Why is a particle here and not there?

For almost a century, physics has lived with a problem it cannot settle.

Quantum mechanics describes an electron with a wave function, a wave spread through space. The textbook account says that until the electron is measured it has no definite position, only a spread of possibilities, and that measurement makes the wave "collapse" so the electron appears in one place. The mathematics has never failed a test. What it means has never been agreed. What counts as a measurement? Why should measuring do something no other physical process does? Physicists have argued about this since the Solvay Conference of 1927, and they still disagree.

Rest-State Inversion Theory answers it by correcting a case of mistaken identity. The electron was never the wave.

The knot and its guide

In RSI the universe is a physical medium under tension, the Eternal Consonance, filling space the way water fills an ocean. Particles are knots tied in it. An electron is a loop that must turn a full 720 degrees to return to its starting state, a behavior quantum mechanics describes mathematically but never pictures. A knot is always somewhere. What spreads through space is the flow of the medium around it, and that flow guides where the knot goes. The wave function describes the guide, not the electron.

This idea has a distinguished history. Louis de Broglie proposed it in 1927, and David Bohm completed it in 1952. Their pilot-wave theory reproduces every prediction of quantum mechanics with particles that always have definite positions. What it never had was an answer to the obvious question: a wave in what? RSI's answer is the Eternal Consonance.

Why the results are probabilities

If the electron is always somewhere, why can we predict its landing place only statistically? Because we never know exactly where each knot starts. Bohm showed that when starting positions are spread the way the wave is spread, outcomes follow quantum mechanics' probability rule exactly and continue to do so. The randomness is like a coin toss: real in practice, and rooted in what we cannot know about each beginning.

The double-slit experiment, as it actually happens

Fire electrons one at a time at two slits, and each one arrives as a single dot in a single place. Only after thousands of dots does a striped interference pattern appear. Akira Tonomura's team at Hitachi filmed this dot by dot in 1989.

In RSI each electron passes through one slit. The medium, being continuous, flows through both, and on the far side its flow carries the shape of both openings. Each knot follows that flow toward the bright stripes and away from the dark ones. The pattern is not one electron in two places. It is many electrons, each in one place, following a guide shaped by both slits.

Recording, not watching

Popular accounts say the pattern disappears when someone watches. No one needs to watch. It disappears whenever anything records which slit the particle used, whether a detector, a stray atom or a single scattered photon, even if no one ever reads the record.

Nor is the cause simply that the detector knocks the particle off course. In 1998 Stephan Dürr, Thomas Nonn and Gerhard Rempe marked which path atoms took with a kick far too small to blur the stripes, and the stripes vanished anyway.

RSI explains why. A detector is made of knots too. The moment it records a path, its state is tied to the flow: the part of the flow through the left slit is joined to a detector reading "left", and the part through the right to one reading "right". Those two parts can no longer combine at the screen, so the stripes are gone. The knot travels in one part, and the other part no longer steers it. That is all "collapse" ever was. Nothing jumps, and nothing needs to be observed.

The uncertainty principle stands

A wave that is narrow in space must be built from many wavelengths, and a wave with a single wavelength must spread wide. That is true of sound and of water, and it is true of the medium. No experiment can prepare knots with both a sharp position and a sharp momentum, because no guide can be both narrow and pure. The limit is real, and its source is the wave nature of the medium, not a mystery about the particle.

Paths can be measured

In 2011 Aephraim Steinberg's group in Toronto used gentle "weak" measurements to reconstruct the average paths of single photons through two slits. The paths bend toward the bright stripes, just as the pilot-wave picture describes. How best to interpret such measurements is still debated, but they show paths where the textbook account says there are none.

A separate question: entanglement

Entanglement is often mixed up with collapse, but it is a different question. Collapse asks why a measurement gives one definite result, and RSI's answer is that the particle was always somewhere. Entanglement asks how two particles far apart can stay linked. Experiments testing Bell's theorem, honored with the 2022 Nobel Prize, show that no local mechanism can explain their correlations; in any theory where particles always have definite positions, as in RSI, the link must be instantaneous, though never usable to send a signal. RSI locates that link in the incompressibility of the medium, where a change in pressure anywhere is felt everywhere at once. The full account is in the paper and in the companion article, The particles were never separated.

What changes, and what does not

RSI changes no prediction of quantum mechanics. Every result quantum mechanics predicts, RSI predicts too. What changes is what the mathematics is about. The electron is always somewhere. The wave function does not collapse. The medium's flow changes, and the knot follows.