Look out into a clear dark sky at all the stars and it comes as a surprise to learn that more than 95% of the mass of the entire Universe is unaccounted for. This “missing” or dark matter has perplexed astronomers and cosmologists for decades.

The most distant galaxies in the Universe seen by HST (click the image to see the press release)

And scientists with their eyes to the sky are not the only ones scratching their heads about mass. Particle physicists, with their eyes figuratively on the smallest, subatomic particles that compose everything in the Universe – things like electrons, quarks and neutrinos – are perplexed about mass too.

The “standard model” of particle physics worked out by physicists predicts the existence of something called the Higgs particle. The Higgs is the subatomic particle that gives everything in the Universe mass. And while the standard model has proven to be correct in every measurable way, the Higgs at its heart has never been observed.

A schematic of the standard model of particle physics (from Wikipedia, click the image to visit the Wikipedia page).

Particle physicists study the Universe at subatomic scales primarily in the ways young boys play with toys: they smash things up. But the toys scientists play with are Big Boy toys – in every possible way.

The newest, biggest smasher that scientists from around the world have put together – indeed, the largest science experiment ever – is on track to be switched on for the first time on Wednesday Sept. 10. The machine, located at the European Organization for Nuclear Research on the border of Switzerland and France, which for historical reasons is just called CERN, is called the Large Hadron Collider, or just the LHC.

An aerial view of CERN and the LHC (courtesy CERN).

In the LHC, two beams of protons will be accelerated in opposite directions around an underground circular track 27 kilometers in circumference at essentially the speed of light then smashed into one another to create tiny controlled collisions at energies that prevailed in the early universe.

From these collisions will emerge the most exotic subatomic particles of the Universe – including, perhaps, the elusive Higgs.

A simulation of a hadron collision in the LHC (courtesy CERN).

The scale and complexity of the LHC is almost as beyond comprehension as the experiment it will conduct. The machine has been in the works for about 25 years and will cost maybe $10 billion. The 27-km accelerator ring is a near-perfect vacuum with superconducting magnets all the way around. The entire affair is cooled by liquid helium to less than 2 degrees above absolute zero. When in operation, the machine will consume about 100 Megawatts of electrical power and the four LHC detectors will produce a flood of data equivalent to playing a DVD every 4 seconds.

In fact, dealing with the data the LHC will produce is not the smallest technical challenge that had to be met. But CERN scientists have considerable experience in computer science. Indeed, one of the computer scientists employed at CERN in the late 1980s when the LHC project was just getting off the ground – Tim Berners-Lee (not Al Gore) – conceived of the World Wide Web and implemented the first web server partly in logistical support of the design, construction and operation of the LHC.

The planned LHC startup has already caused a stir around the web and the world. Maybe you’ve seen the “Large Hadron Rap” video clip on youtube. Maybe you read the NY Times column about the LHC by Gail Collins, in which she fretted about the possibility that the LHC will produce micro black holes that will gobble up the earth. Or maybe you heard about court cases in Europe and the US which seek injunctions against the LHC startup for fears that it will bring the end of the world.

Stay tuned and up to date at http://www.cern.ch/.