Tuesday, July 09, 2019

Why the multiverse is religion, not science.

This is the 5th and last part in my series to explain why the multiverse is not a scientific hypothesis. The other parts are: 1. Does the Higgs-boson exist? 2. Do I exist? 3. Does God exist? and 4. The multiverse hypothesis.

I put together these videos because I am frustrated that scientists discard the issue unthinkingly. This is not a polemical argument and it’s not meant as an insult. But believing in the multiverse is logically equivalent to believing in god, therefore it’s religion, not science.

To see why, let me pull together what I laid out in my previous videos. Scientists say that something exists if it is useful to describe observations. By “useful” I mean it is simpler than just collecting data. You can postulate the existence of things that are not useful to describe observations, such as gods, but this is no longer science.

Universes besides our own are logically equivalent to gods. They are unobservable by assumption, hence they can exist only in a religious sense. You can believe in them if you want to, but they are not part of science.

I know that this is not a particularly remarkable argument. But physicists seem to have a hard time following it, especially those who happen to work on the multiverse. Therefore, let me sort out some common misunderstandings.

First. The major misunderstanding is that I am saying the multiverse does not exist. But this is not what I am saying. I am saying science does not tell us anything about universes we cannot observe, therefore claiming they exist is not science.

Second. They will argue the multiverse is simple. Most physicists who are in favor of the multiverse say it’s scientific because it’s simpler to assume that all universes of a certain type exist than it is to assume that only one of them exist.

That’s a questionable claim. But more importantly, it’s beside the point. The simplest assumption is no assumption. And you do not need to make any statement about the existence of the multiverse to explain our observations. Therefore, science says, you should not. As I said, it’s the same with the multiverse as with god. It’s an unnecessary assumption. Not wrong, but superfluous.

You also do not need to postulate the existence of our universe, of course. No scientist ever does that. That would be totally ridiculous.

Third. They’ll claim the existence of the multiverse is a prediction of their theory.

It’s not. That’s just wrong. Just because you can write down a theory for something, doesn’t mean it exists*. We determine that something exists, in the scientific sense, if it is useful to describe observation. That’s exactly what the multiverse is not.

Fourth. But then you are saying that discussing what’s inside a black hole is also not science

That’s equally wrong. Other universes are not science because you cannot observe them. But you can totally observe what’s inside a black hole. You just cannot come back and tell us about it. Besides, no one really thinks that the inside of a black hole will remain inaccessible forever. For these reasons, the situation is entirely different for black holes. If it was correct that the inside of black holes cannot be observed, this would indeed mean that postulating its existence is not scientific.

Fifth. But there are types of multiverses that have observable consequences.

That’s right. Physicists have come up with certain types of multiverses that can be falsified. The problem with these ideas is conceptually entirely different. It’s that there is no reason to think we live in such multiverses to begin with. The requirement that a hypothesis must be falsifiable is certainly necessary to make the hypothesis scientific, but not sufficient. I previously explained this here.

To sum it up. The multiverse is certainly an interesting idea and it attracts a lot of public attention. There is nothing wrong with that in principle. Entertainment has a value and so has thought-stimulating discussion. But do not confuse the multiverse with science, because it is not.



* Revised this sentence after two readers misunderstood the previous version.

Update: The video now has German and Italian subtitles. To see those, click on "CC" in the YouTube toolbar. Choose language under settings/gear icon.

325 comments:

  1. Dr. Hossenfelder: you can totally observe what’s inside a black hole. You just cannot come back and tell us about it.

    That seems like a very weak argument; the equivalent in religion to claiming God is observable because, by their postulates, you will observe Him when you die, and unexplainable near-death experiences prove the plausibility of that.

    A simpler explanation for why discussing the interior of black holes is science is that we have convincing evidence black holes exist, and they have a radius, and by logic that means they have an interior. Discussing the laws of gravity and quantum physics that applies everywhere else in the universe (to the extent we know the laws and universe) to understand how they would influence any structure of the interior, even if unobservable, is still the application of science.

    I mean, a hundred years ago it is science to discuss fusion in the core of the Sun without physically observing it; and we have still not physically observed it. It is science to discuss the mechanisms of thought and emotion within the confines of what we know about brain operations, without physically observing the neural signaling of an emotion being generated by the amygdalae.

    ReplyDelete
    Replies
    1. Dr Castaldo,

      The problem with the argument that you can observe god after you have died is not that death is irreversible, but that we do not know of any way you can observe something after you have died.

      Delete
    2. True in a non-religious world, but by definition false if there is life after death. I think Castaldo's rebuttal is on the mark.

      Delete
    3. Philip,

      Do you seriously want to argue that "you can observe the inside of a black hole" is as compatible with our existing knowledge about the universe as "you can observe god in afterlife"? Do you know that little about general relativity?

      Delete
    4. I'm not making that comparison. I am agreeing that "one can observe it, but can't come back to tell about it" is a weak argument. (Of course, the rhetorical device of the afterlife works only if one believes in the afterlife, but is a red herring here.) The point is that if "one can never observe it" is the criterion, then it seems strange to trust GR about what is inside a black hole, but discount the multiverse. Of course, GR is a well tested theory, so one has some confidence in what it predicts. Some multiverse proponents see the multiverse not as a hypothesis, but rather as a consequence of theories which are believed to be true for reasons having nothing to do with the multiverse. Granted, such theories don't have the status of GR.

      Delete
    5. Phillip,

      Yes, that is the comparison that you make - just read your own comment.

      You now claim that it is a "weak" argument because (well, really, because it doesn't fit to the convictions you have told us about often enough) you want to put "making an observation inside a black hole" on the same level as "making an observation in afterlife" never mind that we all know this is ridiculous because the very notion of "observation" in "afterlife" is already belief-based.

      If you have any other reason to think this is a "weak" argument (whatever that means), please let us know.

      Delete
    6. Sabine,

      The argument you give in replying to Phillip is a *different* -- and much stronger -- argument than the one you gave in your blog post when you wrote, "you can totally observe what’s inside a black hole. You just cannot come back and tell us about it." In your response to Phillip you are invoking the consequences of an otherwise very well-tested theory to make extrapolations about the effectively unobservable interior of a black hole. This argument is not based on some technically possible (but in practice unattainable) observation of said interior.

      Likewise, it's possible at least *in principle* that some well-tested theory, supported by a quantity and quality of evidence comparable to that supporting GR today, could have a multiverse as an unavoidable consequence. If that were to happen then belief in a multiverse would be as scientifically justifiable as our current beliefs about the interiors of black holes.

      So the legitimate argument against the multiverse is that we have no such well-defined theory with strong evidence backing it. The lack of direct observability is a red herring.

      Delete
    7. Dr. Hossenfelder: ... the very notion of "observation" in "afterlife" is already belief-based.

      Isn't the notion that our consciousness can survive crossing the event horizon also belief-based?

      There may be a firewall just inside the event horizon, as I understand it LIGO observations of a black-hole collision are consistent with that notion, or of GR breaking down at or near the event horizon: https://www.nature.com/news/ligo-black-hole-echoes-hint-at-general-relativity-breakdown-1.21135

      Thus the idea we can observe what is inside a black hole is also a belief system, some physicists believe in firewalls, some don't, but the paradox is not resolved by either camp. (And on an unrelated note IMO that is justification for bigger, better and more gravitational wave experiments.)

      Discussing firewalls is itself speculating on the interior of a black hole, and science because it is a paradox resulting from beginning assumptions, one or more of which must therefore be falsified.

      More importantly, it has nothing to do with whether or not we can observe the interior, but we know an interior exists behind the event horizon, the extent of space enclosed by the event-horizon is an "object" with a mass that isn't nothing. Objects that occupy space have interiors.

      The fact that an interior exists also has nothing to do with whether a conscious being can theoretically observe it. To me the interior exists as a matter of simple and incontrovertible logic. Unlike the multiverse, Gods and the rest of the religious anti-logic.

      Delete
  2. 'But then you are saying that discussing what’s inside a black hole is also not science' - I think you can be braver and say 'So what?' It's true that 'It's possible to observe what's inside a black hole', however, for the foreseeable future it's not possible for *us* to observe what's inside a black hole. That being the case, I'd suggest that while it might technically be science, it's pointless science until there is some prospect of doing so.

    ReplyDelete
    Replies
    1. Brian,

      Well, yes, that is an attitude one can have and I can understand the rationale of saying it's pointless.

      However, the multiverse isn't only not observable in practice but actually not observable in principle (except for the part that is our own universe). I think that puts it conceptually on a different level.

      While for the 'pointless' case one can debate just when is it pointless (exactly what is the "foreseeable future"?) in the impossible case you don't even need to have that debate.

      Delete
    2. About this particular issue of being able to observe things inside a black hole, I'm curious about how 'observe' is defined. Is there a technical definition, or are you using the word in the intuitive way most of your reader would accept it? I'm asking because, for me, being able to observe would mean there is at least one incoming ray of light at your position in your own reference frame. But I thought with my limited knowledge of how this works that inside the black hole all rays of light are outgoing, everywhere, except near the singularity (where the theory breaks down). Which makes me think that we must carefully define what 'observe' means before we can use the word.

      Delete
    3. Good question, dlb.

      Can quarks be observed? If Hawking radiation from an evaporating black hole is observed, does that tell us anything about what is/was inside it? When two black holes merge, do "high resolution" GWR observations tell us anything about what is/was inside either? What if it's an NS-NS merger that results in a BH?

      Delete
    4. dlb,

      There are various ways people go about to define 'observation'. The technically simplest is the two-level system that I explained here. You can of course make it much more complicated if you wish...

      The process of "observation" has not necessarily something to do with light. For starters because one could argue that the absence of light is also an observation. Besides, unless you are also falling with the speed of light inside a black hole, you will have light coming at you "from behind" basically.

      Delete
    5. This last sentence helped me understand what you mean, thank you.

      @JeanTate: I was interested in the definition of 'observe' in the context of the peculiar space-time that is the interior of a black hole.

      Delete
    6. Sabine, thanks - good point.

      Delete
  3. Multiverse are a hypothesis on a stack of hypotheses ...

    It's time to come back on the ground.

    ReplyDelete
  4. Typo:
    "...is certainly necessary to [...] but not necessary."
    I guess last necessary -> sufficient.

    ReplyDelete
  5. "The requirement that a hypothesis must be falsifiable is certainly necessary to make the hypothesis scientific, but not necessary."

    Typo?

    ReplyDelete
  6. Before commenting, everyone should read the book Universe or Multiverse (edited by Bernard Carr).

    ReplyDelete
    Replies
    1. Haven't you noticed yet that the "argument from a book no one wants to read" doesn't help your case?

      Delete
    2. Judging a book without reading it is never a good move.

      Delete
    3. I did not judge the book, I have noted that (a) you do not make any argument, you merely refer people to a book you once read (b) no one has an interest in reading the book, but (c) you still somehow seem to think you have made an argument.

      Delete
  7. The theory of eternal inflation and the many worlds interpretation of quantum mechanics are not science?!
    What have you smoked?

    ReplyDelete
    Replies
    1. Franzi,

      I have used my brain. You should try it some time.

      Delete
  8. Hihi, you don't have to approve this, just
    a good joke:
    You have smoked crack pot.

    ReplyDelete
  9. Multiverse as subject of entertainment I can accept. But religion is not entertainment, the number of victims is uncountable.

    ReplyDelete
  10. The many worlds interpretation was
    first published as a PhD thesis
    in physics at Princeton University
    with John Wheeler, one
    of the most eminent physicists of
    his generation, as advisor.
    When it was finished, Wheeler sent Everett,
    freshly with his Phd, to Niels Bohr
    to discuss it.
    I mean, whatever you think about it,
    it is obviously science.
    Crazy science. But science.

    ReplyDelete
    Replies
    1. Franzi,

      Instead of making stupid jokes and attempting to make arguments from authority, how about you think about what I just explained, huh? At least give it a try.

      Delete
    2. Ignorants seems to cannot discerning that the Assumption behind The Multiverse, Many World Interpretation and "Eternal Inflation" is "Omnipotence" ...

      Obviously, A Theological Argument.

      Scientists should stick to their measurable stuff .... and Let Theological Arguments to Mystics, Artists, Theologians, Philosophers, Mathematicians, Comedians and every body who wants to entertain their imagination without boundaries ....

      But Science has boundaries and constrains such stick to Quantifiable Assumptions.

      Simple, Omnipotence is a non quantifiable assumption ...

      Therefore, The Multiverse, The Many World Interpretation and Eternal Inflation are Religious Claims.

      Period.

      Nothing to argue.

      Are those "Physicists" wanting to replace "Theologians" in the job market ???

      Please Idiots, If You don't want Theologians in your Physicists Clans ... don't do Theological Claims.

      IDIOTS.

      Delete
  11. What multiverse(s) are you actually talking about ?

    Level I,II,III or IV (Tegmark classification)

    Quilted, Inflatory, Brane, Cyclic, Landscape, Quantum, Holographic, Simulated or Ultimate (Greene classicication)

    ReplyDelete
  12. I don't see any evidence that the Multiverse is science either, but I don't think that finding that you don't believe in something means that it makes sense to call it religion.

    Get a dictionary and look the word up - it doesn't mean what you seem to think it means.

    ReplyDelete
    Replies
    1. CIP,

      I have explained that believing in the multiverse is logically equivalent to believing in god. Whether I believe or do not believe in either is entirely irrelevant for that. You can now either proclaim god science or accept that the multiverse is religion. Take a pick.

      Delete
    2. "Logically equivalent" means "if and only if"; I think what you mean is something like "equally unfounded epistemically".

      Delete
    3. Andrew,

      You may be right. I'll have to think about that.

      Delete
    4. I think that Andrew's point is the why you are getting the pushback, mostly from people who probably agree with you on the ultimate fact that both the multiverse and religion lack any reliable evidentiary foundation.

      Delete
    5. Harvey,

      You misunderstand that. The point is not that there is no evidence for the multiverse (though of course that is so). There is nothing wrong with working on a theory for which there is no evidence yet, if that evidence could come in. The point is that this theory contains elements for the existence of which there can be no evidence, by construction, not yet and not ever.

      This is why I am saying the multiverse is logically equivalent to god. It postulates the existence of entities which are unobservable by construction.

      Having thought about Andrew's suggestion to call it "equally unfounded epistemically" I think this is missing the point, because it would leave open the possibility that this situation can changes.

      Delete
    6. OK, but you certainly do not mean "if and only if", which is the meaning of "logically equivalent".

