Imagine a factory capable of producing a million parts per hour, yet it only makes a hundred. That's roughly how our Universe behaves when viewed through the lens of entropy — a measure of disorder that, according to physics, must only increase. The main "machines" of this factory are supermassive black holes. Their event horizons (boundaries from which nothing returns) harbor almost all the entropy of the observable cosmos — more than all the light ever emitted by stars, by a factor of ten million billion.
The authors of a new study decided to test a long-standing conjecture: perhaps the Universe deliberately grows entropy as fast as possible, igniting supernovae and nurturing black holes precisely for that purpose. They reconstructed the history of entropy production over the entire lifetime of the cosmos, separating contributions from different processes: stellar radiation, accretion (infall of matter) onto black holes, and the growth of the horizons themselves. It turned out that the rate of entropy production peaked about 3–4 billion years after the Big Bang and has been declining ever since. Meanwhile, the contribution from black hole horizons has always been $10^{16}$–$10^{17}$ times larger than everything else combined.
But here's the intriguing part: the researchers compared the actual growth rate of black holes with the theoretical "ceiling"—the fastest speed allowed by causality and gas dynamics. This ceiling is set by a simple formula: the speed of sound in cooling gas, cubed, divided by the gravitational constant. Such an ideal "vacuum cleaner" could grow a black hole to 10 million solar masses by the time the Universe was just 600–900 million years old. And it closely resembles the mysterious "little red dots" recently spotted by the James Webb Space Telescope: faint in visible light but bright in infrared, with no X-ray emission.
The authors also tested other ideas that might drive nature to maximize entropy. For instance, if among all possible paths of gas collapse, the Universe "weighed" options by their entropy gain, much like statistical physics weighs states by their probability. Or if the principle of maximum entropy production held: that any system evolves to increase disorder as fast as possible. All these hypotheses failed spectacularly, missing by a factor of $10^{16}$. The cosmos isn't chasing records. It operates with a huge margin, like a factory that could run at full capacity but deliberately keeps its pace at thousandths of a percent of what's possible. Something else, perhaps the complex physics of magnetic fields and radiation feedback, sets its rhythm.
The total entropy of all stars, planets, and interstellar gas in the entire visible Universe is roughly equal to the entropy of a single supermassive black hole of average mass.