  Some experiments, performed at Berkeley, Cologne, Florence, Vienna, Orsay,
Rennes, etc., led to the claim that something seems to travel with a group
velocity larger than the speed c of light in vacuum. Various other experimental
results seem to point in the same direction: For instance, localized wavelet-
type solutions to Maxwell equations have been found, both theoretically and
experimentally, that travel with superluminal speed. [Even muonic and
electronic neutrinos [it has been proposed] might be "tachyons", since their
square mass appears to be negative]. With regard to the first-mentioned
experiments, it was recently claimed by Guenter Nimtz that those results with
evanescent waves (or tunneling photons) imply superluminal signal and impulse
transmission, and therefore violate Einstein causality. In this note we want to
stress that, on the contrary, all such results do not place relativistic
causality in jeopardy, even if they referred to actual tachyonic motions: In
fact, Special Relativity can cope even with superluminal objects and waves. For
instance, it is possible (at least in microphysics) to solve also the known
causal paradoxes, devised for faster than light motion, although this is not
widely recognized yet. Here we show, in detail and rigorously, how to solve the
oldest causal paradox, originally proposed by Tolman, which is the kernel of
many further tachyon paradoxes (like J.Bell's, F.A.E.Pirani's, J.D.Edmonds' and
others'). The key to the solution is a careful application of tachyon
mechanics, as it unambiguously follows from special relativity. At Last, in one
of the two Appendices, we propose how to evaluate the group-velocity in the
case of evanescent waves. [PACS nos.: 03.30.+p; 03.50.De; 41.20.Jb; 73.40.Gk;
84.40.Az; 42.82.Et ]
