Why Trust a Theory? — part III

Munich[Notes: what follows are only lightly edited notes taken while the meeting was in progress, so they are more likely than usual to contain typos and odd phrasing; also, apologies to my readers, but I may not be able to participate much to the hopefully interesting discussion at PlatoFootnote about this series of posts, I’m trying to also get some sleep here in Munich… Below and throughout, comments in brackets are mine.]

This is the last installment of my coverage of the workshop on the current status of fundamental physical theory, organized by philosopher Richard Dawid at the Center for Mathematical Philosophy based at the Ludwig-Maximilians University in Munich, Germany, a conference that was prompted by a high profile, controversial position paper published in Nature by George Ellis and Joe Silk (who are co-organizers of the workshop), entitled “Defend the integrity of physics.”

The first speaker of the day was one of the co-organizers, George Ellis, on “Limits in testing the Multiverse.” The idea of a multiverse has received increased attention, and it has been linked to the Everett (“many worlds”) interpretation of quantum mechanics. Marten Reese and Max Tegmark have been some of its most popular supporters. According to Greene there are a whopping nine different types of multiverse. They can’t be all true, since they conflict with each other. And of course maybe none of them are real, there is only one universe.

The underlying impulse seems to be a philosophical principles along the lines of “everything that can happen does happen.” The multiverse is also claimed to be a necessary outcome of chaotic inflation, and it is invoked as an explanation for life and human consciousness. The key to keep in mind is that the domains considered are beyond the particle horizon that is actually observable to us. This means that no observational data whatever are available, and this situation will not change. To think otherwise is hubris on a vast scale.

Arguments in favor include the “slippery slope” [a fallacy, in favor?], where people say, well, there are likely galaxies beyond the observable limits, so… Right, but this assumes an extrapolation over huge scales, and crossing qualitatively different physical domains. Moreover, if the idea of extrapolation is taken seriously, it actually leads to the old idea of spatial homogeneity forever, known as the Cosmological Principle.

A second argument is that the multiverse is implied by physics, specifically by chaotic inflation. But, again, this is a case of extrapolating known to unknown physics. That extrapolation is unverified and unverifiable.

The problem, in a sense, isn’t with extrapolation per se (which is a time honored practice in science). It is about how far it is reasonable to extrapolate, or how far behind one has left the data (or established, tested, theory).

Inflation is not yet a well defined theory, and the available data is implied by some versions of inflation but not others. Particularly, not all inflation is chaotic. The Encyclopedia Inflationaris considers a whopping 195 different models of inflation. [Again, underdetermination of theory by data rears its ugly head.] At the moment, the data do not actually prefer a universe containing bubbles.

Third argument: fine tuning. Here a multiverse is one of the possible explanations: an infinite set of universe domains allows all possibilities to occur, so somewhere things work out okay — though one ought to be able to demonstrate that the proper multiverse is a physical reality derivable from the theory, not just a conceptual possibility. In a sense the multiverse is used to make the highly improbable appear probable.

The problem is that this is a probability argument predicated on the existence of the multiverse. It is obviously inapplicable if there is only one universe. We can do many observations of that one object (the known universe), but we still have a sample size of one, as far as universes are concerned.

No value of the cosmological constant can prove whether a multiverse does or does not exist. At best the multiverse idea is simply consistent with an anthropically constrained universe, but that doesn’t get us much of theoretical value.

Tom Banks wrote a paper entitled “The top 10^5000 reasons not to believe in the landscape,” where he says that the string landscape is a fantasy. You may or may not agree with that paper, but it shows that the physics underlying the multiverse is simply not uncontroversial or established.

[Interestingly, through Ellis’ talk, David Gross — a supporter of string theory — kept nodding vigorously in first row… He made it clear that he doesn’t believe in the multiverse.]

Now chaotic inflation could be disproved by observing that we live in a small universe. This is currently being tested, by checking whether we can see “all around” the universe. At the moment it doesn’t appear to be so, but it is an open question. The other possibility is about confirmation (rather than disproof), based on the idea of collisions among bubbles, if nucleation is large relative to the rate of expansion. So far, nothing.

An additional issue concerns the claim of physically existing infinities, which the author says can simply not be achieved. “The infinite is nowhere to be found in reality,” according to David Hilbert. Talk of infinity is not scientifically testable. [Here Gross visibly reacted in the negative, and with obvious condescension…]

A second problem is posed by vacuum energy. Quantum Field Theory suggests a huge cosmological constant, discrepant with General Relativity if vacuum gravitates [hmm, I’m afraid I don’t know what the latter means].

The broad problem is that the multiverse makes few if any testable predictions, but it does explain everything. But successful scientific theories are those that make lots of testable predictions, not those that provide all-encompassing explanations.

Ellis argues that Smolin’s Darwinian cosmological natural selection is the best alternative on offer. [I don’t, see here] Still, it is incomplete in a number of ways. [Others during the discussion pointed out that it has recently failed a crucial test.]

There are also worse proposals, like the idea that the universe is a simulation, which raises far more questions than it actually answers. It confuses science fiction with science.

Talk of Popperazzi and falsifiability police is emotional talk and says something about just how thin the critics’ argument really is. What data would allow supporters to abandon the multiverse idea? If the answer is none, than that’s dogma, not science.

Ellis also criticized the use of Bayesianism to support non empirical confirmation, since Bayes theorem actually requires the addition of new data (not just new theory) to change the priors. [I actually think this is an excellent point.]

Next: Joseph Polchinski (in absentia, played by David Gross) on “String Theory to the Rescue.” [A pre-emptive strike about this talk has been published here, based on a version of the paper that has already been uploaded at arXiv.] The talk addresses both string theory and the multiverse. Gross said at the outset that he agrees with the first but not the latter. [This was, of course, not at all warranted and rather discourteous to the missing speaker, but whatever.]

Planck length, time and mass can be considered universal dimensionless constants of nature, to be used throughout the cosmos as natural units. They were arrived at in 1899, before both quantum mechanics and general relativity. The Planck length scale (10^-33 cm) is so far away from what current physics can do that it directly affects the tools and strategies physicists have available to make progress.

Theory has occasionally been able to leap gaps of this type, so we should try, and we should be weary of defining science too rigidly. [Not of defining it too loosely?] It is strange to say, as Smolin does in one of his books, that it is unfortunate that string theorists are not like Einstein, meaning not philosophically savvy. [Here Gross chuckled, stating that he wouldn’t know, since he doesn’t read “those books.”]

