Experimental evidence shows how photons spread across multiple paths in an interferometer

The nature of quantum particles has long puzzled scientists. While single-particle interference suggests that a photon can behave like a spread-out wave, a whole photon is only ever detected in one specific place. Traditional interpretations of quantum mechanics often address this by suggesting the particle is in a superposition of being here and there at the same time. However, this tells us only where the particle is when it is measured, not where the particle physically is when no detector is present.