Science and Unobservable Things

By Sean Carroll | March 15, 2008 1:02 pm

Today’s Bloggingheads dialogue features me and writer John Horgan — I will spare you a screen capture of our faces, but here is a good old-fashioned link.

John is the author of The End of Science, in which he argues that much of modern physics has entered an era of “ironic science,” where speculation about unobservable things (inflation, other universes, extra dimensions) has replaced the hard-nosed empiricism of an earlier era. Most of our discussion went over that same territory, focusing primarily on inflation but touching on other examples as well.

You can judge for yourself whether I was persuasive or not, but the case I tried to make was that attitudes along the lines of “that stuff you’re talking about can never be observed, so you’re not doing science, it’s just theology” are woefully simplistic, and simply don’t reflect the way that science works in the real world. Other branches of the wavefunction, or the state of the universe before the Big Bang, may by themselves be unobservable, but they are part of a larger picture that remains tied to what we see around us. (Inflation is a particularly inappropriate example to pick on; while it has by no means been established, and it is undeniably difficult to distinguish definitively between models, it keeps making predictions that are tested and come out correct — spatial flatness of the universe, density fluctuations larger than the Hubble radius, correlations between perturbations in matter and radiation, fluctuation amplitudes on different scales that are almost equal but not quite…)

If you are firmly convinced that talking about the multiverse and other unobservable things is deeply unscientific and a leading indicator of the Decline of the West, nothing I say will change your mind. In particular, you may judge that the question which inflation tries to answer — “Why was the early universe like that?” — is a priori unscientific, and we should just accept the universe as it is. That’s an intellectually consistent position that you are welcome to take. The good news is that the overwhelming majority of interesting science being done today remains closely connected to tangible phenomena just as it (usually!) has been through the history of modern science. But if you instead ask in good faith why sensible people would be led to hypothesize all of this unobservable superstructure, there are perfectly good answers to be had.

The most important point is that the underlying goal of science is not simply making predictions — it’s developing an understanding of the mechanisms underlying the operation of the natural world. This point is made very eloquently by David Deutsch in his book The Fabric of Reality. As I mention in the dialogue, Deutsch chooses this quote by Steven Weinberg as an exemplar of hard-boiled instrumentalism:

The important thing is to be able to make predictions about images on the astronomers’ photographic plates, frequencies of spectral lines, and so on, and it simply doesn’t matter whether we ascribe these predictions to the physical effects of gravitational fields on the motion of planets and photons or to a curvature of space and time.

That’s crazy, of course — the dynamics through which we derive those predictions matters enormously. (I suspect that Weinberg was trying to emphasize that there may be formulations of the same underlying theory that look different but are actually equivalent; then the distinction truly wouldn’t matter, but saying “the important thing is to make predictions” is going a bit too far.) Deutsch asks us to imagine an “oracle,” a black box which will correctly answer any well-posed empirical question we ask of it. So in principle the oracle can help us make any prediction we like — would that count as the ultimate end-all scientific theory? Of course not, as it would provide no understanding whatsoever. As Deutsch notes, it would be able to predict that a certain rocket-ship design would blow up on take-off, but offer no clue as to how we could fix it. The oracle would serve as a replacement for experiments, but not for theories. No scientist, armed with an infinite array of answers to specific questions but zero understanding of how they were obtained, would declare their work completed.

If making predictions were all that mattered, we would have stopped doing particle physics some time around the early 1980’s. The problem with the Standard Model of particle physics, remember, is that (until we learned more about neutrino physics and dark matter) it kept making predictions that fit all of our experiments! We’ve been working very hard, and spending a lot of money, just to do experiments for which the Standard Model would be unable to make an accurate prediction. And we do so because we’re not satisfied with predicting the outcome of experiments; we want to understand the underlying mechanism, and the Standard Model (especially the breaking of electroweak symmetry) falls short on that score.