The short distance problem is one of the successes of string theory. General relativity and quantum mechanics, when applied to short distances, yield infinities that are non-renormalizable, resulting in something called spacetime foam. This sort of thing already happened to Fermi’s theory of the weak interaction, which gave physicists a clue to the discovery of the W, Z and Higgs bosons.

Another success of string theory: uniqueness of dynamics. String theory was discovered in an incomplete and approximate form, but it is a discovery of mathematical-physical structures that actually exist. [Mathematical Platonism?]

String success: physics from geometry. If general relativity, then gravity is the curvature of spacetime. So it is an attractive idea that the other interactions come from the geometry of time as well. But GR has used up the spacetime that we know, so we need more spacetime. String theories require extra dimensions, plus branes, of a form nicely compatible with the rest of physics.

String success: duality between gauge fields and strings. This is related to the quest for equivalences between classical and quantum theories. Here the string themselves (as well as general relativity, branes, and bulk spacetime) are emergent, and the best context to understand the theory is holography.

Another success of string theory: the relationship between black hole entropy and information. [See yesterday’s talk by Chris Wüthrich.]

Moving to the multiverse. If the physics that we see depends on the (compactified) geometry of spacetime, what determines that geometry? How many solutions does the 10D Einstein equation have that look minimally like our world? Estimates vary from 10^9 vacuum solutions, to combinatorially — with matter — anything between 10^500 and 10^272,000 [yep, you read that last number correctly…]. Einstein encountered a tiny version of the landscape, the radius of the Kaluza-Klein circle.

If there is a landscape, what determines its geometry in the new physics? Dynamics erases much of the initial conditions. Given a positive cosmological constant, we get expansion, then localized tunneling to a new vacuum, and repeat. So: GR + QM + landscape => multiverse. [Aahh…]

A multiverse is the price we pay for getting physics from geometry [too expensive, say some]. Yet there is evidence that we live in just such a universe. This is because all theories that predict a value of the cosmological constant (no supersymmetry, unbroken supersymmetry) get it wrong; the only options are theories where the constant is a free parameter in the dynamical equations, or the multiverse.

Of the various kinds of theories considered, only the multiverse predicts that observers see an unnaturally small (meaning, below the “natural” scale) cosmological constant. But these conditions do not require the constant to be zero, so a small nonzero value is predicted.

It is often said that the discovery of dark energy came as a surprise, except to cosmologists who had paid attention to the data without theoretical prejudice, and to those who had tried to solve the constant problem by conventional means, knew how hard it is, and were aware of Weinberg’s prediction on the subject. The vacuum energy was a prediction of the multiverse. [I bet this claim is gonna be controversial.]

The section of the talk on the multiverse concluded with a “quasi-Bayesian” estimate of the likelihood that there is a multiverse: 94% — and this is a conservative argument. [Laugh in the audience, though I don’t think this was intended as a joke…] The multiverse is on a similar footing as the Higgs, to which Polchinski attached a prior of 99.9%. [Even I can tell that this analogy is, shall we say, a stretch?]

The first speaker after coffee break was Elena Castellani on “Scientific Methodology: A View from Early String Theory.” Questions about scientific methodology are raised by dramatic scale changes in fundamental physics.

Traditionally, philosophers of science are concerned with the modalities followed in building theories, i.e. questions about discovery; they are also concerned with the modalities followed in assessing scientific theories, i.e. questions about justification. They are moreover concerned about the relationship between these modalities, since they are not sharply separated, as well as the influence of external aspects, such as sociological and economic ones.

The problematic aspects concerning participants to this workshop regard assessment methodology, not building ones. We have assessment based on empirical support, which is problematic for scientific reasons, both technical and theoretical. Philosophers have little to contribute here, since these are scientific issues. But we also have “extra-empirical” support, which is problematic for philosophical reasons.

There are general meta-strategies for extra-empirical support: for instance Dawid’s three arguments discussed on the first day. There are also more specific internal criteria: consistency, unifying power, generality, simplicity, fertility, explanatory power, elegance, beauty, etc.

Another internal criterion is the convergence argument: the convergence of results obtained in alternative, independent, ways, even beginning from different starting points. An example comes from early string theory, back to the work by Veneziano (1968) to the first string revolution in 1984.

This is an interesting period because it illuminates the origin of ideas such as strings, duality, supersymmetry, extra dimensions, as well as of mathematical techniques that are basic ingredients in today’s fundamental physics. Historical case studies like this are “data” informing discussions in philosophy of science.

First phase (1968-1973): the so-called dual theory of strong interactions, which was falsified as such. Second phase (1984-1984): those features that were a drawback of the theory for describing hadronic physics (spin-one and spin-two massless particles and extra dimensions) were taken to reveal the true nature of string theory, leading to reinterpret the theory as a unified quantum theory of all fundamental interactions.

In the second period the theory was regarded as so beautiful and having such a compelling mathematical structure that it had to relate to the physical world. This was sufficient motivation to pursue it.

The focus of the author was on the first phase, in particular the string conjecture, which originated in 1969 from three independent authors, in order to arrive at a deeper understanding of the physics described by dual amplitudes. The starting point was Veneziano’s discovery in 1968 of the dual amplitude for the scattering of four mesons. This is a case of discovery, illustrative of both the rationale leading to apparently bold guesses and the kind of evidential support motivating a theory’s progress.

Early work arrived at the conclusion of the number of spacetime dimensions = 26 via three different routes (with a fourth one added later on, in 1981). It was eventually shown that d=26 would fill Hilbert’s space. Of course, the theoretical beauty was achieved at the price of 22 extra dimensions. Nonetheless, these became gradually accepted because of what appeared to be a surprising convergence of different calculation procedures to the same result could be seen as a natural consequence of the theory in its full-fledged form.

Castellani concluded that this is the sort of non-empirical support that has kept string theory alive and well for all these years.

Last talk of the morning: Dieter Lüst on “Aspects of Quantum Gravity.” More than asking whether we can trust a theory we should ask how far we can go in theoretical physics. So far in the history of physics we have been able to probe shorter and shorter distances by accessing higher and higher energies. Extrapolation has always been a good tool, but does it work in the regime of quantum gravity?

