  Since the 1983 definition of the speed of light in vacuum as a fundamental
constant with the exact value of 299792458 m/s the question remains as to what
apart from the wavefront travels at that speed. It is commonly assumed that the
entire wave-packet or an impulse of the electromagnetic radiation in free space
does. Here it is shown, both theoretically and experimentally, that there
exists a region close to the source, where, while the wave-front travels at the
speed of light, the individual impulses comprising the body of the wave-packet
appear to slow down and even go backwards in time. This three-dimensional
near-field late-time effect may also explain some of the free-space
superluminal measurements.
