The Coldest Place in the Universe
David Kaiser · The Large Hadron Collider
Fourteen years in the making, the Large Hadron Collider near Geneva spun to life in September 2008, sending the first batches of protons whirling around its 27-kilometre track at very nearly the speed of light. The goal was to smash the revved-up protons into each other at tremendous energies, mimicking conditions that would have been found moments after the big bang and unleashing new particles and interactions for physicists to scrutinise.
The machine came screeching to a halt a few days later. One of the tanks holding liquid helium (to keep the superconducting magnets ultracold) had ruptured. No one could get close to the affected area to inspect the damage or begin repairs until the entire region had been taken off-line and ever-so-slowly warmed up. Fourteen months and £24 million later, the tank had been repaired, new equipment installed to bolster the LHC’s resistance to similar spikes in electrical current, and the entire machine cooled back down to its operating temperature.
Late in November 2009, the laboratory team celebrated a new world record: they had achieved the highest-energy particle interactions ever recorded in an earth-bound accelerator, edging past the previous record set by a smaller machine at the Fermi National Accelerator Laboratory in the United States. (They’ve surpassed their own record more than once since then, most recently last Friday. Even that, however, was considerably lower than the anticipated peak energy for which the LHC had been designed.)
Once again disappointment eclipsed the momentary cheer. The lab recently announced that it will only be able to operate the LHC at half-capacity until the end of 2011, when it will take the machine off-line for a new round of delicate and costly repairs, which could easily last a year or more. The culprit again appears to be electrical shielding around the delicate superconducting magnets.
With the LHC operating at half its anticipated energy, physicists could still get lucky and find, for example, some evidence for a new type of particle that could account for the ‘dark matter’ enigma. Astronomers have known for decades that some form of matter, inherently different from the familiar atoms and atomic constituents that surround us, seems to be filling the universe, affecting the rates at which galaxies spin. This stuff, whatever it is, can act on ordinary matter gravitationally, but it doesn’t seem to condense into stars or light up: it remains dark. The most recent astrophysical measurements indicate that there should be about five times as much dark matter in the universe as ordinary matter. Theoretical physicists have had little trouble dreaming up exotic candidates for what it might consist of; to date, however, no one’s been able to detect any actual particles. With a bit of luck, even a hobbled LHC could change that.
Most of the terrain that particle physicists are most eager to explore, however, lies at energies greater than the limit at which the LHC will operate for the coming months. So we wait in hope that the full-strength LHC will enable better insight, some time off in the fast-receding future.
It’s not surprising that we have to be patient. The LHC is arguably the single most complicated machine ever constructed. As scientists working on the project have pointed out, the LHC is its own prototype; of course frustrating and unanticipated glitches will interrupt operations. Let’s not forget the sheer audacity behind this hulking machine. Buried 100 metres below the ground, the full length of the 27-kilometre beamline must function flawlessly at temperatures colder than outer space. Ever since the Big Bang, the universe has been cooling. The average temperature of empty space today is 2.8 degrees above absolute zero. (Ordinary room temperature is about 300 degrees above absolute zero.) The inside of the LHC, when functioning properly, hums along nearly a full degree colder than the coldest remnants of the Big Bang, making the massive machine one of the coldest places in the entire universe. With enough luck, patience and money, it may yet help physicists decipher some of the most compelling mysteries of our universe and the fundamental particles and forces that hold it together.