1. Is the fact you are reading this story a decision you arrived at it by your own free choice, or was your interest programmed into the universe from the moment of the big bang? What makes free will such a fun topic is not only that it dives deep into physics, neuroscience, and philosophy, but also that we all feel we have a direct stake in the answers.

    Part of my own interest is that I've never been able to see why people get worked up about a supposed conflict between free will and determinism. To my mind, there is no conflict. Human consciousness and therefore the concept of free will are emergent properties, so whether microscopic physics is deterministic or not is irrelevant. To speak of a conflict is to mix levels of description. In other words, there's no "you" who is steered one way or the other by initial conditions. "You" are a product of those conditions.

    I'll grant that all this depends on what precisely we mean by “free will.” To me, it is the fact that you make choices. To others, though, free will involves some inherent unpredictability. In that case, it might well have something to do with the deep laws of nature. Within quantum mechanics, there are four basic arguments for such a connection:

    1. Quantum mechanics is indeterministic, in that the outcomes of measurements are chosen at random from the slate of possibilities. So, if quantum effects help to shape our conscious choices, they sever the connection between us and the initial conditions of the universe.

    2. When we conduct experiments on quantum particles, we exercise our free will—for example, we make choices about what precisely to ask of the particles.  Or at least we think we exercise our free will. How those particles respond can depend on whether we really do.

    3. If you could predict someone’s decisions consistently, you could conclude that he or she lacks free will. To do that, you’d need to take a full brain scan and simulate his or her thought processes. Yet quantum physics forbids the reliable, nondestructive copying of particles, let alone whole brains. If you could never observe the loss of free will, then you should doubt whether it is ever really lost.

    4. Quantum physics is time-symmetric, so we are as justified in saying that our choices set the cosmic initial conditions as the other way round.

    Here, I'll examine each of these contentions. This is an evolving document. Over time, I'll gradually flesh out the points and add interesting new contributions to the debate. Later this year, Scientific American plans to publish a full-blown magazine feature on these issues.

  2. Background

  3. The question of free will is obviously one of the oldest in philosophy, but as good a place to start as any is a blog post last year by the ever-thoughtful blogger and cosmologist Sean Carroll:
  4. The Stanford Encyclopedia entry is another excellent resource:
  5. Argument #1: Quantum Indeterminism

  6. I find the idea that indeterminism restores free will extremely unpersuasive. What difference does it make if my conscious choices were programmed in at the big bang or decided on the fly by random particle events? Also, at a deep level, quantum mechanics is not random at all. Schrödinger’s equation is completely deterministic and time-symmetric. Carroll feels much the same:
  7. Others, though, do see a role for indeterminism. Quantum gravity theorist and blogger Sabine Hossenfelder recently offered some thoughts. Her paper suggests that there is a third way between determinism and randomness: what she calls “free-will functions,” whose outputs are fully determined but unpredictable. Only those who know the function know what will happen. This is distinct from chaos, in which the function is universally known but the initial conditions are imperfectly known.

  8. My first reaction was that the free-will function is operationally the same as a classical deterministic hidden variable—namely, there is a deterministic description of a system, even if we can’t tell what it is. After chatting with Hossenfelder, I think her point is that whereas hidden variables are part of the state of the system, the free-will function is part of the laws of nature. It is not a hidden variable, but a hidden law. Nature still meets the definition of determinism—a given state evolves in a definite way—even if the rules guiding evolution are unknowable. The free-will function might not be definable as an equation or algorithm, but would be what theoretical computer scientists call an oracle.

    Anyway, Hossenfelder has some more thoughts on her blog:
  9. Argument #2: Quantum Contextuality and Nonlocality

  10. Another connection to free will hinges on the phenomenon of entanglement. Does the spookily coordinated behavior of quantum particles reflect a nonlocal connection between them or, alternatively, some built-in cheat sheet that allows them to arrange their answers in advance? In the 1960s the Irish physicist John Bell devised an experiment to decide between these possibilities. For a visual metaphor to understand the phenomenon and dilemma, see this video that my Scientific American colleagues and I recently put together:
  11. The outcome of the experiment rules out the cheat-sheet option. But one thing we don’t mention in the video is that there’s an escape clause. If we lack free will, the coordinated outcomes can be explained without any nonlocal connection. The reason is that the setup of the experiment assumes the outcomes are independent of the measurement settings. If the two are somehow synchronized, that might produce the illusion of nonlocality. In the video, that would mean Mary did not exercise any free choice in her choice of whether to say “left” or “right.” It was all set up at the big bang to ensure compatibility with the answers that John and I give.

    Bell called this escape clause “superdeterminism”:
  12. Superdeterminism is extremely troubling, because if true it would pull the rug out from under empirical science. If measurement outcomes depended on our experimental choices, we could never conduct a controlled experiment. All the laws of physics would be illusions. And if we couldn’t trust quantum mechanics, why would we bothering with this discussion to begin with? The very idea of superdeterminism is self-negating.
  13. Philosopher of physics Huw Price offered a convincing critique: 
  14. Moreover, how the heck would the big bang have been set up in this way? There had to be a belief-beggaring degree of structuring and coordination among far-flung points in space.

    That said, some physicists take superdeterminism seriously. A notable example is Nobel laureate Gerard ’t Hooft, who has the radical but not entirely crazy idea that quantum mechanics may emerge from a deeper level of physics. I discussed his ideas in a 2004 article:
  15. A few years later, ’t Hooft took on the question of free will directly: