Force | Force particle | Mass
Strong | Gluon | 0
Electromagnetic | Photon | 0
Weak | Weak gauge bosons | 86, 97
Gravity | Graviton | 0

Table 1.2 The four forces of nature, together with their associated force particles and their masses in multiples of the proton mass. (The weak force particles come in varieties with the two possible masses listed. Theoretical studies show that the graviton should be massless.)