Jasper Kirkby inside the CLOUD chamber.
Credit: CERN
It's a summer morning and I'm looking out over a breathtaking vista on the alpine border of Switzerland and France. Puffy cumulus clouds nuzzle the jagged Jura Mountains and rays of sunlight illuminate a meadow dotted with livestock. This peaceful rural scene is in direct contrast to the high-tech wonders I was perusing just a short while before and 80 m below the ground.
There I visited the Compact Muon Solenoid (CMS) detector, situated in the 27-kilometre-long tunnel that houses the Large Hadron Collider (LHC) at the European Organisation for Nuclear Research - more commonly known as CERN.
Little did I realise it at the time, but the clouds above and the particle physics below had more in common than I could have imagined: a short distance away, there was another piece of futuristic technology used to test whether cosmic radiation has a definitive role in creating clouds on Earth.
One hour earlier, I and the rest of a group of visiting journalists were given construction hats and then passed through a setting worthy of the lair in a James Bond movie: a hall filled with blinking computer servers, an elevator which descended 80 m to a security gate and a massive tunnel filled with gantries, pipes and tanks of super-cooled helium. On the way we stop to get our photos taken at the eye scanner and security gate that was featured in the 2009 film Angels and Demons (see "The Hollywood factor" Cosmos 31). Our guide explains that the security measures are not so much to combat an onslaught of bad guys as they are to make sure everyone is safely out of the way before test runs of the equipment.
Standing in front of the CMS, an integral part of the LHC, I feel something like déjà vu. I recognise the detector from images I'd seen in the media when the LHC came to the attention of the public in 2008, following alarmist claims that it might generate a planet-devouring black hole. Even though it's one of many projects on the site, it is easy to see why most people equate CERN with the LHC - the world's largest and most powerful particle accelerator, tasked with colliding particle beams in order to test theories of high-energy physics.
The CMS is a 15-metre-tall scientific instrument that weighs 12,500 tonnes; roughly equivalent to 30 jumbo jets. What really impresses me, though, is the 80-metre-tall skylight through which this US$491-million, superconducting magnetic coil was lowered into the chamber, with just centimetres to spare on either side. The machine is designed to search for, among other things, the Higgs boson, an elusive subatomic particle that may provide insight into the very origins of the universe; all part of the LHC's goal of studying the fundamental particles thought to have formed during the Big Bang (see "Hunt for the God particle" Cosmos 9 and "Cosmic Roulette" Cosmos 20).
Several hours after my LHC experience, I was introduced to a complex machine that might make a big bang of its own - in the universe of climate change. The project, headed by CERN's Jasper Kirkby, is called Cosmics Leaving Outdoor Droplets (CLOUD). Its purpose is to test the extent to which cosmic radiation affects the formation of low clouds across the planet.
If there is a connection, it could lend support to the idea that there's a link between levels of cosmic rays reaching Earth and long-term changes in climate.
Galactic cosmic rays are a spray of protons and other charged particles that have been ejected from distant stars. Cosmic rays less than 15 GeV (giga electron volt) are deflected by the Sun's solar wind and the Earth's magnetic field. Data suggests that when there is increased solar activity and a more ferocious solar wind, levels of cosmic rays reaching Earth are decreased.
"The concept for the experiment is very simple. We build a chamber, fill it with known trace gases and ultrapure air. We then expose it to [simulated cosmic rays] ... and watch what we grow in the chamber. We do this by sampling small amounts of the gases and putting them through very sensitive, state of the art detectors, like mass spectrometers," Kirkby said.
Unlike observational experiments of the atmosphere, the cloud chamber allows the researchers to vary the amount of rays that the mixture of gases is exposed to. They can also vary the temperature, pressure and proportion of trace gases.
The CLOUD chamber itself is a three-metre-wide metal chamber totally sealed from the outside world with gold-plated copper. Despite its advanced design, with ultra-pure gasses identical in composition to the atmosphere and a saturation of water vapour equivalent to many times higher than 100% humidity, Kirkby says that CLOUD is in many ways similar to one of the first experiments to demonstrate the passage of cosmic rays.
Charles Thomson Rees Wilson would win a Nobel Prize for the invention of the cloud chamber in 1927, but in the autumn of 1894 he was just a University of Cambridge physicist with an interest in meteorological optics. He was helping out at an observatory on Scotland's Ben Nevis, the highest mountain in the British Isles.
Alec MacKinnon is an astrophysicist at the University of Glasgow. He says that Wilson's idea was born when he became curious about 'glories'; unexplained, faintly glowing rings observed around the clouds that swept across Ben Nevis.
