A hundred years ago this week, at the height of the quantum revolution, Austrian physicist Erwin Schrödinger submitted a manuscript for publication. Its centerpiece was an innocuous-looking equation that would alter science’s entire conception of reality.
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Even now the Schrödinger equation remains physicists’ foremost window into the quantum realm. It tells scientists how that strange world works; that is, how quantum objects interact with their surroundings. But in doing so, it sets the mysteries of quantum mechanics, many of which elude understanding to this day, in stark mathematical relief.

A full century after Schrödinger penned his famous equation, scientists and philosophers are still seeking to define, and expand, its hazy boundaries. It does a great job describing the quantum systems that physicists study in their labs. But should the physicists themselves really be left out of the equation?

As nonsensical as this question may seem, attempts to answer it are already offering new and surprising lessons about the quantum world. Inserting the observer into the Schrödinger equation, it seems, allows transformative new perspectives on century-old questions.

“We've been trying to do physics as though it’s just there,” says Anne-Catherine de la Hamette, a physicist at the Swiss Federal Institute of Technology Zurich. “And we forgot to ask, ‘Well, who is actually measuring stuff?’

Before Schrödinger’s 1926 breakthrough, the quantum revolution was in full swing but had mainly produced a hodgepodge of confounding truths. A particle could apparently be located in two places at once. Solid objects would sometimes act like ethereal waves of probability. Measuring an electron’s spin on Earth could tell you instantaneously the spin of its entangled partner on Mars.

The Schrödinger equation gave physicists a handle on this weird world. It determines the wave function, a mathematical object, technically, a complex-valued function of probability amplitudes, that captures all of a quantum system’s myriad possibilities. If you have an electron’s wave function, you can calculate how likely you are to find it in one place versus another.

The equation says how the wave function evolves over time but only while the system is left unobserved. The moment you check on, say, the position of an electron, its wave function “collapses,” instantly snapping from a cloudlike distribution of possible places the particle might be to a narrow peak where it actually was. Experts still aren’t sure how the act of measuring disrupts the quantum system, but it’s unavoidable, the “measurement problem” remains the central mystery of quantum mechanics.

Note: Excerpted from "For its 100th birthday, the Schrödinger equation is getting a glow-up from quantum physicists” - ScientificAmerican.com, Joseph Howlett, Lee Billings, January 28, 2026