Sabine Hossenfelder disses the multiverse

September 11, 2022 • 10:30 am

In this 17-minute video, physicist and science popularizer Sabine Hossenfelder discusses the concept of the multiverse, one that’s popular with many physicists (and laypeople)—but one, she says, for which there’s no evidence. (It’s also a topic of her latest book; see an excerpt here and get a link to the book below)

Reader Steve sent me the video link with the note (reproduced below with permission), referring to Sean Carroll, who’s an advocate of the multiverse.

The latest from our friend, Sabine. As much as I like and admire Sean Carroll, I am convinced by Sabine’s argument…for now.

I’m putting her new book on my reading list.

The video is pretty clear, so I’ll just give the take-home message briefly.

To Hossenfelder, the problem with mulitverse theories is that they all “Postulate the existence of unobservable entities”.  That is, although the multiverse is an outcome of some mathematical physics, there is no way physicists have found to test it—to make observations that would make its existence more or less likely.  If it ultimately can’t be tested, she says—and I agree—then it can’t be considered a scientific theory. (This is also true of string theory.)  Now we don’t know if somebody in the future will come up with a clever way to see that the universe keeps splitting into more and more universes every time something happens, but until they do, to quote Laplace, “we have no need of that hypothesis.” I’m glad, however, if some physicists are working on a way to test it. However, Hossenfelder says that there is no observation even in principle, that physicists can make to test the existence of the multiverse. That may change. And of course a failure to find ways to detect multiverses does not mean that they do not exist, of course. Like the idea of an unobservable God, we simply can have no confidence in their existence.

Hossenfelder then considers whether the multiverse theory is science, religion, or pseudoscience. She’s already dismissed science, but argues that the theory either pseudoscience or religion, depending on how you use it. One quote:

“If you assume that unobservable universes exist, and write papers about them, then that’s pseudoscience. Because this is exactly what we mean by “pseudoscience”—pretends to be science, but isn’t. If you accept that science doesn’t say anything about the existence of those universes, one way or another, and you just decide to believe in them, then that’s religion. Either way, multiverses are not science—they’re like Tinker Bell, basically: they exist if you believe in them. 

Hossenfelder thinks that the fundamental error that physicists have made is thinking that multiverses exist because they’re an outcome of mathematical physics.  In other words, “The big problem with the multiverse idea is that physicists are confusing mathematics for reality.”

Finally, she takes on four objections to her own view, but dispels all of them.

Adjudicating this argument is above my pay grade, but I do know that no physicist has found a way to test the predictions of multiverse theory. It’s still a theory widely discussed (Sean Carroll talks about it quite often, and I believe it’s discussed with approbation in his 2017 book The Big Picture). But if scientists, after arduous effort, eventually can’t see a way to find evidence to test it, it will eventually disappear as a matter for serious discourse in physics.

Hossenfelder is an excellent presenter of physics, and passionate about her views. The only flaw in her presentation is that she seems a bit nervous—or perhaps she’s just being very serious and passionate.  A more relaxed presentation would be a better one, but not a lot better.

I also like her because, as I discussed exactly two years ago, she’s a hard determinist with respect to free will. She doesn’t seem to be a compatibilist, either, though she does agree with some compatibilists in thinking we shouldn’t worry about our lack of libertarian free will.  But I don’t think she’s dug deeply enough into the consequences of rejecting “naturalism” (my new word for “determinism”. There are serious social implications, notably in the judicial sphere, to rejecting libertarian free will. Below the fold you can see some of what I wrote about her video on free will.

Wouldn’t it be lovely to see a debate between Hossenfelder and Sean Carroll (who’s a bit of a compatibilist) on the multiverse, on free will, or both?  In such a debate both sides would be smart, rational, quick, and, of course, polite. It would be a delight to watch.

Enough—watch this:

Here’s Sabine’s new book (click on the screenshot to go to the Amazon site), and you can get a peek inside at that site:

Click on “continue reading” to see some of my discussion of Hossenfelder’s take on free will.

You can go here to see her video affirming determinism, and here’s a bit of what I said about it:

Hossenfelder concludes by reiterating that free will is “nonsense” and that “the idea deserves going into the rubbish bin.”  True, that. But that doesn’t mean that we can’t be happy, for we have the illusion of free will, and we can use that as a crutch to go through life. She even suggest a psychological trick for being happy:

If it causes you cognitive dissonance to acknowledge you believe in something that doesn’t exist, I suggest that you think of your life as a story which has not yet been told. You are equipped with a thinking apparatus that you use to collect information and act on what you have learned from this. The result of that thinking is determined, but you still have to do the thinking. That’s your task. That’s why you are here. I am curious to see what will come out of your thinking, and you should be curious about it too.

Why am I telling you this? Because I think that people who do not understand that free will is an illusion underestimate how much their decisions are influenced by the information they are exposed to. After watching this video, I hope, some of you will realize that to make the best of your thinking apparatus, you need to understand how it works, and pay more attention to cognitive biases and logical fallacies.

I’m not sure how it helps to realize that “you have to still do the thinking”, when in reality the thinking is doing itself! Just because we don’t know what will happen—that our predictability is not so hot—doesn’t make us any less a bunch of meat robots who are slaves to the laws of physics. I know this, and yet I’m tolerably happy (for a lugubrious Jew). We know our “choices” are illusions, and my realization that these illusory choices come from a brain embedded in the skull of one Jerry A. Coyne does not give me the consolation Hossenfelder promises. But I still beat on, a boat against the current.

One more point: I’m not sure why compatibilists don’t just admit what Hossenfelder admits instead of trying to find a definition of free will that people do have. The physicist Sean Carroll and philosopher Dan Dennett have taken that route, which I call the “Definitional Escape” rather than Hossenfelder’s “There’s No Escape but Isn’t it Cool to Not Know what Comes Next”?

