Many Worlds & Ontological Commitment

Had an exchange with David Deutsch earlier today. I didn’t have the full context of the original question that prompted him to post a 9 minute video essay on YouTube, but it was in defence of the Everettian Many Worlds Interpretation being seen as part of the “concensus” in 21st C physics.

[My gloss on his argument in the video] His emphasis from the off is on “the reality of Many Worlds being as uncontroversial as the reality of dinosaurs and their evolution” seen by future historians of science.

(He also notes that even proponents of the theory will have / had disagreements and distinct interpretations – visible even from history.)

(IF) we agree it describes reality – not just that observations confirm predictions of the formal theory according to limits in confidence and knowledge – but we disagree about that reality described. Does that “function” describe reality or is it reality? [Lots of technical quantum detail still open to disagreement.]

We don’t have the “Many Dinosaurs” interpretation of evolution, it’s just evolution. It’s just Everettian (true) Quantum Physics, not an interpretation.

Explanatory theory split into formalism and interpretation(s) is wrong. It’s just another interpretation. Institutionalised casuistry – unsound sophistry.

Mistaken about what the world is actually like (in reality). What exactly were the unpersuaded, unpersuaded of.

Physicists incorporate accepted new physics (eg Einsteinian relativity) into their worldviews (or not – quantum theory). People stuck in Kuhnian paradigms are probably those that believe in paradigms (implying we shouldn’t).

Apply the theory, test it, note what that tells us about the world and let that inform your worldview.

[Andromeda / Time / Now / Self – who am I? Self-Identity even in computation theories – more nonsense. Unreasonable gullibility. Ada Lovelace denying that computers could think. Positivism as a poison.]

It has become accepted in science education that learning science doesn’t require you to change your world-view. Shut-up and calculate, toe the party line. Sneer at reality.

What’s noticeable is that there is nothing about “Many Worlds” in there – as a reality or otherwise – just dropping it from the naming of quantum theory or any interpretation of it? But there is lots about what we hold as reality in our world-view.

It was a standing joke that few (if any) quantum physicists actually behaved as if QT were a reality, however they actually described or interpreted it. Obviously one factor might be that at the human living and decision-making scale no quantum effects are observable anyway – even if they / we do hold it as part of our world-view.

Anyway my comment was purely about the Many Worlds interpretation / metaphor and any reality to reality held in a worldview.


And this is where it took a weird turn:


And there it ended, but I thought I’d elaborate here, on the ontological commitment.

[Metaphors / Thought experiments >>> Accepted as reality?]
[Goldstein / ontological commitment / Einstein’s rubber sheets / quarks and their properties.]
[And capture the tweet contents more directly. Matt Segall’s tweets too.]

7 thoughts on “Many Worlds & Ontological Commitment”

  1. He doesn’t mention ontology in the video, so I’m not sure what you meant by “the ontological commitment.” That said, I don’t know where his provocative “Now do dinosaurs” came from. It wasn’t what I’d call a response to your ideas. I know he was referring to his own comparison of the many-worlds interpretation of quantum mechanics with the “many-dinosaur interpretation” of evolution, whatever that means, but as an answer to your comment it was a curve ball. To throw that one, and then another bringing up creationism, seems unfair in a short exchange on Twitter. On short notice, I wouldn’t have known what to do with either of them.

    Having watched the video a few times, I have my opinions about the coherence of his remarks. Let’s just say they seemed off-the-cuff.

  2. Yes, “The Ontological Commitment” was in my first comment to him.
    (Incidentally there’s been a fair bit of chatter on Twitter about this too.)
    It needs expanding in my italic notes at the end … but …

    Ontological commitment says (after Goldstein) that once you’ve described your physics in maths, models, interpretations and metaphors – whatever – as part of being “explanatory” – you have to be able to point at (at least) one of them and say “that’s what (I believe) really exists / existed, in reality, in the real world”. That’s what he’s doing, without using that “ontological” philosophical jargon.

    He’s one of my most respected philosophically-informed scientists, so I was glad of the (provocative) exchange, but I need to finish the job 😉

  3. Thanks, that makes more sense of the discussion. You both agree on making an ontological commitment. Deutsch is committed to the many-worlds interpretation of quantum mechanics, but you aren’t. (Are you committed to another interpretation?)

