7 The fundamental forces

Chapter 7
The fundamental forces

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 $ℏ$ , $c$ and the mass of the proton, $m_{p}$ . 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.

Table 7.1: A summary of the four fundamental forces


Force	Range	Strength	Acts on


Gravity	$\infty$	$G_{N} \approx 6 1 0^{- 39}$	All particles (mass and energy)

Weak Force	$< 1 0^{- 18}$ m	$G_{F} \approx 1 1 0^{- 5}$	Leptons, Hadrons

Electromagnetism	$\infty$	$α \approx 1 ∕ 137$	All charged particles

Strong Force	$\approx 1 0^{- 15}$ m	$g^{2} \approx 1$	Hadrons

In order to set the scale we need to express everything in a natural set of units. Three scales are provided by $ℏ$ and $c$ and $e$ – 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 $e = 1$ we use electron volt as natural unit of energy)

\begin{array}{rcl} ℏ & = & 6.58 \times 1 0^{- 22} MeV s & (7.1) \\ ℏ c & = & 1.97 \times 1 0^{- 13} MeV m & (7.2) \\ m_{p} & = & 938 MeV ∕ c^{2} & (7.3) \end{array}

7.1 Gravity
7.2 Electromagnetism
7.3 Weak Force
7.4 Strong Force

[forward][back][up]

Chapter 7The fundamental forces

Chapter 7
The fundamental forces