The basic picture from quantum mechanics includes the wave-particle duality, Heisenberg’s uncertainty principle and phase space quantization. The other “column” of modern physics, of course, is general relativity. The problem is that the two seem to be mutually incompatible. QM and GR clash at short distances in a variety of ways, leading to infinities. Related questions concern the quantum structure of gravity, the quantum structure of spacetime, the emergence of geometry and gravity, and the storage of information in quantum gravity. Nobody has answers to these issues as yet, but string theory is the most promising framework. [It has been “promising” for quite some time now…]

Graviton scattering in quantum gravity: in quantum gravity, the gravitational force is mediated by the exchange of a massless spin 2 particle, the graviton. Are gravitational waves going to be discovered soon, by LIGO? Meanwhile, one can use a corpuscular model of black holes, which is equivalent to a Bose-Einstein condensate of N gravitons. [Sure, why not… This is one of a number of talks at the meeting that have unfortunately missed the mark. The whole idea of the workshop wasn’t to provide a platform to string theorists to discuss details of string theory and where it may go. It was to focus on a meta-discussion, if you will, of string and multiverse theories vis-a-vis scientific methodology. Oh well.]

String theory, the big picture: particles are string excitations, the spin 2 graviton is always part of the string excitations, it includes the other forces of nature, among other things. We can develop a good understanding of black hole entropy in terms of string states. String theory provides a consistent framework. [There is a lot of emphasis on consistency, which of course is a mathematical/logic requirement, but fairly minimal as far as scientific theories go.]

Of course there is the problem of the landscape, currently estimated at 10^1500 [notice how different people give wildly diverging estimates of the exponent]. But according to Kane [see his controversial talk from yesterday] the theory still has predictive power.

And we are back from the lunch break, with Sabine Hossenfelder and her talk on “Lost in Math.” Theory assessment, non-empirical or not, relies on judgment, which in turn can be trusted only if it is objective. Problem is, cognitive science tells us that human judgment is typically biased. Scientists have of course always suffered from cognitive biases, but the problem becomes much more urgent when data is harder to come by. [I.e., scientists rationalize just as much as anyone else, and if they are free to do that without empirical constraints, then…]

Hossenfelder declared herself offended by an earlier snide remark by David Gross about bloggers. She said as one of the few professionals who blog about fundamental physics she sees her job actually as that of “cleaning up” the mess often left around by science journalists.

The problem with fundamental physics is that it takes a long time to come up with new experiments, which in turn has led to a focus on mathematical consistency. But consistency is clearly insufficient. [See my comment above.] There are infinitely many consistent sets of mathematical axioms, we need to pick the right one(s) in comparison with observation.

The mathematical universe of Max Tegmark is “pretty much useless” because it does not help us to pick the right axioms. Multiverses are merely signs of under constrained theories. They are a symptom of trying to explain everything with nothing. [Ouch!]

Physicists use many assumptions that are never explicitly stated, and they are not required by mathematical consistency. That’s what gets us “lost in math.”

Physics also features “hidden rules,” having to do with the relevance of simplicity, naturalness, elegance and beauty. These requirements get converted into technical statements and their status as assumptions is forgotten.

Beauty used to be a sign of godly influenced (e.g., in Newton), then it became a bonus (Poincare`), then a guide (Hermann Weyl), and finally a mandate (Dirac). As physicists have become more successful they have also become convinced that they can understand nature by introspection. [Double ouch.]

[It strikes me like all this talk of equating beauty and truth is uncharacteristically Platonic…]

Beauty as a guide actually has a pretty bad track record. Many theories were considered beautiful and turned out to be wrong. Contrariwise, some successful theories were considered ugly when proposed.

What about naturalness? It has worked at times (e.g., top quark) but not others (e.g., cosmological constant, Higgs mass). Naturalness too is an aesthetic, not a mathematical principle. It’s empty without assuming a probability distribution.

Any theory is infinitely fine tuned because we have to pick a few sets of consistent axioms out of infinitely many.

Simplicity: by itself it is an utterly empty principle. It only makes sense to require a theory to be as simple as possible given certain data. But simplicity acts in a powerful way through the expectation that fundamental theories should be simpler. This has manifestly not been the case, otherwise we should have stopped with the ancient Greeks.

Perception of simplicity depends on exposure: the more familiar you are with a theory the simpler it seems. This is a phenomenon well known in arts and music, it ought to be acknowledged in physics as well.

Beauty, naturalness and simplicity are human desires. They have a mixed score card, and we have no reason to think that nature conforms to them.

Practitioners come to believe that these criteria are not hypotheses, but rather consistency requirements. This leads to two problems: a) people
forget that the criteria are hypotheses (“lost in math”) and b) the selection of criteria is affected by cognitive and social bias – which then don’t get corrected because they are not recognized as choices to begin with. This is what limits the space of theories that physicists explore in the first place, thus weakening the no-alternatives claim.

Scientific progress relies on objective expert judgment, which is hindered by social and cognitive biases, which need to be explicitly addressed in order to do good science. [Seems to me this was one of the best and most on target talks at the workshop.]

Next to the last talk: Karim Thebault on “What can we learn from analogue experiments?” In 1975 Hawking derived a semi-classical result associating a radiative flux to the black hole event horizon. Direct testing of his prediction seemed and still seems impossible. However, in 1981, Unruh showed that Hawking’s arguments can be applied to sonic horizons in fluids. In 2014, Steinhauer’s group claimed to have created an analogue charged black hole within an atomic Bose-Einstein condensate.

Should we think of the results of analogue experiments as providing empirical evidence for a given notion, or as analogies?

Experimental arguments from analogy have a long history in science. For instance, in medicine, the fact that a given substance X has an effect on experimental animals similar to another substance Y has been used to infer that if X works in humans, then Y will too, with positive results.

Formally, this sort of argument by analogy is invalid. Analogies merely establish plausibility, not proof, giving us reasons to proceed with further research. The suggestion is that if arguments that can provide external validation are added to analogue experiments, then the latter can actually be considered as going beyond arguments by analogy and move into the realm of actual experimental confirmation, the golden standard in science.

The author then developed an argument [much of it very, very technical] for closeness between hydrodynamics and the original context of Hawking’s calculations. where the role of the black hole event horizon is played by the effective acoustic horizon. As he put it, the black hole is replaced by a dumb hole. The general form of the argument can be modeled using Bayesian confirmation theory, which leads to the use of analogue experiments (under the specified conditions, which require the availability for external validation) to provide confirmation in the Bayesian sense of the term.