The one thing I think Hossenfelder neglects comes from her last paragraph. If we do understand that free will in the Hossenfeldian sense is illusory, that has enormous consequences for the judicial system and for how we think about people who are either more or less fortunate than we are. I won’t dilate on this as I’ve discussed it to death. But yes, realizing that our brains are particles and obey the laws of physics should cause us worry—worry about how we treat prisoners and those who are mentally ill, and worry about how some people hold others responsible for making the “wrong choices.”

That aside, I applaud Dr. Hossenfelder for realizing the truth, which, as she says, is the ineluctable outcome of science, and for saying it so straightforwardly. I’m a big fan of hers. And I applaud myself for agreeing with her.

110 thoughts on “Sabine Hossenfelder disses the multiverse

  1. I don’t think it’s correct to say Carroll (or any physicists I’m aware of) are “proponents” of the multiverse as likely correct to be confirmed. What they do note is that such theories have certain attractive features with regards to simplicity, comportment with quantum mechanics, and predictions consistent with some features of the early universe (though not anything to confirm their correctness), that make them worth studying as models.

  2. Good debate, the only point which I would question: “physicists are confusing mathematics for reality”. Isn’t math the basis of our perceived reality? It’s how we understand the Universe. Can math be fantasy?

    1. I don’t think that in theoretical physics a mathematical result can be seen as reality unless you can see it played out in the universe. Even Einstein, I think, was pleased to see the Theory of Relativity confirmed. If that theory was not confirmed, or if there was no way to confirm it, how could you say it said something true about nature?

      1. A journalist asked Einstein what he would do if Eddington’s observations failed to match his theory. Einstein famously replied: “Then I would feel sorry for the good Lord. The theory is correct.”

        1. I would not take Einstein as an authority on theory vs. facts matters.
          “After the [debates] continued for a few days … Ehrenfest said: ‘Einstein, I am ashamed of you; you are arguing against the new quantum theory just as your opponents argue about relativity theory.’ But even this friendly admonition went unheard.”
          (Heisenberg on the 1927 Solvay Conference)

    2. Mathematical truths are tautologies and beyond doubt, like “there are three feet in a yard.” That is not science. Math cannot prove anything about the physical world. It’s usefulness only comes when modeling the world, where it is incredibly useful. For example, if you assume two objects attract each other proportionately to their masses, then Newtonian physics follows. If that initial assumption is false (as it was) then the mathematical conclusions may not be accurate. Einstein made a better guess (assumption), and the conclusions to his theory are better. Newton’s theory served (and serves) us well, being close enough to reality that no one could tell the difference for a long time.

      I assume the multiverse proponents make no mistakes in their math. If the theory is false it’s their assumptions about how that math applies to the real world that are in error.

    3. Isn’t math the basis of our perceived reality?

      No. Mathematics offers a precise way to describe reality, but it is not the basis of reality. And just because you found a mathematical model that seems to describe the Universe doesn’t mean it is correct or that manipulating your model using certain mathematical rules will tell you new things.

      For example, you may choose to model the properties of space with Euclidean geometry. If you do, you can use the maths to make predictions about space. For example, you will predict that any triangle you draw will have angles that add up to 180 degrees. That’s all very nice, but you haven’t proved it. To verify your prediction, you need to draw some triangles and add up the angles. Eventually, somebody will invent a protractor with enough accuracy (if they haven’t already) to show that triangles don’t always have angles that add up to 180 degrees.

      You can’t say anything about the Universe with pure deductive reasoning (which is what maths uses). At some point you have to test it to see if it works.

      1. You don’t need a protractor. Here is how to construct a triangle with angles summing to more that 180 degrees. Start at the north pole, proceed due south along any meridian to the equator, travel along the equator a thousand miles (any distance greater than zero will do), then due north back to the north pole. The two angles at the equator are both 90 degrees, so whatever the non- zero angle is at the north pole, the sum exceeds 180 degrees.

    4. Immediately above my pay grade, but why should that stop me?
      I think a good example where mathematical modeling leads to a prediction that cannot be physically true is the oft-described backwards extrapolation of the expanding universe to its beginning as a dimensionless point — a singularity. So we constantly see talking heads on television explaining how the universe began at a singularity. But bc of quantum fluctuations and all that, there really can be no such thing as a singularity. At least that is how I’ve understood it.

        1. Like this one – maybe relevant to the “multiverse” idea :

          “… the OBSERVABLE portion of the universe was once packed into an incredibly tiny volume. But that primordial pellet of matter and energy was NOT surrounded by empty space… it was surrounded by more matter and energy (which today is beyond the region we can observe.) In fact, if the whole universe is infinitely large now, then it was always infinite, including during the Big Bang as well.”

        2. That’s interesting and all, but a lot of it is bold assertions of truth bc its got elegant math, and claims without evidence. Why would all of space before the big bang need to be already filled with matter and energy? Energy I get (the hot big bang was probably an energy conversion from that), but why does there have to be matter? Why not have it be filled with tremendously powerful and rapidly expanding dark energy (a ‘la the eternal inflation model)? And here i see the claim that the b.b. was expansion of space itself. But that seems to contradict other statements made in the same link — that being that there was already a lot of stuff before the b.b. I keep seeing these contradictions so this is not the only example.

          1. “Why would all of space before the big bang …”

            ->[ reads the queries]
            “But the Big Bang was an expansion of space itself. Every part of space participated in it. “

          2. [ sorry for numerous replies – I’m also wanting some more ]

            “… without evidence.”

            They say :

            “The Big Bang is actually not a “theory” at all, but rather a scenario about the early moments of our universe, for which the evidence is overwhelming…”

    5. Mathematics is a special, very precise that is both logically and internally consistent. It is enormously useful to the application of science, but by itself is not science. Science is based on experiments and the observations thereof.

