Fearful symmetries

The Particle at the End of the Universe: The Hunt for Higgs and the Discovery of a New World, by Sean Carroll, Oneworld RRP£16.99/Dutton RRP$27.95, 352 pages

This summer’s discovery of the Higgs boson at Cern, the European particle physics centre near Geneva, was the science story of the year. The media captured the excitement of the successful chase for the “God particle” and revelled in the superlatives of the $8bn Large Hadron Collider (LHC), in which physicists smash together atomic nuclei at almost the speed of light to recreate the intense energy of the early universe.

Attempts to explain why the particle matters or what it does – beyond a simplistic line that it somehow confers mass on everything – were inevitably lost in all the Higgsteria. Now that the frenzy has faded, the time has come to reflect more calmly on what has been discovered and the work still to be done by the thousands of physicists around the world who are associated with the LHC.

Sean Carroll, a theoretical physicist at the California Institute of Technology with a gift for lucid writing, is a good guide on this journey of reflection. While The Particle at the End of the Universe takes Higgs as its central theme, it gives us a wide-ranging tour to show how the newly discovered boson fits into current thinking about particle physics and cosmology.

The book also describes vividly the personalities of the scientists, administrators and politicians whose decisions help to determine the pace at which research moves forward. A telling story is the exchange during a US congressional hearing in 1969 between Senator John Pastore and the physicist Robert Wilson, who was seeking funds for what would come to be known as Fermilab, the particle physics centre near Chicago.

Three times Pastore asked Wilson whether the project had any connection with US national security, almost begging the physicist to give a positive answer that could justify more federal funding. Wilson’s third response was a wonderful off-the-cuff defence of spending taxpayers’ money on pure science with no practical application. “It has only to do with the respect with which we regard one another, the dignity of man, our love of culture,” Wilson said. “It has nothing to do directly with defending our country except to make it worth defending.”

The scientific story about the Higgs particle turns out to be even more complicated than I had appreciated when covering it for the FT. Take the journalistic line that Higgs is the source of mass in the universe. This is only partly true, Carroll shows. Yes, Higgs is responsible for giving mass to some fundamental particles but there are other mechanisms too.

Although the subatomic Higgs particle or boson has received the media attention, what matters most is the Higgs field, which pervades otherwise empty space and gives structure to everything. The particle is a pulse or vibration in this field, just as a photon (light particle) is a vibration of the electromagnetic field. But whereas a photon is stable and can travel across the universe in a light beam, a Higgs boson lasts about a zeptosecond (a billion-trillionth of a second) before disintegrating into a shower of secondary particles.

Prompted by the opening of the LHC in 2008 and the prospect of Higgs discovery, several books have already tried to explain to non-specialist readers what all the excitement is about. Carroll is particularly skilled at tackling the complexities of particle physics in a readable yet reasonably uncompromising way.

Take the concept of “symmetry”, which is key to understanding how different forces and particles arise and behave. Like many words in particle physics, the meaning of symmetry in everyday life is not a good clue to its scientific significance. Symmetries represent a cosmic equivalence, which holds in some circumstances but is “broken” by a force field in others. To give a simple example, the electromagnetic force breaks the symmetry between two particles that are identical except for one being electrically charged and the other neutral.

As Carroll writes, one of the most astonishing insights of modern physics, and one of the hardest to grasp, is that sufficiently powerful symmetries give rise to forces of nature. Piecing together the broken bits to see the elegance of the underlying symmetries is “like being able to read poetry in the original language, instead of being stuck with mediocre translations”.

With such difficult concepts, analogies may offer a useful insight to the non-technical reader, although they are inevitably misleading to a greater or lesser extent. Carroll came up with a good one for a television programme to explain the Higgs field. Imagine little robots scooting about on the floor of a large vacuum chamber, identical apart from the fact that they are fitted with sails of various sizes. When the space is completely evacuated the sails are irrelevant because there is no air for them to feel, so all the robots move at the same speed. When the atmosphere is let in, the robots with larger sails (greater mass) are impeded more by the air than those with smaller sails (less mass) so they move more slowly.

The robots are subatomic particles and the sails are their couplings to the Higgs field, which is represented by the air. Filling the chamber with air breaks the symmetry of the vacuum in which all move at the same speed. You could even go further and suggest a parallel between making sound waves by clapping your hands and creating Higgs particles.

When Carroll put his analogy to engineering colleagues at Caltech, the universal reaction was: “It sounds awesome.” At heart, science is the quest for the awesome, the awe you feel when you begin to understand something for the first time.

Of course no one – not even the physicists working full-time at the LHC – really understands how the universe works. But thanks to Carroll and other popularisers of particle physics, we can all grasp enough to wonder at what the world’s most powerful atom smasher has already achieved and anticipate what is still to come.

Clive Cookson is the FT science editor

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