    In fact, Deutsch is so committed to the many-worlds interpretation that he resists calling it an interpretation. For him it’s simply the reality, not an “interpretation” of reality. At least that’s how I understood him after three nine-minute listens. (I doubt I’ll commit to a fourth — this is why I dislike videos, especially those where the professor speaks slowly enough for the students to take notes.) As far as he’s concerned, everyone will come to accept it, not as an “interpretation,” but as reality, just as we’ve accepted dinosaurs and relativity and wouldn’t think of calling them “interpretations” of the evidence. Historians of science will wonder why anyone else would think differently. Now that’s what I call commitment!

    Personally I get off the train at the first stop, “ontological commitment.” I don’t see the benefit of insisting that any given interpretation of the math corresponds to “the reality.” Oddly enough, Deutsch seems to agree. He asks what we mean by “reality,” and then suggests that the math itself is “the reality.” This would make many-worlds, or any other attempt to tell ourselves a story about about what the math “says about the world,” an interpretation — that is, an explanatory story of the math for our childlike minds. Deutsch is willing to tell a story about how reality is “many worlds,” but his conviction is so strong that he doesn’t see it as a story. This explains his disdain for physicists caught up in “paradigms,” and his ambivalence about the whole idea of “interpretations” of reality.

    “Now do dinosaurs.” Our belief in dinosaurs is an interpretation of the available evidence. But Deutsch scoffs at the idea of talking about a “many-dinosaurs interpretation,” and presumably he would go further and scoff at a “dinosaur interpretation” of the evidence. As far as he’s concerned, we know dinosaurs existed; it’s not an “interpretation.” If we admitted it were just an interpretation of the evidence, we’d leave ourselves open to alternative interpretations, specifically creationism.

    His opinions notwithstanding, our belief that dinosaurs existed is an interpretation of the available evidence. Our belief that they were cold-blooded precursors of lizards was based on available evidence. Our belief that they are warm-blooded precursors of birds is based on available evidence. This is not about the ontological waffling suggested by “interpretation,” but about the idea that there are better and worse interpretations of available evidence.

    Turning back to quantum mechanics, there is more than one interpretation out there. Deutsch is persuaded by the many-worlds interpretation; others aren’t. If we use the metaphor of a superposition, and these interpretations are in a superposition with respect to the math, then Deutsch has prematurely collapsed that superposition. But the difficulty with this particular interpretation, “many-worlds,” is unique: by definition, there can be no physical evidence for a world parallel to the one we are in. There might be a way to detect pilot waves. There might be hope for discovering the role of relationship or betweenness as integral to reality. There is absolutely no hope for actually finding a single parallel world, much less an infinity of them.

    “The world” is a story. The math is the math. We can try to explain the “meaning” of the math to ourselves by telling a story, and “many-worlds” is one such story. But we will never find bones from a parallel universe. We will never compare the reports of a clock from a parallel universe. Positing an infinity of other worlds completely and utterly disconnected from this one is adding a whole lot of wheels that do no work.

    That’s not to say that the many-worlds interpretation is wrong — although though one might be tempted to say it’s “not even wrong.” But it is a competing interpretation, and from the point of view of “available evidence,” the weakest of the lot.

  4. Hmmm. A long one and I’m pushed for time.

    Deutsch is absolutely NOT committed to the Many Worlds “Worldview” – that’s his whole point.
    (He discards it at the outside – my first comment is that despite being “as advertised” in the original tweet / question, he doesn’t even mention it?)

    Teasing out what he is ontologically committed to would be the point of my unfinished notes at the end.
    He’s extolling the commitment to commitment, but to what – I dunno – reality of (Everettian) Quantum Theory being “the theory as maths”? Maybe.

  5. Now I’m confused again, because David Deutsch seems to be regarded as the main advocate of the many-worlds interpretation, according to multiple sources. What am I missing?

  6. Ha. If his actual view was the one generally accepted why would he publish a response?

    Anyway, you reach my position – the reason for capturing in the first place.

    “What am I missing?”

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