      Delete
    7. Andrew,

      What I mean is that the logic of both (believing god exists and believing the multiverese exists) is identical, not that the two hypotheses are identical. I am not sure where our misunderstanding is here.

      Delete
    8. I think it's just that you misunderstand the English phrase "logically equivalent", which means "if and only if". The "logic of both" is pretty vague - I guess you mean the logic of the arguments for them, as in, same proof, just replace God by MV. "Isomorphic proofs"? That seems too strong.

      Delete
    9. As I said, it’s the same with the multiverse as with god. It’s an unnecessary assumption. Not wrong, but superfluous.
      is quite clear, I thought. That multiverse and god are superfluous in that they add nothing to a scientific explanation - by no means turns them into the same thing.

      I think people are not reading what is written but rather seeing what they're thinking in the words.

      Delete
    10. Andrew,

      This isn't a math paper, it's a blog post. And no, I am not talking about "proofs", I am talking about arguments that people make in defense of the multiverse.

      Delete
    11. Sabine,

      Yes, but that doesn't mean you can make words mean whatever you want them to mean.

      Delete
    12. Andrew,

      Of course not. I am trying to express myself as good as I can and, believe that or not, use this blog to improve my explanations based on the feedback I get. Having said that, the fact that a single person doesn't like a phrase or misunderstood it at first attempt isn't a good reason to change it if worked for the vast majority of people.

      Delete
  13. OK...

    > Theories don’t predict what does and does not exist.
    > We determine that something exists, in the scientific sense,
    > if it is useful to describe observation.

    Wrong. Counter example: Maxwell's theory of electromagentism
    predicted radio waves. They had never been observed.
    Hertz searched for them guided by the theory and found them.

    > They are unobservable by assumption, hence they can exist only in a religious sense.

    This is your major mistake, may be the QM many worlds are unobservable,
    but they are not unobservable by assumption.
    E.g. David Deutsch made a proposal for a thought
    experiment to find experimental evidence for
    the existence of the parallel worlds in 1985.
    He needs hazy concepts like "quantum computer with
    consciousness" so it does not convince
    me that there can be evidence. But it shows
    that David does not make the assumption that
    they are unobservable. And why should anybody
    make this assumption?

    ReplyDelete
    Replies
    1. Franzi,

      Gosh, are you serious? Predicting electromagnetic waves does not demonstrate that they exist. Measuring them does. It's not a complicated argument. Where did I lose you?

      "This is your major mistake, may be the QM many worlds are unobservable,
      but they are not unobservable by assumption.
      E.g. David Deutsch made a proposal for a thought
      experiment to find experimental evidence for
      the existence of the parallel worlds in 1985."


      And you know what, no one has found that evidence. Why not think for a moment about why that is?



      Delete
    2. > Gosh, are you serious? Predicting electromagnetic
      > waves does not demonstrate that they exist.

      Your statement is true, but this was not the issue.
      You claimed "theories don't predict what does ... exist"
      and I gave you a famous example where a theory predicted
      that radio waves exist. It was a pre-diction exactly
      because had not demonstrated, yet, that they exist.

      Admit that your statement was completely wrong.
      Don't be a spoilsport ;-).

      > And you know what, no one has found that evidence.
      > Why not think for a moment about why that is?

      Because it is irrelevant for the argument we have here.
      Implicitely, by changing the subject, you admit that David does not
      make the assumption that many worlds
      are unobservable by assumption.
      Yes, if one would make this silly assumption
      many worlds would be religion. But
      no scientist would make this assumption.

      Delete
    3. Sabine, while your post is spot-on, I also stopped short when reading "Theories don’t predict what does and does not exist." It seems like theories predict the existence of things all the time, unless you're using some nonstandard definitions of "predict". Mendeleev's predicted elements, for example.

      "Predicting [something] does not demonstrate that [it exists]" is an entirely separate claim which I don't think anyone would dispute.

      Delete
    4. Franzi,

      I am not sure what is your difficulty understanding my statement. Let me try to say this differently. By help of theories we make predictions for observations. If these observations are confirmed, that demonstrates the elements of the theory that were necessary to make the prediction exist. Just because a theory contains an element, does not mean that element exist.

      Now, electromagnetic waves happen to be elements of a theory that do give rise to observational consequences and that turned out to indeed exist. Good. It does not follow from that, as you seem to erroneously think, that anything that's part of a theory actually does exist.

      Let me know in case that still was not clear.

      "Because it is irrelevant for the argument we have here.
      Implicitely, by changing the subject, you admit that David does not make the assumption that many worlds
      are unobservable by assumption.
      Yes, if one would make this silly assumption
      many worlds would be religion. But
      no scientist would make this assumption."


      Uhm, what subject have I changed? Of course they do not go and write down "I assume this is unobservable", why would anyone do that? I am saying that it follows from the assumptions, except in some specific scenarios which I mention in point 5.

      Really I get the impression you haven't though about this much.

      Btw, I am no fan of your passive-aggressive attitude and if you want to continue this conversation, please sign with a full name. I do not like to waste my time arguing with people who are insincere. The topic is too important to me for this. Thanks,

      Sabine

      Delete
    5. Boetian,

      I have changed that sentence and hope the revised version is easier to understand. Thanks for the feedback.

      Delete
  14. The short answer to your essay is, It may not be science, but it's still mathematics.

    A longer answer is, Doesn't the multiverse plus a weak form of the anthropic principle have at least some explanatory value toward the coupling constants?

    Re: the coupling constants, I take your larger point to be that compared with the other problems facing physics it's not important enough to warrant driving a serious research program; I'm not arguing with that. I'm merely saying that MV+WAP has some explanatory value, and therefore should not be dismissed as unscientific on the grounds given in this essay.

    ReplyDelete
  15. Sabine,

    I have noticed that arguments about the "multiverse" are inevitably made to "explain" "fine tuning" using the anthropic principle. But from where I sit an explanation that starts with "postulate an infinite number of universes then filter out the smaller infinite number that don’t support physicists" is a sloppy way to explain something.

    I suppose the infinite inflation crowd like it for different reasons, but it really seems more like a blow to the inflation idea then support for a multiverse to me. Perhaps there is a better way to explain texture in the CMB?

    Are you aware of any other reasons to bother with a multiverse? Are they any better then the above (which are bad)?

    J*

    ReplyDelete
    Replies
    1. Jonathan,

      Postulating a multiverse does not explain any observation that you could not also explain without it. The people who think the multiverse "explains" something always use non-scientific versions of "explanation".

      You call it sloppy, I actually think it's worse than that. It's allowing religious explanations in science.

      Maybe I should explain the non-explanation of constants in a separate post. I thought it was obvious, but it seems that this isn't the case. Sorry about that.

      You ask for other reasons to bother with a multiverse. I think one of the major reason is, as I said, that they think it's "simple" in some way. They also tend to think that just because there is mathematics for it, that must mean something about the science of it. Some just seem to advocate it because they consider themselves great intellectual heroes.

      Delete
    2. Look, I don't think it's a _good_ explanation, I don't _like_ it, but it has some explanatory value, and it's "simple" in the sense that it flows naturally from existing equations (I think, IaNaP).

      Maybe my point is that I don't see much value in trying to enforce semantics. If you don't think it's science, fine, don't write papers about it; but if someone else has fun with it and doesn't take funding away from a worthier project, then what's the harm? Ultimately we all do this stuff for hedonistic reasons.

      Maybe it's because I used to be a mathematician (logician in fact), but I don't much care whether a paper turns out to describe the real world accurately, as long as it's interesting and internally consistent. But I share your fear of bad priorities in funding.

      Delete
    3. “… any other reasons to bother with a multiverse?”
      In 1998 David Deutsch said The heart of the argument is that single-particle interference … … existence of the multiverse … . With multiverse the many worlds interpretation (MWI) is meant. For David Deutsch MWI is an “explanation” for superposition.
      If we have a fully entangled state of say 400 qubits then this state is described by N=2^400≈10^120 complex numbers. N is huge (*) and a real number can have a lot of digits. Thus, one could ask “How in this (single) world can QM handle so many data for just a tiny entangled state?”
      Exactly for this question I was at that time a believer in MWI. But I changed my mind, because MWI also comes with Everett’s “solution” of the measurement problem.

      -----------------
      (*) more than e.g. there are matter particles in our universe (or Bekenstein entropy of the de Sitter horizon … - here I am not sure)

      Delete
    4. Andrew,

      Please spell out why you think the multiverse hypothesis has "explanatory value". What data does it help to explain? Please be concrete. What makes you think it is "simple"? Please be concrete. Why is it simpler to assume that infinitely many universes exist than to not make such an assumption?

      "Maybe my point is that I don't see much value in trying to enforce semantics."

      This is not semantics. I have made a clear argument for why multiverse discussions are not scientific discourse because there is no observation that this hypothesis can explain. If you think this is "semantics" then you must equally call secularization "semantics".

      "Maybe it's because I used to be a mathematician (logician in fact), but I don't much care whether a paper turns out to describe the real world accurately, as long as it's interesting and internally consistent."

      Fine if you are a mathematician. But science is not mathematics. If people want to talk about multiverses as mathematical fiction, that would be fine with me, though frankly I highly doubt it's interesting mathematical research.

      Delete
    5. Well, you know that Witten won the Fields medal...

      Delete
    6. Andrew Dabrowski: Well, you know that Witten won the Fields medal...

      That is a medal for Mathematics. Having completed two math degrees, let me assure you that mathematics considers all kinds of things that have nothing to do with reality. Corresponding to reality is not a requirement for mathematical theory or being celebrated for inventing new ideas or solutions or proofs of important conjectures in mathematics.

      Also, this is an appeal to authority, and misplaced. If Witten was as infinitely brilliant as you seem to think he is, he'd be able to resolve the problems in String Theory. There is no evidence he (or anyone else) is anywhere even close to doing that. There is good reason to think Witten is a very clever manipulator of equations, but apparently manipulations of equations has run its course! There is no reason to think he holds any special knowledge about other universes.

      In fact, those are unobservables that seem to be consequences of the equations; if anything it implies the equations are either wrong or an incomplete model of reality, in which only one universe is observable.

      Delete
    7. "Please spell out why you think the multiverse hypothesis has 'explanatory value'. "

      I talked about this in an earlier installment of the series.

      "Why is it simpler to assume that infinitely many universes exist than to not make such an assumption?"

      Well, if you've already got the equations of our universe lying around, it simple to reuse them for another. There are various notions of "simple".

      "This is not semantics. I have made a clear argument for why multiverse discussions are not scientific discourse because there is no observation that this hypothesis can explain. "

      OK, I agree that the general notion of science is that it should have some explanatory value. If you could be convinced that MV had a tiny bit of that, would you agree it's science?

      Delete
    8. I was only responding to Sabine's " I highly doubt it's interesting mathematical research. "

      Delete
    9. Andrew,

      I cannot recall you detailing what explanatory value the multiverse supposedly has, sorry.

      Quite possibly this is because you do not address your posts to people by name. I don't have time to read all comments and usually only look at those directly addressed to me. Please note that the comment notification does not contain information about whether a comment was a response to some other comment.

      If you want to claim that a theory with N+1 assumptions is simpler than a theory with only the first N of those assumptions, then that's a nonsensical version of simplicity. Maybe more importantly, it's a version of simplicity that's incompatible with the scientific method. I have explained this in my earlier posts. The moment you allow adding unnecessary assumptions to a theory, you are sacrificing science.

      It doesn't even matter if you think this is a criterion of "simplicity" (though I would argue it is) or if it has any philosophical basis (it may not), it is a requirement that is necessary in practice. Without this requirement, science just can't work.

      If the multiverse would explain some measurement and the assumption that other universes besides our own exist is necessary for that explanation then, yes, I would agree it is science. But for the types of multiverses presently under discussion this is impossible to happen. If you do not understand why I say that, please let me know and I will explain this again.

      Delete
    10. Sabine,
      I just made the usual MV+WAP (weak anthropic principle) argument for explaining the coupling constants, which, while not exactly endorsed, has been entertained by some prominent physicists. I'm puzzled as to why you think it has zero explanatory value, when it seems more reasonable to say it has very little, but some.

      "If you want to claim that a theory with N+1 assumptions is simpler than a theory with only the first N of those assumptions"

      Of course it's not the number of assumptions that matters, it's the relation between the complexity of the assumptions and the explanatory power. And since there is no precise formula for computing the ratio of power to complexity, a subjective element will always be present in deciding how good a hypothesis is. I would think that as long as the ratio is above 1, the hypothesis would at least count as "scientific".

      Delete
    11. Andrew,

      The weak anthropic principle is an observational constraint on parameters. It is correct whether or not there is a multiverse. Assuming the existence of the multiverse in addition is superfluous.

      "Of course it's not the number of assumptions that matters"

      I did not say that a theory with N assumptions is simpler than a theory with N+1 assumptions, I referred explicitly to "the theory with only the first N of those assumptions". (Or rather I was saying that you are claiming the opposite.) Please read this again because I believe this is a misunderstanding.

      Delete
    12. Sabine,

      "The weak anthropic principle is an observational constraint on parameters. It is correct whether or not there is a multiverse. Assuming the existence of the multiverse in addition is superfluous. "

      Ah, that's an interesting point. Let me see if I understand you: Saying that an infinite number of universes _could have_ existed has the same explanatory power as saying that an infinite number _do_ exist, but the first assumption is more parsimonious.

      We're moving from science to metaphysics here, I'm not sure either of us is competent to judge the truth of that. I still think the MV has more explanatory power than the UV here, because assuming only one exists you are in the position of asserting that it is, as far as we can tell, an extremely unlikely one; whereas the MV hypothesis makes it inevitable.

      To put it another way: we know at least one universe exists. If it is the only one, then it seems to require explanation that it allows intelligent life. Under MV, no such explanation is necessary, but MV is more profligate suppositionally. There's a trade-off.

      " I referred explicitly to "the theory with only the first N of those assumptions". "

      My point was that the assumptions and the explanatory power are both variables here, and both must be considered in determining whether a hypothesis is scientifically warranted. I do think we we're probably just miscommunicating here, the above point is more interesting and important.

      Delete
    13. Andrew,

      No, you misunderstand that. The weak anthropic principle is an observational constraint on certain parameters, it has nothing whatsoever to do with the multiverse. It's a constraint like, say, observing that the sun doesn't collapse puts an upper bound on its mass.

