On Indeterminacy

You will often hear it stated, in certain circles, that nothing can be said about the outcome of some quantum interaction or other, when two infinitesimal shreds of the universe interfere with each other in a given way. In almost all cases, this is in fact an overstatement, and quite incorrect. Usually, the difficulty lies in predicting exactly which outcome from a finite list, or range, of likely results, will manifest in any individual case. Think rolling a dice, or flipping a coin.

Accurately forecasting the outcome of a single toss of a coin may well be (effectively) impossible, but it can be said with certainty that the result will be either ‘heads’ or ‘tails’. You can also know beforehand that a coin tossed often enough, will result in ‘heads’ around half the time, and ‘tails’ the other half. To put it another way: the likelihood, or probability, of a single toss resulting in ‘heads’ (or ‘tails’, for that matter) is 50 percent. This is similar to the infamous indeterminacy in quantum mechanics.

The difference between a classical action, like flipping a coin, and a quantum measurement, is that, theoretically speaking, you could learn more about the mechanical specifics of an individual coin-toss (its hidden variables, so to speak, like the precise weight-distribution of the coin, launch-force and angle, air-humidity, and so on) and so predict the outcome more accurately, whereas the mechanics of, say, the spin of an electron, are – by definition – enclosed in an impenetrable black box, because there is nothing under the hood.

This goes to the heart of the great debate – or schism, as some would have it – in physics over the past century, one on which the jury of experts is still very much divided: is it true that there are no hidden variables to be discovered in certain quantum phenomena, or is it merely that we, as yet, have not developed the means to uncover them? Is existence ultimately decipherable, or is there some inscrutable mystery at the heart of everything?

Which is a question that transcends the world of physics – and a problem, like all great conundrums, whose power lies in its posing, not necessarily in its resolution.

More mundanely, this indeterminacy is a familiar part of all of our lives. Imagine that you return home from work some late afternoon to a partner who seems to be in a bad mood. Should you gently enquire as to how her day went, and how she’s feeling? Yell at her that you’re sick of her bringing you down? Or is it wiser to get out of the line of fire while you still can? You could just proceed straight to trying to lift the mood with some humour, by telling the story of the guy sitting across from you on the train that morning, typing away earnestly on his laptop with a grave frown, his T-shirt on back to front, and a streak of egg-yolk over the full length of his left cheek.

However you decide to act, you must do so on the basis of imperfect information, and you can only guess at how your partner will react. You are essentially probing the situation and confirming the outcome – which is effectively identical to making a quantum measurement. Theoretically, it may be possible to decipher how the subsequent unfolding of events that afternoon flowed from your partner’s state of mind reacting to exactly how your state of mind (as dictated by hormone tables, recent news, events of the day, and so on) tested the waters of your shared histories and recurring behaviour patterns. But to you, it will always remain a mystery precisely why things turned out the way that they did.

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A Quantum Metaphor for Human Being by Ciarán Ó Néill is available to preorder now