The Large Hadron Collider or LHC, the largest and highest-energy particle accelerator in the world, is contained in a circular tunnel 17 miles in circumference that lies between 160 to 574 feet beneath the ground near Geneva, Switzerland. Over 1600 superconducting magnets chilled to near absolute zero are used to keep the particles in the circular track where they’re accelerated to nearly the speed of light. They cycle through the tunnel at around 11,000 times a second. Credit and copyright: CERN
Big news from the Large Hadron Collider at CERN (European Organization for Nuclear Research) yesterday. Scientists succeeded in colliding two beams of protons at 99.999 percent the speed of light with an energy of 7 trillion electron volts (TeV). To understand what all this means, let’s first define our cast of characters. Protons are the positively charged particles in the core or nuclei of atoms. A hydrogen atom, the simplest, consists of just one proton and one electron orbiting about it. A typical carbon atom nucleus has six protons and six neutral particles called neutrons surrounded by a shell of six electrons.
An electron volt or eV is a measurement of energy involving a moving electron. To get a feel for how much "juice" an eV contains we pay a visit to an imaginary ant. The energy of movement an ant expends while crawling in a straight line 5 1/2 feet long is nearly one trillion electron volts. Seven ants moving simultaneously would create the equivalent of the energy focused yesterday in the beams of CERN’s very large and very expensive particle accelerator. So what gives here? Well, an ant is composed of atoms, and each atom contains a healthy number of protons and neutrons. A back-of-the-envelope estimate of the number of nuclear particles in a single ant comes to about 60,000,000,000,000,000,000,000 (60 septillion). Since they all share that large chunk of energy, each single particle contains only a tiny fraction of the total.
Particles created by the colliding beams of protons in the LHC stream away on curved paths as viewed on a computer screen. Credit:Photo: Marzena Lapka /CERN
The trick is to pack large amounts of energy into just a few particles, and that’s exactly what a particle accelerator does. It’s not easy. "Just lining the beams up is a challenge in itself: it’s a bit like firing needles across the Atlantic and getting them to collide half way," said Steve Myers, CERN’s director for accelerators and technology.
When scientists collide two opposing beams of protons at nearly the speed of light only a few protons actually hit head on. With so few, each carries a huge amount of energy of motion (kinetic energy) for its size, and the collisions are much more forceful. During the smash-up the kinetic energy of the moving protons is converted into a shower of other subatomic particles. Scientists examine this exotic debris looking for new particles their theories predict will form under high-energy conditions. The faster they can speed the protons up and smash them together, the better likelihood of creating the particles that have eluded their previous best efforts in lower-energy accelerators. New particles are bound to crop up, and everyone’s hoping that a few of them will shed light on the composition of the mysterious "dark matter" or prove the existence of the Higgs boson (BOE-son), a particle postulated to give matter its mass (weight).
The galaxy cluster CL0024+17 is surrounded by a huge ring of dark matter (blue haze) that’s been digitally superimposed on the cluster. The dark matter is inferred rather than seen directly by the cluster’s gravitational effect on a yet more distant galaxy cluster in the background. The thin blue streaks are some of those more distant galaxies. Credit: NASA, ESA, M. J. Jee & H. Ford et al. (Johns Hopkins U.)
It appears that the ordinary matter you and I are made of accounts for only 4 percent of the material in the universe. The rest — some 23 percent — is dark matter, and 73 percent is something even stranger called dark energy. Dark matter resides around galaxies like the Milky Way and within galaxy clusters. If it wasn’t there our galaxy would unravel into bits and pieces. Dark matter holds it all together yet doesn’t give off any light and doesn’t interact with ordinary matter except through gravity. Scientists have no clear idea yet what it could be.
One of the particles predicted to arise from collisions in the LHC might be a component of the dark matter. Far from being an obscure exercise in throwing particles at the wall to see what sticks, the LHC may point the way to a more complete understanding of what the universe is made of. I’d like to know what all that invisible stuff is, wouldn’t you?
Particles with odd-sounding names like neutralinos and axions are predicted to emerge from the high-temperature beam collisions and are potential dark matter candidates. Researchers around the world who are plugged into the LHC will also be looking for the Higgs boson and perhaps even new dimensions in the quivering aftermath of the proton-proton collisions.
Who knew that civilization would already take us so far? We’re looking for things no one could have imagined back when the monks dutifully copied the ancient manuscripts of the Greeks and Romans. Never mind the monks. Even a hundred and fifty years ago all of this would have been unthinkable. As we probe into the nature of matter we continue to follow the bread crumbs nature has left along the path to understanding.
You may have read that the experiments at CERN will re-create conditions similar to the Big Bang and even spawn mini Big Bangs or black holes. 7 trillion eVs is a lot of energy among a few particles, but the accelerator will double that to 14 TeV when it’s fully up to speed. If you run the tape of our expanding universe backwards in time it gets smaller and hotter until a fraction of a second after its creation at the Big Bang. During LHC collisions the temperature is briefly 100,000 times hotter than the center of the sun and very similar to the state of the universe only a fraction of second after the Big Bang. No scientist expects an actual new universe to suddenly bloom forth inside the accelerator but they do expect to find particles that harken back to the ancient era. As for black holes, matter whose particles are packed so tightly that not even light can escape, any created will be microscopic and fleeting. CERN physicists point out that mini black holes are created all the time when cosmic rays (high speed atomic particles) strike our planet and we appear to be no worse for the wear.
If you have about 15 minutes to spare I highly recommend the excellent video below featuring Dr. Brian Cox. He explains the function and purpose of the collider in a very lucid way.