The next thing to understand is that all of these crazy speculations about multiverses and extra dimensions originate in the attempt to understand phenomena that we observe right here in the nearby world. Gravity and quantum mechanics both exist — very few people doubt that. And therefore, we want a theory that can encompass both of them. By a very explicit chain of reasoning — trying to understand perturbation theory, getting anomalies to cancel, etc. — we are led to superstrings in ten dimensions. And then we try to bring that theory back into contact with the observed world around us, compactifying those extra dimensions and trying to match onto particle physics and cosmology. The program may or may not work — it’s certainly hard, and we may ultimately decide that it’s just too hard, or find an idea that works just as well without all the extra-dimensional superstructure. Theories of what happened before the Big Bang are the same way; we’re not tossing out scenarios because we think it’s amusing, but because we are trying to understand features of the world we actually do observe, and that attempt drives us to these hypotheses.

Ultimately, of course, we do need to make contact with observation and experiment. But the final point to emphasize is that not every prediction of every theory needs to be testable; what needs to be testable is the framework as a whole. If we do manage to construct a theory that makes a set of specific and unambiguous testable predictions, and those predictions are tested and the theory comes through with flying colors, and that theory also predicts unambiguously that inflation happened or there are multiple universes or extra dimensions, I will be very happy to believe in the reality of those ideas. That happy situation does not seem to be around the corner — right now the data are offering us a few clues, on the basis of which invent new hypotheses, and we have a long way to go before some of those hypotheses grow into frameworks which can be tested against data. If anyone is skeptical that this is likely to happen, that is certainly their prerogative, and they should feel fortunate that the overwhelming majority of contemporary science is not forced to work that way. Others, meanwhile, will remain interested in questions that do seem to call for this kind of bold speculation, and are willing to push the program forward for a while to see what happens. Keeping in mind, of course, that when Boltzmann was grounding the laws of thermodynamics using kinetic theory, most physicists scoffed at the notion of these “atoms” and rolled their eyes at the invocation of unobservable entities to explain everyday phenomena.

There is also a less rosy possibility, which may very well come to pass: that we develop more than one theory that fits all of the experimental data we know how to collect, such that they differ in specific predictions that are beyond our technological reach. That would, indeed, be too bad. But at the moment, we seem to be in little danger of this embarrassment of theoretical riches. We don’t even have one theory that reconciles gravity and quantum mechanics while matching cleanly onto our low-energy world, or a comprehensive model of the early universe that explains our initial conditions. If we actually do develop more than one, science will be faced with an interesting kind of existential dilemma that doesn’t have a lot of precedent in history. (Can anyone think of an example?) But I’m not losing sleep over this possibility; and in the meantime, I’ll keep trying to develop at least one such idea.

CATEGORIZED UNDER: Science, Time
  • Peter Shor

    Sean said

    There is also a less rosy possibility, which may very well come to pass: that we develop more than one theory that fits all of the experimental data we know how to collect, such that they differ in specific predictions that are beyond our technological reach. … Can anyone think of an example?

    Do you mean something like the solar neutrino problem? For over 30 years, nobody knew whether our models of the sun’s interior were incorrect, or whether neutrinos had mass and the mass eigenstates didn’t match up with the flavor eigenstates. But remarkably, the experimentalists came through and observed neutrino oscillations.

    Or are you looking for a different kind of example.

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    Should have been more clear — there are plenty of examples where multiple models fit the data but made different predictions that we just weren’t yet able to test, but it was clear how such a test could be done. I was thinking more of examples where it was entirely unclear how the theories could possibly be distinguished, within the realm of technological feasibility.

  • observer

    Sean, do you agree that, in principle, that a new theory that truly unifies general relativity and the standard model, might not need any new experiments to verify it, and that instead, a mathematical proof that the new theory appropriately contains the two old ones would suffice?

  • frdn

    Why is John Horgan qualified to criticize theories in physics? It was painfully obvious in the diavlog that he doesn’t understand 1 thing about physics.

