  Chirality is considered by many scientists to be mainly a geometric concept.
There exists also a physical aspect of chirality which is largely being
overlooked at. Two examples of mechanical devices are introduced here that
represent ``Physical Chirality''. These are a rotating water sprinkler and a
variant of Crookes' radiometer. When interacting with appropriate media, they
both choose only one mode of rotation out of two possible ones. Such a behavior
does not obey time-reversal invariance, which is regarded to be a rule in
classical mechanics. This is due to their chiral nature. Instead, they do obey
a space-time (ST) law of invariance, that is, what is rotating in the opposite
direction is the mirror-image of the given device. In a recent experiment of
Koumura et al. they discovered a similar behavior of a molecular rotor. The
possible biological significance of physical chirality is emphasized hereby,
and the conclusion is that chiral molecular systems do not reach readily
thermal equilibrium. In other words: ``Physical chirality does feed on negative
entropy'', and therefore, it may well be of crucial value to life.
