TABLE 2.3 The Four Fundamental Forces


Force Carrier

Approximate Mass of Carrier







Weak force

W and Z bosons

About 90 times the proton mass

Strong force



Table 2.3 lists the force carriers. Note that although three of them are massless, the fourth is extremely heavy. Given this disparity, it might seem impossible that they could arise from a single mechanism. Yet, as the next section indicates, physicists are optimistic that all the forces can be described in a "unified" framework.

Unification of Forces

Further unification is treated in the following chapter. It has been established that two of the forces listed in Table 2.3 (electromagnetic and weak) are indeed unified, and there is compelling evidence that a third (strong) is as well. It may even be that gravity is also subject to unification so there would be in a real sense just one force.


Underlying the electrical, magnetic, gravitational, and other phenomena of particle physics are a number of general principles. Examples of the most fundamental of these principles (often referred to as laws) are the conservation of energy, the conservation of charge, and the law of cause and effect (causality). Physicists believe these laws to be universal and absolute, applying to interactions between the smallest components of matter that have thus far been observed, to interactions between galaxies of stars, and even to the development of the universe itself.

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