The fundamental forces are normally divided in four groups, of the four so-called “fundamental” forces. These are often naturally classified with respect to a dimensionless measure of their strength. To set these dimensions we use , and the mass of the proton, . The natural classification is then given in table 7.1 . Another important property is their range: the distance to which the interaction can be felt, and the type of quantity they couple to. Let me look a little closer at each of these in turn.
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Force | Range | Strength | Acts on |
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Gravity | All particles (mass and energy) | ||
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Weak Force | m | Leptons, Hadrons | |
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Electromagnetism | All charged particles | ||
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Strong Force | m | Hadrons | |
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In order to set the scale we need to express everything in a natural set of units. Three scales are provided by and and – actually one usually works in units where these two quantities are 1 in high energy physics. For the scale of mass we use the mass of the proton. In summary (for we use electron volt as natural unit of energy)