Electric and magnetic forces, like gravity, are long-range forces; no contact is required for one charged particle to exert a force on another. But this raises some troubling issues. For example, consider the charged particles A and B in FIGURE 22.20 . If A suddenly starts moving, as shown by the arrow, the force vector on B must pivot to follow A. Does this happen instantly? Or is there some delay between when A moves and when the force $\vec{F}{}_{\text{A on B}}$ responds?

FIGURE 22.20 If charge A moves, how long does it take the force vector on B to respond?

Neither Coulomb’s law nor Newton’s law of gravity is dependent on time, so the answer from the perspective of Newtonian physics has to be “instantly.” Yet most scientists found this troubling. What if A is 100,000 light years from B? Will B respond instantly to an event 100,000 light years away? The idea of instantaneous transmission of forces had become unbelievable to most scientists by the beginning of the 19th century. But if there is a delay, how long is it? How does the information to “change force” get sent from A to B? These were the issues when a young Michael Faraday appeared on the scene.

Michael Faraday is one of the most interesting figures in the history of science. Because of the late age at which he started his education—he was a teenager—he never became fluent in mathematics. In place of equations, Faraday’s brilliant and insightful mind developed many ingenious pictorial methods for thinking about and describing physical phenomena. By far the most important of these was the field.