      1. I disagree. Science uses observation and experiments and couldn’t exist without them, but science is based on guesses – which is what scientific theories are – bold conjectures. Empiricism can lend support to the guesses or prove them wrong, but the guess comes first.

        No doubt Darwin’s observations were important, but the theory of natural selection counts most.

          1. I’m not disagreeing with “math is not science.” I agree completely – math is not science (and I am a mathematician). Math is used by and crucial to science, just as experiment and observation are used by and curucial to science. But the theories come first.

  3. In an article posted on the Atlantic site, Alan Lightman is also skeptical of the multiverse theory. He writes:

    “Even if this multitude of other universes are real, there may well be no way to prove or disprove their existence. By definition, a universe is a self-contained region of space and time that cannot send a signal to another such region even into the infinite future. Thus, a universe cannot communicate with another universe. The hypothesized boatload of universes must be accepted or rejected as a matter of faith. Just as scientists do not like accidents, they dislike being forced to accept things they cannot prove. But the multiverse, and other aspects of this strange cosmos we find ourselves in, may be not only not unknown to us at this moment, but fundamentally unknowable. Although such a notion goes against the long tradition of science, it does offer a bit of humility, which is good medicine for any profession.”

    If the multiverse theory is eventually discarded, does not this knock out an argument against creationism? Creationists use the fine-tuning argument as a “proof” that a deity created the universe. If anti-creationists can no longer posit that due to the multiverse our universe is just one of an infinite many, which happens to allow for the existence of life, then what other arguments can be used against fine-tuning? I fear that creationists will jump on these proclamations by scientists that throw cold water on the multiverse theory.

    1. The multiverse as a response to fine-tuning is a philosophical argument. If theists are willing to jettison any arguments which can’t be proven, I’m fine with that.

  4. Wow. That was not an honest presentation and was full of unnecessary and unwarranted ad hominems. The Copenhagen interpretation is seriously problematic. A lot of progress has been made in physics by taking the math seriously and understanding what that implies. For example, Maxwell’s equations imply that light is always observed with the same velocity in a vacuum. Einstein ran with that and came up with special relativity. So if one were to take the Schrodinger equation seriously and what it implies the most straightforward interpretation is that it branches which is the many worlds interpretation. It can’t be tested (maybe at some point) but neither can the Copenhagen interpretation which apparently doesn’t qualify for the same level of scorn by Dr. Hossenfelder. For many decades there was no way to test Einstein’s EPR argument until there was progress in both theory and technology to allow it.

    1. Taking the math seriously and understanding what it implies is fine. What is not fine to Sabine is to present a theory which (she says) cannot conceivably be tested. It’s a possibility, but as its testability wanes it starts to leave the realm of a scientific theory. I happen to believe that if a theory can never be “tested” (finding evidence either for or against it) it’s not science. And don’t throw “Popper has been refuted” at me.

      1. We don’t know whether or not the many worlds theory will eventually be testable. Whether general relativity implies gravitational waves was debated for decades. Einstein changed his opinion more than once on this issue. It took a century of advances in both theory and technology for them to be detected. The Copenhagen interpretation is in the same class of currently unverifiable proposals as many worlds but apparently those in the Copenhagen camp are not practicing religion but those in the many worlds camp are. No serious physicist is claiming that their favorite proposal is correct beyond doubt, they are simply debating the merits of various proposals. Dr. Hossenfelder is doing a disservice by presenting the debate as cults practicing pseudoscience. If a proposal cannot be tested in principle then sure, it’s not science. She can make that argument about multiverse proposals and that’s fine. What she shouldn’t do is disparage those making a good faith effort at advancing our understanding. And I would never throw Popper at anyone.

        1. The interesting thing was that Schrodinger was not in the Copenhagen camp either. The scientific process is fundamentally agnostic, even if the scientists involved are not.

          It’s OK to say, we don’t know, but here is a mathematical description

  5. In my opinion it’s neither science or pseudoscience, it’s just an interesting hypothesis. It’s not a religion either; it’s only comparable to a religion in that it’s a belief with evidence.

    1. I agree and don’t know why she boils it down to only three options – science, pseudoscience, or religion.

      Sabine H is either lying, mentally ill, or willfully obtuse.
      (Or many other possibilities.)

        1. I’m making fun of her three options by making the same ridiculous argument – that there are only three options. So, joking, yes. I like her.

  6. “… for which there’s no evidence.”

    Isn’t that what’s attractive about many worlds, that it explains the weird evidence of quantum theory?

    1. “. . .for which there’s no evidence.”

      It’s always questionable what this observation means–e.g.,

      1. We’ve tested this extensively and can find no evidence

      2. We haven’t tested for evidence because we consider this proposition to be nonsense

      3. We haven’t tested for evidence because to do so would jeopardize our careers

      4. There’s plenty of evidence for this proposition but it’s not the kind we accept as scientific

      5. This proposition is not testable

      In this case, Hossenfelder pretty clearly means #5, but it would be nice if people specified which of the above meanings of “no evidence” applied to the claim.

  7. One should bear in mind that there are several very different multiverse proposals (cosmological multiverse, QM many-worlds multiverse, and string-theory multiverse for starters) and the arguments for and against are different for each. I also disagree somewhat with Hossenfelder on the falsification issue. If a model predicts a multiverse, and the model overall is verified and the best we have, then it is reasonable to infer a multiverse. One needs the model to be testable, but not necessarily every aspect of the model.

  8. I disagree. It’s not “reasonable” to infer a multiverse simply because it’s the best theory we have at the moment. What is reasonable is to say “here’s one suggestion but we have no idea whether it’s right”. You could have said the same thing about creationism in the early 19th century: God’s design was verified by looking at nature and it was the best theory we had to explain the diversity and adaptation in nature. Then Darwin came along.

