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Single-Particle Electrodynamics - Assassination Science

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nonrelativistic denotes the use of Galilean mechanics. Some subtle problems<br />

involved in making the transition between the fundamentally incompatible<br />

structures of relativistic and nonrelativistic mechanics are discussed in Sections<br />

2.6.12 and A.8.25.<br />

It should be noted that the adjectives “classical” and “relativistic” are<br />

linearly independent: relativistic classical physics, nonrelativistic classical<br />

physics, relativistic quantum physics, and nonrelativistic quantum physics,<br />

are separate quadrants of physics.<br />

A.3.13<br />

Quantities<br />

A physical quantity is defined to be any aspect of a physical phenomenon that<br />

may be described in mathematical terms. A mathematical quantity is defined<br />

to be a mathematical construct that obeys some well-defined mathematical<br />

laws. Mathematical quantities may be used to represent physical quantities.<br />

In this thesis, the term quantity is used for either of these concepts, not<br />

always unambiguously.<br />

A.3.14<br />

Explicit quantities<br />

When the author refers to a quantity as being explicit, then it generally<br />

means that some elegant yet highly abstract expression has been “expanded<br />

out” in terms of components that are generally less æsthetically elegant, but<br />

usually more in contact with one’s intuitive understanding of the physical<br />

world.<br />

This often, but not always, means that a covariant expression has been<br />

written in terms of non-covariant components (see Section A.3.18 for a precise<br />

definition of these words, according to the author’s terminology).<br />

333

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