The Double-Slit Experiment: The Simple Test That Broke Common Sense Physics

In the early 1800s, physics felt settled. Light behaved like a wave. Matter behaved like solid stuff. Cause led to effect. Observation did not interfere with reality. Then a deceptively simple experiment punched a hole straight through that confidence. Two slits. A screen. And results so strange that even today, physicists argue about what they actually mean. An Experiment That Looked Almost Childish The setup was harmless. A barrier with two narrow slits cut into it. Behind it, a detection screen. When light was shone through the slits, something expected happened: an interference pattern appeared—bright and dark bands caused by waves overlapping. This confirmed light’s wave nature. No controversy. But when scientists later replaced light with particles—electrons—the universe stopped behaving.…