    By the way, to say “the model overall is verified” is misleading: that implies that the model has been verified by observing nature. What you apparently mean is that the model is mathematically coherent.

    1. The point is that the multiverse isn’t the theory, rather the multiverse is one prediction of a wider theory. If a theory predicts 30 things, and 24 of them are both testable and indeed verified (such that the theory is way better than any alternative), then is it reasonable and scientific to (provisionally) accept the remaining 6 items as likely true, even if we have no direct verification of them specifically? I think, yes it is, indeed we pretty much have to accept implications of tested models in this way.

      1. I agree with Coel. There is an empirical basis, albeit indirect, for the multiverse speculations – it is the empirical backing for the models that, in turn, imply/predict various types of multiverses. Progress in theoretical sciences unavoidably depends in part on giving serious consideration to the implications of the existing models. At the same, insofar as there are a variety of models and corresponding multiverses, with no consensus, it follows that we do not know. Sabine is a strict empiricist, and I agree with her insistence that ultimately we need empirical evidence and with her skepticism that predictions from models alone suffice. But at the same time, ultimately all empirical evidence is in some sense indirect, it is a matter of degree, and the boundaries on where to declare the evidence gets “too” indirect to qualify as being within the ambit of science can be fuzzy.

      2. I think you just hit the most important nail on the head. That’s why it is rational for a scientist to predict that a space probe that goes over the cosmological horizon would keep existing – contrary to Hossenfelder’s reply to Objection 2. Our best scientific model predicts that it would.

  9. I’ve never understood the idea, expressed by both compatibilists and incompatibilists, that “it feels like we have free will,” or that “we have the illusion of free will.” Never mind the fact that the concept of “free will” seems only to be found in W.E.I.R.D. cultures, and seems mostly tied to monotheistic theology; I find that my own lack of free will is powerfully salient in the manifest image. To me it feels like my thoughts, including decisions and choices, just appear in my brain. When I pay close attention, when I carefully observe what is actually going on, I get no sense whatsoever that I conjured up these thoughts. They seem thrust upon me and I sometimes even wish them away to no avail.

    I don’t think I am alone here. There is plenty of evidence all throughout our language that everyone notices our complete lack of free will. “She made me laugh” or “he made me cry” or “I fell in love” or “it made me sad” or “I was overcome with joy.” Consider the extent to which all of your decisions and choices are based on what makes you laugh, cry, love, or become depressed. If you examine our language it appears that the reality of determinism, at least biological determinism, is more than just an accepted fact. It seems like everyone knows it with virtual certainty.

    Consider the moment in the restaurant when you are looking at the menu and you’ve read all of the items but it still takes you a while to male a choice because you “can’t decide’ what you want. You are waiting for your determined unconscious to make that decision for you. If you had free will you’d decide right away. In this moment you should “feel” and notice your lack of free will. You shouldn’t need physics or biology to point it out to you.

    When people say “we feel like we have free will” I don’t know what they mean. I don’t feel that way at all. To the extent that I ever felt like I had “free will” I would blame it on my W.E.I.R.D. upbringing and I would be thankful that I eventually noticed it wasn’t true and got over it.

    I have also never understood any of the proposed downsides to accepting determinism. Life is like watching a movie or riding a rollercoaster. The fact that you are not driving takes nothing away from the thrill and meaning of the experience. Relax and enjoy the ride. Of course I know that you can’t just decide to relax and enjoy the ride, but I hope that me saying these things will help determined you to do just that.

    1. It’s hard to believe you never experienced “the illusion of free will.” That illusion was baked into humans by evolution, as were many of our inaccurate beliefs. It takes work to overcome them.

      I do agree with most of what you write, but the idea that belief in “free will” is restricted to W.E.I.R.D. cultures is false because it’s produced by evolution. St. Augustine was a great proponent of free will and while you might class his society as Western, it was not educated, industrialized, rich, or democratic.

      1. I’ve never seen any “free will” like concepts in eastern philosophy and literature. And I don’t know what you mean when you say the illusion of free will is baked in by evolution. Yes I notice myself making decisions and choices but they feel more like they are compelled than something I would call “free will.”

        In the end this issue comes down to what is the most useful language to describe reality and “free will” feels like the wrong, or less useful term to describe what’s really going on. My decisions feel “compelled.” I do things that I decided before hand that I did not want to do, and that I immediately regret. Like eating that last cookie or getting upset at a late bus. This is not a lack if will power. It is the absence of free will.

      2. My question to this type of argument is, what would an almost complete lack of awareness of the mechanisms going into the making of our will feel like?”

        It is only the awareness of some of the constraints in the formation of our wills and perhaps the ability to confabulate that allow us to mistake having free will.

        1. I think if we had a natural inborn “illusion of free will” we would talk differently. We would say things like “I chose to find her comment funny and decided to laugh out loud at it” or “I decided to be sad and cry for a week in light of my mother’s death.”

          I think the clues that we are well aware of our lack of “free will” are right there in our language. Yes, “I chose” to order the soup, instead of the salad, but not with anything I could rightly call “free will.”

          Again I see nothing like the concept of “free will” in any eastern philosophy or literature. It seems like an artifact of monotheistic theology, and in turn, western philosophy, to me.

          1. Interesting point on “the natural inborn illusion” aspect. I will make a note of that.

            I would agree that free will is more built into western cultures and dogmas, than eastern one’s. But I do seem to recall studies of people from eastern cultures seeing the world as though there is free will. (ie people could have done otherwise)

            And from my minimal reading, although Buddhism does have dependent origination, it is a little more circumspect with respect to the topic of free will.

