Superdeterminism

"’t Hooft thinks the notorious randomness of quantum mechanics is just a front. Underneath, the world obeys perfectly sensible rules. In the models he has toyed with, those rules govern building blocks even more fundamental than particles. You’d see them only if you could zoom into the so-called Planck scale, which, according to many modern theories, is the smallest meaningful distance in nature.

One point in favor of such an approach is that far-flung particles can act in a coordinated way, which you wouldn’t expect if they were purely random. Yet the idea of a deeper level is deeply troubled. In the 1960s, Irish physicist John Bell showed that the degree of coordination among particles is too exacting for any deeper level of physics to explain. Bell argued that particles actively need to communicate with one another, which ’t Hooft’s models don’t allow for.

When I first chatted with ’t Hooft for an article eight years ago, he told me he wasn’t sure how to evade Bell’s reasoning. Since then, he has sought to jump through a loophole known as superdeterminism. It’s a weird and downright disturbing idea. Only three other people I know support it, notably Sabine Hossenfelder of the Nordic Institute of Theoretical Physics, who blogged her views last week.

The sober way to put it is that physicists are never able to conduct a fully controlled experiment, since the experimental setup they choose is not strictly independent of the processes that created the particles. Even if the experimentalists (conventionally named Alice and Bob) live on Earth and the particles come from quasars billions of light-years away, they share a common past in the very early universe. Their subtle interdependence creates a selection bias, misleading physicists into thinking that no deeper level of physics could explain the particle coordination, when in fact it could.

The dramatic version is that free will is an illusion. Worse, actually. Even regular determinism—without the “super”—subverts our sense of free will. Through the laws of physics, you can trace every choice you make to the arrangement of matter at the dawn of time. Superdeterminism adds a twist of the knife. Not only is everything you do preordained, the universe reaches into your brain and stops you from doing an experiment that would reveal its true nature. The universe is not just set up in advance. It is set up in advance to fool you. As a conspiracy theory, this leaves Roswell and the Priory of Sion in the dust.

That said, one person’s conspiracy is another’s law of physics. Lots of things in the world seem conspiratorial at first glance, but are the result of well-established principles. The fact the moon spins on its axis at exactly the same rate it orbits Earth (thereby keeping the same face to us, or nearly so) is not the work of a cabal, but of laws such as the conservation of angular momentum. In the opening panel discussion of the conference, ’t Hooft speculated that some new law of physics might harmonize particles’ properties with humans’ measurement choices: “What looks like a conspiracy today may be due to a conservation law we don’t know about today.… It’s incredible until you find it’s mathematical necessity.”

What follows is an abridged transcript of our lunchtime chat.

The rest is here.