      Adding the assumption that "a universe exist for any combination of these parameters" is entirely unnecessary to explain any actual observation and therefore un-scientific.

      No, this is not meta-science. It is merely keeping track of the assumptions that you make.

      Delete
    14. Sabine,

      "No, you misunderstand that. The weak anthropic principle is an observational constraint on certain parameters, it has nothing whatsoever to do with the multiverse. "

      No, I think it's you who misunderstand the WAP.
      https://en.wikipedia.org/wiki/Anthropic_principle
      Of course it isn't about the MV, but it certainly has something to do with it: in the presence of MV, the WAP means that the existence of intelligent life in our universe is unremarkable.

      "Adding the assumption that "a universe [??] exist for any combination of these parameters" is entirely unnecessary to explain any actual observation and therefore un-scientific."

      You left out a verb there - "might" or "does"? In any case I think you're mistaken - it can explain the presence of intelligent life.

      "No, this is not meta-science. It is merely keeping track of the assumptions that you make. "

      Are you falling for the physicists' folly - that because you have mastered the most difficult subject known to man you therefore know everything? There are philosophical issues at play here that neither of us are expert in.

      Delete
    15. Andrew,

      You claim that it's me who misunderstands the WAP and then say that of course me pointing out it has nothing to do with the multiverse is correct. Fun move, haha, not sure what you hope to gain with that.

      I don't know why you think I left out a word.

      "In any case I think you're mistaken - it can explain the presence of intelligent life."

      Uh, just because you state that it does, doesn't mean it's correct. I have already told you why what you say is wrong. Denying it is not an argument. It's not even a rhetorical strategy. It's just a waste of time.

      "Are you falling for the physicists' folly - that because you have mastered the most difficult subject known to man you therefore know everything? There are philosophical issues at play here that neither of us are expert in."

      I am not talking about philosophy, you are. If you want to talk about philosophy, fine with me. I mean this seriously. You can debate, for example, if the multiverse has an explanatory value other than the scientific one that I am talking about. You can ask the same question about god. But that is not what I am talking about. Because I am not a philosopher.

      Incidentally, you bringing up my educational background rather than engaging with the argument I have laid out is an ad hominem attack, not a serious argument. It doesn't add anything to the debate.

      Delete
    16. Sabine,

      "You claim that it's me who misunderstands the WAP and then say that of course me pointing out it has nothing to do with the multiverse is correct. Fun move, haha, not sure what you hope to gain with that."

      Huh? I said the WAP is not _about_ MV, but has to _do_ with it. In the sense that the two together have interesting implications.

      "I have already told you why what you say is wrong."

      OK, I might have missed it. Where did you most fully lay out your refutation of the claim that MV+WAP explains the constants?

      "Incidentally, you bringing up my educational background rather than engaging with the argument I have laid out is an ad hominem attack,"

      Huh? Suggesting you're not infallible is an "attack"?

      I suspect we largely agree on the substantive matters here. Would you agree to the following?

      1. The MV is unworthy of soaking up any research funding, because it does not make testable predictions.

      2. The MV hypothesis may be true or false, and some scientists have reasonable grounds for believing it; "reasonable" meaning science based but not subject to scientific testing.

      Delete
    17. Andrew,

      The WAP has nothing to do with the multiverse. It's an observational constraint on parameters.

      I don't need to "refute" any claim because there isn't any claim to refute. If you think that the multiverse explains the values of parameters that we observe, then please tell me how you calculate them.

      Delete
  16. The anthropic explanation of the Michelson-Morley experiment: a non-zero ether wind is incompatible with human life.

    ReplyDelete
  17. OMM ...

    [ OMG, contemporary version ]

    ReplyDelete
  18. Doesn't the multiverse plus a weak form of the anthropic principle have at least some explanatory value toward the coupling constants?

    At least one other, crucial assumption is needed beyond multiverse + anthropic principle: You also need to assume the coupling constants are determined environmentally rather than ultimately being fixed by dynamical process(es) which are governed by a fundamental theory. That is a highly nontrivial assumption with absolutely no supporting empirical evidence. It is a philosophical assumption that determines in an important sense what we "should" expect from a fundamental theory.

    ReplyDelete
    Replies
    1. That's a good point. I had the impression that in the Landscape they did arise that way, but IaNaP.

      Delete
  19. To be honest, I think a multiverse explanation is even worse than a religious one.

    For example:
    Question: "Why are you wearing red today ?"
    Religious answer: "Because this is what God wants"
    Multiverse answer: "In a parallel universe, I am wearing green"

    The religious guy is at least trying to give some kind of answer, although it's unverifiable.
    The multiverse guy is just saying "No reason" in fancy language.

    ReplyDelete
  20. What about the existence of galaxies beyond our cosmological horizon?

    ReplyDelete
    Replies
    1. best comment and you get ignored as expected lol

      Delete
    2. sumBTC,

      I don't normally read comments that aren't addressed to me. There's only so much time in my day. Yes, what about the existence of those galaxies. If you have followed my explanation you should be able to answer that question yourself. They are not observable, hence they do not exist in the scientific sense.

      Delete
    3. Sabine,

      They are not known to exist now, but they might be detected in the future, so their existence is predicted. When you wrote something like "science does not predict existence or nonexistence" I think you were making a linguistic error that you would not have made in German.

      Your English is orders of magnitude better than my German, but you do occasionally make mistakes.

      Delete
    4. Andrew,

      No, the multiverse ideas that I am talking about (like the string theory landscape, eternal inflation, many worlds, and such -- see earlier blogpost/video) can not be detected in the future because the other universes are by construction nonobservable. There are some variants of the multiverse in which other universes could become observable to which my primary objection does not apply, but these suffer from other problems, as I said.

      Delete
    5. @Sabine, I didn't mean just you but all the commentators here because this is an excellent comment but I get your point. I almost always agree with your views, especially on the false promises about accelerators, but this time you've taken it a little too far in my opinion. The difference between religion and science is that religion poses absolute truths, while science tries to convince based on theory and observations but is never 100% certain and 100% convincing. In the case of the universe, we know the observable universe is compatible with a flat universe and in that case infinite. The observable universe grows because matter from the whole infinite universe flies towards us (with at maximum the speed of light) making our observable universe bigger with time (http://www.astro.ucla.edu/~wright/infpoint.html). On top of that the universe expands. It is without a shadow of doubt that there are galaxies outside our cosmological horizon, they are just not observable. I think this is still a scientific enough statement to make and not equivalent to religion.

      Delete
    6. sumBTC,

      "science tries to convince based on theory and observations but is never 100% certain and 100% convincing... It is without a shadow of doubt that there are galaxies outside our cosmological horizon"

      You may want to think that over.

      Delete
    7. Sabine,

      "No, the multiverse ideas that I am talking about (like the string theory landscape, eternal inflation, many worlds, and such -- see earlier blogpost/video) can not be detected in the future because the other universes are by construction nonobservable. "

      I wasn't referring to the MV! I was referring to the previous point about presently unobservable galaxies.

      Delete
    8. Andrew,

      Ok, fine. If you're not talking about what I am talking about then you are not talking about what I am talking about. Sorry, I think I'm not getting the point of this exchange.

      Delete
  21. On your fourth point: People who say "But then you are saying that discussing what’s inside a black hole is also not science" are making a logical mistake.

    We know black holes exist, because we were shown a "picture" of one recently, if nothing else. But a real knowledge of "what's inside" evades us because our equations fail. Similarly, we know electrons exist, but if there's an "inside" to electrons, or what it might contain--that knowledge evades us at the moment. But such discussions are entirely different from a discussion of "multiverse."

    With multiverse (or multi-mess?) we're stuck at the existence question. Invoking a multiverse is not logically equivalent to discussing the unknown properties of something (a blackhole, or an electron) that we know exists.

    ReplyDelete
  22. In science we are in a state where many people think: "In principle, we know all. There is only some fine tuning necessary yet, only some few choices are necessary, only some tiny puzzle pieces are missing, then we know all, all is ready. End of the history."

    ... while thinking of "big bang", "inflation", "black holes", "dark matter", "dark energy", "multiverses", "string theory", ... .

    The (western) mankind had been in a comparable state, at the end of the 19th century. The consequences had been terrible.

    I hope, this time it will end better.

    ReplyDelete
  23. Dr B, I had always heard that the multiverse was an "interpretation". Meaning: it's not a theory, or a part of the theory, but rather a story told to make the mathematics (which is the real theory) palatable to the human mind. In quantum-physics-world where our macro-world intuitions no longer have meaning, it seems like one could tell any story (set of axioms?) that fits the mathematics and it would never be provable or disprovable. Perhaps "interpretations" belong in the realm of religion and philosophy rather than the world of physics? What if physics has abandoned philosophical rigor and is now simply about measuring masses and constants?

    ReplyDelete
  24. Replies
    1. IaNaP, but I've always assumed the the law of entropy was just a statistical assumption that does not have the same ontological status as say GR or QM. Maybe Sabine will clarify.

      Delete
  25. 'Multiverse' is a word that leads to multiple ideas*. But a multiness appears in other approaches: e.g. sum-over-spacetimes or, generally, sum-over-_____s. Some might seem (to some) more reasonable than others. But if the word "multiverse" disappeared from my newsfeed headlines, I think that would be good.

    * https://en.wikipedia.org/wiki/Multiverse#Classification_schemes

    ReplyDelete
  26. I do not agree that all mutliverses are not science. I find that the quantum multiverse is science. It is equivalent to unitarity or that quantum superpositions can be constructed out of any number of particles. I find that superpositions are convincing evidence for the quantum multiverse and it seems to just be an engineering problem to create larger (observable) superpositions.

    But for inflation I think your arguments are convincing. To first assume that we live in a universe that is different from the one we observe and then make up a mechanism to make it look like ours. But then I do think inflation is science. Just a bad kind of science that waste our time and money. As far as I know the predictions from inflation has not come true so far.

    With eternal inflation and matematical ensamble I completly agree with you.

    ReplyDelete
    Replies
    1. Matti,

      This isn't a matter of opinion. Look, I have laid out my argument. Unless you find something wrong with it, that's how it is.

      When it comes to many worlds ("quantum multiverse") please note that this isn't just about superpositions. It's about postulating that any possible outcome of an experiment "exists" even if you do not observe is. This is not existence in the scientific sense.

      Delete
    2. I was wrong to say it's a matter of semantics, because Sabine's is the accepted notion of science. But I do think there's room to argue about that accepted notion - on another occasion.

      Delete
  27. I think I am going to disagree largely on this. I will though not say the multiverse is science, but rather that we really do not know. String theory is much the same; it is an hypothesis and not a theory and as such is not fully scientific as yet. The same for the multiverse, we really do not understand the possible empirical aspects of this, so it remain hypothetical. However, I would not say it is religion, at least not yet.

    To start I really disdain the term multiverse. No matter what there is still a single universe. In the type II multiverse these pocket universes are either regions in an inflationary spacetime, or maybe they have bubbled off. By bubbling off I mean the boundary of the inflationary pocket on a slow roll pinches off so the boundary information, think Gauss-Bonnet theorem, defines a different topology and maybe quantum charges and so forth. So these I would call local worlds. But ... to my considerable chagrin the term multiverse appears here to stay.

    Now suppose we have these pocket worlds bubbling off an inflationary de Sitter manifold. These might then interact with each other. There are in the CMB some kurtosis or non-Gaussian distributions; one of them is the famous dark spot. This could be a fingerprint for some sort of interaction between pocket worlds.

    Just as we can't enter a black hole and report data back, we most likely can't enter another cosmology or local world and report data back. It is not at all clear that time "here" can be parallel translated to some other pocket. Since there are no Killing vectors it means there does not exist a global generator of time. As best some transient scattering between pockets maybe a common time held there was an overlap region with a common time for two pocket worlds. This might have had some influence of the vacuum and there is already a funny data problem with H = 67km/sec-Mpc based on CMB and H = 74km/sec-Mpc. So interesting things might be up, and with this uncertainty I see the multiverse as one of the things to carry in the toolbox.

    I think it is premature to say the multiverse is religion, just as it is premature to really call it a theory. There could be observable consequences from the multiverse, even if we can't look directly into another one of these pocket worlds.

    ReplyDelete
    Replies
    1. Lawrence,

      Look, this is science, not politics. You cannot just "disagree" with an argument because you don't like it. You have to come up with a reason.

      Delete
    2. This is a matter of judgment. I would agree the multiverse is not "fully canonized" as a scientific theory with empirical support. My departure on this is then not so much a statement of deductive reasoning but inductive reasoning. While we agree that for any number N there is a successor N+1, there is no deductive proof of a quantifier statement. With cosmology there is some plausible reason to think there might be observational data that supports the multiverse. While we can't go into one and see it, these pocket worlds may interact with each other and leave finger prints of such interactions. This forces one to make a judgment of inductive reasoning, and as I see it the multiverse is not something I would be willing to throw out just yet.

      To compare with black holes, if one were to go into a black hole then from the split horizon there may well be data from other pocket worlds. The Penrose Schwarzschild diagram implies an entanglement between two black holes, and observing across the split horizon would be observing another cosmology. More realistically you would get data from a great ensemble of such pocket worlds.

      Delete
    3. Lawrence,

      I have explained that the multiverse cannot be a scientific theory because it contains assumptions that are unnecessary to explain observations. A scientific theory should not make such assumptions because that would put science on the same level as religion. What about this do you think "a matter of judgement"?

      Delete
    4. The multiverse tends to lend some plausibility for why the observable universe has the vacuum energy density, say given by the cosmological constant, we observe and certain gauge parameter values. In general spacetimes do not define energy, and with the Wheeler-DeWitt equation we have HΨ[g] = 0. Time is only definable locally in Petrov type O spacetimes, and so there is no general vacuum. So contrary to what we might want to think, there does not appear to be any reason for why the local gauge forces and vacuum are what they are. It could just then be a matter of probability.

      If the current searches for planets were finding none it would be highly remarkable that this solar system exists. But we are finding a wide range of planets with different physical characteristics. There may even be a mole of planets in the observable universe. So whether one wants to see this as a decent Bayesian prior for Earth or similar planets or a frequentist idea of a large enough sample space, the findings of so many planets makes is less impossible for Earth to exist. The same could be said of cosmologies. Vacuum expectations and likely the QFT that defines them may just be local principles, and that globally what exists here can't be extended “way out there.”