            1. The Tao Te Ching is all about “The Way” or the natural unfolding of things. “The master” goes with the flow. Becomes one with the flow. This is practically the same idea as determinism. The philosophy of life being more like “a ride” predates the idea of free will.

              Also in Hinduism is the idea of monism and oneness with the universe which is antithetical to the idea of individual free will. People in these cultures do not operate on the individual free will idea at all. It’s completely foreign to them. So it makes no sense to consider “the illusion of free will” as being evolved into our nature. In fact, observation and acceptance of our lack of free will seems far more adaptive.

              Modern science confirms determinism but it has been intuited by humans for millennia before the monotheistic individualistic idea of “free will” was dogmatically inserted into our western culture.

              1. I am not arguing about the dogmas or beliefs … it is more the Eastern behaviours that belie their dogmas.

                Also the judgement is out on whether determinism is true at a fundamental level.

              2. Understood. It still seems to me to be more adaptive to be aware of one’s lack of free will than to believe one has the kind of control that one does not have.

  10. “But I don’t think she’s dug deeply enough into the consequences of rejecting ‘naturalism’ (my new word for ‘determinism’)

    Rather than a position that can be arrived at by either observation or testing, determinism has always seemed to me to be a logical extension of an a priori commitment to naturalism: if naturalism is true, then free will is impossible. Do I take it, since you’re now collapsing the two terms, that you agree with this?

      1. When you say “determinism” you just mean that everything is governed by natural law, yes? So standard QM with its fundamentally probabilistic laws would still count as “determinism” in this sense, right? I suggest that “naturalism” is a much better word to minimize miscommunication, given that most physicists use “determinism” in the narrower way, where fundamental laws are non-probabilistic.

  11. “But I don’t think she’s dug deeply enough into the consequences of rejecting “naturalism” (my new word for “determinism”. There are serious social implications, notably in the judicial sphere, to rejecting libertarian free will. Below the fold you can see some of what I wrote about her video on free will.” (Jerry)

    I think you are wrong on that part, and will attempt to debunk it. A brief layout on the conditions:

    {1} Determinism is the notion that any state of the universe (nature, reality etc) is wholly determined by any previous state.

    {2} Quasi-Determinism (my term) covers the case of True Randomness, where the future is not wholly determined, because True Randomness is a feature of the universe, but it still works all the same regards Free Will (we don’t have it). If we somehow knew the outcome of the randomness, we’d be back at 1.

    {3} Regardless of whether 1 or 2 is true, we don’t have Free Will in the sense that we could “chose otherwise”, if we could set the universe back right before we make a decision. In other words, there is no Libertarian Free Will that could magically push matter or electrons etc around.

    {4} Such determinism does NOT mean that whatever we end up doing is irrelevant. Of course, each action, each thought, each word we say or omit, each wrinkle on our shirt is part of the universe and is going to determine any future state. This is also trivially true.

    {5} Therefore, there is no “actual” social argument to make in the sense of actually changing the course of history. Your arguing and their reactions are, per 4, part of the “machinery” that indeed determines any next state. And yet since nobody can do otherwise anyway, there are no actual consequences from a “deterministic” standpoint.

    Therefore, the elemination of a Free Will as a concept entails that EVERY other human conception of agency has to be eleminated as well. All and any choosing, any and all counterfactuals (that rely on assumptions of doing things differently than we end up doing etc) while adopting that perspective (or model).

    In my (model-dependent) view of things, we switch models when we discuss determinism, and then social factors. They simply do not mix at all. And I mean, at all! Once you switch to determinism, you cannot meaningfully talk about anything else, above all social consequences of adopting one view over another, with the implication that anyone could feel or think otherwise, because in that frame, nobody can. However, in the other frame, the “everday” model, we can and do persuade, influence, and affect the world.

    1. No, I think you are wrong and I reject your debunking. Our brains are wired up to behave adaptively, and therefore when we encounter environmental influences, like arguments, we can change our behavior. Yes, I am wired up to promulgate the bad judicial consequences of libertarian free will, but people are wired up to accept them or not accept them. I would argue that society would be better off if we accept the bad consequences, and yes, the argument comes from determinism.

      Your view of determinism means that if we don’t like a dog, and keep kicking it, there are no changes that can be made in the dog’s behavior, by avoiding the human.

      I presume from your argument that you accept libertarian free will, which I reject because there is no empirical/mechanical basis for it.

      This argument is over, so don’t bother to respond. You are arguing that no environmental effects from other people’s behavior or words could ever change our own behavior. And that is wrong.

      The end.

  12. Can’t help it :

    “If it disagrees with experiment it is wrong. In that simple statement is the key to science. It does not make any difference how beautiful your guess is. It does not make any difference how smart you are, who made the guess, or what his name is – if it disagrees with experiment it is wrong. That is all there is to it.”

    -Richard Feynman
The Character of Physical Law (1965)

    Chapter 7, “Seeking New Laws”, p.150 (Modern Library edition, 1994)

  13. It is indeed a strange topic! I get it that models that postulate the existence of a multiverse are several steps off the path of direct observation, and so they are all extreme extrapolations. I can also appreciate how the considerable attention they get makes them comparable to religion. But what led to the models — and especially to the eternal inflation model — were observations about our dark energy filled universe. The e.i.m. comes from an extrapolation of those observations.
    Its the eternal inflation model in particular that seems to be the best … lets say speculation about the cause of the big bang. Its the one I like the most, but of course it is speculation.

    I’ve never understood some of the other models. The Many Worlds model, for example, always seemed deeply flawed to me. If items with mass, including people, could virtually split and exist along separate paths in alternative universes, where did the extra mass come from? That seems against the law to me somehow.

    1. From what I understand about MW, the mass was already there. From listening to explanations from experts like Sean Carroll the “new worlds” are not newly created mass/energy/space. Rather the math shows that they are simply divisions in the over-universe. And yes, this implies that if the universe is not infinite then there is a limit to how many worlds, or divisions, are possible.