The last talk of the three-day workshop was by Georgi Dvali on “Secret quantum lives of black holes and dark energy.” [Another speaker who wrote his slides out by hand! Is this a new trend among slavic physicists? Not a good one, not a good one. But at the least his accent was not as incomprehensible as Mukhanov’s yesterday.] The author is concerned with how black holes process information [which of course is only marginally related to the actual topic of the workshop].

Classical black holes carry little information because they are featureless. Quantum mechanical black holes, however, do carry huge Beckenstein entropy. [He was talking as if the two were different objects, which is true mathematically, though I thought this was a conference about physics.] But in the classical limit black holes carry infinite information, except that it takes an infinite amount of time to decode.

[Unfortunately, the rest of the talk was a technical (obviously, theoretical) discussion of black holes physics, which was entirely irrelevant to the topic of the workshop, so I will not bore you with it.]

That’s really it, folks! It was a very interesting experience, not only because I learned quite a bit about physics and ongoing discussions among leading physicists, but because I got an invaluable first-person experience of the personalities and attitudes behind the controversy. You should keep an eye on the conference web site, where the videos of the talks will soon be published. The organizer, Richard Dawid, is also working on publication of the proceedings, either in book form (he is in conversations with Oxford Press, at the moment of this writing) or, less desirably in my mind, as a special issue of some journal. So stay tuned, there is much more to come, the string wars continue…

This update from Lee Smolin, concerning the alleged falsification of one of his predictions derived from his model of cosmological natural selection:

“Sabina was referring to this paper. From the abstract it claims the ‘measurement of a 2.01 +/- 0.04 solar mass pulsar.’ This is clearly not in contradiction with my prediction of an upper mass limit of 2 solar masses. For the reasoning and other checks of this prediction, See page 20 and reference 31 of Lee Smolin, ‘A perspective on the landscape problem,’ Invited contribution for a special issue of Foundations of Physics titled: Forty Years Of String Theory: Reflecting On the Foundations, DOI: 10.1007/s10701-012-9652-x arXiv:1202.3373. That reference 31 is: James M. Lattimer, M. Prakash, What a Two Solar Mass Neutron Star Really Means. 4. arXiv:1012.3208 , to appear in Gerry Brown’s Festschrift; Editor: Sabine Lee (World Scientific), which is by the people who did the nuclear physics that the 2 solar mass limit is based on. So I think its correct to say that this prediction is still standing up.”

78 thoughts on “Why Trust a Theory? — part III

  1. Massimo Post author


    “it was also a missed opportunity. Ellis and Silk made points in their Nature article last year that were simply not addressed. Instead, the conference was broadly configured as a way to defend string theory against the charge that it is untestable and so unscientific”

    Yes, that was the distinct impression I got too.

    “I was really struck by the consensus in the room that string theory is NOT confirmed or validated. In his opening presentation Gross explained that it’s actually not even a theory”

    Indeed, that was striking. And also notice that he was most definitely seem to be rejecting the whole multiverse thing.


    “You have clearly misquoted me on the very precise distinction that I made between the multiverse and the Higgs and the Big Bang. I was careful to write precisely, it would be useful if others would do the same”

    Apologies, but it isn’t easy to take detailed notes on the basis of fast flying slides for three full days in a row. I have now amended the blog post on the basis of further feedback I got on that particular point. If you still think it misrepresents your views, let me know and I will correct it further.


    “Given the lack of a blackboard during the conference, hand-written slides are the next best thing for a blackboard-oriented scientist”

    I hear you, I just hope that scientists will at some point stop being blackboard-oriented… 😉

    “Regarding Mukhanov’s talk, I really feel sorry that you couldn’t follow it, because it was a great lecture! 🙂 It was actually so good that I feel motivated to make a full transcript of it, once the video comes online. I’ll share as soon as I do it.”

    Excellent, let me know and I’ll add a link.


    “Your link about holography failing an empirical test made me laugh out loud and makes it completely clear that you do not have the faintest hint of what holography is”

    I’m glad you got a laugh out of it. Now, how about a constructive comment to go with it?


  2. Coel

    Hi Massimo,

    We have evidence of one Big Bang. […] Period, end of story.

    If you wandered into a distant rain forest and saw a monkey unlike anything ever seen by science, would you, as a biologist, conclude it more likely that: (1) there is one and only one such monkey; (2) that that monkey is one of many like it that do exist or have recently existed?

    If you go for the latter (which you would!), it means that “we’ve seen one so we assume there is only one unless we see more” is too simplistic.

    you are seriously asking for data that convince people that there has been a single Big Bang.

    Sure, if they are indeed asserting that there was indeed only one BB, or if they are asserting that multiple BBs is the less-likely hypothesis.

    The whole *point* of the multiverse is that it allows for a physicist’s version of the principle of plenitude, and that it solves the so-called problem of fine tuning to boot.

    Well, no. That is the point of ONE VERSION of a “multiverse”. There are lots of multiverse concepts. The Munich conference seems to have been mostly about string theory. But the multiverse as motivated by cosmology has a different motivation.

    The reason many cosmologists favour a multiverse is that it is very hard to make a model of the Big Bang that (1) works, and (2) does NOT produce a multiverse. Essentially the inflationary state expands too fast for it to do anything other than create a multiverse.

    E.g. “In fact, in any successful inflationary model the rate of exponential expansion is always much faster than the rate of exponential decay.” […]

    “Most important of all is the simple statement that once inflation happens, it
    produces not just one universe, but an infinite number of universes.”

    [Guth, http://arxiv.org/abs/hep-th/0702178, see that whole Section 2]

    Now, that argument ONLY gets you to the “vanilla-flavour” multiverse, where all the pocket universes might have the same physics (whether they do or not really is a different matter, one that we can ask the string theorists about, but the argument that I’m giving is not about string theory, it’s about cosmological models of the Big Bang!).

    A “vanilla” version would do neither, and on top of that now you would have an infinity of fine tune problems to solve!

    Such problems should always be considered in terms of information content. With regard to fine-tuning, a multiverse with an infinity of pocket universes (all with the same physics) is no different in information content from simply extending our own universe to infinity.

    But, again, I’m not trying to make an argument out of fine tuning or whatever, I’m making a much more basic argument about trying to make one BB in a way that does not automatically make multiple BBs.

