Force. Before fields were recognized, forces were thought {except by Newton} to happen through "action at a distance". That is, a body or particle in one place causes a body in another place to move, without any medium in between. When Faraday introduced the concept of fields, this picture was changed: The first body creates a field in the surrounding space and this field then exerts a force on the second body. In QFT, everything is fields, even the bodies; reality consists only of fields and interactions between fields. The effect of force comes from terms in the field equations that describe how one field influences another. Thus the force field does not exert a force on another "body" in the classical sense. Instead it interacts with the field that constitutes the other "body" and alters its evolution, causing its spatial distribution to change. This change in evolution is equivalent to the older classical picture of a particle experiencing a force. Indeed, Newton's laws of motion can be derived from the equations of QFT!
( Rodney A. Brooks )
[ Fields of Color: The theory ]
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