A choir where every singer hits the notes precisely sounds louder than you'd expect from a simple sum of voices. A hundred singers aren't just a hundred times louder than one: they're ten thousand times louder. In the world of atoms, something similar happens. In collective behavior discovered by Robert H. Dicke, synchronously emitted photons amplify each other. The brightness grows with the square of the number of atoms.

But a choir is easily ruined. Slight stochastic modeling in rhythm or off-key notes blur the overall harmony. To understand exactly how noise destroys collective emission, physicists included two effects in their model: local loss of synchronization (decoherence) and spontaneous emission by individual atoms. It turned out that depending on their strength, the system can be in three regimes: fully collective, partially collective, and independent loners.

What proved far more interesting was the boundary between these regimes. The transition from full collectivity to partial resembles the moment a choir loses its conductor: a second ago the singers held the line, and now each is singing on their own. If noise is strong, adding more atoms does not boost the light — the system works as a sum of loners. entropy imposes hard limits. Even increasing the number of atoms won't bring back the collective power.