A worker wearing a hardhat is dwarfed by the ALICE detector’s red magnet assembly in the Large Hadron Collider.
CERN physicist Detlef Kuchler holds a piece of the lead source material used to create heavy ions for the LHC.
Alan Boyle writes: The world’s biggest particle collider has switched over from shooting beams of protons to shooting heavy ions — leading to experiments that could cook up the kind of “soup” produced by the big bang. And even before those experiments have begun, critics have cooked up a fresh batch of doomsday talk as well.
For the past year, the Large Hadron Collider has been smashing protons together at progressively higher energies, 300 feet (100 meters) below ground at the French-Swiss border, in a ring-shaped tunnel that measures 17 miles (27 kilometers) around. A milestone was reached last month when the beams’ luminosity hit its target for the year.
“This shows that the objective we set ourselves for this year was realistic, but tough, and it’s very gratifying to see it achieved in such fine style,” Rolf Heuer, director general for Europe’s CERN particle physics center, said in a news release issued today. “It’s a testimony to the excellent design of the machine as well as the hard work that has gone into making it succeed.”
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High-energy proton collisions could unlock the secrets of higher dimensions, or reveal the nature of dark matter and antimatter, or point to an as-yet-undetected field that is thought to give some particles mass while leaving other particles massless. The particle associated with this field is called the Higgs boson, sometimes known as the “God particle.”
But when it comes to creating the conditions that existed just after the big bang, the LHC needs heavier ammo. That’s why CERN has switched from protons to lead ions — that is, lead atoms that have been stripped of their electrons. The ions are more than 200 times heavier than protons, and when they’re smashed into each other at nearly the speed of light, the blast is expected to shatter particles into a hot soup of free-flying quarks and gluons.
Current theory suggests that the whole universe existed as a dollop of super-hot quark-gluon plasma in the first few millionths of a second after the big bang. Since then, quarks have been virtually impossible to pull apart — but an ion-smasher in New York, known as the Relativistic Heavy-Ion Collider or RHIC, is thought to have done it five years ago. Such experiments help physicists understand exactly how the universe was, and is, put together.
CERN says the LHC should be able to collide heavy ions with energy levels 28 times higher than those achieved at RHIC. Some theorists have suggested that at those energies, the big bang soup would no longer exist as a liquid, but as a gas. And so, for the next few weeks, the LHC’s spotlight will turn to a huge detector called ALICE (which stands for “A Large Ion Collider Experiment”).
More than 1,000 physicists, engineers and technicians are on the ALICE team, but they’re able to take data only during the four weeks of the year that precede the LHC’s winter break. So they didn’t waste any time getting started. The proton-on-proton action finished up this morning, and the first test beam of lead ions made 75 laps around the LHC tunnel tonight, CERN spokesman James Gillies told me.
“It’s going well,” Gillies said. “We’re looking at the first collisions in the next few days.”
Two other detectors at the LHC, the Compact Muon Solenoid and ATLAS, will also be taking data during the heavy-ion run. Then the beams will be turned off for maintenance during the winter break. The schedule calls for proton beams to start up again in February, Gillies said.
**Return of the strangelets** This week’s heavy-ion switch is good news for physicists at the LHC … but it has also sparked a renewed campaign by folks who worry that the collisions will destroy the world. Remember them? Before the LHC’s startup in 2008, some critics voiced concerns that high-energy collisions could give rise to catastrophic phenomena ranging from globe-gobbling black holes to atom-wrecking particles. Similar objections were raised about RHIC, and in response, CERN conducted a series of safety reviews that concluded LHC operations would be safe. The critics were unsatisfied, however. With the switch to heavy ions, they’re shifting their focus from the black-hole scenario to the atom-wrecking scenario.
A group called Heavy Ion Alert claims that the LHC could create a dangerous breed of strangelet — that is, a never-before-seen combination of quarks that includes some with a strange flavor. In this case, “strange” is a technical term, representing one of the six flavors of quarks. (The others are up, down, charm, bottom and top.) The claim is that just the wrong kind of strangelet could turn nearby atoms into strangelets as well, setting off a catastrophic chain reaction.
The case for killer strangelets is similar to the case for globe-gobbling microscopic black holes. If there’s any chance at all that the LHC could produce an Earth-killer, the experiment should not be done. “For Earth, one [chance] in 1,000, or one in 100,000 is still something you don’t want to do,” James Blodgett, a member of the group, told me this week.
The reassurances from particle physicists follow a similar format as well. The most recent LHC safety report says theory as well as observations would rule out such a catastrophe. If such strangelets could arise, they would have been observed beyond Earth, where there are cosmic-ray collisions far more powerful than anything the LHC can dish out. The report’s authors say it’s theoretically harder to create the dangerous kind of strangelets at higher energies — which means that if anything bad could happen, it would have happened at RHIC.
“For this reason, the likelihood of strangelet production in relativistic heavy-ion collisions can be compared to the likelihood of producing an ice cube in a furnace,” the authors write.
**’A teachable moment’** The LHC’s critics point to earlier reports from researchers, speculating on the prospects for producing stable, negatively charged strangelets — the supposedly scary kind. They cite this as evidence that “CERN has misled the public.” But some of those reports date back 15 years or so and don’t reflect the latest thinking about the production of exotic matter.
Other reports are more recent, but refer to what might be found using a subdetector known as CASTOR. The CASTOR researchers themselves voice no concern about a catastrophe. Instead, they see their experiment as a straightforward effort to find evidence of exotic phenomena previously associated with cosmic-ray collisions, including centauros and strangelets. The doomsday connection is being made by the doomsayers themselves … plus maybe a few physicists exercising their imagination.
A newly published book about the quest for the Higgs boson, titled “Massive,” devotes an entire chapter to the strangelet controversy, recounting how it grew out of a speculative comment that Nobel-winning physicist Frank Wilczek made in an 1999 magazine article. “I thought I’d use the opportunity as a teachable moment,” the book’s author, Guardian science correspondent Ian Sample, quotes Wilczek as saying.
At the time, Wilczek didn’t realize his strange speculation would set off a years-long debate. And even if the hubbub over strangelets settles down over the next few weeks, that’s unlikely to end worries about the end of the world. Here’s how Sample puts it in “Massive”:
> “History suggests there will always be some world-ending entity lurking among scientists’ theories, and the chances of unleashing it by accident will almost certainly be shrouded in uncertainty. If dangerous strangelets and magnetic monopoles are ever ruled out, another possibility will emerge from physicists’ theories. How then should society decide whether an experiment that has a minute risk of causing total disaster be carried out? In the distant past, the consequences of an experiment gone wrong affected only those involved or nearby. One argument says that, since particle colliders are primarily of direct benefit only to pure science, we have already come too far. But that is short-sighted. High-energy physics experiments have brought us revolutionary technologies as disparate as the World Wide Web and ion beams for cancer treatment. When we make progress in pure science, technological benefits often follow. Perhaps the best we can hope for is a truly open and public debate in which real risks are laid out. Without that, society as a whole has no chance of making an informed decision. How we achieve this will only become a more pressing issue as science advances.”
What do you think? Feel free to weigh in with your comments below.
**More from MSNBC:**
* Special report on “The Big Bang Machine” * Nightmares and dreams at the LHC * What’s a hadron? Tour the particle zoo
**More from the Web:**
* CERN: The safety of the LHC * CMS Times: Looking forward with CASTOR * APS: Looking for strangelets … and not finding them
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