      Unless somebody comes up with some definitive global theory of the vacuum that is stable, I think we are most likely faced with a prospect for a sample space of different local vacua. If there is a global theory of the vacuum it is likely a false vacuum that is unstable. This means then there are these local domains with different vacuum energy, and possibly entirely different gauge principles. This runs into some interesting issues with the stability of de Sitter vacuum and CFTs or string theory. This has lead to something called the swampland. However one looks at this some distribution of possible internal symmetries and vacua makes the unusual distribution of parameters, 19 of them that differ by up up to 20 or so orders of magnitude, in the standard model a bit more palatable.

      I agree the multiverse is not really a proper theory, and of course before it does become so we need to have better empirical handles on inflation. So I would certainly not go so far as to say it is religion. I think people proposing alternatives need their day in court as well. In fact given that neither has really convincingly solved much as yet I would say that if the multiverse is to be called religion then so should rival hypotheses that insist on only one world. This is an area of physics where things are not at all certain either way, and I think an open mind is best.

      Delete
  28. What I was once told to be a reason for the assumption of a multiverse is the fine-tuning problem. If our universe can only be stable if certain (several!) physical constants are as they are with a precision of 1 : 10^50 , then the following is said to be a solution: There is a permanent generation of multiverses in our world, most of them have a short lifetime as they are so unstable. But one out of 10^100 may by chance have the necessary parameter values to make a universe stable like ours.
    I once attended a lecture of Loenard Suesskind about this problem and in his view this assumption could be a functioning theory. (“If it is not God who did this fine-tuning, this could be the best explanation”). Do you think it is, if there is no other explanation available?
    I personally think that there are better solutions thinkable for the fine-tuning problem. But those are not main stream and so not subject to this discussion.

    ReplyDelete
    Replies
    1. antooneo,

      Please tell me what measurement the assumption of a multiverse explains that is not also explained without the multiverse. The parameters in our theories have certain values that we cannot presently calculate. We determine these parameters by measurement and then use them to make predictions. This is the case with and without a multiverse. Adding an infinite number of universes on top of this makes no difference for any prediction. These universes are superfluous, hence assuming they exist is not science.

      Sure it is possible that we will one day be able to find an explanation for the values of these parameters. Eg, if there is indeed a "theory of everything" then maybe we will be able to calculate the values from it.

      Delete
    2. The idea of Suesskind was that in the moment, when a new multiverse is generated, there is kind of a random number process which fixes these numbers (like speed of light, gravitational constant etc). In almost all cases these numbers are not appropriate for a stable system, but in 1 out of 10^100 case they may fit sufficiently.

      But to say it again, this is not my understanding of physics, it's for me only a formal point. My personal understanding is that these so called constants are not really constant (which means: not long-time constants) but may be set by a long-term adaptive process. And such feed-back process may be able to adjust the numbers to values for a stable system. - But as I said, this is not main stream.

      Delete
    3. Antooneo: The problem with the "fine tuning" arguments is the implied assumption that the constants can be any different from what they are.

      Suppose I am the first to notice that the ratio of the diameter of a circle to its circumference always seems to be the same dimensionless physical constant (i.e. there are no units attached): 3.14159. I can ask myself why it isn't different for bigger or smaller circles. And it is so exact, no matter how much I improve my measurement capability, I always get the same ratio.

      Presume I have not developed the symbolic mathematics to prove this must be true, nor have I any ideas on how to approach that problem. All I can do is measure it.

      To me it seems extremely fine-tuned! Why is it this exact number? The digits seem random!

      Oh, I know! I postulate this strange ratio is so precise because we are just one universe of an infinite number of universes, and in each universe circles are different: At the inception of each universe this ratio is fixed to some random number, it can be any number, but it will hold throughout the lifetime of the universe. Of course, we can't see any such alternate universe, the alternative laws of physics won't let us.

      Thus I assert that alternative universes are an "explanation" for why pi takes the exact value that it does?

      I don't think that is scientific, and like religion and other non-scientific "explanations" it is actually detrimental to science, by offering "explanations" that really explain nothing at all, and certainly nothing that needs to be explained: We have no reason at all to think pi can be anything but the constant it is, no matter how "fine tuned" it may be, out to millions of digits.

      The same goes for other constants; sqrt(2) is what it is, it won't change in other universes!

      Fine tuning presumes the ratios of constants can be different with zero justification for why they should be different.

      But better math can actually explain them. For example, Euler's identity, e^(i*pi)+1=0 shows us that e and pi, which look like two constants, are actually intimately related.

      Alternate universes are just another way of saying "it is what it is", presuming the constants are random numbers drawn out of a cosmic hat. Why are there alternate universes? Because that is also just the way it is.

      But we can cut through the complications by going straight to the same conclusion: There is one universe, and things are the way they are, because that is just how it is, there is no explanation.

      Or we can do the scientific thing, and say we don't know why the dimensionless constants have the values they have, likely because we are missing something in our theory that could reduce the number of constants via functions or relationships (like Euler's Identity). This is superior to either alternate universes or just accepting the values, because "something missing from our theories" may present avenues of research that actually do explain why some values seem to have close relationships, with a reason other than a lucky throw of the cosmic dice.

      Delete
    4. This comment has been removed by the author.

      Delete
    5. Dr. A.M.C.
      I guess that something is confused here. Those who use the idea of multiverses are addressing the fine-tuning of physical constants. Has nothing to do with mathematical constant you refer to.

      Ardrew Dabrowski:
      I should make it clear again: I personally do not believe that multiverses exist and that they are a solution for something. I have only explained what I have understood from Leonard Suesskind and others, what they argue to be an advantage of such concept.

      Delete
    6. antooneo: I see no difference; are you telling me pi has nothing to do with physics? The dimensionless constants in physics are just numbers.

      pi and e appear to be independent of each other, but they are linked and this shows why they are both transendental, and indirectly may show why they are of similar magnitude (I haven't seen that investigated).

      My argument is the same may be true for the physical constants, the "fine-tuning" you see may be, not due to random chance, but due to relationships between the dimensionless constants we have not yet perceived.

      Or it may be due to nothing! Despite the insistence of the fine tuners, following their natural survival instincts of seeking predictive clusters of values, there is zero evidence anywhere that these constants can be "tuned" at all! Zero evidence they can be anything different than what they are.

      And hypothesizing a multi-universe to "explain" the clusters is useless, it is just another way of saying "they are what they are, don't worry about how close or far apart they are, don't worry about the appearance of fine-tuning."

      But we can do that without any multi-verse hypothesis!

      In fact, believing the constants are just random values depresses the incentive to look any further into whether they are related; why would I look for relationships amongst numbers I believe came out of a random number generator? That's a fool's mission!

      Delete
    7. Dr Castaldo:

      If I understand you correctly, you believe that further theoretical work might explain the constants. That's of course true, but further theoretical work might always explain anything; the point is that the explanation does not exist now. Whereas MV + WAP does provide some explanation now. In the terms of your allegory, back in prehistory before much was understood about geometry, the MV explanation of pi would have been perfectly reasonable. At that time, just imagining other possible worlds would have been a great intellectual advance.

      To repeat, I don't like MV, I don't think it deserves funding, but I grant it has a small explanatory value. The position that it has 0 value seems a bit extreme.

      Delete
    8. Andrew Dabrowski: back in prehistory before much was understood about geometry, the MV explanation of pi would have been perfectly reasonable.

      If by "reasonable" you mean it would have a logical reason, that is false.

      If further work reduces the number of constants or proves (like e and pi) that they are not independent but related, or manifestations of each other, that improves our level of understanding but doesn't address the central issue.

      The central issue is your belief that some explanation is necessary, and that just is not true. And in fact, claiming that something unobservable is responsible for what you perceive as fine-tuning locks the door on science, in the same way religion (or partisan politics) will selfishly reject or embrace science depending on whether the science comports with its existing beliefs.

      It is important to understand that if you "explain" a phenomenon in a way that offers zero predictability of observable consequences in this universe, you do not have an "explanation" at all, you have an empty assertion of a fact without evidence.

      This is the essence of religion, too. They are all designed (or evolved) to "explain" what happens by attributing it to some form of supernatural Will that humans cannot comprehend; thus they have zero predictive power, while claiming vociferously they have complete predictive power.

      But, should a god-fearing church-attending ten-year-old from a god-fearing church-attending family be raped to death, that was "God's will," "God's Plan," or "Karma" for a past life, or the "Devil's work," or they will find some excuse for why devout ten-year olds are never safe, while insisting prayer and belief will protect them from evil.

      Conceiving of MV is a precursor to science, investigating if some form of MV can be made predictive is science, believing that a MV without any predictive power "explains" anything is religion.

      Delete
    9. Dr. Castaldo,

      'Andrew Dabrowski: back in prehistory before much was understood about geometry, the MV explanation of pi would have been perfectly reasonable.

      If by "reasonable" you mean it would have a logical reason, that is false.'

      I did not mean logical, I just meant it would have been an advance on not thinking about pi at all.

      "It is important to understand that if you "explain" a phenomenon in a way that offers zero predictability of observable consequences in this universe, you do not have an "explanation" at all, you have an empty assertion of a fact without evidence."

      You are too categorical, even science can have shades of gray. I agree that the absence of testable predictions makes the MV hypothesis unattractive; but that does not warrant your saying that it has no explanatory value at all.

      Delete
    10. Andrew Dabrowski: What is your definition of "explanation?" It doesn't tell us why the constants have the values they have, it just tells us they are random numbers that happen to work.

      Believing that is even worse than not knowing why they have the values they have.

      I've heard this saying, "What you don't know is less likely to hurt you than what you know that ain't so."

      Delete
    11. Dr. Castaldo,

      "It doesn't tell us why the constants have the values they have, it just tells us they are random numbers that happen to work."

      MV + WAP tells us that our universe is unremarkable. Without MV we are in the uncomfortable position of having to explain why the only universe that exists happens to be one from the near zero measure set that admits intelligent life.

      Delete
    12. Andrew,

      You write (in response to Dr Castaldo):

      "Without MV we are in the uncomfortable position of having to explain why the only universe that exists happens to be one from the near zero measure set that admits intelligent life."

      Please state exactly what observation you think the multiverse explains. I have already asked you this above and you have ignored my question.

      Look, if you postulate a multiverse theory, you will still have to postulate the values of the constants of nature that we have observed. The other universes do not add any explanatory power to the theory. If you need any evidence for that, please take the fact that no one who actually fits any data ever starts from a multiverse hypothesis, because that's totally useless.

      And neither of these theories, of course, explain why the universe or multiverse "exist" because "existence" in the scientific sense is something we infer from observation. We are pretty confident that the universe "exists" because the idea that we live in a universe (by which we mean a specific space-time with such and such properties and such and such matter fields and so on) explains our observations very well. This is what it *means* for something to exist.

      Let me note that I already said this several times above, but you keep insisting that something is wrong with my English.

      Delete
    13. Andrew Dabrowski: MV + WAP tells us that our universe is unremarkable.

      No, it does not.

      Without MV we are in the uncomfortable position of having to explain why the only universe that exists happens to be one from the near zero measure set that admits intelligent life.

      You are still relying on an illogical assumption. You have no proof, not even any suggestive evidence, that any of the constants of nature even have statistical distributions, much less any of the parameters or constants or formulae of those distributions, thus you cannot construct any metric to measure the relative size of the set we occupy.

      It makes no sense to look at a constant and claim it is drawn from a distribution without any evidence for how the constant is produced or what random element influences its production.

      As for "discomfort", sure, religion is designed to relieve people's discomfort with death, non-existence, the possibility of random brutality destroying the people and things they love.

      And I have ample proof within my own large extended family it actually accomplishes this mission. But religion is still filled with bad logic, ridiculous assumptions, and circular arguments.

      Which seems to be where we are headed with your argument. First, you assert constants can be other than they are, drawn from a distribution you cannot describe, but are mysteriously able to measure the relative size of our "set" and it should be exceedingly rare, discomfortingly so.

      Well, the chance of drawing any specific number from a continuous distribution is zero. The first mistake is assuming there is a distribution, but the second mistake is assuming the distribution is continuous, so the constant could be just a little bit different. What if the distribution is discrete? Heck, a coin flip is described by a discrete distribution with just two possible values, and we have all kinds of two-value discrete distributions in nature, so why not here?

      And on top of all that bad logic, you throw in a circular argument. If you form any kind of distribution, it is going to have parameters and constants and operations for the cumulative distribution function, it will have some set of discrete values and probabilities for a discrete distribution. So we are left asking, in both cases, why those exact values? Why are these the parameters that describe the distributions of our physical constants? Are these parameters actually the "real" constants of the universe, or are they also random numbers drawn from their own meta-distributions, with their own meta-parameters, ad infinitum?

      The MV explains nothing, it multiplies the number of new constants and formulaic relationships with every iteration.

      As a religion, it may relieve your discomfort. But you could easily just stop at level zero, realize that you are embarking on an infinite regression of "explaining" constants with other constants, and in consequence have an ever growing set of unexplainable values. Instead, you can accept the constants we can measure are currently unexplained, but might be related by heretofore undiscovered relationships which might explain why they are what they are. If you are going to assume mystery math exists, it makes more sense to try and find unifying relationships between existing constants than to speculate about things we cannot possibly measure or deduce, like the parameters of distributions given a single sample.

      Delete
    14. Sabine,

      "Look, if you postulate a multiverse theory, you will still have to postulate the values of the constants of nature that we have observed. The other universes do not add any explanatory power to the theory."

      But they do: Under MV the existence of intelligent life is inevitable; under UV, it is remarkable.

      I distinguish here between a scientifically based belief, which I think MV could be, and a scientific research program, which it couldn't. You seem to want to conflate "testable" and "explanatory", but they are not the same.

      Delete
    15. Andrew,

      "But they do: Under MV the existence of intelligent life is inevitable; under UV, it is remarkable."

      We cannot observe the "existence of intelligent life" in any part of the multiverse other than our own, so both hypotheses explain our observations equally well, and they do so via the WAP as you already noticed. You need no multiverse for that, it is superfluous.

      Delete
  29. "I have explained that believing in the multiverse is logically equivalent to believing in god" Steven Hawking spent the last years of his life in an attempt to prove "multiverse". What could have been the motivation for this? Why is "multiverse so important?

    ReplyDelete
    Replies
    1. @Joe Potts In the minds of many, it preserves a form of 'realism'.

      Delete
  30. God had witnesses, miracles, and representatives. That is unless advanced beings were mistaken for angels, devils, and Gods. Many hope to repeat such experiments. LeMaitre's Big Bang was hoped to settle sime of the mystery. Perhaps souls exists in a multiverse of sorts when we shed our mortal coil. Discover that and progress will be made unless that brings trouble like another bite from the tree of knowledge...ouch!

