June 14, 2000 — The first spectacular images of atoms smashing together at near-light speed were released Wednesday as part of an experiment scientists say will eventually generate a state of matter that existed a millionth of a second after the Big Bang.
A milestone in physics, the researchers’ effort has also generated heated debate and several doomsday theories — including one that argues the experiment might release particles called “strangelets,” which could gobble the globe.
The collisions began June 10 in New York at Brookhaven National Laboratory’s $600 million Relativistic Heavy Ion Collider — the most powerful machine of its kind. The first images of particles streaming from a collision point, which was the definitive evidence scientists were waiting for, were produced late Tuesday night and Wednesday morning.
“We have just detected the most spectacular subatomic collisions ever witnessed by humankind, and are launching a new era for the study of nuclear matter,” said Satoshi Ozaki, associate laboratory director for RHIC. (The acronym is pronounced like “rick.”)
Scientists will begin analyzing the data collected from continuous collisions held throughout the summer and hope to release the first results at the beginning of next year.
Long-lost particle soup
The experiment aims to smash gold nuclei together at 99.95 percent of the speed of light — creating temperatures of more than a trillion degrees. That would be 10,000 times hotter than the sun.
“Under those conditions, neutrons and protons in the atomic nuclei would literally melt into a plasma of quarks. It’s a thermodynamic phase transition, like water changing from a solid to a liquid, or a liquid to a gas when it boils,” said Tom Ludlam, associate project director for RHIC.
Physicists say that the neutrons and protons within ordinary matter are actually built up from combinations of quarks, particles that were first postulated in the 1960s. The quarks are bound together through the exchange of particles whimsically dubbed gluons. Thus, the object of Ludlam’s 15-year quest at Brookhaven is to create a brew called quark-gluon plasma.
In the first millionth of a second after the universe’s beginning, the entire cosmos consisted of this ultradense, ultrahot brew, scientists say. But they have never observed this brew in the current universe — although a less powerful collider experiment at CERN in Switzerland may have provided indirect evidence of its existence last year.
Brookhaven’s experimenters expect to create tiny bursts of quark-gluon plasma for only a billionth of a trillionth of a second. Then the plasma would coalesce again into ordinary matter, Ludlam said.
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“The real motivation is to look at this phase transition from ordinary matter to this deconstructed plasma, and then back again — and then try to answer the question of why is it that there are these preferred configurations of quarks, and could there in fact be other configurations. ... It opens up a vast new realm of exploration for people who do nuclear physics.”
The magnitude of the mystery is the prime factor behind the collider’s allure — and the controversy as well.
Last year, physicist Walter Wagner wrote a letter to Scientific American, asking whether the creation of a quark-gluon plasma might create a globe-gobbling black hole.
That particular doomsday scenario — as well as another involving a catastrophic transition in the nature of empty space — has been shown to be without foundation. But in his answer to Wagner’s letter, Frank Wilczek of Princeton’s Institute for Advanced Study referred to a speculative scenario involving something called “strangelets.”
Strangelets would contain “strange” quarks — which are somewhat heavier and less understood than the garden-variety “up” and “down” quarks that make up ordinary protons and neutrons. If a series of highly unlikely conditions apply, strangelets could in theory start consuming ordinary matter, turning the entire Earth into a sphere of strangeness.
It’s this scenario that has captured the attention of physicists and the press.
For example, The Sunday Times of London headlined its story “Big Bang Machine Could Destroy Earth.” Chicago Sun-Times columnist Zay N. Smith regularly published “Defcon” alerts about RHIC’s status. And Wagner, the author of that Scientific American letter, filed federal lawsuits in San Francisco and New York aimed at stopping the collisions at RHIC by court order.
Brookhaven’s director, John Marburger, issued news releases downplaying the concerns — but also asked a panel of scientists to investigate the potential risks.
‘A series of unlikelihoods’
Last September, the panel ruled out even the worst-case scenario for a strangelet doomsday.
“There is a series of unlikelihoods that you’d have to string together like a Rube Goldberg invention,” said Robert Jaffe, director of the Center for Theoretical Physics at the Massachusetts Institute of Technology, who headed up the panel.
The panelists said that even if RHIC were able to create strangelets, the evidence indicates that they couldn’t persist long enough to cause trouble. And even if strangelets did somehow persist, they wouldn’t necessarily be dangerous.
“The most likely scenario is that a strangelet would have a positive charge, but a small charge,” Jaffe told MSNBC.com when the report was released. In that case, strangelets would be admittedly bizarre but basically harmless — for example, something like grossly overweight helium atoms.
But if stable strangelets carried a negative charge, that would create a “dangerous situation,” Jaffe acknowledged. Tiny lumps of strange matter would attract ordinary nuclei and consume them like so many dots in a Pac-Man game.
“It would kind of burp a few times, and after readjustment it would have a negative charge again,” Jaffe said. “It would eat more, and burp and capture, and burp and capture to the point that it has eaten all the matter around it.”
Could this actually happen? The panelists argued that if such a scenario had any validity, cosmic-ray collisions already should have created enough strange matter to be detected.
“The fact that planets and stars have not been converted to strange matter is evidence that this Rube Goldberg string does not exist,” Jaffe said.
In the wake of such reassurances, RHIC was formally dedicated last October. Since then, Ludlam and his colleagues have been fine-tuning every element of the system, including two collider rings that are each more than 2 miles in circumference, and four detectors looking for signs of the quark-gluon plasma.
In this week’s first run, collisions were achieved at an energy level of about 30 billion electron volts per nucleon. That’s four times more energetic than the CERN collisions. Eventually, the collisions will reach an energy level of 100 billion electron volts. At that level, the colliding ions will for a fraction of a second reach a temperature 100,000 times hotter than the core of the sun.
Wagner, meanwhile, is continuing with his legal challenge. In an interview with MSNBC.com, Wagner argued that the Brookhaven experiment opened the way for scenarios that were “qualitatively different” from those involving cosmic rays. In a follow-up e-mail message, he complained that the risks of creating a world-gobbling strangelet were being understated so that the experiment could proceed.
“I disagree with that philosophy, as it places the future of all humanity at risk, just for the benefit of a very few,” he said.
Wagner’s New York lawsuit was dismissed on a technicality. In San Francisco, Wagner’s requests for a restraining order have been turned down repeatedly.
Ludlam said the doomsday debate hasn’t affected the efforts at Brookhaven.
“It’s just one of those things that certainly does capture the imagination of people, even some people who feel they have some understanding of the science and feel compelled to take strong measures,” he said. “But in fact, this has been looked at very thoroughly by people who understand and know how the science of these collisions works. ... You can always invent scenarios, but in fact these are really not scientifically valid scenarios.”
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