Is it Time to Reexamine the Standard Model of Particle Physics?

By Amir Aczel | October 12, 2011 2:36 am

Fermilab’s Tevatron, the largest particle accelerator in the United States, was shut down on September 30 after a celebrated career of 28 years that has provided us with some of the greatest discoveries in particle physics. This leaves the European lab CERN (see photo on left) to lead the way into future discoveries with its Large Hadron Collider.This landmark in experimental physics is an opportunity to reexamine the theoretical model physicists have constructed and relied on in their search to understand the workings of the universe: the standard model of particle physics. The standard model is a comprehensive theory about nature’s elementary particles and the forces that control their behavior, and it has been constructed over a half-century of intensive work by many theoretical physicists as well as experimentalists. The model has worked amazingly well, harmoniously combining theory and experiments and producing extremely accurate predictions about the behavior of particles and forces. But could the model now be beginning to show some cracks?

It all started on a wintry evening in 1928. While staring at the flames in the fireplace at St. John’s College, Cambridge, Paul Dirac made one of the most important discoveries in the history of science when he saw how to combine the Schrödinger equation of quantum mechanics with Einstein’s special (but not general) theory of relativity. This achievement launched relativistic quantum field theory—which forms the theoretical basis for the standard model—and produced two immediate consequences: an explanation of the spin of the electron, and Dirac’s stunning prediction of the existence of antimatter (confirmed a few years later with the discovery of the positron).

In the late 1940s, Richard Feynman, Julian Schwinger, and Sin-Itiro Tomonaga, all working independently, presented the first quantum field theory, called quantum electrodynamics, which explained the electromagnetic interactions of electrons and photons. It forms the first part of the standard model by handling interactions that are controlled by the electromagnetic field. The theory’s success inspired other theoretical physicists to construct similar quantum field theories for addressing the actions of the weak and strong nuclear forces—thus together accounting for everything in particle physics except for the action of gravity, the subject of Einstein’s general theory of relativity. By the 1970s, the result, the standard model, was ready: a quantum field theory of all elementary particles—leptons and quarks and their interactions through the actions of particles (such as the photon) called bosons.

Experiments using increasingly more powerful particle accelerators at Stanford, Brookhaven, Fermilab, and CERN over the years have led to the discoveries of a “zoo” of particles, all of them and their interactions explainable by the model. The standard model, whose underlying mathematics is steeped in the notion of symmetry, led in two new directions: one was the postulation of what is now known as the Higgs mechanism—acting through a Higgs boson—to “break the symmetry” in order to give elementary particles their mass. (The assumption is that there was a primeval “symmetry” under which all particles were massless–the “broken symmetry,” through the Higgs mechanism, leaves the photon massless but gives mass to other particles.) And the second, called supersymmetry, was an attempt to extend the inherent mathematical symmetry of the standard model into a larger framework that would include yet-undiscovered particles that may identify the mysterious “dark matter” believed to permeate galaxies.

It is for the goals of finding the Higgs and discovering at least one new particle predicted by supersymmetry, that the Large Hadron Collider (LHC)—a colossal project costing over $10 billion—was built by CERN between Switzerland and France near Geneva. The LHC began its operations (at half its maximum energy) on March 30, 2010, and in the year and a half since then, has provided invaluable new information about the particles and forces of the standard model. But to the surprise of many physicists it has so far failed completely in discovering either a Higgs boson or any particles predicted by supersymmetry. To add to the conundrum, a related project that uses particle collisions at CERN to create neutrinos sent through the earth to Italy has led to the bizarre finding—seriously doubted by most physicists—that neutrinos, leptons explainable by the standard model, may travel at speeds greater than that of light. These wholly unexpected findings place the old standard model in new light. Its extension into supersymmetry is all but dead; the Higgs idea—central to the model—may have to be replaced by an alternative mass-endowing mechanism; and neutrinos and their behavior would have to be thoroughly reexamined. While the first two-thirds of the last century has been the age of great theories in physics, the present era may well belong to the experimentalists—for they are the ones most likely to provide us with answers to the big questions.