    ReplyDelete
  31. I think it's presumptuous of you to think you know what people believe, and why. I can't see that "believing", or perhaps more accurately "being convinced", that there are multiple universes because it fits with existing knowledge and observations, and believing in a god because it's written in a book and somebody told you it's true without any physical evidence, are equivalent at all.

    We know a universe exists because we live in it, so postulating others exist isn't inventing something out of the blue. In contrast, nobody has ever observed a single god, despite which the multi-god hypothesis still exists.

    Usually it's religious people who insult scientists with the "B" word, as a specious argument for their own irrational obsession.

    ReplyDelete
    Replies
    1. Gussss,

      I have never claimed that I know why people believe what they believe, which in fact I do not. I know what they believe because they tell me what they believe, or they write about it. It's no big secret. Now you may say that maybe they are lying when they say they believe in the multiverse, which is a possibility, but I consider it unlikely and also, to be honest, uninteresting to speculate about their motivations. To first approximation I assume people mean what they say unless I have reason to think this is unlikely.

      Having said that, I do not see the difference between people who believe in god because some books have been written about god and people who believe in multiverses because some papers have been written about multiverses. What distinction do you think there is? I cannot see any.

      "We know a universe exists because we live in it, so postulating others exist isn't inventing something out of the blue."

      You missed the point entirely. The moment you allow yourself to postulate something that is unnecessary to explain anything you observe (in fact, can observe), you throw science out the window. If you allow hypotheses that contain superfluos elements as "scientific" this also allows gods as scientific hypothesis.

      You are trying to make a distinction that doesn't work. At least think about it for a moment, will you?

      Delete
  32. Sabine thank you for your article and efforts. However, if we go by your reasoning thence theoretical science never has existed. I do believe that you may have broad brushed your hypothesis so much that you leave no room for the scientific methodology.

    Over 60 years ago as a young child we were taught that the only known planets were only in our solar system. There were theories on both sides pro and con. As a child I already logically knew that we couldn’t possibly be the only solar system.

    And as we have witnessed many theories even presented in Star Trek and other SciFi Films have actually come to be true.

    The existence of a multiverse for me seems to be very logical, especially with the new pop science chitchat regarding Dark Matter and Dark Energy.

    I personally believe that this so called dark energy is actually gravitational pull from other universes and because of our own universe specific perceptions, we so far have been unable to develop the necessary tools to comprehend what all is going on.

    Now with realized successful experiments regarding singularity and entanglement theories I believe we will soon, like within the next 100 years or so, sparing we don’t nuke ourselves out of existence, be well on our way towards a new era in Quantum Communications where we may well begin communicating not only throughout our own universe but more throughout the “Multiverse “

    ReplyDelete
    Replies
    1. KurtG,

      What "hypothesis" are you even speaking about. I have explained that the multiverse is not a scientific theory because it contains elements that are unnecessary to explain observations. This is not a hypothesis, it's an argument. You cannot just chose to not believe it.

      I don't know why you are talking about planets. You were taught that the only know planets are in the solar system because then the only known planets were in the solar system. Planets in other solar systems were a hypothesis, but a testable hypothesis, and one that was eventually confirmed. Different story entirely.

      Please avoid discussing your own theories of something in my comment section. Comment rules are here.

      Delete
  33. Sabine Hossenfelder, you are mistaken. Many worlds do explain observations. The many worlds are described by quantum mechanics and quantum field theory. To make predictions one has to calculate many possible paths of particles, the many possibilities of particle creation and destruction at any given place and time, and all kinds of possible interactions between particles. If there were no many worlds we would for instance only need to calculate one path of a particle.

    You have to at least acknowledge one type of multiverse. That is the universes causally separated by cosmological event horizons.

    ReplyDelete
    Replies
    1. Patat,

      No, what you refer to is not many worlds, it's standard quantum theory. The many worlds interpretation posits that all possible outcomes of a measurement "exist". I am pointing out that this is a non-scientific type of "existence" by construction. It's equivalent to postulating the existence of gods because you do not need this assumption to explain anything you observe (that's tautologically correct). You can believe in these other worlds, if you want to, but they are unnecessary.

      Before accusing me of making mistakes, please consider the possibility that I think about what I write before publishing it.

      I have no problem with 'acknowledging' multiverses. I acknowledge that these are ideas people like to talk about. I am saying this isn't science for the reasons that I have laid out, I hope clearly.

      Delete
    2. But isn't the collapse postulate an unnecessary assumption? We strictly speaking don't need it to explain observations. And the collapse postulate goes against the grain of quantum theory according to which information cannot be destroyed.

      You can reverse the argument by saying that wave function collapse invokes some kind of God which cuts out the other parallel universes.

      We don't have to believe in a God/postulate/assumption which destroys universes.

      What is the extra assumption? Quantum theory is a many worlds theory. The extra assumption is that when a measurement is made, all universes disappear except for one.

      The other worlds are necessary to explain our observations. You could believe the other worlds disappear when a measurement is made. But it wouldn't explain anything.

      Delete
    3. Patat,

      In many worlds the collapse postulate is replaced by the idea that the forward evolution of a detector is no longer a detector. That's an equally ad hoc assumption which does not follow from the Schroedinger equation and which, surprise, no one has yet been able to derive from the Schroedinger equation.

      Delete
    4. Patat,

      Sorry, forgot

      "The other worlds are necessary to explain our observations. You could believe the other worlds disappear when a measurement is made. But it wouldn't explain anything."

      As I said, the simplest assumption is no assumption. You do not need the "extra worlds" (measurement outcomes you do not measure) to describe anything you do measure. Therefore talking about them is not science. This does not mean that they "disappear", which is also an assumption that you should not make.

      Delete
    5. "In many worlds the collapse postulate is replaced by the idea that the forward evolution of a detector is no longer a detector."

      Sorry, I'm not a fully schooled physicist. I dropped out in the fourth year. I have nearly completed the first two years.

      You mean that one detector is split into many detectors? So, it is not one detector anymore? I see no problem. One detector measures one result, the other measures the other.

      What I understand from many proponents of the many world interpretation/theory of quantum theory, is that they assume that the Schrödinger equation fully describes reality, or in quantum field theory, that all these many paths of particles and the many interactions with each other, and all these events of creation and destruction in the Feynman diagrams (etc...), actually all physically happen.

      They remove the collapse postulate. They add no other postulates. Some remove the Born probability postulate (David Deutsch). They believe the Born probability postulate can be derived from other quantum mechanical principles.

      They see the splitting worlds (and detectors) as automatically following from quantum theory. They don't add it as a postulate. That's what the many worlds do. At first some are joined to each other, and then some go up, some go down.

      The many worlders do have problems with the concept of probability. I have been following this theory for years. And I cannot get my head around it either.

      Say, there is a 50 percent chance of measuring a particle to be spin up, and 50 percent to be down. That is simple, there is one universe with spin up, and one with spin down.

      Now then, let's say the probability is two thirds that the spin is up. Simple, there are two clone universes with spin up, and one with spin down.

      But what if the probability is a transcendental number?

      Now there are infinitely many clone universes with spin up, and infinitely many with spin down. Infinity divided by infinity is... not defined. Or are there secretly a very large number of universes, but not infinitely many?

      And the complex waves can cancel each other out. Probability zero. Quantum field theory calculates all the paths. The paths reach all places. So, a particle goes through one place where the amplitudes of all the paths combined cancel each other out, it is physically there, but it is not there, because the probability is zero. That is a contradiction. I have seen some many worlders are baffled by this.

      It is as if God first calculates all the complex amplitudes using Quantum Field Theory, and then creates a whole slew of universes, many of which are clones of each other using the Born probability postulate as a guideline to determine how many clones of particular universes he should create.

      Delete
  34. By reading the several comments here on Sabine Hossenfelder's perfectly legitimate criticism of the multiverse, it was confirmed to me that a big portion of wishful thinking must be involved to write such argumentative and logically weak lines of reasoning.

    Hossenfelder is quite right by stating that modern scientists (and especially popular science bookwriters) are more and more driven by wishful and sloppy thinking instead of for example driven by the scientific principle of non-contradiction. It all tends towards belief-systems, hence a kind of religious faith, and logics is regularily biased by a huge lack of self-reflection on the part of those populists that try to promote their pet theories as if they where proven to be the absolute truth.

    A nice example is the belief that our universe (or multiverse) could have existed forever (instead of having a beginning). I debunked this when analysing Sean Carroll's paper "Why is there something rather than nothing?". Carroll, himself a huge proponent of the multiverse hypothesis, makes some more - irrational - logical errors in that paper and if the reader here is interested in that, he can find my analysis her:

    https://www.michaelgstrauss.com/2019/01/why-is-there-something-rather-than.html

    I hope that the fact that this analysis had appeared on a christian-scientist's website is not an excluding criterium for posting it here - since the analysis as such should count, not the place published. I would have much more liked it to be posted on Carroll's website, but the discussion about it was closed.

    By reading my analysis, you will find that also the belief in a universe out of literally nothing (yes, nothing at all) is as irrational as a universe that existed forever. My conclusion is that Carroll's question cannot be answered by the brute fact of "nothing", nor by the brute fact of an eternally existing universe.

    Have fun!

    ReplyDelete
  35. I don't think the concept of a multiverse is a religion. It has no tenets, no doctrine, no holy text or power hierarchy. In essence, I think you're selling religions short. Religions tend to have a lot more structure and are more well-defined than multiverse concepts.

    I'd argue that the multiverse is more mythology than anything else.

    ReplyDelete
    Replies
    1. I think this is spot on: while the distinctions are not at all clear-cut, in English "Why the multiverse is mythology, ..." is better than "Why the multiverse is religion, ...". "Religion", the English word, carries a lot of baggage that is beside the main point of your blogpost, Bee.

      Also, "mythology" is better than "a myth" or "mythical" (though I think the latter is more, um, lyrical) because the multiverse is a hydra ;-)

      Oh and my German is far too poor to offer any comments on Religion vs Mythologie.

      Delete
  36. Sabine,

    (Unsolicited advice follows, which, I don't have to tell you, you may feel perfectly free to ignore)

    I have been a reader of your blog for a long time, really enjoyed your book, find most of your blog posts interesting, tend to agree with almost all of your points... and still find myself rooting for the other party in more and more "debates" in this comments section. I assume this is because you come across as rather impatient and and allergic to even moderate criticism. Sentences like "at least think about it, will you" or the repeated enquiries or speculation about the other parties background/affiliation don't help (before you ask, PhD in theoretical physics, really different field though, have since left academia). I apreciate that you may have gotten tired of having to repeate the same arguents all the time, but then maybe it would be a better idea to just get rid of this comments section. I know, no one forces me to read it or even participate, juts my two cents.

    ReplyDelete
    Replies
    1. Felix,

      (1) Pseudonmous commenters have no incentive to stick with reasonable debate. That's why, if someone begins making stupid comments, I ask them to sign with their name or shut up.

      (2) I sometimes ask people for their background to figure out what technical level to aim at.

      (3) Yes, I am tired of having to repeat myself all the time, which is why I urge people to please think before commenting.

      (4) I am not "allergic to criticism", I am allergic to nonsense criticism from which I do not learn anything. Like yours. The only thing I learned from your "unsolicited advice" is that you "root" for arguments depending on how likable you think the person is who makes the argument. This means you are, simply put, not someone I am interested in discussing with.

      Delete
    2. "(4) I am not "allergic to criticism", I am allergic to nonsense criticism from which I do not learn anything. Like yours."

      See, and what I was *hoping* you'd learn from it is that there are people who agree with (almost all of) your arguments and are still put off by the hostility that permeates this comments section. On display, e.g., in the quoted part of your response, judging from which I failed in my endeavour.

      Goodbye.

      Delete
    3. Felix,

      I treat people the same way they treat me.

      Delete
    4. Well, Sabine, you should treat others as you would have them treat you. Naughty girl.

      Delete
    5. Gametheory shows that treating people the same way as they treat you is a simple and highly successful strategy.

      Delete
  37. You should re-name your blog "HALF-BAKED REACTION". Obviously theory has predicted reality in many cases: Gravity bends light, Relativity),
    The Higgs Boson( std theory), Gravitational waves (Spec Rel), and many others.

    ReplyDelete
    Replies
    1. Thommy,

      Yeah, and you know what, none of those theories were multiverse theories. Do you have any idea what we are even talking about?

      Delete
    2. Also surely gravitational waves are a prediction of general relativity, not special relativity.

      Delete
  38. Great blog! Now if believing in multiverses is like believing in religion, we should expect multiverse believers to be unmovable and hyper critical of unbelievers, to form strong bonds with fellow believers, and to want to eliminate or convert all unbelievers in any way possible.

    ReplyDelete
  39. Leaving aside for the moment the question about whether the multiverse is "scientific" or not, is not the alternative to the multiverse an acknowledgement that our universe, if we take it as the one and only universe, is astonishingly, amazingly fine-tuned to support life and consciousness, and that the odds of that happening by chance are so minuscule that the conclusion will be pressed upon us by religious folk that our universe must have been made by or emerged from some sort of God or Cosmic Mind or gods? And is it not the case that many scientists found that and other religious ideas a danger to science and preferred chance as the designer of worlds, and that the multiverse provides that kind of chance designer, and thus an escape from the theism or other religious views some find supported by fine-tuning? After all, as I suppose you'll agree, if ours is not the only universe, but just one universe in some huge or infinite number of universes, then the fact that our universe is so incredibly fine tuned to support life and consciousness is no longer incredible, since given an infinite number of universes, some small fraction of them are bound by pure random chance to be fine tuned to support life and consciousness. In that view, no God is needed to explain our universe's fine tuning. I don't claim to know the motive for certain, but it strikes me as likely that one significant motivator driving the development of multiverse theory is a desire to "protect" science from "religion." To the extent the multiverse is driven by such a motive rather than by evidence, to that extent it is not science.

    ReplyDelete
    Replies
    1. If there is only one universe and this is all there is or ever was, there is no "chance" in any of its parameters. The concept of chance only makes sense if you talk about something that could in principle be repeated.
      Furthermore, talking about "chance" requires some kind of probability distribution which can also not be defined for singular events.