  • Luis

    Sean said

    There is also a less rosy possibility, which may very well come to pass: that we develop more than one theory that fits all of the experimental data we know how to collect, such that they differ in specific predictions that are beyond our technological reach. … Can anyone think of an example?

    I’m not a physicist –only a modest theoretical linguist, but nonetheless, here is something from our field (excerpt from the preface to “Compositionality in formal semantics: selected papers of Barbara Partee”). No relation to physics, but I like the anecdote.

    When Mike Flynn was finishing up, we went for a farewell lunch. During lunch he said: “I want to ask you what’s probably a really stupid question: You and Edwin Williams –it has always seemed to me that your theoretical frameworks are at odds with each other […] Are they actually compatible in a way that I just don’t see, or are they incompatible and you don’t bring up the subject for some reason?” […] We [Williams and Partee] immediately decided to co-teach Introduction to Semantics next spring […] followed by two or three weeks for debate where we would jointly try to identify some empirical prediction on which the two approaches disagreed. […] By the end, we had identified one sentence type, illustrated below, about which our theories made opposite predictions

    On whom can you depend to do the dishes?

    We asked the students about whether the sentence was well-formed with “whom” controlling the implicit subject of “to do the dishes” (i.e., on the reading “which person can you depend on such that he will do the dishes?”). When we asked the class for judgements, the class split 50-50

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    observer — that’s exactly the pickle I was speculating about above. I don’t think it would “suffice,” absent some reason to believe that no as-yet-undiscovered model were equally viable, but it would certainly be quite an achievement, one well worth working toward.

  • Ellipsis

    All true — however methinks thou doth protest a bit too much. ;)

    A clear example of “two theories” that are undifferentiable in that they give the same predictions up to essentially all imaginable experimental tests is Copenhagen interpretation vs. many worlds.

  • Anne

    I’m far from an expert, but if you’re looking for two competing interpretations for which we can’t see a way experiment will ever distinguish them, how about quantum mechanics? The Copenhagen interpretation and the multiple-worlds interpretation are wildly different, but I don’t see how they could ever be experimentally distinguished.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    frdn,

    And what are your qualifications to criticize John Horgan? Other than being one of the all too numerous juvenile cretins who think writing in to physics blogs anonymously to attack people is a good way to spend your time?

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    Peter, thanks for setting an example of high-minded discourse. Your deep concern for the tone of discussion has been duly noted, many times. If you feel a need to reiterate it further, please do so somewhere else.

    Everyone else, please try to keep the discussion on-topic and free of insults.

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    Anne, most often different interpretations of quantum mechanics have precisely the same set of predictions for every conceivable experiment, so they are not really different theories. I was wondering about theories that may differ in principle — e.g., for dynamics at the Planck scale — but give identical predictions for every conceivable experiment within our technological reach. There’s certainly no reason why two such models couldn’t exist, especially in the case of gravity where the force is so weak.

  • John Ramsden

    It’s perhaps not quite what you had in mind when asking for examples of multiple theories that fit all the physical facts, but as these theories would both presumably be expressed mathematically maybe it’s not too far off the mark…

    There are many examples in maths of more than one “rubric” being applicable to the same range of problems, with some of the latter better suited to one approach and different problems the other.

    One example would be modern(ish) algebraic geometry, where you had the analytic approach as expounded in the tome by Griffith and Harris for example and by contrast the algebraic approach of Weil and Zariski. These developed in parallel over roughly the first half of the 20th C.

    But they were pretty much united by Grothendieck’s theory of schemes, and I imagine the same would occur with the multiple physical theories – In due course some overarching formalism and abstract understanding would be developed so that both ended up under the same umbrella.

    Another example, this time within algebra, would be the theory of ideals: In the 19th century one had Kummer’s system, and then Kronecker came along and developed his theory of primary decompositions. It was only some years later that Dedekind devised the simple formalism which united both and is used today.

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    Sean,

    The question is whether you should provide a forum for anonymous insults. I gather from your comment that you intend to continue to do so, that it’s only my objections to this that you see as being worth criticizing. It’s your blog….

