Quantum by Manjit Kumar

It started with an attempt to build a better light-bulb, and ended with the dissolution of our notions of reality. Quantum is the story of how our understanding — if understanding is the right word — of the subatomic world progressed from not-quite-believing in atoms at the end of the 19th century to a point at the end of the 20th century where scientists wondered if perhaps the best explanation for it all wasn’t that there were an infinite number of universes out there, enumerating each and every combination of all possible outcomes for all possible events. This could be what Lovecraft was going on about in the opening paragraph of “The Call of Cthulhu” (first published in 1920, the year the two main protagonists of Manjit Kumar’s narrative, Albert Einstein and Niels Bohr, met for the first time):

“…some day the piecing together of dissociated knowledge will open up such terrifying vistas of reality, and of our frightful position therein, that we shall either go mad from the revelation or flee from the deadly light into the peace and safety of a new dark age.”

Max Planck

Although, so far, we’ve done neither.

Quantum begins with Max Planck sitting down to work out some equations that tally with the results of experiments into the relationship between the temperature of a piece of metal (the filament in a light-bulb, for instance), and the light it emits. But Planck’s equations were a bit of a hack, because they had no scientific reasoning behind them. So, once he’d got them, he set about trying to explain why they worked. And he found an answer, but only — to his chagrin — by bringing in some ideas he didn’t quite agree with, such as the existence of atoms, and also the idea that energy, in this light-bulb set-up, had to be released in discrete, tiny packets, rather than as a continuous flow.

It was Albert Einstein who took things a step further, using this idea of quantised energy to solve one of physics’s then-mysteries, the photoelectric effect (the fact that electrons are emitted from metal when it’s exposed to electromagnetic radiation, but only if the radiation exceeds a certain minimum wavelength), publishing a paper on it in the same year (1905) as his name-making paper on the special theory of relativity. This idea of energy quanta, it seemed, could explain things classical physics couldn’t.

Niels Bohr

Increasingly, what became known as “the Copenhagen interpretation” came to dominate the world of quantum theory. This centred around Danish physicist Niels Bohr, who thought that asking what quantum mechanics meant, in terms of how it explained physical reality, was a nonsensical question. What mattered was that the theory predicted results that were verified by experiments. To ask more of it — that, for instance, it might paint a visualisable picture of reality at the subatomic level — was to ask too much. After all, we couldn’t ask what an electron looked like, it was just too small an entity to affect the light waves we human beings use for looking. In fact, the only way to know anything about an electron, or any other subatomic entity, was to interact with it in some disruptive way, and measure the results. The old idea of a scientist as a passive observer didn’t work at such a tiny level, when observation meant active interference. And measuring one aspect of a subatomic entity’s state in this knockabout way blurred any chance of measuring certain complimentary aspects, thanks to what became known as the Heisenberg Uncertainty Principle. We could, then, never get the whole picture.

Albert Einstein

Einstein didn’t like this “it works, let’s leave it at that” approach. He thought physics should, as well as predicting the results of experiments, provide a model of reality. He wanted to know, for instance, that electrons were like tiny billiard balls, or tiny waves, or whatever it was they were like. He wanted a picture, not just an equation. (Which makes sense when you consider how he did his physics — mostly by sitting down and imagining his way through thought experiments, like what the universe would look like if you were riding on a beam of light, which is what led to his development of the special theory of relativity.)

Our (by which I don’t mean “my”) understanding of quantum reality advanced through the work of a lot of scientists, some of whose differences (as between Heisenberg’s “matrix mechanics” and Schrödinger’s “wave mechanics” approaches) could get pretty personal, as though this were a matter of faith rather than science. (Even when matrix mechanics and wave mechanics were proved to be mathematically equivalent, Heisenberg got annoyed at how his method was sidelined by physicists who found Schrödinger’s easier to work with.)

But always at the core of it were Einstein and Bohr. Einstein loved coming up with often stunningly simple theoretical experiments to thwart the consistency of Bohr’s “Copenhagen interpretation”, after which Bohr would spend frantic hours or even days trying to see through them — which he always would. Einstein, still the more famous name today, came to seem to his colleagues at the time like the old man of yesterday’s science, stuck in the past by his refusal to be convinced by this new approach, while incoming generations took up Bohr’s approach unquestioningly, simply because it worked.

Despite this difference, Einstein and Bohr maintained a mutual respect and friendship throughout most of their lives. A distance grew between them when Bohr became increasingly exasperated by Einstein’s refusal to accept the “Copenhagen interpretation”, but this was perhaps as much down to physical distance as a philosophical one, once Einstein moved to the US (driven there by Nazi Germany’s ridiculous need to purge itself of “Jewish science”), and there’s a wonderful anecdote in the book of how, on a visit to America, Bohr was dictating a letter, staring out of the window, and at one point paused to think over the one subject that constantly preoccupied his mind. Musing aloud, he muttered, “Einstein… Einstein… Einstein,” only to turn and find the man himself standing there as if summoned by name. (Einstein had, it turned out, snuck in to purloin a little of his friend’s pipe tobacco.)

The thing I liked about Kumar’s Quantum is that it’s not so much an explanation of quantum mechanics as the story of its discovery, and the lives of the scientists who helped it at each step. It’s about the collaborative, discursive and sometimes competitive struggle to both advance science and make a name for oneself, and the battle between reaching understanding and finding something that just works. At times, it reminded me a bit of my reading of Gareth Williams’s book on the Loch Ness monster — another (sometimes) scientific quest for an unexplainable beast. Of course, there’s a big difference. The Loch Ness monster remains to be found, while the quantum, even though it will never be seen, has proven its existence consistently through experimentation and practical results.

As to what a quantum is, and what its existence means… There, it still seems as much of a hard-to-pin-down beast as Nessie herself. Analogies with concepts that apply to our macro-level, human-sized world, just don’t work. Whenever we poke at a subatomic entity to try to work out what it is, the very act of poking prevents our being able to grasp its fuller nature. Treat it like a wave — measure its wavelength — and it acts like a wave, giving you a wavelength. Treat it like a particle — measure its momentum — and it acts like a particle, giving you its momentum. But once it’s done that, it won’t give you the other side of its dual nature. Mathematically, it acts more like a probability than a solid thing. It’s all very confusing. Whatever it is, down there, that is a quantum, whatever strange soup of indecision it’s swimming in, the only law it seems to obey is that, the closer you move towards it, the stranger it gets.

(Any scientific errors in the above account are entirely down to my own Uncertainty Principle, which states that this Mewsings may be an article, or it may be a rave, but it’s probably a bit of both.)

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