Since it started up again in March 2010, the world’s largest particle accelerator, the Large Hadron Collider (LHC), has been responsible for much excitement. But what’s the fuss about? The LHC is the next step on a journey of discovery that began centuries ago, whose goal is to figure out as much as humanly possible the laws that govern our universe. From the realisation that the earth is not flat, through the harnessing of electricity and magnetism that led to a technological revolution, to the development of the mind-boggling theory of quantum mechanics, science has transformed our lives. The researchers at the LHC are attempting to understand the universe at a microscopic level, pushing the frontiers of knowledge to a point that we cannot yet predict.
The huge machine is inside a 27-kilometre circular tunnel, situated 175 metres underground beneath the Franco-Swiss border near Geneva. It uses cutting-edge technology to smash together beams of subatomic particles known as protons, travelling at close to the speed of light. The protons interact and break up and new particles are produced, allowing us to probe the tiny building blocks that make up all matter, from our bodies to the distant stars.
In the 1960s and 1970s, a theory describing these particles, known as the “standard model of particle physics”, was developed. It is a successful theory that has survived many tests and predicted the existence of particles that were later discovered. But it is not the entire story. For a start, it does not include the weakest of all known forces, gravity, and there are indications that it is an approximation of a more complete theory of the universe.
We do not yet know what such a theory would include. One possibility is the existence of extra dimensions of space, in addition to the three (left-right, forward-backward and up-down) with which we are familiar. What is more, an important piece of the standard model is yet to be verified. It predicts the existence of an as-yet-undiscovered particle known as the Higgs boson (named after the physicist Peter Higgs, who first proposed its existence). Without the Higgs, the standard model cannot explain how particles acquire mass.
As well as searching for evidence of more complete theories beyond the standard model, scientists at the LHC aim to confirm or exclude the existence of this particle. Excluding it would, perhaps, be even more exciting than discovering it, as it would mean that the theory that has described the building blocks of our universe is wrong. Theorists would have to go back to their blackboards and come up with a new one.
I am one of 3,000 particle physicists working on Atlas, one of the four huge detectors surrounding points on the LHC where the proton beams collide, designed to detect the new particles created. Discovering these particles is not an easy task. If the Higgs boson exists, it would be produced roughly once in every four billion proton-proton interactions. Your chances of winning the National Lottery are about 300 times greater than the chances of producing a Higgs boson – pretty miserable odds.
The solution is to have many interactions. At the LHC, proton-proton interactions can occur up to 800 million times a second. Under these conditions, a Higgs boson could be created once every five seconds. This doesn’t sound so miserable, but the challenge lies in finding the Higgs boson “needle” in the “haystack” of interactions. It’s analogous to sorting through 800 million Lottery tickets every second.
Working collaboratively with thousands of people from universities and laboratories across the world is an experiment in sociology. Successful science relies on independent thinking; yet, with so many people, a management structure is required. There is an elected spokesperson of the experiment, whose term lasts for two years. There is a physics co-ordinator and many group convenors. Until March this year, I was convenor of the group responsible for the measurements made with the first data we collected in March 2010. The role can be inspiring, working with bright colleagues, but also difficult – you are co-ordinating the work of many people, some of whom are your seniors, all under pressure to produce high-quality results quickly.
Like many scientists, we particle physicists are our own worst enemy. We scrutinise and try to disprove our ideas and those of our colleagues. We have a strict approval process that any result must go through before being shown in public. This process is essential to producing reliable results, and any results that are leaked before undergoing it should not be taken seriously. We want to make sure our results are correct because we all have a common goal: to find the truth about how things work.
The next few years will be exciting for particle physics and, by extension, for humankind. What we discover could change the way we view the world, but the nature of discovery does not allow us to predict how. When J J Thomson discovered the electron in the late 19th century, he had no idea what it would lead to. His favourite after-dinner toast was “To the electron – may it never be of any use to anybody”. Yet, more than a hundred years later, the electron, as the lifeblood of much modern technology, including computers, televisions and phones, is of use to just about everybody. I can’t wait to find out what we will discover next.
Emily Nurse is a researcher at University College London and has a Royal Society university research fellowship