  • George Musser

    A sociological question: why does John Horgan continue to get any traction with his argument, considering that positivism was thoroughly discredited within science and within the philosophy of science more than half a century ago?
    George

  • Mike

    Even if a branch of physics were not empirical, that would not mean it’s theology. It would mean it’s ‘just’ mathematics. There’s a big difference between mathematics and theology. In the context of curved geometries or closed universes, there’s a question as to whether pi is an element of reality. But this is very different than the question of whether reality contains a god or not.

  • Elliot

    I, Elliot Tarabour, also believe that Horgan’s arguments are without merit. With respect to Copenhagen vs. MWI, it is not at all obvious to me that there is no way in principle to experimentally distinguish them.

    e.

  • chemicalscum

    Sean
    Anne, most often different interpretations of quantum mechanics have precisely the same set of predictions for every conceivable experiment, so they are not really different theories. I was wondering about theories that may differ in principle

    David Deutsch has proposed an experiment that may be able, when future advances in the technology of quantum computing become available, to distinguish the many worlds interpretation from any interpretation involving state vector reduction. Indeed as I remember he discusses it in “The Fabric of Reality”.

  • chemicalscum

    Sean

    corrected block quote (damn no preview)

    Anne, most often different interpretations of quantum mechanics have precisely the same set of predictions for every conceivable experiment, so they are not really different theories. I was wondering about theories that may differ in principle

    David Deutsch has proposed an experiment that may be able, when future advances in the technology of quantum computing become available, to distinguish the many worlds interpretation from any interpretation involving state vector reduction. Indeed as I remember he discusses it in “The Fabric of Reality”.

  • http://skepticsplay.blogspot.com/ miller

    I find this post extremely interesting, because I actually disagree with Sean for once. At least, I sort of disagree.

    You draw a distinction between making predictions and understanding. But if a particular understanding of a mechanism doesn’t in any way help to make predictions, what have you understood? It seems to me that you’ve understood something that has no effect whatsoever on reality, and is thus not real. I would argue that all science must in some way make predictions. These need not be the immediate goal of science, nor do they need to be practically testable. It’s also allowable to develop simpler ways to reach old predictions. “Ironic science”, as John Horgan calls it, is ok because it does make predictions, as obscure as those predictions are.

    As for that “less rosy possibility,” it’s already happened with miracles, hasn’t it? Theory: The laws of physics are time-invariant, with the single exception of two thousand years ago, when someone’s body spontaneously decayed into neutrinos and anti-neutrinos. This makes the prediction that if we went back in time, we could observe it directly, but this is untestable in practice. Quite the existential dilemma we’ve got there, huh? How do we stay sane in light of this mystery?

  • anonymous

    “There is also a less rosy possibility, which may very well come to pass: that we develop more than one theory that fits all of the experimental data we know how to collect, such that they differ in specific predictions that are beyond our technological reach. … Can anyone think of an example?”

    The Continuum Hypothesis in Math.

  • anonymous

    woops… the quote in the above post should be this one:

    “If we actually do develop more than one, science will be faced with an interesting kind of existential dilemma that doesn’t have a lot of precedent in history. (Can anyone think of an example?)”

  • observer

    Re: Sean#6, Me#3, Not to nitpick, Sean, but actually my pickle was intended as a subpickle of your pickle.

    Re: John Ramsden#12, the difference is that in mathematics it is usually clear that a unification or generalization has been found, or at least it can be proved, while in physics you also have to contend with the connection between model and reality for each of the old and new theories.

    On a practical level, it seems most theories don’t have such lofty ambitions as to unify GR and SM, but at the same time they still manage to be theoretically robust enough to stick their neck out and make a falsifiable prediction. There are exceptions, of course.

  • HB

    Sean,

    At around 10:30 you said “… the amount of curvature will grow …” I thought K(t)=k/a(t)^2 meant that amount of curvature wouldn’t grow. What am I missing?

