Abstract
The Standard Model of particle physics encapsulates our current best understanding of physics at the smallest distances and highest energies. It incorporates quantum electrodynamics (the quantized version of Maxwell's electromagnetism) and the weak and strong interactions, and has survived unmodified for decades, save for the inclusion of non-zero neutrino masses after the observation of neutrino oscillations in the late 1990s. It describes a vast array of data over a wide range of energy scales. I review a selection of these successes, including the remarkably successful prediction of a new scalar boson, a qualitatively new kind of object observed in 2012 at the Large Hadron Collider. New calculational techniques and experimental advances challenge the Standard Model across an ever-wider range of phenomena, now extending significantly above the electroweak symmetry breaking scale. I will outline some of the consequences of these new challenges, and briefly discuss what is still to be found.This article is part of the themed issue 'Unifying physics and technology in light of Maxwell's equations'.
Highlights
I will start the tour of the Standard Model (SM) at typical atomic scales of around 102 electronvolts. (The gluon and the photon masses, at zero, are off the low end of a logarithmic scale, and neutrino masses which I will return to later.) Precision atomic physics measurements played a critical role in the development of the quantum electrodynamics (QED) sector of the SM, and the current poster-child for high-precision quantum-field theory is the anomalous magnetic momentum of the electron, where theory and experiment are in agreement at the level of one part in 1013 [1,2]
Some of the principles behind the theory trace their origins back to Maxwell’s equations for electromagnetism, and those equations remain the classical form of the quantized electromagnetic force within the theory (QED)
QED itself, as a gauge theory, is the template for the weak and strong forces, themselves based on larger, non-Abelian gauge symmetries
Summary
Answering this question is one of the goals of physics. It is a reductionist approach which is not the whole story, —whatever tiny constituents are revealed, their interactions lead to rich emergent phenomena revealing new physics, not to mention chemistry, biology and the rest. Like most answers in science, this is a provisional statement, determined by our current ability to halve things, or, less destructively, to resolve ever-tinier objects. It has just achieved a major predictive success with the discovery of the Higgs boson, and it is remarkable that we have a selfconsistent theory in which these objects are pointlike, and which can describe phenomena over an enormous range of energy and distance scales. I will recount some selected highlights of the model, and look at where further progress may be expected
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