Amir D. Aczel is a researcher at the Center for the Philosophy and History of Science at Boston University and the author of 18 books about mathematics and physics, as well as numerous research articles. He is a Guggenheim Fellow and a frequent commentator on science in the media. See more at his website or follow him on Twitter: @adaczel.

CATEGORIZED UNDER: Space & Physics, Top Posts
  • Igor Fodor

    There are phenomena, which fit into the present thought pattern, e.g. six quarks. We searched so long until we found also the sixth top quark. Now we are searching for the Higgs particle. Not to miss anything, just in case, because there are also competing alternative higgsless theories, we are searching simultaneously also for the Kaluza-Klein particles.
    But it’s about more than to find „only“ an elementary particle or not – it’s about our worldview. Therefore, on one hand, we spend so much money for the experiments. On the other hand, such a gigantic particle accelerator is a “relict” from the times of the „Big Science“.
    The Nobel prize winner from 2004, Frank Wilczek predicts that with the particle accelarator LHC will begin a “new golden era“. Sean Carroll thought that it is to be counted with „dramatic changes in our understanding of the architecture of the reality“.
    But the physicists don’t make only predictions, they also make bets. So, for example, British physicist Stephen Hawking made a bet with the American Gordon Kane in 2000, that no Higgs particle will be found. Gordon Kane (a proponent of the supersymmetry) predicted by the way in 1999 that if we are not missing any basic ideas, in roughly next 6 years (from that point in time) supersymmetry particles and a light supersymmetric Higgs particle will be found with the LEP which was the predecessor of the LHC (or Fermilab in the USA) which hasn’t happened.

    Tommaso Dorigo, a particle physicist from Padua Univ. in Italy, made a bet in his Weblog in 2006 for $1000 that no physics “beyond the Standard Model” will be found with the LHC until the end of 2010 (at that time he couldn’t foresee that the LHC will be switched off for so long because of the fault with the superconducting magnet). This bet was taken on by his colleague, particle physicist Gordon Watts and the string theorist Jacques Distler.

    Already Robert Laughlin (Nobel prize 1998) noted, in all areas of science it was recognized that the reductionism prevented further progress. One should not forget that current thinking in the particle physics ist still influenced by reductionism, i.e. despite the evidence that the reductionist paradigm in physics is in difficulties, the particle experiments are described in form of reductionism.

    In the particle accelerator it came so far that the CERN theorist Alvaro de Rujula once said, the best result for the particle experiments would be if we found no Higgs particles! That would force the physicists to revise some details of the Standard Model. “Then we would learn something revolutionary”, he said. Physicists like Greg Landsberg believe anyway that the Standard Model is wrong…

    People are already curious when the LHC particle accelerator at CERN will produce the primordial matter quark-gluon plasma, from which originated the whole universe. Can scientists find something unexpected after all? The problem is that we don’t see something, until we found a suitable paradigm.

    Peter Higgs was quoted in the German newspaper “taz” from 12th Nov. 2011: „It would mean that I no longer understand things, which until now I believed to have understood“. But perhaps Alvaro de Rujula is right when he said: „…a complete lack of understanding often precedes a scientific revolution”.

  • Aashwin Basnet

    I didn’t understand what the explanations of neutrinos direct to! I think it has been confirmed with much insights and experimental details that neutrinos are not massless at all and thus they travel at speed less than light does. So, I didn’t find the idea of reviewing the neutrino’s experiment plausible! Correct me if I am wrong!


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About Amir Aczel

Amir D. Aczel studied mathematics and physics at the University of California at Berkeley, where he was fortunate to meet quantum pioneer Werner Heisenberg. He also holds a Ph.D. in mathematical statistics. Aczel is a Guggenheim Fellow, a Sloan Foundation Fellow, and was a visiting scholar at Harvard in 2005-2007. He is the author of 18 critically acclaimed books on mathematics and science, several of which have been international bestsellers, including Fermat's Last Theorem, which was nominated for a Los Angeles Times Book Award in 1996 and translated into 31 languages. In his latest book, "Why Science Does Not Disprove God," Aczel takes issue with cosmologist Lawrence M. Krauss's theory that the universe emerged out of sheer "nothingness," countering the arguments using results from physics, cosmology, and the abstract mathematics of set theory.


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