MIT physicists have performed the most precise version of the famous double-slit experiment, using ultracold atoms and single photons to reveal the strange dual nature of light as both wave and particle.

This quantum balancing act—long debated by Einstein and Bohr—was tested without traditional “spring” components, instead relying on atomic “fuzziness” to confirm Bohr’s view: you can’t observe both properties at once. The experiment not only showcases the subtleties of quantum mechanics but also revisits and resolves a historic scientific rivalry