I admire Sabine Hossenfelder, the iconoclastic physicist. In her writings and videos, she is blunt, clear, courageous, funny. So her advocacy for superdeterminism distresses me. In a recent video, Hossenfelder touts superdeterminism as “a way to make sense of quantum mechanics.” She disparages free will, which superdeterminism rules out, as “logically incoherent nonsense.”
Some background. Superdeterminism is a response to several peculiarities of quantum mechanics: the apparentrandomness of quantum events; their apparent dependence on human observation, or measurement; and the apparent ability of a measurement in this place to determine, instantly, the outcome of a measurement elsewhere, an effect called nonlocality.
Einstein, who derided nonlocality as “spooky action at a distance,” insisted that quantum mechanics must be incomplete; there must be hidden variables that the theory overlooks. Superdeterminism is a radical hidden-variables theory proposed by physicist John Bell. He is renowned for a 1964 theorem, now named after him, that dramatically exposes the nonlocality of quantum mechanics.
Bell said in a BBC interview in 1985 that the puzzle of nonlocality vanishes if you assume that “the world is superdeterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined.”
In her recent video, Hossenfelder notes that superdeterminism eliminates the apparent randomness of quantum mechanics, as well as the measurement problem and nonlocality. Hidden variables determine in advance how physicists carry out experiments; physicists might think they are choosing one option over another, but they aren’t.
I’m baffled by superdeterminism, whether explicated by Hossenfelder or another prominent proponent, Nobel laureate Gerard t’Hooft. Their arguments seem circular: the world is deterministic, hence quantum mechanics must be deterministic. Superdeterminism doesn’t specify what the hidden variables of quantum mechanics are; it just decrees that they exist, and that they determine everything that happens, including my decision to write these words and your decision to read them.
Hossenfelder and I argued about free will in a conversation last summer. I pointed out that we both made the choice to speak to each other; our choices stem from “higher-level” psychological factors, such as our values and desires, which are underpinned by but not reducible to physics. Physics can’t account for choices and hence free will. So I said.
Invoking psychological causes “doesn’t make the laws of physics go away,” Hossenfelder sternly informed me. “Everything is physics. You’re made of particles.” I felt like we were talking past each other. To her, a non-deterministic world makes no sense. To me, a world without choice makes no sense.
Other physicists insist that physics provides ample room for free will. George Ellis argues for “downward causation,” which means that physical processes can lead to “emergent” phenomena, notably human desires and intentions, that can in turn exert influence our physical selves. Mathematicians John Conway and Simon Kochen go even further in their 2009 paper “The Strong Free Will Theorem.” They present a mathematical argument, which resembles John Bell’s theorem on quantum nonlocality, that we have free will because particles have free will.
To my mind, the debate over whether physics rules out or enables free will is moot, and inappropriate. It’s like citing quantum theory in a debate over whether the Beatles are the best rock band ever (which they clearly are). Physics, which tracks changes in matter and energy, has nothing to say about love, desire, fear, hatred, justice, beauty, morality, meaning. All these things, viewed in the light of physics, could be described as “logically incoherent nonsense,” as Hossenfelder puts it. But they have consequences, they alter the world.
Bell, the inventor of superdeterminism, apparently didn’t like it. He seems to have viewed superdeterminism as a reductio ad absurdum proposition, which highlights the strangeness of quantum mechanics. He wasn’t crazy about any interpretations of quantum mechanics, describing them as “literary fictions.”
Why does the debate over free will and superdeterminism matter? Because ideas matter. At this time in human history, many of us already feel helpless, at the mercy of forces beyond our control. The last thing we need is a theory that reinforces our fatalism.
Scientific Curmudgeon is an Opinion column written by CAL Professor and Director of the Stevens Center for Science Writings, John Horgan. Columns are adapted from ones originally published on ScientificAmerican.com.
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