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Quark–gluon plasma (QGP) is an extremely hot, dense state of matter in which quarks and gluons can move through the material instead of remaining confined inside ordinary particles such as protons and neutrons. It existed in the early universe and can be created for a fleeting moment in high-energy collisions of heavy atomic nuclei. Scientists study it indirectly by measuring the particles produced as the hot matter expands and cools.
What quark–gluon plasma is
Protons and neutrons are hadrons: particles made from quarks held together by the strong interaction, whose force is carried by gluons. Under sufficiently extreme temperatures and energy densities, matter enters a different regime. Quarks and gluons are no longer restricted to individual hadrons in the usual way and can move through the plasma. CERN describes them as weakly bound and able to move independently—not as particles that have stopped interacting altogether. CERN’s overview of heavy ions and QGP explains this state and how it is studied.
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Here, “plasma” means a state of matter, but QGP is not simply the familiar ionized gas found in examples such as lightning or fluorescent lamps. It involves quarks and gluons and the strong interaction. If you encounter the term “color charge” in explanations of QGP, color is a technical label in the theory of the strong interaction, not visible color.
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Why it is called the primordial soup
The name evokes the early universe, which was hot and dense enough to contain matter in a QGP-like phase. As the universe expanded, it cooled; CERN’s explainer says that quarks aggregated to form protons and neutrons a few millionths of a second after the Big Bang. That is an approximate timeline from the explainer, not a precisely timed, instantaneous switch applying identically to every part of the universe. CERN’s account of the early universe describes this cooling and aggregation.
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The comparison with a soup is a metaphor for a dense mixture of interacting constituents. It does not mean the early universe was a familiar liquid, nor that quarks and gluons behaved as completely independent particles.
How scientists create and study QGP
Collide heavy ions
At high-energy facilities, experiments collide heavy atomic nuclei, including lead or gold nuclei. The collisions briefly create matter at extreme energy density and temperature, conditions relevant to studying QGP. CERN’s ALICE experiment is dedicated to heavy-ion physics and the study of matter at extreme energy density. In the United States, Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (RHIC) is also a facility for QGP research. CERN’s heavy-ion overview and the U.S. Department of Energy’s explanation of QGP describe these research efforts.
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Infer the short-lived state from its aftermath
The hot matter produced in a collision expands and cools quickly. By the time particles reach detectors, the QGP itself is gone; researchers analyze the particles and their patterns, including correlations, to infer properties of the earlier state. The primordial universe is not directly observed in these accelerator experiments: collisions provide a way to investigate matter under relevant extreme conditions in the laboratory.
A CMS Experiment explainer gives an approximate QGP temperature threshold of 2,000 billion degrees—about 100,000 times the temperature at the Sun’s core. Treat those as explanatory figures attributed to CMS, not as a universal, sharply defined switch or a temperature measured for every QGP-producing collision. CMS’s QGP explainer provides the comparison.
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What newer small-collision results do—and do not—show
Heavy-ion collisions are not the only systems under study. In a July 2026 report, CERN said that all four main LHC collaborations reported signs that collisions of oxygen and neon may create QGP. The careful wording matters: these are signs, and the report says the collisions may create the plasma. It does not establish that every oxygen or neon collision, or every small collision system, definitively produces QGP. CERN’s July 2026 report on oxygen and neon collisions gives the finding and its qualification.
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What to keep in mind
- QGP is a state of strongly interacting matter, not a collection of particles that have ceased interacting.
- The early universe passed through a QGP-like phase; as it cooled, quarks formed protons and neutrons.
- Heavy-ion colliders recreate relevant extreme conditions briefly, and scientists infer properties of the state from collision products.
- Claims about newer small-system findings should retain the source’s level of certainty and the specific collision system being discussed.
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