When objects
move at speeds comparable to the speed of light, a
variety of effects come into play which are not taken
into account in standard visualisation systems.
Systems such as the popular commercial 3D
visualization tool Lightwave make a key assumption -
that the speed of light is infinite. The speed of
light, more than a billion kilometers per hour, is so
much greater than the kinds of velocities we
encounter in our daily lives that this approximation
causes no significant problems. However, in
astronomy, where high velocities and vast distances
are the norm, relativistic effects abound.
BACKLIGHT
can be used to model these astronomical effects, but
it is more instructive to use it as an aid to the
kind of thought experiments Einstein conducted when
he was formulating the theory of Special Relativity.
We imagine a world where the speed of light is much
slower, so that everyday vehicles move at
relativistic velocities.
BACKLIGHT
allows us to construct and photograph such worlds. In
essence a four-dimensional raytracer, it produces
scenes demonstrating the optical effects of special
relativity - delayed observation, angular aberration,
Doppler shifting and the headlight effect.
Until the 1960's it was widely
believed that the length contraction was directly
visible - that objects moving at relativistic speeds
simply looked shorter. Papers by Penrose and Terrel
showed this to be false - the length contraction
exists, but there is a fundamental divide between observing
and seeing. When we observe, we use clocks
and tape measures to construct a schematic picture of
the world. When we see, we gather light - and at high
speeds light does not obey familiar rules. The
apparent direction, size, shape abd colour of objects
can all be radically changed by relativistic motion.