      Delete
    2. I guess this being true or not depends on whether the parameters were fixed before the universe came into being, or instead the parameters took shape along with the universe in processes that involve some contingency. At any rate, I was under the -- perhaps mistaken -- impression that many scientific cosmologists think that even if ours is the only universe, its parameters took shape in partly contingent processes and thus could have become other than they in fact became due in part to chance.

      Delete
    3. Ed U: "is not the alternative to the multiverse an acknowledgement that our universe, if we take it as the one and only universe, is astonishingly, amazingly fine-tuned to support life and consciousness"

      Sorry, I don't get it. For starters, it can only be "life and consciousness" as we know and love, here on Earth. We have zero knowledge of any such that might be, say, Si-based, plasma-based, even dark matter-based.

      And yeah, what MartinB said.

      Delete
    4. MartinB,

      "If there is only one universe and this is all there is or ever was, there is no "chance" in any of its parameters. "

      How do you know? Are you saying we live in the only universe which is logically possible?

      Delete
  40. Loving the discussion! It reminds me of this party game that's guaranteed to start arguments and randomly offend people (while making you the center of attention), especially when there's sufficient lubrication. You just defend this thesis against all comers: "All human intellectual activity is either physics, religion, art, or gossip." Math? Obviously religion (and therefore shouldn't be taught in public schools, as all Calvin and Hobbes fans know). Chess? Art (you don't believe the rules, you just follow them). Chemistry?
    Physics (and now you've offended the anti-reductionists). History? Gossip, obvo. If cornered, you can slide a little: Psychology? Gossip that might be moving slowly toward physics. Buddhism (and most Judaism)? Art, because no one cares what you believe, you just have to do weird stuff. Multiverse theory? Religion (apparently with a big whiff of gossip), who knew, thanks Dr. B!

    ReplyDelete
  41. We cannot DIRECTLY" observe inside a black hole, from outside. However, we can "observe" its effects outside the EH and make some deductions as to its internals can we not?

    Take the phenomenon of time, for instance. We know from Schwarzschild that time has reduced to zero rate at the EH, relatively. But is this effect purely relative or is it also absolute too? After all, your clock also stops at a velocity of "c" and if you continue at speed, then your elapsed time will remain at zero. Surely this is applicable to the EH? Stay there and no time will elapse.

    Now, we also know that it doesn't matter to us gravitationally, if say the Sun were to collapse to a BH and we would continue in our orbit as usual If the mass is the same and we remain at the same distance, then gravitational effects are unaffected. (I guess you know all this, sorry).


    Surely then, at the moment all the matter of a star collapsing lies within the EH then the gravitational effects outside the EH have reached their final state and this includes time having reduced to zero rate too. In which case, would not all events within the BH cease from that moment? Would not the central "singularity never form? At least one might say that it will form (since the math' shows us it will), but not until the end of the universe or longer? In which case, no BH can ever have the impossible central singularity?

    Oh, and so I agree, the multiverse idea is complete garbage, scientifically. We can never observe it effects remotely as we can for a BH.

    ReplyDelete
  42. this reminds one so much of Comte

    ReplyDelete
  43. Science is believe - with a small testable amount of content. The rest is called "hypotheses" and "theories".

    Back to the bottom! Downclimbing from the shoulders of alleged giants.

    Multiverses are Spiritism. Same as searching senseful signals within noise. (Think of "Paranormale Radiostimmen".)

    ReplyDelete
  44. Another two cents from me:

    As it is today, the multiverse hypothesis is a metaphysical / philosophical construct. Maybe in the future there are ways to conclusively test it. But today, i see no such conclusive test being available.

    The next logical error is to construct a dichotomy between two concepts, namely between God and a multiverse. It could well be that an existing God (and i believe in that God) has indeed instantiated such a multiverse (for whatever reasons). But if God created such a multiverse, it had to have a beginning. But wait a minute: even without a creator, such a multiverse necessarily had to have a beginning (for the reasons i annotated in my last post)!

    The next error is to conclude from Feynman's path integral method that a particle's "real" path does indeed include all possible paths. Certain paths then cover all of the universe, many only the half, and more surprising: the set of all paths does include and therefore scribble all graphical pictures that ever can or have been displayed on a display the size of the universe. Therefore also the contours of the famous Mona Lisa etc. pp. and of course also the picture of you and me.

    Now, some say that Feynman's path integral method is a hint towards a multiverse. Maybe, but maybe also simply not. I tend to the latter, since otherwise every particle interaction would generate an infinitude of paths (and therefore universes?), every interaction including all the known graphical depictions here on earth.

    Additionally, the Everett version of many worlds was, besides some other reasons, developed to solve the question of why a superposition does decohere into one solution instead of another one. But this question remains unsolved. Why? Because imagine a particle going trough a superposition device, like for example a half-silvered mirror. Besides the mathematical probabilities, we cannot figure out something more about the actual particle's choice. It does not help to say, well, it went both paths and there is a clone of you that observes the other result. I want to know why *I* observe result A and my clone does observe result B - and not vice versa. Saying to me that *I* and my clone are identical, so it doesn't matter, misses the point. Since me and my clone cannot be identical, they are two, not one person. Moreover, the one person (clone) sees result B, whereas I see result A. How could these two persons be the same? Even when answering the "why"-question by saying, well, you have been entangled with result A whereas your clone has been entangled with result B, this is neither an answer to the why-question, nor an answer to the how-question. Because it could well be also the other way round.

    Last but not least, maybe in such superposition states, a "particle" doesn't really have a path at all - because reality as we know it is much nore like the display of a computer. Here "particles" are even allowed to jump from one place to another - if properly programmed.

    ReplyDelete
  45. The problem I have with this logic is that we can split our own universe into a multiverse by invoking locality. I can only ever directly "observe" my own brain processes. My brain is programmed to interpret what it experiences as the effects of an external world, but there always exist an alternative brain-in-vat-like model that doesn't invoke an external world.

    My present state of consciousness compels me to believe that I live in a large universe, containing many galaxies, but could I be just a Boltzmann brain that fluctuated into existence for a microsecond and then vanished? Did the past really happen, or is it just an illusion due to fake data stored in my brain? There is no way I can do an experiment to verify that "yesterday" is physically as real as the present moment.

    So, a conventional "single universe" model as described by ordinary physics is already a multiverse in disguise. We make reasonable assumptions about things we can never directly verify because it follows from a model that has great explanatory power.

    ReplyDelete
  46. I posit that the (our) universe is not infinite but is just really, really big. (This from Janna Levin's book "How the universe got its spots") Given that we can say that it has finite boundaries and occupies a particular region of the cosmos (or space, or the field, whatever). In that case it is also possible that another, or perhaps many others, might exist in other regions. This, I know, is not what proponents of "multiverses" imply, but it is ot an impossible hypothesis, and it is definitely not a religion.

    ReplyDelete
  47. I realize this is a complete waste of time, but here goes anyway...

    Say we have a theory which predicts A, B, C and D. A, B and C are experimentally testable and have, indeed, been verified. D is utterly unobservable.

    According to you, belief in D is "religion" not "science."

    I am speaking, of course, about (instanton-induced) baryon-number violation in the Standard Model.

    Implications for the multiverse (etc) should be obvious.

    ReplyDelete
    Replies
    1. Jacques,

      No, this is not what I am saying. I have really tried to make my argument slowly and carefully and it pains me to see that someone I know to be highly intelligent cannot follow it.

      So, let me try this once again:

      You have a theory with assumptions A,B,C,D. It predicts observations x,y,z. You have a second theory with assumptions A,B,C. It predicts the very same observations x,y,z.

      What I am saying is that the first theory, A,B,C,D is not scientific because it has an assumption that is unnecessary to explain any observation. That assumption is "the multiverse exists". This is the case for all presently discussed multiverse theories, except for the ones which make observable predictions (like bubble collisions). The problem with those, as I said, is conceptually entirely different. (If you want I can go into this, but it's not my point here.)

      What you are instead talking about is that a theory with assumptions A,B,C which are necessary to explain actual observations may also predict something that is not observable (as we have, say, in quantum mechanics). There is nothing scientifically wrong with doing that and I didn't say there is.

      Please let me know in case that didn't answer your comment-not-a-question.

      Delete
    2. According to you, belief in D is "religion" not "science."

      Well yes, a belief in invisible entities like instantons, which is in turn motivated by the unscientific mathematicism belief, is itself unscientific. Empiricism is more fundamental to science than mathematics.

      Favoring the latter over the former has reduced modern theoretical physicists to prattling endlessly about the metaphysics of their incoherent, empirically-challenged, mathematical models.

      Delete
  48. "There is only one Universe, and Sabine is Its prophet".

    ReplyDelete
  49. Different multiverses are not created equal, in my view: the Everettian MWI is an empirically sensible programme, the landscape/anthropic/inflationary/multiverse (hereafter, LAIM 😉 ) is not.

    To expand somewhat: quantum mechanics is a hugely well-supported predictive calculus, but has a significant foundational problem insofar as the measurement problem renders it borderline incoherent as a scientific theory. The MWI is a serious and well-motivated attempt to address this problem, adhering scrupulously to mathematical structure of QM. So ontological claims that it makes are empirically reputable. Clearly the theory may or may not be right – personally I am not at all convinced that attempts to explain the role of probabilities in MWI are viable – but I don’t think it is fair to lump it in with LAIM.

    My problem with LAIM is simple – unlike MWI, which is designed to address the measurement problem, and does (if it is correct), I don’t think that LAIM helps with any real problem. So whilst MWI is empirically justified because it is an attempt to make sense of QM, and there is a sound argument that we are ontologically committed to those entities we need to make sense of our best scientific theories, LAIM has no such justification.

    PS I don’t mean the theory of inflationary cosmology per se. I’m not qualified to have any opinion on that and don’t. But I don’t think that it requires a professional training in physics to see that anthropic arguments are bogus.

    ReplyDelete
    Replies
    1. Rollo,

      So ontological claims that it makes are empirically reputable.

      I have no idea what you mean by empirically reputable but the ontological claims of MWI are not empirically verifiable. The same also holds for the MV conjecture. Whatever their metaphysical attraction, they are scientifically worthless.

      Delete
  50. Sabine

    Doesn't MWI just follow directly from the equations, without making additional assumptions? And isn't the wave function collapse postulated in the Copenhagen Interpretation an additional unfounded assumption? That's why MWI proponents like Sean Carroll say they prefer that interpretation. They claim that they're just taking the math at face value and not making additional assumptions. And there's nothing in the math that says those additional world branches disappear.

    It's not that I believe in MWI. I don't. But wave function collapse just seems like an ad hoc "trick" and it makes sense for people to try to find a way to resolve the matter.

    ReplyDelete
    Replies
    1. i Am wh,

      That's how the story is usually told, but it's not true. Just try to actually calculate something with the many worlds interpretation. You will also have to assume that the thing you call the detector is actually only part of the wavefunction of the forward evolved past detector. This does not follow from the schroedinger equation. It's an additional assumption that is is logically equivalent to the measurement postulate.

      Let me put this differently. There is no reason, in the Schroedinger equation, why a thing that we call "detector" does not spread out over all branches of the many worlds, in which case the detector just detects any possible outcome, which is nonsense of course. This means even in many world's you still need more information than the Schroedinger equation.

      Phil Ball in his recent book I think explained this very nicely, though it seems that some people didn't like his explanation. Maybe that is because he chose to use an example that hinges on the question what you mean by "you" which opens several cans of worms. But really that reference to identity is unnecessary for his argument to work, you can just use detectors instead of people.

      And Lee Smolin in his recent book has a great summary about people's effort's to arrive Born's rule from many worlds. They always end up drawing on other assumptions. The current fad seems to be decision theory.

      Best,

      Sabine

      Delete
    2. Thank you for this information Sabine. What I have read from Philip Ball seemed to me like a lot of hand waving. I have not had the opportunity to look at Smolins book, but I was wondering if there is an paper academic paper I can download to try understand this argument about hidden implict assumptions in Everett's measurement theory.

      "which is nonsense of course." Umm, that did not explain much to me, I do not see the nonsense, sorry.

      Delete
    3. Ripi,

      A detector that measures all possible outcomes is nonsense of course because no one has ever seen that happening.

      Delete
    4. Sabine,

      The best criticism of MWI I've heard about came from David Albert, a philosopher of science. Sean Carroll had him on his podcast, and didn't really even respond to the objections made. I would really love to hear the response to this from a physicist who believes MWI but haven't been able to find anything. It goes like this:

      Suppose that you are a physicist who believes that the only thing that really exists is the wave function, as described by the Schrödinger equation, and that the wave function branches according to MWI.

      Then, suppose that you perform a quantum mechanics experiment in which the statistical results don't agree with the predictions of the Schrödinger equation.

      You would have two options at that point (after making sure you didn't make a mistake in your experiment). You could:
      1) Conclude that the Schrödinger equation is incorrect

      or

      2) Conclude that you happen to be inhabiting a "branch" in which your results don't need to match the statistical predictions because all possible outcomes always actually occur in one or another of the branches.

      My question is which option would somebody like Sean Carroll choose if he found himself in such a scenario? A scientist should choose the first option, because the results didn't match the predictions. If you choose the second option, then you remain true to the Schrödinger Equation and MWI but you'd have to acknowledge that the results of your experiment didn't agree with the predictions, but that you're going to nevertheless continue believing in your worldview because you believe in the Schrödinger Equation and MWI and that's that. "Highly unlikely outcomes are to be expected because of the branching of the wavefunction. Therefore I can continue to believe in the Scrödinger Equation and MWI regardless of the results of experiments"

      This second option is obviously anti-scientific. It's saying that the scientific method only works in certain branches. The first option, on the other hand, is scientific, but it's implicitly assuming that the branch the physicist happens to be located in is somehow "preferred" for the purpose of doing physics experiments, or that it's really the only "branch" that exists.

      What I would really like to ask Sean Carroll is if all those "other" Sean Carroll s who inhabit all of those "other" branches, where the results of QM experiments don't statistically match up with predictions, still believe in science.

      (I know, I'm picking on Sean. I respect him alot, but in this one matter he just seems so sure of himself and I can't understand why.)

      Delete
    5. I am wh,

      Yes, I am familiar with that argument. It's somewhat tangential to the question of existence of the other universes though. At least I don't see how they're related.

      Delete
    6. Sabine,

      It's related only if you make the assumption that the scientific method should work everywhere, regardless of which branch you're in. Because there are clearly branches that exist in which the scientific method wouldn't work.

      Of course, you could believe that the scientific method doesn't work everywhere. But then I don't see how one could call himself a "scientist" or justify beliefs about the universe based on science that one has already acknowledged doesn't work everywhere.

