Does quantum mechanics rule out free will?


A conjecture called superdeterminism, outlined decades ago, is an answer to several peculiarities of quantum mechanics: the evident randomness of quantum events; her evident dependence on human observation or measurement; and the apparent ability of a measurement at one location to immediately determine the result of a measurement at another location, an effect called non-locality.

Einstein, who scoffed at nonlocality as “spooky action at a distance,” insisted that quantum mechanics must be incomplete; There must be hidden variables that theory overlooks. Superdeterminism is a radical hidden variable theory proposed by physicist John Bell. He is known for a 1964 theorem, now named after him, that dramatically reveals the nonlocality of quantum mechanics.

Bell said in a 1985 BBC interview that the conundrum of non-locality disappears if one assumes that “the world is superdeterministic, not only with inanimate nature running the clockwork behind the scenes, but with our behavior, inclusive our belief that we are free to choose one experiment and not another, absolutely predetermined.”

In a recent video, physicist Sabine Hossenfelder, whose work I admire, states that superdeterminism eliminates the apparent randomness of quantum mechanics. “In quantum mechanics,” she explains, “we can only predict probabilities for measurement outcomes and not the measurement outcomes themselves. The outcomes are undetermined, so quantum mechanics is indeterministic. Superdeterminism takes us back to determinism.”

“The reason why we cannot predict the outcome of a quantum measurement,” she explains, “is that we are missing information, i.e. hidden variables. Superdeterminism, she states, eliminates the measurement problem and eliminates nonlocality and randomness. Hidden variables determine in advance how physicists conduct experiments; Physicists could superior they select one option over another, but they don’t. Hossenfelder calls free will “logically incoherent nonsense”.

Hossenfelder predicts that physicists may be able to confirm superdeterminism experimentally. “At some point,” she says, “it will turn out that measurement results are actually much more predictable than quantum mechanics claims. Maybe someone already has the data, they just didn’t analyze it properly.” Hossenfelder defends superdeterminism more fully in a technical paper co-authored with physicist Tim Palmer.

With her commitment to determinism, Hossenfelder is in good company. Einstein also believed that certain causes must have certain non-random effects, and he doubted the existence of free will. He once wrote: “If the moon were gifted with self-awareness as it completed its perpetual journey around the earth, it would be firmly convinced that it was making its way of its own accord.”

I am nonetheless baffled by superdeterminism, whether explicated by Hossenfelder or another prominent proponent, Nobel laureate Gerard t’Hooft. Reading their arguments makes me feel like I’m missing something. The arguments seem to be circular: the world is deterministic, so quantum mechanics must be deterministic. Superdeterminism does not specify what the hidden variables of quantum mechanics are; it merely decrees that they exist and that they specify everything that happens, including my decision to write those words and your decision to read them.

Hossenfelder and I had an argument last summer in a conversation about free will. I pointed out that we had both decided to talk; Our decisions are based on “higher” psychological factors such as our values ​​and desires, which are underpinned by but not reducible to physics. Physics cannot explain decisions and thus free will. So I said.

The appeal to psychological causes “does not overrule the laws of physics,” Hossenfelder explained to me sternly. “Everything is physics. You’re made of particles.” I felt like we were talking past each other. For them, a non-deterministic world makes no sense. To me, a world without choices makes no sense.

Other physicists insist that physics offers a lot of room for free will. George Ellis argues for “downward causality,” meaning that physical processes can give rise to “emerging” phenomena, particularly human desires and intentions, which in turn can exert an influence on our physical selves. Mathematicians John Conway and Simon Huhn go even further in their 2009 paper The Strong Free Will Theorem. They present a mathematical argument, similar to John Bell’s quantum nonlocality theorem, that we have free will because particles have free will.

In my opinion, the debate about whether physics excludes or enables free will is moot. It’s like citing quantum theory in a debate about whether the Beatles are the greatest rock band of all time (which they clearly are). Philosophers speak of an “explanatory gap” between physical theories about consciousness and consciousness itself. First of all, the gap is so great that it could be called an abyss. Second, the divide affects not just consciousness, but the entire realm of human affairs.

The physics that track changes in matter and energy have nothing to say about love, desire, fear, hate, justice, beauty, morality, meaning. In the light of physics, all these things could be described as “logically incoherent nonsense”, as Hossenfelder puts it. But they have consequences; they change the world.

Physics as a whole, not just quantum mechanics, is obviously incomplete. As the philosopher Christian List recently told me, humans are “not just clusters of interacting particles”. We are “deliberate agents with psychological characteristics and mental states” and the ability to make decisions. Physicists have recognized the limits of their discipline. Philip Anderson, a Nobel laureate, argues in his 1972 essay More Is Different that increasingly complex phenomena require new methods of explanation; not even chemistry can be reduced to physics, let alone psychology.

Bell, the inventor of superdeterminism, apparently didn’t like that. He seems to have viewed superdeterminism as a proposition made ad absurdum, highlighting the oddity of quantum mechanics. He was not enthusiastic about interpretations of quantum mechanics, once describing them as “like literary fiction”.

Why is the free will and superdeterminism debate important? Because ideas matter. At this point 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.


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