    Can you give me evidence that “many cosmologists” believe what you propose?

    It’s not so much that they “believe” it, it’s that current Big-Bang models require it. [And, again, whether you then go on to ponder whether the different pocket universes have different physics really is a separate issue.]

    [Origin of life] I simply gave you an example of what you asked: a case of a natural phenomenon that, as far as we know, occurred only once.

    But that wasn’t quite what I asked for. I asked for an example of a natural phenomenon where people would generally argue that “happened only once” had a higher probability than “happened lots of times”. If we do have an effectively infinite universe, then there is no argument for “happened only once”.

    unless we somehow gain empirical access to it. I see no reason whatsoever why one should believe it.

    We’re not talking about “believing” either the multiverse or the single-BB claim. We’re talking about expectations, about Bayesian priors. If you want to regard the number of Big Bangs as being completely unknown (other than not being zero!) then fine, but there is no reason to prefer N = 1 to N = 10^10 or whatever.


  3. SocraticGadfly

    Coel, your BB vs multiverse claim sounds like an argument in statistical illiteratcy, like the stereotypical “which is more likely”:
    A. A pro-choice Democrat
    B. A pro-choice Democrat who’s also an atheist.

    Your last attempt to reframe it is unconvincing for me.


  4. brodix


    Ecumenism works best if there is some underlaying assumption universal to all theories, like monotheism is the underlaying assumption of most, if not all western religions.

    If that assumption is not open to question, then one can only hope it is right.


  5. Disagreeable Me (@Disagreeable_I)

    Hi Massimo,

    OK, so we can probably agree that the MUH in particular is not very scientific, even as we disagree as to whether it is likely to be true.

    > First off, the multiverse is not at all the same thing as the MUH.

    There are different varieties of multiverse, the MUH being one of them. But the MUH also entails the existence of all other varieties of multiverse within it. So there is at least one scenario where the different multiverses all exist. This suggests that they’re not *completely* mutually contradictory, except in the sense that *our* being in multiverse type A may rule us out from being in multiverse type B (though A and B would both exist, we could only be in one of them).

    > At any rate, I take it Ellis knows what he’s talking about, and nobody contradicted him in Munich on that point.

    I’m not so much contradicting him as trying to figure out what he meant.

    > Nice try with the scientistic judo move.

    I’m not trying to trip you up or catch you out! You just *seemed* to be saying something scientistic which you obviously didn’t intend, so I asked you to clarify and you did. Thanks!

    > You may not care about the genealogy of ideas, but I do.

    I agree that one should give credit where credit is due. But what I’m interested in discussing is mostly the idea itself and not so much where it came from, because it probably came from multiple places at multiple times independently. Independent discovery is entirely possible after all. I should know, as I only learned about Tegmark’s MUH after I’d already come up with pretty much the same idea myself — I originally thought of it as “The Platonic Algorithm”.

    Anyway, Tegmark does give credit to both Plato and Pythagoras, but I don’t think he’s just reiterating what they said. What he is promoting certainly rhymes with many ideas of the ancient Greeks, but it’s not quite the same in my view. How well Tegmark appreciates the similarity of his views with what others before him have said doesn’t have much bearing on the validity of the ideas themselves. Since he is not a professional philosopher, it’s not necessarily reasonable to expect him to know the ins and outs of thoughts the ancients had along similar lines. One can be an expert on the idea itself without being an expert on the history of the idea.

    I think he deserves credit in his own right anyway for reviving or taking up the mantle of the idea in a modern context. There’s a world of difference between treating it as a historical or metaphysical curiosity (e.g. the study of Aristotle’s ideas about motion) and treating it as something that actually may be true and relevant today. I don’t see too many other prominent cheerleaders for it these days, do you?


  6. brodix

    I would agree with Coel that multiverses do seem a logical extension of the Big Bang theory, much as wormholes are a logical extension of spacetime, but there is a term for this; reductio ad absurdum.


  7. Philip Thrift

    I suppose the “monotheism” of scientific-theory ecumenism would be materialism (or whatever people call it). So I guess the intelligent-design “theorists” are ignored, for example.


  8. Coel

    Hi Socratic,

    Coel, your BB vs multiverse claim sounds like an argument in statistical illiteratcy, like the stereotypical “which is more likely”:
    A. A pro-choice Democrat
    B. A pro-choice Democrat who’s also an atheist.

    That is indeed the argument in a nutshell! Except that the choices are:

    A: Mechanism for producing a Big Bang.
    B: Mechanism for producing a Big Bang + reason why it only happened once.


  9. Joe Polchinski

    Dear Massimo, Thanks for the correction. Just to be clear, there is a world of difference between 2 sigma and 5 sigma (it is exponential in the square). I do let my sense of humor out (had I given my talk, I had a nice analogy between multiverse opponents and Dick Cheney), but I try to be very precise. Unfortunately, those who do not wish to think will use the humor as an excuse not to.

    Liked by 1 person

  10. brodix


    Yes, but how do you define “material?” Physics says matter is both particle and wave, but there is a distinct bias toward particles, with waves being treated as statistical effect. Is this because there is irrefutable evidence that particles are primal, or is this an epistemic and mental bias toward static form?

    What about “spooky action at a distance? Might it be better explained as more a wave like property?

    What evidence do we have of elementary particles which isn’t simply some expression of force, be it weight, motion, etc? Given their quantum uncertainty, wouldn’t they seem likely to be the peaks of waves?

    Yet if we were to describe reality as fundamentally wave-like, wouldn’t the conceptual impression be more of a hologram, than “material?’

    So, yes, materialism is the underlaying assumption, but is it open to question? Lemaitre tried to explain the whole universe as essentially one object, but as Coel observes, this implies a multitude of such objects that we have no way to explore.

    So might there be some effort to at least go back and examine some of these underlaying assumptions and see if there might be further insight from looking at reality through different concepts, or do we just sit here and obsess over what is beyond any possible consideration, because we just know it to be “material?”


  11. brodix

    Keeping in mind that according to the matter/particle view, reality is 99% empty space, but all that fuzziness filling space seems quite real to me, at least.


  12. Philip Thrift

    What is material (or physical)?

    With something like MUH or CUH, there is a one-to-one correspondence between mathematical/computational entities and physical entities. Whether that extends or restricts what’s mathematical/computational, or it extends or restricts what’s physical, is debatable. 🙂


  13. brodix


    That is the theory, but with epicycles, there was assumed to be a one to one correspondence between the patterns of the motions of the stars and a physical apparatus to convey them. Where did that lead?

