Yup, the strong, weak, electromagnetic and gravitational forces are the
big four forces we all know and love. Actually, since the 1960's we've
known that the electromagnetic and the weak nuclear force are really
different forms of the same force, called the "electroweak" force.
But I must complain a small bit about your choice of words.
"Change" and "movement" do not need forces. Newton's first law says
that in an inertial reference frame, if an object has no forces acting
on it, it will move with constant velocity (that is, with constant
speed and direction). You can find a frame of reference moving with an
object so that it won't appear to be moving in that frame, but in other
frames of reference the object will be moving. Motion really is the
rate of change of position, so if you have motion without force, you
have change without force.
Forces govern interactions. They cause accelerations, classically,
or they define the allowed quantum states quantum-mechanically, or
govern scattering. The quantum picture of the three forces (not
including gravity) is one of exchange of force-carrying particles. The
strong force is mediated by the exchange of gluons, the electroweak
force is mediated by the exchange of photons and the weak force
carriers W+, W- and Z^0. We're still at a bit of a loss as to how to
get gravity to work quantum mechanically.
Tom
Not only can you have change (say relative positions changing)
without any forces, you can also have forces without change. For
example, the lowest-energy state of an atom is held together by
electrical forces (and nuclear ones in the nucleus) but it is
unchanging in time. So there's no necessary or sufficient connection
between forces and change.
Mike W.
(published on 10/22/2007)
