The work behind this year’s Nobel for Physics advances the search for a grand unifying theory on the fundamental aspects of nature

The work of Peter Higgs and Francois Englert on how elementary particles acquired their mass is a cornerstone of modern particle physics in general, and of the Standard Model, a theoretical framework in particle physics, in particular. Conducted almost 50 years ago in 1964, the research of this year’s winners of the Nobel Prize in physics has definitely been “tested by time”, one of the Nobel Committee’s criteria to be selected for the prestigious prize

Their research unravels an event called spontaneous symmetry breaking that happened 10-11 seconds after the Big Bang 13.82 billion years ago. The event violated the symmetry in the sea of energy unleashed by the Bang and gave rise to particles with different masses. Mr. Higgs and Mr. Englert (working with Robert Brout, who died in 2011) attributed these masses to the Higgs field, an invisible field of energy pervading the universe. The smallest disturbances in this field were encapsulated as particles called Higgs bosons. When other elementary particles move through this field, Higgs bosons couple with them in varying degrees — stronger the coupling, more the retardation of the particle’s motion through the field, and greater its mass. This mechanism has come to be known as the Higgs-Englert-Brout (HEB) mechanism, for which Mr. Higgs and Mr. Englert were awarded the Nobel Prize.

The Standard Model, into which the HEB mechanism was incorporated by Steven Weinberg and Abdus Salam in 1968, rests on the validity of this mechanism. Without mass, elementary particles would be like photons, zipping through space at the speed of light and unable to participate in any of the reactions that are the reason anything exists, whether atoms, molecules, life forms, planets, stars or galaxies.

These efforts are part of a grander context: that of bringing the laws of physics under one umbrella to explain everything from the smallest of scales to the largest. At the moment, though, there exist two stubbornly irreconcilable ‘laws’ of physics: Einstein’s theories of relativity and gravitation for the cosmos, and quantum mechanics for elementary particles. Unifying gravity and quantum mechanics is one of the biggest problems in physics. The Standard Model is not complete either, and it is in its failures that physicists believe the clues to a grand unified theory lie.

Correct predictions

Apart from prophesying the discovery of the Higgs boson, the Model also correctly predicted the existence of the bottom quark (experimentally found in 1977), W and Z bosons (theorised by the Higgs mechanism, found in 1983), top quark (1995), and the tau neutrino lepton (2000). That’s an impressive track record for a framework that has no idea what dark matter is, why there are three types of elementary particles (bosons, quarks and leptons) and not two or four, or why some forces in nature are incredibly stronger than others — questions probing deeper and ever more fundamental aspects of nature.

LHC's role

One place where answers to these questions can be found is at what is possibly one of the world’s most complex experiments, constructed and operated at the largest scale of human endeavour: The Large Hadron Collider (LHC), a 4.3-km wide atom-smasher located near Geneva, Switzerland. In July 2012, it spotted the first physical hints of the Higgs boson, paving the way for the HEB mechanism to be firmly cemented into the Standard Model canon. There is a bit of tragedy here: while the Nobel Prize went to Mr. Higgs and Mr. Englert, their achievements couldn’t have been validated without the collaborated efforts of more than 10,000 engineers and scientists from hundreds of universities around the world, with more than $9 billion in funding (as of 2010) involved in building and operating the collider. Sadly, the collaboration was mentioned only in passing.

The silver lining is that the LHC is not yet done. It is slated to reopen post-upgrades in 2015, and will continue to search for more elusive particles, perhaps finding one beyond the Standard Model itself. Such an event could open the window for a newer, more comprehensive model of particle physics, and pave the way for a grand unified theory of everything.

(A. Rangarajan interviewed Francois Englert and Robert Brout in 2008, which was published in The Hindu the same year. You may read that here.)

vasudevan.m@thehindu.co.in

Blog: The Copernican

Correction

A sentence in "Lending weight to the question of mass" (Oct. 10, 2013, Op-Ed page) read: "There is a bit of tragedy here: while the Nobel Prize went to Mr. Francois and Mr. Englert, their achievements couldn’t have been validated ..." It should have been Mr. Higgs and Mr. Englert.

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