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    The McMaster Department of Philosophy has now put together the following notice commemorating Barry: Barry Allen: A Philosophical Life Barry…

Just when you thought the humanities were safe from postmodernism…

Brian Leiter

…along come the physicists to inform us there is no objective reality:

Nobel Prize-winner Eugene Wigner described a thought experiment in 1961 that highlighted an uncommon paradox of quantum mechanics. Specifically, it reveals the strangeness of the universe when two observers, like Wigner and his friend, observe two distinct realities….

In 2020, physicists realized that recent quantum technology advances had made it possible to create Wigner's Friend test in a real-world experiment. In essence, we can create different realities, and compare them in a lab to see if they can be reconciled, or cohere, in one system. And researcher Massimiliano Proietti of Heriot-Watt University, Edinburgh, along with a handful of researchers, said they performed this long-awaited experiment for the first time: Creating distinct realities, compare-and-contrasting them, and discovering that they are, in fact, irreconcilable.

Wigner's initial thought experiment was simplistic in principle, starting with a single polarized photon that can have either vertical or horizontal polarization, upon measuring. The laws of quantum mechanics hold that a photon exists in both states of polarization simultaneously, in what's called superposition. In his thought experiment, Wigner imagined a friend measuring the state of a photon in a different lab and recording the result while Wigner watched from afar. He has no clue what his friend's measurement is, and is thus forced to assume that the photon and its measurement are in a state of superposition of every possible outcome for the experiment.

Wigner can say, however, that the "fact" of the superposition's existence is real. And, strangely, this state of affairs suggests that the measurement can't have taken place. Obviously, this stands in direct contradiction to Wigner's friend's point-of-view, who just measured and recorded the photon's polarization. He can even call Wigner and tell him the measurement was taken, without revealing the results. This means there are two realities at odds with one another, and it "calls into question the objective status of the facts established by the two observers," explained Proietti and colleagues, in an MIT Technology Review report.

And the new research reproduced Wigner's thought experiment by using entanglement techniques for many particles at the same time.

This is a breakthrough experiment from Prioretti and his colleagues. "In a state-of-the-art 6-photon experiment, we realize this extended Wigner's friend scenario," they added in the report. And it raised some baffling questions that have forced physicists to confront the nature of reality. There might be a loophole to some assumptions that made this unknowable reality conclusion necessary, but if everything holds up to future scrutiny, it turns out reality does not exist.

I invite those readers knowledgeable about the physics to comment on what this experiment does or does not show.

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8 responses to “Just when you thought the humanities were safe from postmodernism…”

  1. Stephen Maitzen

    Beware of physicists giving philosophical interpretations of their equations and experiments! In the original article from Science Advances 5.9 (2019), Proietti et al. say that their result shows that at least one of three assumptions must be false: "free choice, locality, and observer-independent facts" (4).

    They never define "free choice," but I'm willing to bet that they mean simply "indeterministic choice." As Neil Levy has documented, scientists routinely conflate freedom with indeterminism, as if compatibilism weren't even a logical possibility. I myself am happy to say that indeterminism "must be wrong," and nothing in quantum mechanics except a particular *interpretation* of the formalism says otherwise. As for locality, it was cast into doubt long ago by experimental violations of the Bell inequalities. Nothing new here.

    Egged on by credulous journalists seeking a headline, scientists sometimes try to make news by offering some extreme interpretation of their data while failing to see that the interpretation rests on assumptions that philosophers have long questioned. Don't believe the hype.

    Reply
  2. Daniel Swaim

    "But if everything holds up to scrutiny" is one hell of a proviso.

    Reply
  3. Kenny Easwaran

    One of the worst offenders on the "free choice" terminology is the Conway and Kochen "Free Will Theorem" – they state it as, "if humans have free will then so do fundamental particles", but it literally just shows that "if human behaviors are not a deterministic function of their past then neither are fundamental particle behaviors". In order for this not to be a triviality, their point holds even if you think of humans as disembodied observers, rather than as beings constituted out of fundamental particles.

    https://en.wikipedia.org/wiki/Free_will_theorem

    Reply
  4. Stephen Maitzen

    One of the worst offenders indeed! But it has plenty of company. Here is the physicist Nicolas Gisin in 2013: "I know that I enjoy free will much more than I know anything about physics. Hence, physics will never be able to convince me that free will is an illusion. Quite contrary [sic], any physical hypothesis incompatible with free will is falsified by the most profound experience I have about free will." A celebrated physicist telling us that his "experience" of indeterminism (what could that even be?) is more reliable than anything he knows from physics.

    Reply
  5. Peter Moss

    What does this have to do with postmodernism?

    BL: Postmodernists deny objectivity, albeit in a number of different senses.

    Reply
  6. Tim Maudlin

    As anyone might guess, the commentary about this experiment is total nonsense. First, Wigner's thought experiment involved asking whether the wave-function of a complete, conscious human being can get into a superposition of different "states of consciousness". The answer to that question is not known, and not addressed by this experiment, which only involves a handful of photons. If an experiment with a human could be done, that could arbitrate between objective reduction theories, such as those proposed by Ghirardi, Rimini and Weber, and Roger Penrose, versus "no collapse" theories such as Bohmian Mechanics and Everett. This experiment does not do that, as the experimenters acknowledge, and every present "interpretation" makes the same prediction for it. The prediction of how it actually came out.

    Second, obviously no experiment can prove there is no "objective reality". That's pretty analytic, since to take the experiment seriously in the first place you have to accept that you know how it—objectively—came out. Different theories will give different accounts of what is going on, but each will make a proposal about what the objective facts are. The evidence will not decisively pick out. single such theory, but we have known that forever, ender the rubric "underdetermination of theory by evidence.

    Reply
  7. Allen Hazen

    (Not sure whether my previous comment went through — this "version" is more developed anyway.)
    I tend to think about these things in the light of some discussions with David Lewis. In his metaphysics of possible worlds, one can have a pair of worlds whose "history" parallels each other up to a certain time, diverging after that. He strongly preferred that description: that there are, in such cases, two distinct worlds, and that the earlier part of one is distinct from (being part of a different whole world) the earlier part of the other, even though the two parts are (in what I hope is an obvious sense) isomorphic to each other. Another way of thinking about the situation — equivalent for at least some purposes — is to think of there being in this situation a single, "Y-shaped," world, within which there is a "branching" temporal order: from the point of view of someone living in the earlier, pre-divergence, part of the world, there are two different futures. (Lewis discusses reasons for preferring one view over the other in some of his late papers: "How many lives has Schrödinger's cat?" for one.) My (admittedly lay: I am not a physicist) take is that when physicists talk about "objective reality," what they have in mind can at least be modelled in this way (but with physically rather than metaphysical possible "worlds"): they would describe the "branching time" model as a denial of objective reality: before the time of divergence there is no "objective reality" of the matter as to whether we are in the world with one future or the world with the other.

    Reply
  8. Keith Douglas

    Mario Bunge suggested (starting in the 1960s!) to do semantics on the theories of physics supposedly that give vindication to subjectivism. What are the referents of them, in other words. Minds, wills, etc. (especially not dualistic ones!) have no place in the theories and so any interpretation that uses them is wrong. (You do not need to buy his semantics of 1974 to get the same conclusion, I think.) That said, I'm no philosopher of physics, but the argument seems correct enough (spelled out in more detail than I can do here.) It cured me of the naive subjectivism I'd picked up from bad popularizations and misleading presentations in the few semesters of physics I'd done, that much is sure.

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