    As I asked previously, how do we arrive at mathematical patterns, except by distilling the stable forms from our perceptions of reality. It is a map of the territory, not the foundations of the territory.

    Consider that space is assumed to be nothing more than a measure between point particles, because it is not “physical.” While all that fuzzy physicality we perceive is just statistical probabilities. Consequently the entire universe is assumed to be emergent from a single point, based on some eternal mathematical formula. While I can see why some people might think they have unearthed the Holy Grail of platonic form, I tend to see it as worshipping another ideal, as all communities have their guiding principles.

    For instance, a dimensionless point is an ideal of location, but if you eliminated all dimensionality, than as a location, isn’t it a multiple of zero? Which would make it non-existent, not omnipresent.

    I’ve butted heads with too many true believers in too many dogmas to think I am going to convince anyone with basic logic, but if I’m the crackpot, then I will remain a happy crackpot and not feel compelled to follow others beliefs. There have been enough people, over the years, willing to see sense in what I have to say and expressed thoughts similar to mine, that I know I’m not totally alone, but until someone time travels through one of those wormholes and brings me some actual, physical evidence that it’s all just math, I remain a skeptic.


  14. SocraticGadfly

    Coel, thanks for confirming, other than noting you got it backward on the A and B of your part of the analogy. I stand by my original statement and say that you’re committing statistical illiteracy.


  15. Robin Herbert

    As I said in the previous thread, if the BB is just the shape of one end of a four dimensional object then you have:

    A. The shape of one end of a four dimensional object and;
    B. The shape of one end of a four dimensional object and a reason why there are no other four dimensional objects with one end shaped like that

    Nor quite so convincing.


  16. Coel

    Hi Socratic,

    A better question would be: You have one pro-choice Democrat. Is it more likely that:

    A: There are other pro-choice Democrats.
    B: There are no other pro-choice Democrats ?

    Given that our initial data points shows that “pro-choice Democrats” are the sort of thing that does occur, the most likely answer is A.

    Note that your adding “… who is an atheist” does indeed reduce the probability. That’s because that is *different* from the specification of the original data point. That’s not the same as having more of exactly the same, which is not less probable.

    E.g. consider sand grains on a beach. You seem to be wanting to argue that: the probability of having one grain of sand is P, the probability of a second is also P, therefore the probability of two is P*P, the probability of three is P*P*P, etc, and you quickly deduce (since P is necessarily < 1) that having millions of grains of sand on a beach is wildly improbable. The fallacy here is that the events of "having a grain of sand", being the *same* *thing*, are not independent.

    Thus the comparison in your question is misguided.


  17. Robin Herbert

    And the MUH, well I think that is wrong for the same reasons I have been saying it is wrong for a while now. Tegmark tries to get round it in his original paper, but unsuccessfully, I think.


  18. brodix


    Would energy precede matter?

    The reason math has such a hold on our minds is that it is static form, distilled from reality and our nervous system is designed to extract form from reality. Consider your vision; If the light simply poured straight into the conscious executive function, it would quickly white out. We “see” things because our visual function creates still images, like a movie projector is flashes of stills.

    So as with all our other thought processes, we are extracting the signal from the noise.

    Now matter is a form of energy, E=mc2. What makes it so appealing to us is that it is a static form of energy. It is lots of stored information. Which logically makes it a composition.

    But just like it took us all of human existence, up until 500 years ago, to appreciate that the earth is only our point of view, not the center of the cosmos, so too might we have to get used to the idea that matter is emergent from deeper dynamics and it is the ordering of our point of view which makes it seem primal.


  19. 45SURF (@45surf)

    Why were Einstein, Feynman, Newton, Galileo, Copernicus et al. banned from the abstracts, papers, presentations, and coverage of the Munich conference titled, Why Trust a Theory? Reconsidering Scientific Methodology in Light of Modern Physics. I couldn’t find one single quote from any of the Greats concerning the nature of science. I have included many great quotes below, so that you might be able to share them with your students and at future conferences.

    It is almost as if the fake pseudoscience of String Theory/Multiverse Mania needs fake experiments (BICEP2 dust observations) and fake philosophers and philosophies so as to keep the billions of taxpayer dollars flowing into the massive anti-science hoax. It is almost as if the multimillionaire multiverse maniacs are denying the bright light of Einstein, Feynman, Newton, Galileo, and Copernicus so that the anti-Philosophy, anti-Physics, talentless televangelist hacks can create the largest, darkest version of Plato’s cave ever known to mankind–a dark, sordid cave where belligerent bloggers shall rule the multi-billion-dollar industrial hype complex for all of eternity via phony press releases and legions of useful idiots, exiling anyone who actually ventures beyond the cave into the Light (dx4/dt=ic).

    When it comes to defining science and scientific theories, should not the words and thoughts of Feynman, Newton, Galileo and Einstein be included?

    Should not the words, thoughts, and ideas of the likes of Einstein, Feynman, Maxwell, Faraday, Newton, Galileo, and Copernicus be included front and center in books and at conferences contemplating the character of physics and science?

    Might anyone know exactly when Brian Green’s lie(s)–“Superstring theory successfully merges general relativity and quantum mechanics”–will be removed from Einstein’s noble book The Meaning of Relativity?

    Please be sure include the spirit and soul of Einstein, Feynman, Maxwell, Faraday, Newton, Galileo, and Copernicus in future conferences, books, and publications!

    The words of the Greats allow us to see String Theory for what it is–a failed hoax by which tens of thousands of pseudoscientists, televangelists, and faux philosophers have profited massively at the expense of the taxpayer, student, physics, and physicists, writing blurbs for one-another’s hype-based books while occupying the university and transforming it into the darkest version of Plato’s Cave ever known to mankind, during their ruthless reign of darkness and deceit.


  20. 45SURF (@45surf)

    If we simply replaced the entire content of the Munich conference with the words, thoughts, and philosophies of the likes of Max Born, Richard Feynman, Einstein and other Nobel Laureates and Luminaries such as Sir Isaac Newton and Galileo, would not physics and its future be better off?

    R.P. Feynman: I don’t like that they’re not calculating anything. I don’t like that they don’t check their ideas. I don’t like that for anything that disagrees with an experiment, they cook up an explanation-a fix-up to say, “Well, it might be true.” For example, the theory requires ten dimensions. Well, maybe there’s a way of wrapping up six of the dimensions. Yes, that’s all possible mathematically, but why not seven? . . . So the fact that it might disagree with experience is very tenuous, it doesn’t produce anything; it has to be excused most of the time. It doesn’t look right.

    Max Born: All great discoveries in experimental physics have been made due to the intuition of men who made free use of models which for them were not products of the imagination but representations of real things.

    Einstein: Time and again the passion for understanding has led to the illusion that man is able to comprehend the objective world rationally by pure thought without any empirical foundations—in short, by metaphysics.

    Gerard ‘t’Hooft: Actually, I would not even be prepared to call string theory a “theory” rather a “model” or not even that: just a hunch. After all, a theory should come together with instructions on how to deal with it to identify the things one wishes to describe, in our case the elementary particles, and one should, at least in principle, be able to formulate the rules for calculating the properties of these particles, and how to make new predictions for them. Imagine that I give you a chair, while explaining that the legs are still missing, and that the seat, back and armrest will perhaps be delivered soon; whatever I did give you, can I still call it a chair?

    Einstein: Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius—and a lot of courage—to move in the opposite direction (dx4/dt=ic).

    Sheldon Glashow: It is tragic, but now, we have the string theorists, thousands of them, that also dream of explaining all the features of nature. They just celebrated the 20th anniversary of superstring theory. So when one person spends 30 years, it’s a waste, but when thousands waste 20 years in modern day, they celebrate with champagne. I find that curious.

    Einstein: The theory must not contradict empirical facts. . . The second point of view is not concerned with the relation to the material of observation but with the premises of the theory itself, with what may briefly but vaguely be characterized as the “naturalness” or “logical simplicity” of the premises of the basic concepts and of the relations between these which are taken as a basis.

    Sheldon Glashow: But superstring physicists have not yet shown that theory really works. They cannot demonstrate that the standard theory is a logical outcome of string theory. They cannot even be sure that their formalism includes a description of such things as protons and electrons. And they have not yet made even one teeny-tiny experimental prediction. Worst of all, superstring theory does not follow as a logical consequence of some appealing set of hypotheses about nature.

    Philip W. Anderson Physicist and Nobel laureate, Princeton: “Is string theory a futile exercise as physics, as I believe it to be? It is an interesting mathematical specialty and has produced and will produce mathematics useful in other contexts, but it seems no more vital as mathematics than other areas of very abstract or specialized math, and doesn’t on that basis justify the incredible amount of effort expended on it.

    My belief is based on the fact that string theory is the first science in hundreds of years to be pursued in pre-Baconian fashion, without any adequate experimental guidance. It proposes that Nature is the way we would like it to be rather than the way we see it to be; and it is improbable that Nature thinks the same way we do.
    The sad thing is that, as several young would-be theorists have explained to me, it is so highly developed that it is a full-time job just to keep up with it. That means that other avenues are not being explored by the bright, imaginative young people, and that alternative career paths are blocked.”

    Would not young physicists be better off hearing these words of wisdom, as opposed to the words of Bee, Kane, Dawid, et al.?

    How many undergraduates, graduate students, or professors could recite Newton’s or Einstein’s rules for physics?

    Einstein’s Three Rules of Work:
    1. Out of clutter find simplicity (dx4/dt=ic).
    2. From discord find harmony.
    3. In the middle of difficulty lies opportunity.

    Newton’s Four Rules of Science and Natural Philosophy
    Rule 1: We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances.

    Rule 2: Therefore to the same natural effects we must, as far as possible, assign the same causes (dx4/dt=ic).

    Rule 3: The qualities of bodies, which admit neither intensification nor remission of degrees, and which are found to belong to all bodies within the reach of our experiments, are to be esteemed the universal qualities of all bodies whatsoever.

    Rule 4: In experimental philosophy we are to look upon propositions inferred by general induction from phenomena as accurately or very nearly true, not withstanding any contrary hypothesis that may be imagined, till such time as other phenomena occur, by which they may either be made more accurate, or liable to exceptions.

    I contend that if the brilliant light of this wisdom were allowed to shine forth, the murky string theory and multiverse fog would dissipate like an early morning sea mist kissed by the rising sun.

    What we need, more than ever, is to turn towards the wisdom of those who actually advanced physics. We should look to apply their diverse array of mathematical, philosophical, and physical methods in our own context!

    Einstein: The theory must not contradict empirical facts. . . (there are no empirical facts supporting 11 nor 42 dimensions; nor tiny, vibrating strings) The second point of view is not concerned with the relation to the material of observation but with the premises of the theory itself, with what may briefly but vaguely be characterized as the “naturalness” or “logical simplicity” of the premises of the basic concepts and of the relations between these which are taken as a basis.

    Schrodinger: The world is given but once. . . (No multiverse!) The world extended in space and time is but our representation. Experience does not give us the slightest clue of its being anything besides that.

    Nobel Laureate Robert Laughlin: [String Theory] has no practical utility, however, other than to sustain the myth of the ultimate theory. There is no experimental evidence for the existence of strings in nature, nor does the special mathematics of string theory enable known experimental behavior to be calculated or predicted more easily. . . String theory is, in fact, a textbook case of Deceitful Turkey, a beautiful set of ideas that will always remain just barely out of reach. Far from a wonderful technological hope for a greater tomorrow, it is instead the tragic consequence of an obsolete belief system-in which emergence plays no role and dark law does not exist.—A Different Universe, Laughlin

    Planck: That we do not construct the external world to suit our own ends in the pursuit of science, but that vice versa the external world forces itself upon our recognition with its own elemental power, is a point which ought to be categorically asserted again and again . . . From the fact that in studying the happenings of nature . . . it is clear that we always look for the basic thing behind the dependent thing, for what is absolute behind what is relative, for the reality behind the appearance and for what abides behind what is transitory. . this is characteristic not only of physical science but of all science.

    Einstein: Mathematics are well and good but nature keeps dragging us around by the nose.

    Poincare: Geometry is not true, it is advantageous.

    Sir Francis Bacon: And all depends on keeping the eye steadily fixed upon the facts of nature and so receiving their images simply as they are. For God forbid that we should give out a dream of our own imagination for a pattern of the world; rather may he graciously grant to us to write an apocalypse or true vision of the footsteps of the Creator imprinted on his creatures.

