Saturday, 9 January 2021

Chiral asymmetries

The word 'sinister' says it all: it means, originally, left, and its unabashed negativity stands in stark contrast to the positive connotations of 'dexterity', which derives similarly from the Latin word for 'right'.  But it is no wonder: Nature itself discriminates.  If it were literally even-handed, there would be as many people born with hearts on their right as those with them on the left; in fact this reversal of all the body's organs is extremely rare.

Chirality - that is, handedness - is altogether a mysterious business.  Consider the mirror:  facing it, your right side becomes your left, and your left, your right; and yet top does not swap places with bottom.  Actually, nothing swaps over; it is simply that chirality is intimately bound up with the 'sense' of space - a sense which the mirror reverses.  Unsurprisingly, perhaps, for such a profound concept, chirality crops up frequently in the world of sub-nuclear physics.  Handedness goes to the heart not just of life, but of reality too.

Mysterious it all may be as a philosophical abstraction, but the many practical consequences of Nature's unfair habits are not in doubt.  Since there can be no compromise between right and left, the sinister part of the world loses out in a vote decided by a crude show of hands.

We dextrists may take corkscrews for granted; imagine, though, if the turn went the other way.  Handles in general presuppose that your right arm is the stronger; if it is not, you are faced by a difficult choice: a weak, but natural action, or a strong, unnatural one.

Things are improving.  As the world population has increased, so has the viability of catering for the minority group of the left-handed.  Consequently, many everyday objects that imply or have acquired a handedness can be obtained in a mirror-image form.  Leaving aside the joke left-handed teacups, there are now scissors for the left-handed, as well as flutes, violins and guitars.  At least the widespread availability of the left-handed pen nib, along with writing tools that assume no one chirality, has brought equality to a crucial area; after all, Arabic script is produced right to left with the right hand - an equivalent situation to that of the sinistrist scribe in a dextrist writing system.

But there remains one domain that is stubbornly handist, with little hope of any remedy: that of traditional Western art.  Representational paintings expect to be read from left to right.  Typically an optimistic image will rise across the canvas, a gloomy and despondent one fall.  Thus, like chirality, the mood of a picture also is reversed in its mirror-image.  That this was explicitly understood is proved by the habit of composing subjects with the emphases switched in the other direction when painting cartoons for tapestries, for example in Raphael's great series.  Transferring the cartoon image to the tapestry reversed the sense, and so restored the traditional chirality and created the intended effect.  As a consequence, for those with a leftish take on the world most of the greatest masterpieces of Western art must seem subtly but irredeemably flawed; no sinister plot, for a change, but a dextrist one.


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