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basic_notions:units

Explanations in this section should contain no formulas, but instead colloquial things like you would hear them during a coffee break or at a cocktail party.

**The International System of Units (SI)**- the modern metric system of measurement.**Gaussian**- commonly used in electromagnetism.**Heaviside-Lorentz (rationalized Gaussian)****Natural units**- commonly used in quantum electrodynamics and particle physics in general.

- A great discussion can be found in Section 2.1 in Klauber's "Student-friendly Quantum Field Theory".
- See also BABEL OF UNITS by Neal J. Carron

Any physical quantity can be expressed by using as fundamental unit either energy, mass, length or time.

\begin{align} ct&\approx \ell\Longrightarrow {\rm time}\approx{\rm length},\\ E&\approx mc^2\Longrightarrow {\rm energy}\approx{\rm mass},\\ E&\approx pv\Longrightarrow {\rm energy}\approx{\rm momentum},\\ Et&\approx \hbar\Longrightarrow {\rm energy}\approx{\rm (time)^{-1}}\approx {\rm (length)^{-1}}. \end{align}

The motto in this section is: *the higher the level of abstraction, the better*.

basic_notions/units.txt · Last modified: 2018/04/06 15:37 by jakobadmin

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