Schrödinger's cat is alive and dead at the same time: so goes the famous paradox. But no one has ever seen such a cat. The macroscopic objects around us always sit in one definite state, not in a superposition of several. So why is the quantum world, which allows opposites to coexist, so categorical on large scales? The standard answer appeals to decoherence: interaction with the environment destroys the fragile quantum superposition, turning it into a mixture of classical alternatives. But this explanation is incomplete. It doesn't say why exactly one outcome materializes out of many possibilities, or with what probability. The Born rule, which links the square of the amplitude to probability, has to be introduced as a separate postulate rather than derived from the theory itself.

A new paper offers an elegant way out. Instead of viewing a macroscopic object as a single whole, the author treats it as a vast ensemble of microstates. Each macrostate, for instance "cat alive" or "cat dead," contains an astronomical number of microscopic realizations, differing in the positions of atoms, their momenta, their spins. When we move from the exact Schrödinger equation for all microscopic degrees of freedom to an equation for macroscopic amplitudes, something remarkable emerges. The matrix elements connecting different macrostates behave like white noise: a random signal with no correlations in time. This internal noise, generated by the ensemble of microstates itself rather than by the external environment, acts like a tireless conductor, keeping a crowd of microscopic possibilities moving in step. And here is the result: the superposition of macrostates collapses rapidly, leaving only one.

The equation for macroscopic amplitudes turns out to be reducing: it exponentially suppresses all superpositions, leaving only one macrostate. The survival probability of each state equals its initial squared amplitude, which exactly reproduces the Born rule. No nonlinear terms need to be added: nonlinearity appears automatically from the transition to macroscopic variables. This makes the solution to the measurement problem more economical and consistent with known physics. Previously it was unclear why macroscopic superpositions are not observed, even though the Schrödinger equation permits them to exist. Now it has been shown that the ordinary Schrödinger equation itself collapses macroscopic superpositions through the internal noise of microstates. The Born rule is derived, not postulated.

The result matters for the interpretation of quantum mechanics and for experiments aimed at creating macroscopic quantum states. It could also shape our understanding of quantum computing, where macroscopic superpositions of qubits must be protected from collapse. One can test the prediction about the maximum size of a superposition that can still exist. The condition ΔE·ΔX ≫ ħc sets the boundary between quantum and classical behavior. Experiments with massive objects, such as nanoparticles or mechanical oscillators, could check whether superpositions really vanish faster than ordinary decoherence predicts.

So Schrödinger's cat stops being a paradox. It is not alive and dead at the same time, because the crowd of microstates making up its body calms itself down in vanishingly small fractions of a second. The internal noise that is usually considered a nuisance here plays the role of the creator of classical reality. And this is not science fiction but a direct consequence of an equation discovered almost a hundred years ago.