(Roughly) Daily

Adam Becker explains why demanding that a theory is falsifiable or observable, without any subtlety, will hold science back…

The Viennese physicist Wolfgang Pauli suffered from a guilty conscience. He’d solved one of the knottiest puzzles in nuclear physics, but at a cost. ‘I have done a terrible thing,’ he admitted to a friend in the winter of 1930. ‘I have postulated a particle [the neutrino] that cannot be detected.’

Despite his pantomime of despair, Pauli’s letters reveal that he didn’t really think his new sub-atomic particle would stay unseen. He trusted that experimental equipment would eventually be up to the task of proving him right or wrong, one way or another. Still, he worried he’d strayed too close to transgression. Things that were genuinely unobservable, Pauli believed, were anathema to physics and to science as a whole.

Pauli’s views persist among many scientists today. It’s a basic principle of scientific practice that a new theory shouldn’t invoke the undetectable. Rather, a good explanation should be falsifiable – which means it ought to rely on some hypothetical data that could, in principle, prove the theory wrong. These interlocking standards of falsifiability and observability have proud pedigrees: falsifiability goes back to the mid-20th-century philosopher of science Karl Popper, and observability goes further back than that. Today they’re patrolled by self-appointed guardians, who relish dismissing some of the more fanciful notions in physics, cosmology and quantum mechanics as just so many castles in the sky. The cost of allowing such ideas into science, say the gatekeepers, would be to clear the path for all manner of manifestly unscientific nonsense.

But for a theoretical physicist, designing sky-castles is just part of the job. Spinning new ideas about how the world could be – or in some cases, how the world definitely isn’t – is central to their work. Some structures might be built up with great care over many years and end up with peculiar names such as inflationary multiverse or superstring theory. Others are fabricated and dismissed casually over the course of a single afternoon, found and lost again by a lone adventurer in the troposphere of thought.

That doesn’t mean it’s just freestyle sky-castle architecture out there at the frontier. The goal of scientific theory-building is to understand the nature of the world with increasing accuracy over time. All that creative energy has to hook back onto reality at some point. But turning ingenuity into fact is much more nuanced than simply announcing that all ideas must meet the inflexible standards of falsifiability and observability. These are not measures of the quality of a scientific theory. They might be neat guidelines or heuristics, but as is usually the case with simple answers, they’re also wrong, or at least only half-right.

alsifiability doesn’t work as a blanket restriction in science for the simple reason that there are no genuinely falsifiable scientific theories. I can come up with a theory that makes a prediction that looks falsifiable, but when the data tell me it’s wrong, I can conjure some fresh ideas to plug the hole and save the theory.

The history of science is full of examples of this ex post facto intellectual engineering…

[Becker recount’s The Story of Herschel’s discovery on Uranus, the challenge it posed to Newtonian gravity, and Einstein’s ultimately saving theory; then returns to Pauli and to Bohr’s attempts to use it to refute the principle of conservation of energy; and finally explores the disagreement among, Boltzmann, Maxwell and Clauisus (on the one hand) and Mach (on the other) over atomic theory. He then considers competing theories for similar outcomes (that’s to say, theories that are observationally identical)…]

… the choices we make between observationally identical theories have a big impact upon the practice of science. The American physicist Richard Feynman pointed out that two wildly different theories that have identical observational consequences can still give you different perspectives on problems, and lead you to different answers and different experiments to conduct in order to discover the next theory. So it’s not just the observable content of our scientific theories that matters. We use all of it, the observable and the unobservable, when we do science. Certainly, we are more wary about our belief in the existence of invisible entities, but we don’t deny that the unobservable things exist, or at least that their existence is plausible.

Some of the most interesting scientific work gets done when scientists develop bizarre theories in the face of something new or unexplained. Madcap ideas must find a way of relating to the world – but demanding falsifiability or observability, without any sort of subtlety, will hold science back. It’s impossible to develop successful new theories under such rigid restrictions. As Pauli said when he first came up with the neutrino, despite his own misgivings: ‘Only those who wager can win.’…

We need madcap ideas: “What is good science?,” from @FreelanceAstro in @aeonmag.

Apposite: Charles Sanders Peirce on “abduction”

* Carlo Rivelli, Reality Is Not What It Seems

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As we ponder proof, we might spare a thought for Donald William Kerst; he died on this date in 1993. A physicist, he helped develop the experimental approach (and apparatus) that let Enrico Fermi confirm the existence of Pauli’s neutrino (among many other discoveries).

Kerst specialized in plasma physics, and worked on advanced particle accelerator concepts (accelerator physics). He developed the Betatron (1940), the first device to accelerate electrons (“beta particles”) to speeds high enough to have sufficient momentum to produce nuclear transformations in atoms. It influenced all subsequent particle accelerators.