This episode explores the fascinating and often perplexing world of quantum mechanics.●It begins by examining the fundamental challenge posed by locally hidden variables, a concept that suggests there might be a deeper level of reality underlying quantum phenomena.●It then discusses the Aspect and Grangier experiment, which used a Mach-Zehnder interferometer to demonstrate the wave-particle duality of light. The experiment showed that photons behave as waves, exhibiting interference patterns, even though they are detected as individual particles.●The episode then explores the measurement problem, which highlights the difficulty of defining the boundary between the quantum realm and the classical world we observe. It raises questions about how the act of measurement affects quantum systems and whether reality exists independently of observation.●Next, the episode focuses on John Wheeler's delayed-choice experiment, a thought experiment that challenges our understanding of causality and time. In this experiment, a photon appears to "choose" its behavior (particle or wave) retroactively, depending on the presence or absence of a beam splitter, even though this choice seemingly violates the temporal order of events.