Turning light on its head.

The article focuses on the longstanding debate over whether light behaves as a wave or a particle, a question that has been experimentally settled in 2025 through modern realizations of thought experiments originally proposed by Albert Einstein and Niels Bohr. Using ultracold atoms as “springy slits,” research teams at the University of Science and Technology of China (USTC) and the Massachusetts Institute of Technology (MIT) demonstrated the trade-off predicted by Bohr’s complementarity principle: the clearer the particle-like path information obtained, the more the wave-like interference pattern diminishes. These experiments confirm that light exhibits both wave and particle characteristics simultaneously, though not with perfect clarity, resolving a century-old quantum physics debate with advanced atomic physics techniques. [Extracted from the article]