Everything below is true until you check.

Five things the universe will show you, but not while you are looking. Each note is unmeasured. Press one to measure it. It will not be the same afterward. Neither will you, technically.

observable 01 · position, momentum

A particle knows where it is, roughly, and where it is going, roughly, and it will not tell you both. Pin down the where and the where-to blurs. Pin down the where-to and the where dissolves. This is not shyness about equipment. It is the universe's actual policy. You asked where. It answered, precisely, and in the same breath forgot where it was going. The knowing of one thing was paid for with the other. The bill is called Heisenberg, and it is never waived.

[ unmeasured. both readings true. press to collapse. ]

observable 02 · spin

An electron carries a tiny turning that is not really a turning, in a direction that is not really a direction, taking values off a menu with almost nothing on it. Before you ask, it holds its options open. You asked. It snapped to one of the allowed answers, instantly, like a guilty child standing straight. Whatever it was doing before your question, it is not doing it now, and it will not say what it was.

[ unmeasured. both readings true. press to collapse. ]

observable 03 · polarization

Light waves at an angle of its own choosing, every angle at once if nobody insists. A photon in flight is not being evasive. It genuinely has not decided. The filter asked: this way or that way? The photon, which had been every way, became one way. Ask it again and it will swear it was always so. Light is a very confident witness with a very poor memory.

[ unmeasured. both readings true. press to collapse. ]

observable 04 · entanglement

Two particles, prepared together, stay one question with two locations. Whatever distance you put between them, they have agreed to agree. Nobody has caught a signal passing. There is no signal. There is only the agreement. You measured one. The other, however far, settled at the same instant, as if the distance were a rumor. And in that instant the agreement was used up. Entanglement is a promise that keeping breaks.

[ unmeasured. both readings true. press to collapse. ]

observable 05 · superposition

Before the question, a particle takes every allowed option: both slits, both paths, both answers, humming all of its possible selves at once. This is not a metaphor. The interference pattern is the audit trail. After the question there is one self, one path, one answer, and a suspicious lack of humming. The other selves are not hiding. As far as the record shows, they never happened. The record was written by your question.

[ unmeasured. both readings true. press to collapse. ]

Fair objection: if the state was unknown before the measurement, how does anyone know the measuring changed it?

Because the universe left fingerprints. Run the double slit with no path detector: interference. Add a detector at the slits: the interference dies. Same slits, same light. The only new ingredient was the asking.

Because the asking can be unasked. In the eraser experiments, the which-path record is destroyed after the particle has already flown, and the interference comes back, as if the question had never been raised. Whatever collapse is, it books its charges to the question, not to the flight.

Because the choice can come late. In the delayed versions, whether to ask is decided after the particle is committed. The pattern still obeys the decision. The universe grades the exam after the answers are in and never gets caught changing them.

Because the sums only work that way. Take collapse out of the equations and the predictions stop matching the detectors. Put it back and they match to eleven decimal places. Whatever is going on, the arithmetic votes for it.

appendix · instruments of the asking

this page arrived in superposition. observables collapsed by you so far: 0 of 5. the record is permanent, and it is kept on both sides of the screen. leaving does not help. neither does another device. nobody warned you. the universe does not issue warnings.