      1. Right. Other points worth noting: (A) The “worlds” are a thought-convenience for divvying up states into those that have a non-negligible chance of interacting with each other (same “world”) or not. And, (B) no additional postulates are needed to divide up the “worlds” (contra Sabine H), other than perhaps your own personal definition of “non-negligible chance”, which doesn’t matter anyway. It doesn’t matter because (A again) the “worlds” are just a convenient shorthand, and (C) decoherence is so fast that a chance threshold of one-in-a-million or one-in-a-quadrillion will be passed in the same nanosecond in a Schrodinger’s Cat type experiment.

  14. > Hossenfelder then considers whether the multiverse theory is science, religion, or pseudoscience. She’s already dismissed science…

    I’ve heard this argument before. The consensus terminology I’m most content with is that it is scientific metaphysics or scientific philosophy. It is not a testable theory, but is perfectly compatible with what we are able to know. It does not – and cannot – have any bearing on material physics. The same could be said about much of simulation theory, whether we are all living in one giant simulation (or the solipsistic simulation: maybe I am, and all of you folks are just NPCs.). It’s fun to think about, but has no overall bearing on reality.

  15. I always liked what Schopenhauer wrote about solipsism, which may apply to the matters being discussed in these comments.

    … a small frontier fortress. Admittedly the fortress is impregnable, but the garrison can never sally forth from it, therefore we can pass it by, and leave it in our rear without danger.

  16. I don’t think it’s quite right to call the Everettian (many-worlds) interpretation of quantum mechanics either pseudoscience or religion, even if it’s untestable in principle. A better term might be something along the lines of “coherent conjecture”, or “theoretical extrapolation”.

    One associates pseudoscience with preposterous “theories” like astrology, psychokinesis, or clairvoyance. It’s neither accurate nor fair to put the many-worlds hypothesis in the same group. And it’s less appropriate still to equate it to religious beliefs, which tend to be even more preposterous.

    Whether you agree with him or not, Sean Carroll can cogently explain why he thinks the many-worlds interpretation is a coherent and sensible inference, something that neither an astrologer nor the pope could do to defend their beliefs. That difference would be lost if we labeled Carroll’s position “pseudoscientific” or “religious”. One could even be induced to think him, in this respect at least, a charlatan or a religious nut, which couldn’t be further from the truth.

    An appropriate adjective for such conjectures would be “ascientific”. It’s accurate and doesn’t have the pejorative connotation of the other two categorizations. In fact, Sabine Hossenfelder herself uses it in an interview with Michael Shermer (The Michael Shermer Show. Podcast #294 from August 23. Highly recommended. Here’s the video:

    1. Exactly right, Ddel. Also, if the mathematics of a theory predicts a whole bunch of things which are observable and also predicts things which are in principle un-observable, then all that evidence of observed predictions is also evidence for the un-observable predictions. Sabine tries to get around that by saying that Mathematics is not reality, which is true, but not relevant to this argument. Sean makes a pretty compelling case that Everett’s theory is scientific based on that consideration. Getting around the undefined nature of what constitutes an observation in the Copenhagen interpretation of QM is what makes Copenhagen manifestly incomplete while Everett is a complete story which ties together all the observations within QM.

      1. The same would be true if no mathematics were involved (but most theories seem to use some mathematics).

        Here is a general argument (by David Deutsch):

        Almost everyone accepts the existence of things that have never been observed empirically. One example are dinosaurs. We only observe their fossils. Our best theory says that these fossils are a result of Dinosaurs having existed. Therefore we conclude that Dinosaurs have existed (until a better theory can explain the existence of fossils without requiring Dinosaurs).

        Hard empiricists will say: Wait, we have never seen a dinosaur. The only thing we can say is that fossils behave *as if* Dinosaurs have existed. So if we go to place X and dig there, we may calculate using theory (which includes mathematics) which fossils we are likely to find there, and our predictions will be correct. But nowhere does a real Dinosaur appear. Dinosaurs are only abstract entities in our theory. Therefore Dinosaurs do not exist.

        Most people would agree that the second view is a bit contrived, but then why not also for the non-existence of the multiverse as described in the theory of quantum mechanics?

            1. Perfect – another run to the library will be the beginning of an infinity for me!… pretty sure I had this at some point…

        1. I love this book. I love the challenge to all those longing for the golden age of yore:

          Progress that is both rapid enough to be noticed and stable enough to continue over many generations has been achieved only once in the history of our species.

          Deutsch, David. The Beginning of Infinity . Penguin Publishing Group. Kindle Edition.

          and his epistemology:

          But, in reality, scientific theories are not ‘derived’ from anything. We do not read them in nature, nor does nature write them into us. They are guesses – bold conjectures. Human minds create them by rearranging, combining, altering and adding to existing ideas with the intention of improving upon them. We do not begin with ‘white paper’ at birth, but with inborn expectations and intentions and an innate ability to improve upon them using thought and experience. Experience is indeed essential to science, but its role is different from that supposed by empiricism. It is not the source from which theories are derived. Its main use is to choose between theories that have already been guessed. That is what ‘learning from experience’ is.

          Deutsch, David. The Beginning of Infinity (p. 4). Penguin Publishing Group. Kindle Edition.

            1. Thanks Lysander. Notice “multiverse” wasn’t mentioned in the things I loved about the Deutsch book. I don’t understand the theory well enough to even have an opinion about its truth.

    2. I agree. First, all caveats about not being an expert and all that, but in my opinion I think a lot of people are too hung-up on the idea of uncountable parallel universes. I think this is a rather naïve interpretation of Everett, at least at this point in our knowledge. It probably would have been better to avoid labeling it “Many Worlds.”

