Actually the relationship between the weak nuclear force and the electromagnetic force is well understood. It would have to be related, given that the weak int

Actually the relationship between the weak nuclear force and the electromagnetic force is well understood. It would have to be related, given that the weak interaction is the cause of beta decay, which results in a neutron becoming a proton (which has a positive electromagnetic charge) and the creation of an electron (which has a negative charge). The force carrying particles of the weak force can also have electromagnetic charge, further demonstrating the connection between the two phenomena. You can reason about all the forces being related in some way. For example, beta decay happens in free neutrons, but does not happen in a helium-4 nucleus; there should be a connection with the strong nuclear force that explains this. In some sense the fact that we can observe or measure an interaction implies that it must be related to other forces, since our ability to make an observation is itself dependent on such connections (in the end you need some electromagnetic effect that your eyes can perceive).