      In short, I think that MWI is hogwash, and anti-science unless one of its knowledgable proponents can tell me something I don't know.

      Also, the "superdeterministic" aspect of it is unfalsifiable philosophy.

      Delete
  51. Great blog post. It seems to me that something that is lost in the discussion is that whether or not you can directly observe something does not make it unfalsifiable.
    For example, hypotheses such as black holes, evolution, solar fusion, etc do not need direct observation to be falsifiable. They all have implications as to what you should see, or not see, as a consequence.
    The opposite is true for religious propositions because they are a-priori constructed to be unfalsifiable, not because they cannot be observed, but because they are formulated so as to allow one to always gainsay any counter-evidence. THe question is: What could you see, or not see, and if that occurred you could know the multiverse is false?

    ReplyDelete
  52. Hi Sabine,

    I worked myself in some toy models trying to make sense of the multiverse idea. Here is what I learned, in case you are interested. A multiverse model has two ingredients: A state space and a probability distribution. The latter is not fixed from first principles, thus non-expert people omit its discussion (this is called the "measure problem" is cosmology). States are causally disconnected universes, which means no signal can travel between them, so, as you stress tirelessly, they are unobservable by its very inception, except perhaps the one we live in. Models focus on states, trying to find if some fraction of them resemble our universe. The ultimate goal of the multiverse hypothesis would be, as I understand it, to yield a non-vanishing probability to some state more or less analogous to our own Universe. But lacking a probability distribution, this goal simply cannot be accomplished. Moreover, as we have just one Universe sample (ours) to work with, we cannot experimentally test a probability distribution with a single measurement. I believe that this caused some experts to stop pursuing the multiverse idea.

    On a parallel track, there are a variety of interpretations of the states of the multiverse. Interpretations always come after predictions, and as such they cannot predict anything. No interpretation can change the details and predictions of a model, and the plain truth is that, lacking a probability distribution, no multiverse theory can predict anything. End of the story.

    So when I read from any source over the Internet something about the multiverse, no matter where, I always take it as non-scientific and poorly informed. No mathematics can ever predict the existence of other (physical) Universes, in exactly the same way that no mathematics can predict the existence of anything: Mathematics is a closed discipline. It is applied to real world when you feed it with data coming from the real world. Without data, no prediction is possible.

    So, summarizing: I absolutely agree with you, Sabine, keep up the good work.

    ReplyDelete
  53. "no one really thinks that the inside of a black hole will remain inaccessible forever"

    Really? I must have misunderstood. I do not think humans will ever make to mars. Half of the probes we send there crash.

    My comment is out of topic, but it is important because so many people think that if we make this planet inhabitable we can just hop on to the next planet. This is not how it will pan out.

    These are just fantasies. The distances, the dangers, the technical difficulties are understimated all the time. Interstellar space is a VERY hostile environment, and the distances are beyond imaginable. Going to the moon was an incredible feat that we might never repeat, economically there is no point in doing it.

    ReplyDelete
    Replies
    1. Ripi,

      I think this is a misunderstanding. I not not mean it will become accessible because we go there, but because the horizon eventually vanishes.

      Delete
    2. What is meant by the horizon vanishes?

      Delete
    3. How does an event horizon just vanish? That seems to violate the cosmic censorship and chronology hypotheses. Does this refer to Hawking radiation? Are you referring to the replacement of the horizon by a firewall?

      The only way to make the horizon disappear is to enter the black hole, but of course the event horizon is replaced by an apparent horizon.

      Delete
    4. Lawrence,

      Quantum effects/no one knows.

      Delete
  54. Oh. I see. You're arguing against a straw man: the multiverse as input, rather than as output.

    No one is seriously advocating that. Any theory that (for instance) predicts eternal inflation has a multiverse as output. That's the context which everyone has in mind, when they talk about the multiverse.

    (That said, there are lots of papers -- perhaps too many -- that start off with a multiverse and explore its consequences. It would be superfluous and silly for every such paper to begin at the beginning and re-derive how a multiverse arises before launching into their analysis.)

    But, of course, there's nothing unscientific about unobservable inputs (be they "asymptotic safety" or "preons" or the multiverse). So you first need to set the straw man ablaze:

    "...is not scientific because it has an assumption that is unnecessary to explain any observation."

    You're arguing against superfluous inputs.


    Breathtaking!

    You don't need to go to such elaborate lengths to argue against superfluous inputs. All you need to do is utter the phrase "Occam's Razor" and you're done.

    ReplyDelete
    Replies
    1. Jaques,

      Well, at least you now understand what I am saying, that's progress. Indeed, Occam's razor. As I have said very clearly and explicitly, congrats for noticing! You evidently fail to see how it matters, but let me try.

      Take your multiverse theory of choice, eternal inflation, landscape, many worlds, what have you. Now tell me what justifies saying other universes besides our own exist.

      The answer is, of course, nothing. They are unnecessary to describe anything we see. Therefore, the only way they can exist is if you postulate their existence, which Occam's razor forbids.

      Still with me?

      The superfluous input is not "the multiverse" (which isn't an input anyway, not sure why you'd even say that) but the assumption "universes besides our own exist". This "existence" can only be a religious type of existence.

      A scientifically correct perspective on multiverse theories is instead that we cannot say anything about whether other universes exist or not.

      You may now feel the urge to complain that this is linguistics, but note what the careless treatment of the situation has led to.

      If you erroneously think all these universes exist you may be compelled to treat them as an ensemble on which you postulate a measure from which you derive probabilities for parameters and so on. Sounds familiar? But this construction is superfluous. You do not need a measure on an ensemble if you want to postulate what parameters we measure in our universe. Just postulating the parameters is simpler. Yes, Occam again.

      Even in the (hypothetical) case in which you'd have a measure from which you can derive the parameters in a way that's simpler than just postulating them, you still don't need the ensemble. You can just take the equation from which you derive the parameters (presumably as some maximum of a probability distribution or such).

      And then you get people who speculate about the lives of their copies in the many worlds interpretation because these supposedly "exist". And so on.

      Please let me know in case I still haven't made clear what it is that I am objecting to.

      Delete
    2. "Take your multiverse theory of choice, eternal inflation, landscape, many worlds, what have you. Now tell me what justifies saying other universes besides our own exist.

      "The answer is, of course, nothing. They are unnecessary to describe anything we see. Therefore, the only way they can exist is if you postulate their existence, which Occam's razor forbids."

      "Take the Standard Model. Now tell me what justifies saying that (instanton effects in) the Standard Model, which violate baryon number, exist.

      The answer is, of course, nothing. They are unnecessary to describe anything we see. Therefore, the only way they can exist is if you postulate their existence, which Occam's razor forbids."

      Plainly, this is nonsense.

      Your argument makes sense only if the multiverse is a free-standing postulate (which, moreover, can be discarded without any observable ramifications), as opposed to a consequence of other aspects of the theory in question. But no one is advocating that. As I said, any theory that predicts eternal inflation also predicts a multiverse.

      The rest of your response has to do with questions that arise in the presence of a multiverse. This is totally beside the point. You point out that some of these questions also arise in other (non-multiverse contexts). That, again, is totally beside the point.

      Delete
    3. Jacques,

      You are not following. If your theory has consequences that are possibly observable but have not been observed, you also of course do not postulate their existence. You may predict their observational consequences, which is a different thing entirely. Of course in the case of the multiverse there are no such observational consequences.

      I never said that "the multiverse" is a free-standing postulate. You did. Read what you wrote above about "inputs". I already said above that this isn't so. I have already corrected this mistake of yours. Why do I have to repeat myself?

      "The rest of your response has to do with questions that arise in the presence of a multiverse. This is totally beside the point."

      It's the consequence of the mistake that you make. Look, go and write down your assumptions and tell me by what chain of argument it follows that universes besides our own exist. Be clear what you mean with "existence" and avoid making assumptions that are unnecessary to explain any observation.

      Btw, it's because of confusions like yours that my book is called "Lost in Math". Physics isn't mathematics. Physics is science and it's about describing observations, not more and not less. You are defending a philosophically unfounded position that attaches reality-value to mathematical entities which have no support in observations. All I am asking is that you realize this isn't a scientific argument, it's a belief-statement.

      Delete
    4. AM I correct id I understand Occam's razor as saying that elements of a hypothesis or theory which do not add anything to explaining the observations are unnecessary and therefor not scientific. And that the principle does not imply whether these (at least for now) unnecessary are true or not true?

      Delete
    5. "If your theory has consequences that are possibly observable but have not been observed..."

      Sorry. No. That is not what we are talking about..

      Standard Model instanton effects violate baryon number, but at a rate so small as to be completely and utterly unobservable. A rate so low that not a single proton in the entire universe has ever decayed via that mechanism, nor will one in the lifetime of the Earth.

      Given the two propositions:

      * Standard Model instanton effects violate baryon number at a rate so low as to be completely and utterly unobservable.

      * The Standard Model preserves baryon number.

      are you not claiming that it is unscientific to assert the former in preference to the latter (Occam's Razor and all)? Surely, that's what you mean, when you say

      "You are defending a philosophically unfounded position that attaches reality-value to mathematical entities which have no support in observations."

      Have I misunderstood the above statement?

      "...tell me by what chain of argument it follows that universes besides our own exist."

      In eternal inflation, spacetime has a structure that contains multiple FRW patches, each of which is an FRW universe all its own. So any theory that leads to eternal inflation necessarily leads to a multiverse.

      Coleman-de Luccia bubble nucleation leads to a spacetime structure that contains multiple FRW patches, each of which is an FRW universe all its own. So any theory whose scalar potential contains multiple local minima satisfying Coleman and de Luccia's criterion necessarily leads to a multiverse.

      Those are what people are talking about, when they use the word "multiverse" If you mean something else, when you use the term, then you are arguing against a straw man that no one is asserting.

      "Btw, it's because of confusions like yours that my book is called 'Lost in Math'."

      Delete
    6. Martien,

      Roughly speaking, yes. Phrasing this so carefully because I am not sure what you mean by an "element of a hypothesis to be true", which doesn't make a lot of sense. You could either say that an element of a hypothesis exist, or you could say that the statement it is exists is true. In the former case, that's exactly what I am saying, in the latter case I would complain (sorry) that "true" is too strong of a word for science because it never in practice proves anything "true".

      Delete
    7. Jacques,

      "are you not claiming that it is unscientific to assert the former in preference to the latter (Occam's Razor and all)?"

      No, because there is no assumption that's superfluous here. You have a theory that predicts things we have not yet observed. One can quibble about exactly what it means for a prediction to be falsifilable because some predictions may be falsifiable in principle but not in practice, which I wrote about here, but that's a separate issue.

      "In eternal inflation, spacetime has a structure that contains multiple FRW patches, each of which is an FRW universe all its own. So any theory that leads to eternal inflation necessarily leads to a multiverse.

      Coleman-de Luccia bubble nucleation leads to a spacetime structure that contains multiple FRW patches, each of which is an FRW universe all its own. So any theory whose scalar potential contains multiple local minima satisfying Coleman and de Luccia's criterion necessarily leads to a multiverse.

      Those are what people are talking about, when they use the word "multiverse"..."


      First, as we both know, people use the word multiverse to refer to very different things, so please don't pretend otherwise.

      Second, please take the assumptions of that theory and figure out whose of those you need to actually explain observations, by which I mean that they simplify data.

      Third, you have entirely ignored my question what reason you would have to think the other FRW patches exist in any scientific sense. If you believe they exist, that's fine with me. But that doesn't make this belief science.

      Delete
    8. Thanks for replying Sabine. Yes, I formulated my statement not carefully enough. I am aware that 'truth' is not the right word. I mean to say the the elements of an hypothesis which are superflous (and so unscientic and unnecessary) are not necessarily ruled as a valid contribution to the current hypothesis. In future htes might explain new observations.

      I am making this statement, because I often read statements which can be interpreted as: not necessarily according Occam's razor, so wrong, or false. What, I think, are too strong statements. But it is fine to argue that these superfluous elements are unscientific, or even comparable with religious beliefs.

      Then there is also a wider context of the hypothesis which can give meaning to seemingly superflous elements of a certain hypothesis. In the case of God this wider context doesn't give me any confidence that God exists.

      It seems that a lot of the heated responses to your blogposts are based on a wider context, (maths, beliefs, and so on). As far as I understand, if people just stick what you write, your statements are quite straightforward and logically correct.

      Delete
    9. "No, because there is no assumption that's superfluous here. You have a theory that predicts things we have not yet observed."

      No. Not "things we have not yet observed", thing that are even in principle completely unobservable -- even if you could somehow harness all of the protons in the universe and were willing to wait longer than the age of the universe, you still could not detect them.

      So, sorry, these are every bit as unobservable as those other FRW patches that you don't believe in.

      The only thing unscientific here is your blessing one unobservable phenomenon as "observable in principle but not in practice."

      "First, as we both know, people use the word multiverse to refer to very different things, so please don't pretend otherwise."

      If you think that there are some kinds of "multiverse" to which your arguments still apply, then you should specify.

      "No, because there is no assumption that's superfluous here. You have a theory that predicts things we have not yet observed."

      No. Not "things we have not yet observed", things that are even in principle completely unobservable -- even if you could somehow harness all of the protons in the universe and were willing to wait longer than the age of the universe, you still could not detect them.

      So, sorry, these are every bit as unobservable as those other FRW patches that you don't believe in.

      The only thing unscientific here is your blessing one utterly unobservable phenomenon as "observable in principle but not in practice."

      "First, as we both know, people use the word multiverse to refer to very different things, so please don't pretend otherwise."

      If you think that there are some kinds of "multiverse" to which your arguments still apply, then you should specify.

      I just explained that in the theories that people actually talk about, the multiverse emerges as a prediction of the theory, in the same way that instanton-induced baryon number violation emerges as a prediction in the Standard Model. Neither is directly observable (in any sane definition of the word "observable").

      But, if you're unwilling to call the latter a "religious belief" then you should be equally unwilling to call the former one.

      Delete
    10. Jacques,

      I do not know what it means to predict something that cannot be observed unless possibly you simply mean a mathematical consequence. If you cannot observe it ever, then before which event did you "pre-dict" it?

      In any case, the point is moot because, as I have told you repeatedly, the issue is not whether a theory allows you to calculate things that are unobservable, but whether all assumptions of the theory are necessary for what actually can be observed.

