TABLE OF CONTENTS The failure of all explanations of the null result of the Michelson Morley experiment indicates that we need to question the foundations of Newtonian physics. We must abandon the absolute character of time and of length, and we must abandon the Galilean transformation equations and the addition law for velocities. This involves a far-reaching modification of spacetime, as first recognized by Minkowski soon after Einstein published his work. But in one regard the spacetime of relativistic physics remains the same as in Newtonian physics the spacetime remains four-dimensional. To determine the coordinates of a spacetime point, we use a reference frame of rigid measuring rods and synchronized clocks, just as in Newtonian physics. The synchronization of clocks can be performed by transport of an auxiliary clock. However, in relativistic physics, a moving clock suffers a time dilation (see Section 6.6), and to achieve a valid synchronization it is necessary to transport the auxiliary clock at low speed with respect to the given reference frame; more precisely, it is necessary to proceed to the limit of zero speed ( v ?0) for the clock transport. Such a synchronization ensures that when the reference frame is used to describe dynamics, Newton's laws remain valid for particles moving at low (nonrelativistic) speeds. In practice, the implementation of the limit of zero speed for clock transport is difficult and inconvenient. Because of this complication, an alternative but equivalent synchronization procedure is preferable.
The simple alternative synchronization procedure adopted by Einstein relies...