      Sean Carroll forthrightly explains that we don’t know what the math of the MW interpretation means. That’s kind of his whole point. That we don’t know what QM means, what it entails about the actual nature of reality and that he thinks that trying to figure that out is a worthwhile thing to do. Many others argue the “shut up and calculate” school of thought is enough, but I strongly disagree.

      As a non expert who has read and listened to many experts explain the various interpretations of QM, and the history of them, Sean’s arguments in favor of Everett are pretty convincing. Fewer assumptions, just 2, and do the math. But again, he doesn’t claim that the naïve interpretation of the math, that there are a gazillion new universes being spawned every second, is an accurate depiction of the true nature of reality. He says he doesn’t know what it means and neither does anybody else.

      1. ” … we don’t know what QM means, what it entails about the actual nature of reality …”

        [this is not snark – this is harmonious to your point ]

        Ask anyone who had a PET scan what quantum mechanics means to their “actual nature of reality”, or people they know – quite a lot, I’d guess – assuming they generally know it entails positrons or annihilation, operating at the subatomic level.

        That’s admittedly a Hollywood or “out there” argument, but I thought I’d point it out.

      2. I agree with Ullrich Fisher and darelle. Sean Carroll is philosophically sophisticated and he makes a good argument that if we take the evidence for quantum mechanics seriously at face value then the simplest, most direct, interpretation is Many Worlds. That is not enough to conclude that Many Worlds is literally correct, but to make progress there is a need for theorists to work within an interpretation (the interpretation is relevant for setting the agenda/focus).

    1. Sean Carroll defends using “free will” as poetic language. He also says we should draw the line at not contradicting what science tells us. This appears to be a self-contradiction on his part. My guess is that he is misleadingly redefining “free will” under the table to have it both ways.

  17. For a while I was an avid reader of Brian Greene’s books but after finishing “The Hidden Reality” it struck me that there was no way of testing the multiverse, so it was more akin to religion than science.

  18. “The big problem with the multiverse idea is that physicists are confusing mathematics for reality.”

    In 100% agreement with Tegmark: mathematics *is* reality. (Or rather, reality is a subset of mathematical possibility.)

      1. “No, mathematics describes reality.”

        And obviously Tegmark and I would disagree. “What is it that breathes fire into the equations and makes a universe for them to describe?” (Hawking quote). Answer: nothing! It’s unparsimonious to add some mysterious substance to the math, when the math is enough.

        “And what ‘mathematical possibility’ tells you that whales evolved.”

        What aspect of quantum physics tell you that whales evolved?

        1. Crossing the leap from mathematical to material would seem to require a herculean feat of strong emergence. The leap from the material to the mental seems puny by comparison.

          1. Mapping our everyday experiences of our universe to our universe as it reveals itself via deeper empirical investigation can be a Herculean feat. Reversing that sequence and instead mapping from within the framework of modern physics to our everyday personal experience perspective rooted intuitions reveals that our commonly held intuitions can be parochial, short-sighted, misleading, and mistaken.

          2. I assume Sean Carroll is not alone in rejecting strong emergence. Maybe the physicists who endorse equating with universe with mathematics also accept strong emergence?

            1. “Maybe the physicists who endorse equating with universe with mathematics also accept strong emergence?”

              Doesn’t ‘strong emergence’ imply that upper-level phenomena influence lower level? In that case, I’m don’t see why you’d think that mathematical monists would accept it.

      2. Our universe manifests itself in levels with higher levels emergent from lower levels (a strict higher versus lower levels hierarchy may be an oversimplification, yet emergence is ubiquitous). My impression/assumption is that when some physicists argue that the universe is a mathematical phenomenon, they are referring primarily, or maybe only, to the lowest level, or maybe levels.

        1. ‘Emergence’ is normally understood as an epiphenomenon with characteristics that can’t be seen in its constituents. As a common example, the ‘wetness’ of water is not a characteristic of H2O molecules, and can in fact emerge from completely different ionic or polarized substances (eg. bromine). However, the fact that emergent phenomena are in a sense ‘independent’ of their constituents has led many people to think that emergent phenomena are something that can’t even in principle be derived from constituents. Sometimes it’s even claimed that emergent phenomena display properties that are impossible for their constituents. I think that that is all incorrect. I would say that emergent phenomena are a *subset* of all that the constituents can do. In some cases (eg. water), this subset of constituent potential is highly probable, instantly swamping out the alternatives. But in many other cases you have the reverse situation, where there is a vast diversity of equally (im)probable behavior. Emergence then amounts to drawing a ‘signal’ out of a noisy background.

          1. I know Sean Carroll says he rejects strong emergence. I do not know who among his colleagues accepts strong emergence or whether a chain of weak emergence can produce a result that resembles strong emergence.

  19. Q: Given that we have no free will, why don’t we do something about the judicial system?
    A: Because we have no choice in the matter.

    It is isn’t actually what determinists are trying to say, but it always seems to feel that way.

    1. Well, I’m not responsible for those feelings. Many of us know what that statement means: those of us who advocate judicial change have no choice in that advocacy, but we can influence other to change the justice system.

        1. Just like you can influence what Alexa does depending on what you say to “her”.

          Alexa doesn’t need free will to react according to your input. A dog doesn’t need free will to adapt its behavior according to what it learns is likely to bring about punishment or reward. People don’t need free will to want to institute a more humane criminal justice system upon the realization—which realization may be the result of influence from others—that free will is an illusion. All of the above is compatible with a fully deterministic universe.

    2. Philosophers have very carefully framed the discussion around the “will”. If we rephrase the answer to:
      A: Because we do not have the will in the matter.
      Makes much more sense.

    3. The argument can be used both ways. Criminals may have no choice in their actions, but I have no choice but to want them dead, too.