      Delete
    11. Martin,

      Yes, that's right. Just because Occam's razor tells you a certain assumption is unscientific doesn't mean it's wrong. It merely says that science cannot tell you whether it's right or wrong (or give you a confidence level etc).

      Delete
  55. Dr. Hossenfelder, you claimed in your previous article that:

    "Now, as we discussed previously, scientists say something “exists” if it is an element of a theory that is useful to explain observations. The Higgs-boson exists in this very sense. So do black holes and gravitational waves.

    However the measurement outcomes of superposition states (e.g. the spin of a particle) are not explained without the adoption of realism with respect to the wavefunction, or some modified model (Bohmian or GRW). You are precisely right that in science we require explanation of observations in the way you describe and the model behind such explanations are what we consider to "exist". In science we seek models, ontologies that explain data and observations, e.g. the existence of the Higg's field and its excitations explain decay products observed in our experiments. The issue with this however is that in unmodified versions of QM (e.g. not Bohmian or GRW etc), we aren't explaining the observation of spin-up or spin-down in an experiment (observations) unless we take a wavefunction realist + Schrödinger dynamics approach, anything else is not a scientific explanation, it isn't giving an account for why we observed what we did. For example, taking the approach of wavefunction collapse doesn't explain the data, there is no account that refers to things in the external world that explains why spin-up over spin-down obtains, but explaining such a thing is precisely what you are saying is what it means for something to "exist", as such the model that gives an actual explanation of this data meets your above stated criteria, but the only unmodified QM that does that is the wavefunction realist + Schrödinger dynamics model and that commits you to exactly what it is that you don't appear to like. *shrugs*

    Kind Regards,
    Cam

    ReplyDelete
    Replies
    1. Dear Cam,

      "we aren't explaining the observation of spin-up or spin-down in an experiment (observations) unless we take a wavefunction realist + Schrödinger dynamics approach, anything else is not a scientific explanation, it isn't giving an account for why we observed what we did. For example, taking the approach of wavefunction collapse doesn't explain the data, there is no account that refers to things in the external world that explains why spin-up over spin-down obtains,"

      Unless we take a wavefunction realist + Schrödinger dynamics? No, even that doesn't explain why *I* see spin up - and an imagined clone of me must see spin down. It could be well vice versa. So, the multiverse does not explain why we see the results we see in our QM laboratories. I made this point earlier here, please see my last comment from Juli, 11.

      It's a myth to say that the multiverse explains these data. It was developed to do so, because otherwise one had to accept events without physical causes (at least without some strictly deterministically working causes).

      But the multiverse does not explain the results in our branch, since it cannot explain why *I* am seeing what I see (spin up instead of spin down) and not vice versa. So, concerning the multiverse, there is, as in standard interpretation, no causal explanation offered for me seeing spin up instead of spin down.

      When the collapse postulate has to be accepted as a kind of brute fact, the multiverse does replace this by another brute fact, namely the entanglement of me with result A instead of result B.

      Note that you can't argue with the clones and *me* being identical, so this all doesn't matter. Even an infinite stack of identical *me* at the beginning of some multiverse contains an infinity of different objects - like an infinite stack of identical photons does contain infinitely many distinct objects. And the distinctness of these objects does not change according to multiverse theory. They do not transform into one another, but they preserve their identity.

      Delete
  56. All of this metaphysical hand-wringing simply evaporates if you discard the notion that the observed cosmos is a unified entity which can be thought of as "our universe". The cosmos we observe is, empirically speaking, of unknown and likely unknowable extent.

    The standard model of reality simply ignores that fact and wraps the unknown cosmos into a unitary model, one which effectively claims knowledge of the unknown, at the same time it violates a fundamental tenet of Relativity Theory (the non-existence of a universal frame). The resulting model is, contrary to its defenders, absurd, incoherent and discordant with empirical observations.

    Like many mathematical models, the standard model of cosmology can be massaged to agree with observables but it must invoke unobservable entities and events to do so. The Multiverse conjecture is just an offshoot of the standard model's incoherence about the nature of the cosmos. The Many Worlds Interpretation is just the incoherent equivalent from quantum theory. Neither one represents a scientifically plausible account of physical reality. That both have defenders in the scientific community says nothing good about the state of modern theoretical physics.

    ReplyDelete
  57. I can well imagine that the mono-universe adherents will get more and more into trouble on the long run. The reason being Fermi's paradox. It is already quite disconcerting that we haven't seen advanced life out there (at least of type II and III on the Kardashev scale).
    If this continues to be so, notwithstanding ever improving search, and experimental data more and more support the fact that we are the only advanced civilisation in the cosmos, then one is basically left with three options, a freaky accident, a creator or the multiverse.

    ReplyDelete
    Replies
    1. How would the multiverse resolve Fermi's paradox? If other intelligent life isn't found in OUR universe the paradox is still there because it's based the expectation that other intelligent life SHOULD be found in our universe. Even if intelligent life were to exist in other universes, there would still be the question (even more so) of why we seem to be alone in our universe.

      Delete
    2. MarkusM: And I would vote for freaky accident. More specifically, a form of runaway arms race, on intelligence.

      We went basically half a billion years with brains but no advanced life. As far as we can tell, all life stalled out on the intelligence front at about the level of chimps, dolphins, elephants, corvids and octopi, all of which show some impressive levels of problem solving ability, some of which seem to have at least a rudimentary language. For other animals, we see some intelligence but essentially emotionally driven lives. Many animals have self-awareness and apparently inner lives. Dogs dream and enjoy it, we can see that on fMRI of their brains.

      The freaky accident for humans, which other animals either do not display or display in only limited function, is (for lack of a better description) infinite recursion.

      Only humans generalize first level generalizations to second, third, fourth, and higher generalizations. Only humans make plans for weeks, much less years and lifetimes; most animals (including chimps) do not seem to anticipate or plan more than a few hours ahead. Dolphins and Elephants may embark on purposeful trips (non-instinctively) that will take a week or more, usually for hunting or water, but other than that do not seem to plan more than some hours in advance.

      Everything else humans do, including creating and using novel tools, doing arithmetic, solving unique puzzles, comforting the grieving, being altruistic, sharing with a less fortunate fellow member of their species, etc, are exhibited in lesser brains, as small as a mouse. Speaking of which, if you lower the pitch of the voice, mice love being tickled, and make squeaks in the cadence of laughter. If you stop tickling them, they will seek your finger to tickle them again. There is no health benefit to being tickled, they are doing it for the fun of it.

      What is special about humans is not opposable thumbs; or even language. What is special about humans is the mental ability to stack abstractions and indirection to apparently any depth.

      And that is likely a happy genetic accident, occurring about 250,000 years ago, apparently without occurring for hundreds of millions of years before that.

      The universe may be filthy with habitable planets that stalled out at single cellular life, or at the equivalent of dinosaur life, or at the equivalent of chimps, dolphins, elephants and octopi. The universe may e filthy with galaxies that harbor one or two intelligent species.

      Or it may be filthy with intelligence that stalls at our technological level without ever developing any viable methods to make an interstellar trip.

      It is not a given that our primitive level of intelligence (on average) can actually be improved upon; just asserting it can be is not credible. And it is primitive, the vast majority of people on this planet are still true believers in childish fairy tales of supernatural beings.

      Fermi's Paradox makes the false assumption that alien life would naturally solve the problems of interstellar travel, or inter-galactic travel. And the false assumption that life must inevitably evolve to intelligence beyond our own state.

      It has been said we humans are the next meteor, we are responsible for the next mass extinction, already in progress. It may be inevitable that when our current level of intelligence and civilization is achieved, it is always so short-sighted it ends up killing itself with the unintended consequences of its exploitation of its home planet, for its own selfish procreation, comfort and irrational tolerance of individuals destroying their habitat to accumulate wealth (or have fun).

      I have very little optimism we can avoid that fate. Collectively speaking, The human population of this world is too stupid to build a sustainable technological civilization. Heck, we aren't even smart enough to agree it is necessary!

      Unlike Fermi, I see no reason to believe aliens would be any better at this.

      Delete
    3. The simplest explanation is a freaky accident.

      A creator leads to infinite regress. Who created the creator? Turtles all the way down.

      The multiverse? Which is more likely, one freaky accident or an infinity of freaky accidents?

      Or possibly, in our current state of evolution, humans just don't have the mental capacity to answer questions like these.

      Delete
    4. Nature is unity of Classic and Quantum world.
      When we cannot understand their unity, we talk about
      Many Worlds Interpretation as Turtles all the way down
      ===

      Delete
    5. Dr. A.M. Castaldo,

      "I have very little optimism we can avoid that fate. Collectively speaking, The human population of this world is too stupid to build a sustainable technological civilization. Heck, we aren't even smart enough to agree it is necessary!"

      While i not necessarily agree on your happy genetic accident, i nonetheless agree with the citation above.

      Scientists preach that we should take into account the large timescales when searching for intuitively compelling explanations for life, the universe and all the rest, but – as you have shown - they ignore these timescales when talking about their pet theories by extrapolating all kinds of things and about the supposedly astonishing progress we will make in the foreseeable future due to that.

      Instead of preaching their personal pet theories at countless events like TED, in public talks of any kind around the whole world, they better should globally collaborate and publish an open letter in many, many newspapers around the whole world, warning politicians and companies about making further business as usual.

      Mass population on earth is dangerously growing, without having the right strategy to satisfy the needs of those people, producing billions of tons of waste, using up the resources and on the other side these scientists purport the almightiness of science - it is no wonder that the majority of people tacitly think that in the not so far future there surely will be some clever scientists who can transform all the waste into some kind of gold.

      Instead of figuring out the least common denominator about what science really can say reliably, compare it with where our civilisation is at present from a psychological point of view and then deduce what has to be told to the public to correct all the exaggerations they purported publicly during the last 30 decades, they go just further with self-advertising their intellectual "brilliance" and make science a kind of religious system: self-liberating, astonishing, awe and wonder, giving sense to our individual lifes, even without a God, all terms that describe merely the feelings of a minority of very privileged human beings that accidentally are on the sunny side of life. The majority has neither the time nor the money nor any other resources to also phantasize themselves into such a wonderland of Alice, not to talk about all the really suffering beings with too less food, and all the criminals, all the war victims etc.

      Science is limited, despite what some futurists and science-fiction adherents may think. Science cannot in any way counteract future collective human psychological dynamics (chaotic) when the fight and struggle for resources gets more pressing.

      So, if aliens have similar psychological mechanisms like humans, i am also really sceptical that these aliens may have lived long enough to be capable of interstellar travelling (the attitude of some scientists is indeed that we are already capable of that - we just have to facilitate the stuff and then let's go).

      Delete
  58. We might be able to proof the we are the only civilization at a certain moment in the galaxy. But it is unlikely we will be able to make a prediction for the other galaxies. In my view of the three options lucky coincidence would be the case anyway, irrespective of the other two options.

    ReplyDelete
  59. I'd just like to point out that MWI can in fact be tested. You need a lab assistant, and it's risky and immoral, but it can be done.

    Set up a sample with 50% probability of spin-up and 50% probability of spin-down. Hook your detector up to a gun. Spin-up and a bullet gets fired into your head. Spin-down and the gun doesn't go off. Repeat this experiment 100 times. If you're still there then you, and your assistant, and anyone who's there witnessing the experiment, would have some good evidence in support of MWI.

    Of course, you don't even need the drama of quantum suicide. You could simply record the results of the detector. Spin-down 100 times in a row would be strong evidence. BUT THAT HAS NEVER HAPPENED... (at least not in the branch I'm in)... not even close! And if it DID happen physicists would be convinced that there's something wrong with QM theory. They would have to because they're scientists so when an event with only 1 in 2^100 probability occurs in an experiment the assumption has to be that there's something wrong with the theory.

    So it seems pretty clear to me now that belief in MWI is tantamount to religious belief. But it's strange because the "religion" is QM theory, and the "believers" are really saying that QM theory would be "true", regardless of experimental results. Yet QM itself exists BECAUSE of respect for experimental evidence. MWI says that the Schrödinger Equation is divine and runs not only our universe but also an almost infinite number of other universes we don't have access to, even if experimental evidence and the principles of science were to suggest otherwise.

    ReplyDelete
    Replies
    1. i aM wh,

      Not being a physicist, I don't know what the current status of the MWI is. I recall reading years ago that it was the most popular interpretation among physicists themselves. But has the problem of source and meaning of the probabilities in QT been solved?

      Delete
  60. Sadly,the multiverse had infected Hollywood with a reference as to why it's real in one of the latest superhero movies. Of course, this doesn't mean it's anymore real and the public could probably care less,but they are likely to start believing it's true when the subject matter experts of their favorite fictional film testifies that it's true. The real question is whether theoretical physics is going to be a professional in the next decade or two, with no validation of any new theories, why would anybody risk their career going into it? As is true with physicists (which are humans, which are in turn animals), they squander their resources and rarely think of the future.

    ReplyDelete
  61. According to Dr. Don Lincoln at 7:10 in his Fermilab video on the multiverse he states: "It is not something we should believe." I agree.

    https://www.youtube.com/watch?v=dC0FCUNnmDc

    The multiverse is just an absurd idea concocted by atheists to delude themselves into thinking there is no God. The multiversers never ask themselves where did the multiverse come from. Obviously a multiverse solves nothing for an atheists unless they try really hard to delude themselves, which they do.

    ReplyDelete
    Replies
    1. Peter Wadeck: I am an atheist, I do not subscribe to multiverse theory. I also deny God, for the simple reason it makes no sense, by infinite descent: If someone believes the universe had to come from somewhere, then why don't they believe God had to come from somewhere? But they don't they just claim God existed forever.

      That is logically inconsistent; once it is allowed soemthing can exist forever, there is no reason to demand that the Universe had a beginning.

      Perhaps not in its current form, but forever. It is possible, for example, that resolving the issues around dark matter and dark energy and some quantum anomalies will lead us to a Big Bounce scenario that has been going on forever.

      Whatever mysteries you think God or the Multiverse "explains" they do not, they just increase the volume of explained mysteries. It is like a compression algorithm (producing a self-contained result) that increases the size of what it was supposed to compress. A common occurrence when compressing random noise.

      Real explanations reduce the number of unknowns and mysteries, they don't expand them.

      Delete

PLEASE READ THE COMMENT RULES BEFORE COMMENTING.

Comment moderation on this blog is turned on.
Submitted comments will only appear after manual approval, which can take up to 24 hours.
Comments posted as "Unknown" go straight to junk. You may have to click on the orange-white blogger icon next to your name to change to a different account.