The standard model of particle physics consists of a list of elementary particles, the four known forces of nature: electromagnetism, gravity, the nuclear strong force, and the nuclear weak force, and their corresponding fields (Young and Freedman 1530).
Forces: Fields or particles?
Electromagnetism and the two nuclear interactions obey the laws of quantum mechanics, including the Heisenberg Uncertainty Principle, and the concept of wave-particle duality, thus permitting their interactions to be conceptualized either in terms of quantum fields, or as being mediated by force carrier particles (Carroll 125-30). To clarify, in a classical field theory, a ‘force field’ is ascribed a value at every point in space-time and can be “scalar” (possessing a magnitude but no direction), or vector (possessing both a magnitude and a direction).
When physicists apply quantum mechanics to fields, they call it “quantum field theory,” (or just QFT for short), which is at the heart of the modern understanding of the physical world on the fundamental level (Carroll 129). Specifically, our modern understanding of particle physics is based largely on “relativistic” Quantum Field Theory, which incorporates Einstein’s Special Theory of Relativity. In a quantum field theory, forces are conveyed by ripples in the field which form waves and – because waves can also be interpreted as particles – as quantum particles of the field (Baggott). The most important difference between classical and quantum physics has to do with the relationship between reality and what we can actually know about it (Carroll 128). Quantum mechanics puts fundamental limits on the precision with which the state of a sub-atomic scale system can be measured that cannot, even in principle, be circumvented (Carroll 128). However, we will reserve a more concentrated look at quantum theory itself for another lesson (except insofar as it bears directly upon the formulation of The Standard Model).
Elementary Particles: Fermions and Bosons
The elementary particles can be grouped into two broad categories: fermions, which take up space, and bosons, which can pile on top of each other indefinitely (Carroll 293). The fermions, of which there are twelve in total, can be arranged into two families consisting of six quarks and six leptons respectively (Carroll 293). The bosons consist of the particles which mediate the interactions of the four aforementioned forces, as well as the Higgs (Young and Freedman 1530).
In part II, we’ll go over the elementary fermions and some of their properties.
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