Beyond Weird: Why Everything You Thought You Knew about Quantum Physics Is Different

by Philip Ball

It is not a place where different physical rules apply, so much as a place where we are forced to rethink our ideas about what we mean by a physical world and what we think we are doing when we attempt to find out about it.

Here are the most common reasons for calling quantum mechanics weird. We’re told it says that: • Quantum objects can be both waves and particles. This is wave-particle duality. • Quantum objects can be in more than one state at once: they can be both here and there, say. This is called superposition. • You can’t simultaneously know exactly two properties of a quantum object. This is Heisenberg’s uncertainty principle. • Quantum objects can affect one another instantly over huge distances: so-called ‘spooky action at a distance’. This arises from the phenomenon called entanglement. • You can’t measure anything without disturbing it, so the human observer can’t be excluded from the theory: it becomes unavoidably subjective. • Everything that can possibly happen does happen.

Many researchers would shrug or roll their eyes when the ‘meaning’ of quantum mechanics came up; some still do. ‘Ah, nobody understands it anyway!’ How different this is from the attitude of Albert Einstein, Niels Bohr and their contemporaries, for whom grappling with the apparent oddness of the theory became almost an obsession. For them, the meaning mattered intensely.

We can now put quantum paradoxes and puzzles to the test – including the most famous of them all, Schrödinger’s cat. These experiments are among the most ingenious ever devised. Often they can be done on a benchtop with relatively inexpensive equipment – lasers, lenses, mirrors – yet they are extraordinary feats to equal anything in the realm of Big Science.

They enable a kind of ‘teleportation’; they challenge Werner Heisenberg’s view of uncertainty; they suggest that causation can flow both forwards and backwards

It is a theory about information. This new perspective gives the theory a far more profound prospect than do pictures of ‘things behaving weirdly’. Quantum mechanics seems to be about what we can reasonably call a view of reality. More even than a question of ‘what can and can’t be known’, it asks what a theory of knowability can look like.

When words come too easily, it’s because we haven’t delved deeply enough (you’ll see that scientists can be guilty of that too). ‘We are suspended in language’, said Bohr, who thought more profoundly about quantum mechanics than any of his contemporaries, ‘in such a way that we cannot say what is up and what is down.’

Quantum physics implies that the world comes from a quite different place than the conventional notion of particles becoming atoms becoming stars and planets. All that happens, surely: but the fundamental fabric from which it sprang is governed by rules that defy traditional narratives.

Indeed, it is possible that we might never be able to say what quantum theory ‘means’. I have worded that sentence carefully. It’s not exactly (or necessarily) that no one will know what the theory means. Rather, we might find our words and concepts, our ingrained patterns of cognition, to be unsuited to articulating a meaning worthy of the name.

There is no reason to believe that the most important aspects of the theory are those that were discovered first, and plenty of reason to think that they are not.

But telling quantum theory chronologically can become a part of the problem that we have with it. It yokes us to a particular view of what matters – a view that no longer seems to be looking from the right direction.

they possessed extraordinary physical intuition informed by their erudition in classical physics. They had amazing instincts for which pieces of conventional physics to use and which to throw away. This doesn’t alter the fact that the formalism of quantum theory is makeshift and in the end rather arbitrary.

But most of the fundamental equations and concepts of quantum mechanics are (inspired) guesses.

With quantum mechanics it is not so simple. For it is not so much a theory that one can test by observation and measurement, but a theory about what it means to observe and measure.

Planck’s constant. The energy can be equal to hf, 2hf, 3hf and so on, but cannot take values in between. This implies that each oscillator can only emit (and absorb) radiation in discrete packets with frequency f, as it moves between successive energy states.

Planck’s proposal excited no controversy or disquiet until Albert Einstein insisted on making the quantum hypothesis a general aspect of microscopic reality. In 1905 Einstein proposed that quantization was a real effect,

Quantization was just what alerted Einstein and his colleagues that something was up with classical physics.

When, then, do you learn about quantization of Planck’s ‘oscillators’? In the last chapter. In fact ‘The Importance of Quantization’ is the last section of that final chapter. That’s how modern physics judges the conceptual significance of Planck’s hypothesis, and it’s a fair assessment.

by the time objects get as big as tennis balls, quantum rules have conspired to generate classical behaviour. The significance of the size difference is not in terms of what objects do, but in terms of our perceptions.

The key distinctions between classical mechanics and quantum mechanics, in Susskind’s view, are these: • Quantum physics has ‘different abstractions’ – how objects are represented mathematically, and how those representations are logically related. • Quantum physics has a different relationship between the state of a system and the result of a measurement on that system.

You should worry about the second, though. In a sense, all of quantum theory’s counter-intuitive nature (I am trying very hard not to call it weirdness) is packaged up here.

The tennis ball had the pre-existing property of a speed of 100 mph, which I could determine by measurement. We would never think of saying that it was travelling at 100 mph because I measured it. That wouldn’t make any sense. In quantum theory, we do have to make statements like that.

Quantum objects are neither wave nor particle (but sometimes they might as well be) One of the problems in talking about quantum objects is deciding what to call them. It seems like a trivial point, but actually it’s fundamental.

Are waves the wake left behind to fil the void created by energy moving in front ? That’s how wave spreads each being the succession of filing the void created by the preceding effort of filling the void in front ?