  This talk was given at the Tunguska-2001 international conference but it is
not about the Tunguska event. Instead we tried to give some flavor of mirror
matter, which is predicted to exist if parity is an unbroken symmetry of
nature, to non-experts. The possible connection of the mirror matter ideas to
the Tunguska phenomenon was indicated by Foot and Gninenko some time ago and
was elaborated by Foot in the separate talk at this conference. If the mirror
world interpretation of the Tunguska like events is indeed correct then the
most fascinating (but very speculative) possibility is that some well known
celestial bodies with strange properties are in fact made mostly from mirror
matter, and so maybe the mirror world was discovered long ago and we just have
not suspected this.
