like interference pattern, unless you measure which slit the photon passed through. Once you try measuring the path, the interference pattern disappears and the light acts like a stream of particles.
This strange result caused many years of scientific debate. Einstein argued that if a photon caused a small “kick” as it passed through a slit, its path could be traced. He believed this might let you observe both the photon’s path and the interference pattern. Bohr disagreed, using the uncertainty principle to argue any measurement would destroy the interference pattern. His explanation became a key part of quantum theory. Still, Einstein was not convinced.
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Going Smaller, Colder, and Clearer
To test this idea more purely, Wolfgang Ketterle and his MIT team used ultracold atoms. They trapped over 10,000 atoms in a tight grid using lasers and cooled them to microkelvin temperatures. That’s just above absolute zero, where atoms behave in fully quantum ways. These atoms acted as the tiniest slits ever used.
Earlier experiments used fixed slits or physical barriers. But here, each atom stood alone, identical, and ready to interact with just one photon. The researchers shone a weak beam of light on the array. Most atoms scattered only one photon each.
They adjusted the atoms’ “fuzziness,” which means how well the atom’s position was known. Fuzzier atoms gave away more information about a photon’s path. That made the interference pattern weaker. When the atom’s position was clearer, less path information was revealed. That made the interference pattern stronger. They tuned the fuzziness by tightening or loosening the laser traps. This let them control whether the light behaved more like particles or waves.
Light, Fuzziness, and Quantum Correlations
Their findings were published in Physical Review Letters. They showed the interference pattern weakens when more path information is available. This result agrees with quantum theory and supports Bohr’s interpretation. Einstein had imagined that a photon would disturb one slit, like a bird brushing a branch.
But the experiment did not support that idea. Ketterle’s team found physical disturbance or “spring” setups were not important. The key was quantum fuzziness—uncertainty in the atom’s position.
Ketterle said, “Einstein and Bohr would have never thought that this is possible, to perform such an experiment with single atoms and single photons.” “What we have done is an idealized Gedanken experiment.” Vitaly Fedoseev, the lead author, said, “We realized we can quantify the degree to which this scattering process is like a particle or a wave.” The team could measure how one photon scattered between two atoms, like light going through slits.
Cutting the Strings—And Still Getting the Same Result
To test the role of disturbance—Einstein’s “spring”—the team made a change. At first, atoms were held in place by lasers, like slits fixed by springs. In later trials, they turned off the lasers and let atoms float freely. They measured scattering in just microseconds, before gravity pulled the atoms down or made them fuzzier.
The results matched the previous ones when the atoms were held. That showed the spring-like setup didn’t affect the photon’s behavior.
Fedoseev explained, “In many descriptions, the springs play a major role. But we show, no, the springs do not matter here; what matters is only the fuzziness of the atoms.” “One has to use a more profound description, which uses quantum correlations between photons and atoms.” So it wasn’t any physical movement that caused the change. It was how much quantum information was shared between photon and atom.
A Quantum Year, A Quantum Result
The experiment came at a perfect time. The United Nations named 2025 the International Year of Quantum Science and Technology. This marks 100 years since quantum mechanics was introduced. Bohr and Einstein’s debate happened just two years after that, in 1927. Now, almost a century later, MIT scientists offer one of the clearest answers yet.
Their version of the experiment used single atoms as the tiniest slits possible. It confirmed that wave-particle duality depends on quantum uncertainty. You cannot know a photon’s path and still see its wave pattern. While this may not change quantum theory itself, it proves how far technology has come. It lets scientists revisit old questions with sharper, cleaner experiments.
Note: The article above provided above by The Brighter Side of News.
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