By Jim Baggott
Earlier today the Royal Swedish Academy of Sciences announced the award of the 2013 Nobel Prize in Physics to English theorist Peter Higgs and Belgian François Englert, for their work on the ‘mechanism that contributes to our understanding of the origin of mass of subatomic particles’. This work first appeared in a series of research papers published in 1964.
The announcement ends almost 15 months of intense speculation. Was there now enough hard evidence from CERN to justify the Prize for the theoretical work that had predicted the existence of the Higgs boson, 49 years earlier? And, if there was, just who would get it?Timing is everything. On 4 July 2012 scientists at CERN’s Large Hadron Collider declared that they had discovered a new particle ‘consistent’ with the Higgs boson, with a mass around 133 times that of a proton. Peter Higgs, then aged 83, was sitting in the lecture room at CERN listening attentively to the announcement. He declared: ‘It’s really an incredible thing that it’s happened in my lifetime.’
But for the Nobel Committee, ‘consistent’ clearly wasn’t strong enough to justify the Prize last October. However, just five months later, in March 2013, the results of the analysis of a larger data set gathered through 2011 and all of 2012 allowed the experimentalists to firm up their conclusion: ‘… we are dealing with a Higgs boson though we still have a long way to go to know what kind of Higgs boson it is.’In the ‘standard model’ of particle physics, particles are represented in terms of invisible quantum fields that extend through spacetime. Particles of matter, and the particles that carry forces between them, are interpreted as fundamental vibrations of different kinds of quantum fields. The electron is the ‘quantum’ of the electron field. The photon is the quantum of the electromagnetic field, and so on.The quantum field theories of the early 1960s seemed to suggest that all force carriers should be massless. This is fine for the photon, which carries the force of electromagnetism and is indeed massless. But it was believed that the carriers of the weak nuclear force, responsible for certain kinds of radioactivity, had to be large, massive particles. How then did these particles acquire mass?
The solution was to invoke something called spontaneous symmetry-breaking. There are many examples of this phenomenon in everyday life. If we had enough patience, we could imagine that we could somehow balance a pencil finely on its tip. We would discover that this is a very symmetric, but very unstable, situation. The vertical pencil looks the same from all directions around it.
But tiny disturbances in the immediate environment, such as small currents of air, are enough to cause the pencil to topple over. When this happens, the pencil topples in a specific, though apparently random, direction. The horizontal pencil now no longer looks the same from all directions. The symmetry is spontaneously broken.
In this example, it is the barely detectable currents of air that trigger the symmetry-breaking. Theorists realized that they needed to add something to the background environment that would help to break the symmetry in their quantum field theories. Not surprisingly, they reached for another kind of quantum field, a special kind of ‘scalar’ field whose magnitude doesn’t reduce to zero in empty space.It is the power of this idea that has now been recognized by the Nobel Committee. In 1964 there appeared a series of papers detailing a mechanism for symmetry-breaking in quantum field theories, published independently by American Robert Brout and François Englert, and Peter Higgs at Edinburgh University. From about 1972, the mechanism has been commonly referred to as the Higgs mechanism and the scalar fields are referred to as Higgs fields. The quantum of a Higgs field is a Higgs boson, which the rather self-deprecating Higgs has himself referred to as ‘the boson that has been named after me’.
Ironically, Higgs’s first paper detailing the Higgs mechanism was rejected by the editor of the scientific journal to which he sent it in July 1964. Higgs was indignant: ‘I believed that what I had shown could have important consequences in particle physics,’ he wrote some years later. But at that time quantum field theory was out of fashion.
He made some amendments and re-submitted his paper a month later to another journal, by which time a similar paper had appeared by Brout and Englert. Higgs acknowledged their paper in a footnote, and added a new paragraph referring to the possible existence of a massive boson, the one that would become named after him.
Three years later Steven Weinberg used the Higgs mechanism to predict the masses of the carriers of the weak nuclear force: the W and Z bosons, sometimes referred to as ‘heavy photons’. These particles were found at CERN about 16 years later, with masses very close to Weinberg’s original predictions. This built confidence in the Higgs mechanism but, until the Higgs field could be shown to be real, its existence betrayed by its tell-tale field quantum, there would always be room for doubt (and room for alternative theories).
I met Peter Higgs on a wet Thursday afternoon in Edinburgh, a little over two years ago in August 2011. Higgs retired in 1996 but has remained in Edinburgh close to the University department where he first became a lecturer in mathematical physics in 1960. ‘It’s difficult for me now to connect with the person I was then [in 1964],’ he explained, ‘But I’m relieved it’s coming to an end. It will be nice after all this time to be proved right.’
Now we have evidence that at least one kind of Higgs field does exist, and that Higgs was right.
The award of the Nobel Prize to just two individuals is somewhat controversial. Sadly, Robert Brout died in 2011, after a long illness, and the Prize is not awarded posthumously. But there was a third paper, published a little later in 1964 by American theorists Gerald Guralnik and Carl Hagen, and British physicist Tom Kibble, who were all gathered at Imperial College in London at the time. The Prize can be awarded to only three recipients, and if the Nobel Committee had decided to include this work its members would have had a bit of a problem. However, it seems that the Committee judged that Englert and Higgs had priority.
In a press release issued during the Prize announcement by Edinburgh University, Higgs remarked: ‘I am overwhelmed to receive this award and thank the Royal Swedish Academy. I would also like to congratulate all those who have contributed to the discovery of this new particle and to thank my family, friends and colleagues for their support. I hope this recognition of fundamental science will help raise awareness of the value of blue-sky research.’
Jim Baggott is the author of Higgs: The Invention and Discovery of the ‘God Particle’ and a freelance science writer. He was a lecturer in chemistry at the University of Reading but left to pursue a business career, where he first worked with Shell International Petroleum Company and subsequently as an independent business consultant and trainer. His many books include Atomic: The First War of Physics (Icon, 2009), Beyond Measure: Modern Physics, Philosophy and the Meaning of Quantum Theory (OUP, 2003), A Beginner’s Guide to Reality (Penguin, 2005), The Quantum Story: A History in 40 Moments (OUP, 2010), and Farewell to Reality (Constable, 2013). His next book, titled Origins: The Scientific Story of Creation, will be published by OUP in 2015. Read more from Jim Baggott on the OUPblog.
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Image credits: (1) Peter Higgs. By Gert-Martin Greuel [CC-BY-SA-2.0-de], via Wikimedia Commons; (2) François Englert. By Pnicolet [CC-BY-SA-3.0], via Wikimedia Commons