Physical Chirality. It Feeds on Negative Entropy *

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.