    In Einstein’s Mistakes, Dr. Hans Ohanian reports on how physics advances via the emphasis not on math, but on physical reality, “(Max) Born described the weak point in Einstein’s work in those final years: “. . . now he tried to do without any empirical facts, by pure thinking. He believed in the power of reason to guess the laws according to which God built the world.”

    In Disturbing the Universe, Freeman Dyson writes, “Dick [Feynman] fought back against my skepticism, arguing that Einstein had failed because he stopped thinking in concrete physical images (as MDT does!) and became a manipulator of equations. I had to admit that was true. The great discoveries of Einstein’s earlier years were all based on direct physical intuition. Einstein’s later unified theories failed because they were only sets of equations without physical meaning. Dick’s sum-over-histories theory was in the spirit of the young Einstein, not of the old Einstein. It was solidly rooted in physical reality.”[xxxiii] In The Trouble With Physics, Lee Smolin writes that Bohr was not a Feynman “shut up and calculate” physicist, and from the above Dyson quote, it appears that Feynman wasn’t either. Lee writes, “Mara Beller, a historian who has studied his [Bohr’s] work in detail, points out that there was not a single calculation in his research notebooks, which were all verbal arguments and pictures.”[xxxiv] Please see MDT’s Fig. 1, presenting a physical model, at the end of this document. (Many more to come!)

    In Dark Matters, Dr. Percy Seymour writes, “Albert Einstein was a great admirer of Newton, Faraday, and Maxwell. In his office he had framed copies of portraits of these scientists. He had this to say about Faraday and Maxwell: “The greatest change in the axiomatic basis of physics—in other words, of our conception of the structure—since Newton laid the foundation of theoretical physics was brought about by Faraday’s and Maxwell’s work on electromagnetic phenomena.”

    Yes! And in his book “Einstein,” Banesh Hoffman and the great Michael Faraday exalt physical reality over mere math:

    “Meanwhile, however, the English experimenter Michael Farady was making outstanding experimental discoveries in electricity and magnetism. Being largely self-taught and lacking mathematical facility, he could not interpret his results in the manner of Ampere. And this was fortunate, since it led to a revolution in science. . . most physicists adept at mathematics thought his concepts mathematically naïve.”

    “We don’t know what we are talking about.” –Nobel Laureate David Gross on string theory

    “It is anomalous to replace the four-dimensional continuum by a five-dimensional one and then subsequently to tie up artificially one of those five dimensions in order to account for the fact that it does not manifest itself.” -Einstein to Ehrenfest (Imagine doing this for 10-30+ dimensions!)

    “String theorists don’t make predictions, they make excuses.” – Feynman, Nobel Laureate

    “String theory is like a 50 year old woman wearing too much lipstick.” -Robert Laughlin, Nobel Laureate

    “Books on physics are full of complicated mathematical formulae. But thought and ideas (the fourth dimension is expanding relative to the three spatial dimensions at c), not formulae (dx4/dt=ic), are the beginning of every physical theory.” —Einstein/Infeld, The Evolution of Physics

    Einstein: “As far as the laws of mathematics refer to reality, they are not certain, and as far as they are certain, they do not refer to reality.”


  21. Philosopher Eric

    Sabine, I think what you’re doing is extremely important, but also find it disturbing that you yourself have been placed in such a position. I would hope for the philosophy community in general to come to your aid, though philosophers have challenges of their own to overcome. Wouldn’t it be wonderful if philosophy were to actually cleanse itself, by sorting this issue out for physics? HA! In practice physics and philosophy square off more like fighting dogs. Nevertheless apparently there are indeed sensible voices around, and this is where progress must be made.

    I did find your provided theory-model discussion quite useful, which isn’t surprising since our ideas do conform. I believe that there is great need to formally acknowledge one unique method by which the conscious entity figures things out (and even with no language): It takes what it thinks it knows (evidence), and then uses this to assess things that it’s not so sure about (phenomenological models). Thus evidence should be considered quite integral. But among those who have become heavily invested in ideas beyond evidence (whether physicist or theist) this pill should not be a pleasant one!

    Then at least as important, I think, is the nature of definition itself. I interpret your following observation to touch upon this somewhat:

    Physicists rarely if ever even write down the assumptions that they use. They typically leave this to mathematical physicists (who then write textbooks that physicists never read).

    It might help if our encyclopedias and such would stop phrasing our definitions by means of the term “is.” Instead the writer should be free to develop his/her definitions (such as “universe,” “consciousness,” “life,” and so on) however he/she sees fit. Here the reader would be obligated to assess the writer’s ideas through the writer’s definitions. But given that this principal has not yet become accepted, and that compliance should add a cumbersome condition, it’s no wonder that philosophers/scientists do commonly talk past each other.

    As a youngster, it was actually the great wonders of physics which inspired me to take up a nonstandard approach to philosophy and mental/behavioral science. Observe that over the past few centuries our “hard” science seems to have provided humanity with amazing power, though without similarly increasing our understandings of how to properly use it. Thus I believe that on the “soft” side, a “Sir Isaac Newton” type of figure shall emerge one day to help balance humanity out in this regard.


  22. Robin Herbert

    Hi Philip,

    When you say matter precedes mathematics, Do you mean that there might be a physical realm where the ratio of the circumference of a circle to its diameter on a Euclidean plane might be 27?


  23. brodix


    My larger point is that if the only way forward is to speculate over the nature of multiverses, as that would seem to be the logical conclusion of a unitary BB model universe, than maybe some section of the physics community could put some effort into going back and re-examining the various intuitive assumptions built into the foundations of our current models.

    As I’ve pointed out, some of this could even go back to the very nature of math, as to whether it is patterns extracted from reality, or if it is the foundations of reality. Idealizations are not absolutes. There might be a perfect circle, but an absolute circle would make no sense. Even trying to imagine one and it will shrink to a point and disappear. Why? Because it is form and form is a construct. There are no circles in a void, because there is no relationship between circumference and area in a void.

    We look at math as elemental in the same way we used to see the earth as the center of the cosmos. It is foundational to our reality, because our minds are designed to pick out patterns and form. Our digestive, respiratory and circulatory systems deal with the flows of energy.

    Not to rant on, but it’s either go back and seriously review, or speculate on the multiverse. I suspect that wave has crested and future generations will have a field day going through the mental attic.

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