  20. Laura Mersini-Houghton has a theory on multiverses and made a prediction that was subsequently supported by the Planck telescope.
    A book review and a quote from another

    “…Intrigued, the author considered the matter and found a solution that combines quantum theory with gravitational theory (both long accepted) and string theory (still under debate), producing a testable concept that required innumerable worlds: a multiverse…Mersini-Houghton’s long explanation of her concept will be heavy going for those unfamiliar with physics, and she does not deny that it remains controversial, but the possibilities suggested by her research are undeniably intriguing…A well-informed cosmology lesson for dedicated readers.”

  21. Isn’t the question then whether mathematics is merely a human description of things, or if it has a fundamental existence? If the latter then she is surely wrong to dismiss the multiverse?

  22. I recommend listening to Sean Carroll (in his Mindscape podcast) talking with Sabine. Healthy agreement and disagreement.
    Sean is very (very) precise in his language, and it is clear that even though he ‘wants’ the Multiverse model to be correct, he in no way posits it without evidence.
    Having listened to hundreds of hours of his physics discussions, it is too easy to misconstrue his position – and while I really do like Sabine’s output, it does have a small flavour of ‘I am the subverter.’ (Wow, so badly phrased by me…)
    In the discussion with Sean, I realised his precision with language did make her takes a little less convincing.
    Still follow both of course!
    And…do not (automatically) conflate ‘multiverse’ with ‘many worlds’ – and which one Sean advoctaes for. Only an extended listen to his podcast of writing (over time) can do it justice.
    Here is a morsel from him:
    All fascinating stuff.

  23. The problem is of course that Hossenfelder is factually wrong, despite popular claims a test for the multiverse was successfully predicted and then observed as passed in the 80s. Nobel Laureate Steven Weinberg proposed the anthropic multiverse as an explanation for, and quantitatively predicting a value of, the vacuum (“dark”) energy.

    The history of reflexively disliking and even erroneously describing the multiverse is long and storied and as a popular science crusader against windmills Hossenfelder seems to have pulled the odl and tired “postulate unobserved entities”. But quantum field physics especially is noted for this, having infinite unobserved Hilbert spaces filled with potential entities to explain the one that observations pick. This is no different, it doesn’t matter how many entities of the same type we need to explain the individual circumstances – a process that can produce one entity can produce any number. This is a feature of processes and not a problem.

    That also comes to mind when our host in a comment immediately conflates multiverse theory with many world physics, which is an entirely different area.

    I have earlier voiced my distaste for Sabine Hossenfelder populism and tendency to step into pseudoscience – unfairly making string theory and now multiverse theory out to something it isn’t without having an observational basis but merely opinion – but now I must add a warning. It is good to listen to critics, even uninformed such (see the “forgotten” test above), but one must do so on own risk.

  24. I’ll add some other dissenting voices to the gist of the article to confirm that this is accepted science. Akin to how the LCDM big bang cosmology allows for vast volumes of space with galaxies and other stuff that are “unobservable entities”, and I assume Hossenfelder has no problem with that.

    – The large eBOSS Collaboration in a 2020 publication with almost 100 authors notes, based on 20 years of observation, that the finetuning of the cosmological constant – vacuum dark energy density – is a “difficulty without any agreed-upon resolution and one that may not be resolvable through fundamental physics considerations alone”, referring to Weinberg’s and similar models as the potential resolution.

    – Martin Reese, Astronomer Royal for UK, says in an interview after a 2014 meeting at Carnegie Institution for Science:

    Plausible models for 10~16 GeV physics lead to so-called eternal inflation. “Our” Big Bang could be just one island of space-time in a vast cosmic archipelago. This is speculative physics – it is perplexing today, just as the shape of the Solar System was to Newton and the “Big Bang” was until fifty years ago. But it is physics, not metaphysics; we can hope to push the casual chain back farther still.

    – Another popularizer. astrophysicist Ethan Siegel:

    One of the most successful theories of 20th century science is cosmic inflation, which preceded and set up the hot Big Bang. We also know how quantum fields generally work, and if inflation is a quantum field (which we strongly suspect it is), then there will always be more “still-inflating” space out there. Whenever and wherever inflation ends, you get a hot Big Bang. If inflation and quantum field theory are both correct, a Multiverse is a must.

    [“This is why physicists suspect the Multiverse very likely exists”, Big Think, 2021]

  25. If we have no say in our decisions because they are predetermined, then we don’t have a say either in whether crimes are to be punished.. The punishment is predetermined too..

    1. Age-old philosophical problem, with lots of commentary.
      You could, in a very basic way, consider that if a person is committing (say) violent crimes, even if they are pre-determined, we would still want to be protected from them.
      So you still remove that sort of person from society so that others are not harmed. It does not matter if the actions are pre-determined or not.
      From this sort of thought experiment, you can build a system of action/ethics. Fun stuff.

  26. I think what’s sometimes missing from these discussions is an explanation as to why the majority of physicists who investigate the deeper mathematical and physical structure of quantum theory typically follow the Copenhagen Interpretation.

    If one picks up actual academic texts like Asher Peres’s “Quantum Theory: Concepts and Methods” or Roland Omnès’s “The Interpretation of Quantum Mechanics” one finds the Copenhagen point of view given. Similarly from most texts by physicist-philosophers such as Bernard d’Espagnat.

    Many-Worlds is disproportionately common in popular expositions compared to the academic literature.

    I can’t give a full exposition in a blog comment, but the main reason Copenhagen (with its observer dependence) is more common is that to most of us it seems to be the literal reading of quantum mechanics. The quantum state as a mathematical object obeys theorems corresponding to probability, inference and information theory and so taking it as a “physical wave” à la electromagnetism is not natural to most of us. This is even more the case in quantum field theory than in non-relativistic quantum theory.

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