Wednesday 7 March 2012

Higgs Force

Higgs Force: The Symmetry-Breaking Force that Makes the World an Interesting Place by Nicholas Mee

Literary Review, March 2012

Last December, with the Internet having been awash with rumours for weeks, saw the official announcement of the latest results in the search for the Higgs particle from the fellowship of the ring – the physicists working at CERN’s 27km circular Large Hadron Collider (LHC). The Higgs is the missing piece of the theory that describes the behaviour of fundamental particles and the forces that act between them. It plays a special role in giving all the other particles mass.

The teams running the two giant detectors at the LHC independently put the mass of the Higgs, which is measured in what physicists call gigaelectron volts (GeV), somewhere between 116–130 and 115–127 GeV respectively. Although the scope of the search for the Higgs has now been narrowed, particle physicists demand an extraordinary degree of precision in their measurements. As the CERN press release made clear, even a 98 per cent chance of being correct is ‘not yet strong enough to claim a discovery’.

Particle collisions at CERN
If all the data generated by the LHC were stored on CDs it would fill more than a million every second. This is one of the more astonishing facts that Nicholas Mee reports in his book Higgs Force. To overcome this problem detectors are designed to be highly selective about the data passed on for storage. When the LHC smashes beams of particles together there are a billion or so collisions per second within the ATLAS detector alone, yet only the data from a couple of hundred collision events that have the telltale signs of interesting and possibly new physics are recorded.

The system that performs the selection process and determines which information is discarded and which is stored for analysis is called the trigger. Nicholas Mee acts as the trigger as he selects the tales to tell of those whose work has helped reveal the structure of matter and the laws of nature, culminating in the present hunt for the Higgs particle. The result is an intellectual journey that ends at the LHC near Geneva but begins with the Big Bang 13.75 billion years ago.

When the universe was born there was only a single force, which Mee calls the Higgs force. Moments after its birth the temperature began to fall as the universe expanded and the original force was shattered into four disparate pieces. The strong force would hold the quarks together in the atomic nucleus, while the weak force would transmute matter and make the different elements. The electromagnetic force would bind atoms and control their chemical reactions, and then there was gravity. Mee focuses on the three forces that matter when it comes to particle physics – electromagnetism, weak and strong – and attempts the difficult task of trying to explain how physicists have discerned that although ‘the universe began in a perfectly symmetrical state, the Higgs broke this symmetry and enabled the matter that formed within the universe to evolve into complex and diverse structures’. Without the Higgs particle the universe would have remained in a state that was ‘homogeneous, lifeless and uninteresting’.

Most people have an intuitive feel for what symmetry means. They recognise symmetrical patterns when they see them. However, physicists understand symmetry in terms of transformation, such as a reflection in a mirror, a rotation around an axis or a translation through space. An object or a pattern possesses a symmetry if it does not change when it is transformed in some way. For instance, if a snowflake is rotated around its centre by sixty degrees (one sixth of a complete revolution), it will appear exactly the same after the rotation as it did before. In fact all rotations through multiples of sixty degrees are symmetries of a snowflake.

Symmetry has become fundamental to the way that physicists view the universe, and an increased understanding of the symmetries of nature has been one of the major themes in the development of physics. When a quantity remains unchanged throughout a physical encounter it helps physicists to disentangle the details of what might be an extremely complicated event. This is true of the collisions that take place at the LHC. Mee does an admirable job of explaining all this before tackling ‘spontaneous symmetry breaking’, which lies at the heart of the Higgs story.

Peter Higgs
This book is far broader and more accessible than its title may suggest. For instance, we learn that the scientific investigation of magnetism dates back to William Gilbert, the personal physician of Elizabeth I. He was one of the first to try to understand the workings of nature through experimentation rather than philosophical argument. He concluded from his many experiments that the Earth is a magnet, explaining why a compass needle points north. Among others that we meet is a physicist who compared his power to transmute the elements to the mythical alchemist Hermes Trismegistus; an astronomer who was captivated by the beauty of a falling snowflake; the British physicist whose work predicted the existence of antimatter; the theorist who transformed particle physics with his eightfold way; and Peter Higgs, whose long wait for the discovery of the particle that bears his name may soon be over.