\n<\/p>\n
When the universe first burst into being, all of space was a cosmic cauldron filled with a roiling, fiery liquid of fundamental particles heated to trillions of degrees. But this seething primordial soup\u2014the stuff of future galaxies, stars, planets and people\u2014only lasted a few microseconds. Matter\u2019s more ordinary building blocks, protons and neutrons, settled out of it as the universe expanded and cooled, and the strange stuff vanished, never to be seen again.<\/p>\n
Until, that is, it showed up 13.8 billion years later in, of all places, Long Island\u2014specifically at Brookhaven National Laboratory (BNL) around the turn of the millennium, summoned by a newly built experiment called the Relativistic Heavy Ion Collider (RHIC). RHIC was designed to recreate the universe\u2019s earliest moments by smashing together proton-and-neutron-packed atomic nuclei at close to the speed of light, rekindling the long-lost fire of creation in subatomic explosions that endured for less than a trillionth of a billionth of a second.<\/p>\n
And for the past quarter-century it\u2019s done just that, again and again, making this revolutionary replication of the early universe seem almost routine. During its record-breaking 25-year run, RHIC illuminated nature\u2019s thorniest force and its most fundamental constituents. It created the heaviest, most elaborate assemblages of antimatter ever seen. It nearly put to rest a decades-long crisis over the proton\u2019s spin. And, of course, it brought physicists closer to the big bang than ever before.<\/p>\n
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But much like the short-lived soup itself, RHIC\u2019s days were numbered and are now at an end. Today at BNL, a control room full of scientists, administrators and members of the press gathered to witness the experiment\u2019s final collisions. The vibe had been wistful, but the crowd broke into applause as Dar\u00edo Gil, the Under Secretary for Science at the U.S. Department of Energy, pressed a red button to end the collider\u2019s quarter-century saga.<\/p>\n
Dar\u00edo Gil, the U.S. Department of Energy\u2019s under secretary for science (right) and interim laboratory director John Hill (left) officially ended the operational era of the Relativistic Heavy Ion Collider at an event held at Brookhaven National Laboratory on Friday, February 6, 2026.<\/p>\n
Kevin Coughlin\/Brookhaven National Laboratory<\/p>\n
\u201cIt\u2019ll be good to sleep well for a while,\u201d says Travis Shrey of BNL, who coordinated the final run\u2014the experiment\u2019s longest. \u201cI\u2019m excited to reach the finish line.\u201d<\/p>\n
Others had more mixed emotions\u2014such as Angelika Drees, a BNL accelerator physicist. \u201cI wish I could go sit in a corner and cry, to be honest,\u201d she says. \u201cI\u2019m really sad\u2014it was such a beautiful experiment and my research home for 27 years. But we\u2019re going to put something even better there.\u201d<\/p>\n
That \u201csomething\u201d will be a far more powerful electron-ion collider to further push the frontiers of physics, extend RHIC\u2019s legacy and maintain the lab\u2019s position as a center of discovery. This successor will be built in part from RHIC\u2019s bones, especially from one of its two giant, subterranean storage rings that once held the retiring collider\u2019s supply of circulating, near-light speed nuclei.<\/p>\n
RHIC\u2019s purpose was to shed light on the strong force, the most obscure and counterintuitive of the four fundamental ways we know of that nature tugs on things.<\/p>\n
The strong force operates between quarks, the particles that physicists realized must exist when they discovered in the 1960s that protons and neutrons can be split like atoms. Three quarks come together to form protons and neutrons alike, which in turn form the nuclei of atoms.<\/p>\n
That would suggest the stuff we see all around us is, by mass, mostly quarks. But counterintuitively, the three quarks that make up a proton only sum to about 1 percent of its mass. The rest comes from the \u201cglue\u201d that binds them together\u2014particles called gluons that are constantly interchanged between quarks and, stranger still, are themselves entirely massless. How could it be, physicists wondered, that a few light quarks and a sea of massless gluons add up to the mass of a bulky, giga-electron-volt proton?<\/p>\n
Where the proton gets its spin is an even gnarlier puzzle. Like almost every other particle, protons have \u201cspin,\u201d a quantum property akin to a twirling top. The proton\u2019s quantum spin should come from its constituent quarks, but in 1987 physicists found that it didn\u2019t. To find the missing source of the spin, they realized they\u2019d need a way to shatter protons and study their innards.<\/p>\n
Even to particle physicists, quarks are slippery, almost whimsical things\u2014the six specimens have names such as \u201cstrange\u201d and \u201ccharm,\u201d and they carry an arcane analogue of electric charge called \u201ccolor.\u201d All these eccentric titles befit their elusive nature. Unlike the three other forces, the confusingly named strong force between quarks actually gets weaker, not stronger, as the particles get closer together. Quarks crammed in tight can roam about freely, but try to separate them and the glue kicks in with a vengeance.<\/p>\n
This explains why quarks and gluons behave so very differently now than they did in the first split seconds of cosmic time. In today\u2019s relatively cold and diffuse universe, quarks have settled down to sedate lives within their protonic and neutronic homes. But in the inconceivably hot and dense conditions immediately following the big bang, quarks and gluons alike were so squeezed together that they briefly behaved as one omnipresent fluid\u2014that is, the fiery primordial soup. Physicists named this distinct phase of weird matter the quark-gluon plasma.<\/p>\n
