Physicists with the STAR collaboration have observed particles emerging directly from empty space during high-energy proton collisions at Brookhaven National Laboratory. The experiment provides strong evidence that mass can arise from vacuum fluctuations, as predicted by quantum chromodynamics. Quark-antiquark pairs promoted to real particles retained spin correlations tracing back to the vacuum.
The STAR collaboration, an international team at the Relativistic Heavy Ion Collider in Brookhaven National Laboratory, New York state, smashed high-energy protons together in a vacuum. This produced a spray of particles, including rare quark-antiquark pairs pulled from vacuum fluctuations. These pairs, which normally vanish quickly, gained enough energy to become detectable hyperons with correlated spins inherited from the vacuum's quantum disturbances, according to quantum chromodynamics theory (QCD). The hyperons decayed in less than a tenth of a billionth of a second, but the spin alignment persisted, confirming their vacuum origin. The team traced these origins for the first time, as reported in Nature (DOI: 10.1038/s41586-025-09920-0). Zhoudunming Tu, a STAR collaboration member, stated, “This is the first time we’ve seen the entire process.” The finding could allow direct study of vacuum properties and how quarks acquire mass through vacuum interactions, Tu added. Daniel Boer at the University of Groningen, who was not involved, welcomed the measurement, saying, “I’m very happy to see this measurement.” He noted ongoing mysteries, such as why quarks cannot exist alone. Alessandro Bacchetta at the University of Pavia cautioned that the result is not yet definitive, urging researchers to rule out other explanations for the signal amid the complexity of collision reconstructions.