In the Standard Model the weak and the electromagnetic interactions have been combined into a
unified electroweak theory.
Physicists had long believed that weak forces were closely related to electromagnetic forces.
Eventually they discovered that at very short distances (about 10-18 meters)
the strength of the weak interaction is comparable to that of the electromagnetic. On the other
hand, at thirty times that distance (3x10-17 m) the strength of the weak interaction is 1/10,000th
than that of the electromagnetic interaction. At distances typical for quarks in a proton or neutron (10-15 m) the
force is even tinier.
Physicists concluded that, in fact, the weak and electromagnetic forces
This is because the strength of the interaction depends
strongly on both the mass of the force carrier and
the distance of the interaction.
The difference between their observed strengths is due to the huge difference in
mass between the W and Z particles, which are very massive, and the photon, which has no mass as
far as we know.