PART 11 · QUANTUM EXPERIMENTS
The Double-Slit Experiment — Observation and Creation
One particle, two paths, and a pattern that appears only when we do not ask which path.
1Two paths, one wave
Send photons or electrons one at a time: each detection is a single dot.
After many detections, the dots build bright and dark interference bands.
This is the memory image: two slits, but many bands.
Interference comes from quantum amplitudes; no appeal to human consciousness is required.
2When we ask which path
A path detector makes which-slit information physically available.
The interference bands disappear and the distribution approaches two main clumps.
What matters is the measurement interaction and distinguishability of the paths.
Remember: which-path information ↔ loss of interference.
3The image to keep
Left: two slits → many bands. Right: path measurement → two clumps.
One picture, one rule: “If you can tell which way, you lose the stripes.”
Interpretations differ on what this means about reality.
Foundational references: Young; single-particle interference experiments; standard quantum mechanics texts.
◦Three things to remember
The image that should stay with you
From interference we move to an experiment that challenges the idea of local hidden properties.