Double Slit Experiment explained! by Jim Al-Khalili

This segment introduces the fundamental enigma of quantum mechanics, highlighted by Richard Feynman as the essence of quantum weirdness, using the double-slit experiment as an illustration. Initially, the experiment is described using monochromatic light to demonstrate wave interference patterns, showcasing classical physics principles. The narrative progresses to replicate the experiment with particles like grains of sand, which instead of an interference pattern, form two distinct piles, demonstrating particle behavior. The true quantum mystery unfolds when atoms are used instead of light or sand, revealing an interference pattern similar to light waves, even when atoms are fired through the slits one at a time. This phenomenon challenges classical intuition, suggesting atoms exhibit both particle and wave-like behaviors, defying simple categorization and illustrating the core quantum mechanics puzzle.

The second paragraph delves deeper into the quantum conundrum by conducting the atom double-slit experiment slowly, sending atoms through one at a time. Remarkably, even when atoms are fired singularly, they contribute to the wave-like interference pattern over time, suggesting each atom interacts with both slits simultaneously. The mystery deepens when a detector is introduced to observe which slit an atom passes through, resulting in the disappearance of the interference pattern and the emergence of two distinct bands, mirroring classical particle behavior. This implies the act of observation alters the outcome, a phenomenon further complicated when the detector is secretly disconnected, and the interference pattern returns. This suggests atoms behave differently when observed, a cornerstone of quantum mechanics that challenges the boundaries of classical logic and highlights the peculiar nature of quantum entanglement.