Observation of Locally Negative Velocity of the Electromagnetic Field in Free Space

Neil V. Budko
2009 Physical Review Letters  
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
more » ... mpulses 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.
doi:10.1103/physrevlett.102.020401 pmid:19257249 fatcat:esfrtfsxznc6nl4wyv7eudtjom