The Largest U.S. Particle Collider Has Shut Down, Ending One Era and Quietly Beginning Another

The long circular tunnel beneath the pine barrens in Upton, New York, came to a halt on a calm winter morning. For 25 years, atomic nuclei were flung around the 2.4-mile ring of the Relativistic Heavy Ion Collider at almost the speed of light, and they were violently and precisely smashed together. Then it stopped abruptly.

Computer monitors inside Brookhaven National Laboratory’s control room were still glowing, showing the most recent collision data. Some engineers paced slowly, while others stayed longer than usual, staring at screens. When a machine made to simulate the universe’s creation just stops working, there’s a peculiar emotional gravity to it.

As scientists referred to it, RHIC was more than just a research instrument. In the US, it was the only particle collider of its kind. By creating temperatures hotter than the Sun’s center and creating the exotic state known as quark-gluon plasma, this facility, which was constructed in the 1990s and turned on in 2000, enabled physicists to replicate conditions that existed microseconds after the Big Bang.

Something surprising was discovered in this plasma, which is frequently referred to as a sort of primordial particle soup. It flowed more like a liquid than a gas would have. Because of this subtle difference, physicists were forced to reconsider how matter formed in the early stages of existence. As those discoveries became apparent over time, there was an increasing perception that the machine was more of a time machine pointing backward than a tool.

However, time machines also age.

There was no crisis or failure that led to the shutdown. It was prearranged. After RHIC’s scientific mission was completed, its tunnel will be used for a new project called the Electron-Ion Collider, or EIC.

That change seems symbolic.

The next device will shoot electrons into protons and nuclei rather than slamming heavy ions together, allowing for a more detailed examination of their internal structure. The EIC will try something more subdued and possibly more challenging—mapping the inner architecture of the particles themselves—than RHIC, which investigated how matter behaved in its early years.

Scientists are hoping it will provide answers to long-standing questions. What gives protons their mass? How is spin produced by quarks and gluons? Although no one says that with much confidence yet, it’s possible that the answers could change the fundamentals of physics.

The practical reality of incomplete work is another. In its last years, RHIC produced vast amounts of data, most of which has yet to be examined. Scientists anticipate that new information will keep coming to light long after the machine has ceased to function. Its scientific life isn’t quite over, in a sense.

It’s easy to overlook the collider when strolling around Brookhaven’s campus today. Except for a few low buildings strewn across flat terrain, the tunnel is hidden underground. The fact that they are standing above a machine that momentarily replicated the conditions of the early universe may go unnoticed by the average visitor.

It’s difficult to ignore how unremarkable it appears.

However, the shutdown has wider ramifications. Large, costly machines have influenced particle physics for decades. With its Large Hadron Collider, Europe’s CERN leads the field, and China has stated plans to construct even bigger facilities. Although America’s pause seems short-lived, it also calls into question scientific priorities and leadership.

Always lurking in the background is funding. Decades of planning and billions of dollars are needed for projects like the Electron-Ion Collider. Governmental organizations, taxpayers, and legislators who fund science appear to still think these devices are important. However, public sentiment can change suddenly.

A deeper philosophical tension exists as well.

Particle colliders have long held out the promise of providing answers to important questions about reality. However, new mysteries are usually revealed with every discovery. The universe seems to get more complex as physicists gain more knowledge.

As this is happening, it seems like the shutdown is more of a break between chapters than a conclusion. The RHIC tunnel will not stay unoccupied. Soon, engineers will start rebuilding it with new detectors, magnets, and goals.

Collisions won’t happen again for almost ten years.

The ancient collider lies somewhere under Long Island’s frozen ground. Maybe it was waiting for its next incarnation.