The Experiment That Broke Reality

Here's an experiment you can describe in thirty seconds that has baffled physicists for over a century.

Fire tiny particles — electrons, photons, even whole atoms — at a barrier with two narrow slits. Behind the barrier, put a detection screen.

If particles were just little balls, you'd expect two bands on the screen, one behind each slit. Instead, you get an interference pattern — alternating bright and dark stripes, exactly what you'd see if waves were passing through both slits simultaneously and interfering with each other.

OK, weird. So particles act like waves. But here's where it breaks your brain:

Fire the particles one at a time. A single particle can't interfere with itself... right? But it does. Over time, individual particles build up the exact same interference pattern. Each particle somehow passes through both slits at once.

The act of observation changes the outcome. Not metaphorically. Literally. Measuring which slit a particle passes through forces it to "choose" one path — and the wave-like behaviour disappears.

Richard Feynman called it "the only mystery" of quantum mechanics. A century of physics has failed to fully explain why observation changes reality.