Wave Propagation in Linear Media | re-examined

the quest for superluminality and to speculate what life beyond the speed of light could be
like. By contrast, it was Einstein who postulated that the velocity of light is the utmost speed
for the transmission of energy or information, and the bare mention of perhaps the best-known
physicist ever is su cient toevoke interest. Even more thrilling was the fact that his legacy
seemed to be at stake. His relativistic theory, perhaps the best-known physical theory ever,
seemed to be endangered and eventually falsi ed by experimental evidence. What followed
looked pretty much like a strife between disciples and opponents of Einstein. In fact, the
entire discussion was and still is rather circling around the question how a signal can be
de ned. This was, however, much too involved for many commentators, compared with the
exciting imagination of signal transport faster than light. So they often forgot to point out an
important limitation: superluminality, as it is currently discussed, is con ned to extremely
short distances that span but a few centimetres, depending on the frequency range of the
waves under consideration. This creates an odd contrast to the notion of comprehensive
unboundedness we are so inclined to associate with the propagation of light.
The preceding remarks account for the somewhat `scienti cal' ingredients of the story. But
there is also a rather cultural aspect. At present, the quarrel about superluminal wave
propagation is maintained by two parties that happen to work in Germany and the United
States, respectively. 5 Consequently, some reports were interspersed with slightly patriotic
(but nonetheless super uous and annoying) undertones. One could, at times, not escape the
feeling that the writer painted the picture of a sports competition rather than an academic
discussion. So to answer our initial question, I believe itwas the mixture of popular names,
scienti c rivalry, and the dream of bringing science ction one step closer to reality that made
the subject so fascinating for journalists and readers alike. Who cares that accuracy was left
behind in the attempt of making things comprehensible? After all, physics got a mention
in the media, and I was greatly surprised how many people outside the so-called `scienti c
community' took notice of it.
It would be dishonest to deny that this thesis was stimulated by the discussion raging about
the interpretation of the recent experiments. But by the time the work began, the controversy
still belonged to the main contenders, and it could not be foreseen that the subject would
sometime merit public attention. The present text has several objectives. First, it is meant as
asurvey of the eventful history of wave propagation, its discovery and comprehension, with
a particular emphasis on the superluminality issue. Furthermore, it provides case studies on
wave propagation phenomena. They are intended as supplements to earlier theoretical work
along these lines | in the spirit of what Sir Karl Popper declared to be the core of a scienti cal
theory: that it must, in principle, be subjectable to falsi cation. 6 Now the idea of carrying
out case studies is neither ingenious nor spectacular, it is as old as science itself. What
has changed in the recent past are the ways and means that are at hand to reach the goal.
While in former times researchers had to use approximation methods to evaluate complex
expressions by hand, the ever-growing power of computers and their software today enables
us to numerically solve problems in greater detail and accuracy. The formulation of the
5 Prof. Nimtz at the University of Cologne (http://www.uni-koeln.de/math-nat-fak/ph2/) and Prof.
Chiao at the University of Berkeley, CA(http://physics1.berkeley.edu/research/chiao/)
6 Karl R. Popper, The Logic of Scienti c Discovery, 1934.
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