The universe is expanding at an accelerating rate, like dough that keeps rising faster even though the yeast ran out long ago. For twenty years, astronomers have been searching for the cause and call it dark energy. But what it is remains a mystery.
New work proposes an unexpected source: the vacuum inside the atomic nucleus. More precisely, the vacuum of quantum chromodynamics — the theory describing how quarks stick together to form protons and neutrons. This vacuum is not empty: special clumps of fields constantly pop in and out of existence, like knots on an invisible fabric. As space expands, this "fabric" stretches, and the knots create a global tension: that very dark energy. No new particles or fields are needed.
The authors tested the model for the first time against the full set of cosmological data: cosmic microwave background from Planck, ACT, and SPT-3G, baryon acoustic oscillations from DESI, and type Ia supernovae. The model didn't just fit: it proved more convincing than the standard cosmological constant ΛCDM. Moreover, it naturally behaves like some exotic theories but without their problems. For example, at intermediate redshifts (around z~0.67), dark energy temporarily becomes "phantom"—its density grows faster than usual, but without catastrophic instability.
The expansion of the universe ceases to be a puzzle of a separate substance. Perhaps it is simply the breathing of the vacuum we already know — the very one that binds matter inside us. The dough rises not because of a secret ingredient, but because the flour itself harbors a hidden power.
The density of dark energy predicted by the model roughly matches the energy contained in the volume of a proton if "smeared" across a cubic meter of space. One proton per cubic meter, and the universe goes haywire.
In Stanisław Lem's novel "Solaris," the planet's ocean was a single thinking structure. Here, the QCD vacuum is a silent ocean whose tension governs the expansion of the cosmos.