Indexing the archive…
Your Universe of Digital Possibilities
Each quantum leaves the source, meets a barrier with two slits, and strikes the screen at a single point — a particle. Yet where the points fall is governed by interference: let them accumulate and bright and dark bands appear, as if each quantum passed through both slits at once. Then turn on the which-path detector. The instant the path can be known, the bands dissolve into one smooth blur — the wave is gone. Nothing touched the quanta but the availability of information.
Matter has a wavelength set by its momentum — the reason a particle can interfere at all. Heavier or faster ⇒ shorter λ ⇒ finer, harder-to-see fringes.
A single-slit diffraction envelope times a two-slit interference fringe. The cos² term is the interference; kill it and only the smooth envelope is left.
How far apart the bright bands sit. Wider wavelength or closer slits ⇒ wider fringes — the two spatial knobs on the panel move exactly this.
The exact trade. V is fringe contrast (wave), D is how well the path is known (particle). You can buy one only by selling the other — never both at once.
This is the experiment Feynman called the one that holds “the only mystery.” The dots arrive one at a time, each a definite, local hit — and still the crowd remembers a wave, because before it was measured the quantum took every path at once. What ends the wave is not a touch but knowledge: open a channel that could record which slit, and the interference is already gone, even if no one ever reads the record. The duality relation V² + D² ≤ 1 is the price list — every bit of which-path information is paid for in fringe contrast. It is the rack’s sharpest version of the question under all of it (docs · 05 - Research & Curiosities): if merely making the world knowable changes what it does, how much of “reality” is the thing itself, and how much is the act of measuring it?