Wigner's Friend Experiment

Wigner's Friend experiment explores how different observers might perceive a quantum event differently. Imagine a friend inside a lab measures a quantum system, like a particle's spin, and sees a definite outcome. Outside, Wigner treats the entire lab, including his friend, as a quantum system in a superposition (multiple possibilities). The paradox raises questions: Does the friend's observation collapse the quantum state? Is Wigner obligated to see a superposition until he checks? It highlights the strange nature of quantum measurement and how observation affects reality, prompting debates about whether reality is observer-dependent.