The strong force\u2019s paradoxes make its interactions incredibly difficult to predict. The behavior of even a few quarks and gluons is incalculable without the world\u2019s most advanced supercomputers. In a sense, the quark-gluon plasma seems impossible. And yet it\u2019s the origin of everything.<\/p>\n
In the early 1980s physicists began planning for what would eventually become RHIC\u2014a way to recreate that plasma and then hopefully settle the proton crises and pin down the most elusive force of nature. The trick was to concoct the plasma from precise, head-on crashes between two nuclei of a heavy element such as gold, each moving fast enough (99.995 percent the speed of light) to spit out ample quark fuel. (The technical term for such nuclei, which have been stripped of their electrons, is \u201cions,\u201d which accounts for RHIC\u2019s full name.) The facility would also, however, be able to separately send two protons colliding with precisely aligned spins\u2014something that, even today, no other experiment has yet matched. Both operating modes would rely on a pair of 2.4-mile-wide particle-storage rings\u2014which, even now, remain the largest in the U.S.<\/p>\n
When RHIC at last began full operations in 2000, its initial heavy-ion collisions almost immediately pumped out quark-gluon plasma. But demonstrating this beyond a shadow of a doubt proved in some respects more challenging than actually creating the elusive plasma itself, with the case for success strengthening as RHIC\u2019s numbers of collisions soared.<\/p>\n
By 2010 RHIC\u2019s scientists were confident enough to declare that the hot soup they\u2019d been studying for a decade was hot and soupy enough to convincingly constitute a quark-gluon plasma. And it was even weirder than they thought. Instead of the gas of quarks and gluons theorists expected, the plasma acted like a swirling liquid unprecedented in nature. It was nearly \u201cperfect,\u201d with zero friction, and set a new record for twistiness, or \u201cvorticity.\u201d<\/p>\n
For Paul Mantica, a division director for the Facilities and Project Management Division in the DOE\u2019s Office of Nuclear Physics, this was the highlight of RHIC\u2019s storied existence. \u201cIt was paradigm-changing,\u201d he says.<\/p>\n
But the collider had much more to offer. In 2023, based on RHIC\u2019s trillions of spin-aligned proton collisions, BNL physicists announced they were a huge step closer to solving the proton spin puzzle. They accounted precisely for the spin of both the quarks and the gluons. But a hefty slice remains unexplained, arising mysteriously from the two constituents\u2019 combined motion.<\/p>\n
RHIC\u2019s last smash isn\u2019t really the end; even when its collisions stop, its science will live on.<\/p>\n
\u201cMost of our scientific productivity sits ahead of us,\u201d says David Morrison of the sPHENIX collaboration, which used an eponymous detector that began collecting data at BHL just three years ago to squeeze a final set of answers out of RHIC before its closure. sPHENIX\u2019s focus was on how particularly energetic particles burst through the muck of quarks and gluons, and it proved so prolific that it generated most of the hundreds of petabytes of data gathered during RHIC\u2019s last run\u2014more than all of RHIC\u2019s previous campaigns combined.<\/p>\n
\u201cI\u2019m elated,\u201d says Linda Horton, interim director of the Office of Science at the DOE, which owns and operates BNL. \u201cThe collider\u2019s gone, but RHIC will live on through the data.\u201d<\/p>\n
In fact, data from the final run (which began nearly a year ago) has already produced yet another discovery: the first-ever direct evidence of \u201cvirtual particles\u201d in RHIC\u2019s subatomic puffs of quark-gluon plasma, constituting an unprecedented probe of the quantum vacuum.<\/p>\n
The Electron-Ion Collider (EIC) will use many of RHIC\u2019s existing components, including one of its large ion-storage rings, and is scheduled to be constructed across the next decade.<\/p>\n
Valerie A. Lentz\/Brookhaven National Laboratory<\/p>\n
RHIC\u2019s end is meant to mark the beginning of something even greater. Its successor, the Electron-Ion Collider (EIC), is slated for construction over the next decade. That project will utilize much of RHIC\u2019s infrastructure, replacing one of its ion rings with a new ring for cycling electrons. The EIC will use those tiny, fast-flying electrons as tiny knives for slicing open the much larger gold ions. Physicists will get an unrivaled look into the workings of quarks and gluons and yet another chance to grapple with nature\u2019s strongest force.<\/p>\n
\u201cWe knew for the EIC to happen, RHIC needed to end,\u201d says Wolfram Fischer, who chairs BNL\u2019s collider-accelerator department. \u201cIt\u2019s bittersweet.\u201d<\/p>\n
EIC will be the first new collider built in the US since RHIC. To some, it signifies the country\u2019s reentry into a particle physics landscape it has largely ceded to Europe and Asia over the past two decades. \u201cFor at least 10 or 15 years,\u201d says Abhay Deshpande, BNL\u2019s associate laboratory director for nuclear and particle physics, \u201cthis will be the number one place in the world for [young physicists] to come.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"
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