    HB

  • John Merryman

    Here is one I’ve raised a number of times; If time is a fundamental dimension, than physical reality moves along it from past events to future ones, but if time is a consequence of motion, than events are caused by this motion and proceed from future potential to past circumstance. So does time go from past to future, or from being in the future to being in the past?
    (Does the rotation of the earth proceed along the passage from one day to the next, or are days the consequence of the rotation of the earth and go from being in the future to being in the past?)

    a black box which will correctly answer any well-posed empirical question we ask of it.

    Reminds me of the old “What would a real guy do?” joke;

    If an alien came down to earth and gave you a black box and said it would save humanity from future calamity, would you; 1) Give it to the President? 2) Give it to the Pope? 3) Take it apart and figure out how it works?

  • http://www.math.columbia.edu/~woit/wordpress Peter Woit

    George,

    Painting John Horgan (or Steven Weinberg, or just about anyone else) as a pure positivist is just a way of trying to not deal with the real issue here. Some parts of particle physics (string theory) and some parts of cosmology (the multiverse) just inherently don’t predict or explain anything (using “explain” in the scientific sense, which carries with it a requirement that your explanation of how the world works be testable by experiment). The amount of attention and effort that has gone into such theories over the last quarter century is remarkable and very unusual in the history of science. Horgan more than ten years ago was one of the first science journalists to notice that something funny was going on.

    As more and more time goes on, and some serious physicists start engaging in more and more speculative behavior, getting farther and farther from any hope of testability (see, the Landscape and the multiverse), the argument that there’s a problem here is getting more and more traction. Among serious physicists these days, I don’t think this is even any more a very controversial claim, with many of them prepared to admit that parts of the subject are in a bit of a crisis.

    Horgan’s complaints about inflation are somewhat more unusual, and Sean is right that for the general idea there is serious circumstantial evidence. But even there, Horgan has a point and some versions of inflationary cosmology have serious problems with the question of testability.

    Horgan’s truly controversial views are not in this area, but in his arguments about the “end of science”. For those, he definitely does have trouble getting traction, especially among scientists, who pretty uniformly believe that what they are doing is not at an “end”, or they wouldn’t be doing it….

  • MedallionOfFerret

    I watched the whole thing. Sean was persuasive, in what I’ve always been trained to believe is the best possible connotations of the word persuasive. I Thank him for the experience.

    Whether or not John Horgan does, or does not, “…understand 1 thing about physics” he does a good job of setting up questions that could be answered, and following up answers with other questions that could be answered. He misses sometimes but not often. He got good answers even when he missed. It would be hard for anyone watching the video and trying to understand it to be able to come away more confident that Horgan’s opinion of modern cosmology as science is the superior one.

  • Spencer

    Sean,
    I think you do a superb job arguing that theories are necessary, but I’m not sure that addresses the argument about observability. While you are right that we can’t rely purely on empiricism and experiments, that is an extreme form of the argument you are opposing.
    “If making predictions were all that mattered” is a flimsy straw man. The stronger argument is that “all theories need to be testable,” which is slightly different. You explain why “just experiments” is a bad framework in response to the criticism that “just theories” is bad, but “experiments and theories” is still clearly superior to “just theories.” That’s the argument you need to be more worried about – that modern theories have no room for experiments at all.

  • spaceman

    Sean,

    You mentioned the discovery of density fluctations larger than the observable Universe as a piece of evidence which supports inflation. Doesn’t this discovery also mean then that, by definition, the Universe cannot be smaller than the horizon distance e.g. with an observable non-trivial topology?

  • http://www.website.com Amanda

    “Sophomore-level philosophy of science” — ha ha!
    Well said.

    What is really funny here is that Horgan poses as this hard-headed Popperian who is amazed and appalled by things like multiverse theories and inflation, while at the same time writing Templeton-style books like “Rational Mysticism: Dispatches from the Border Between Science and Spirituality”. I’m sure that his mystical experiences have been subjected to experimental test, right? What a phony.

    What is not so funny is that he is being given an absolutely world-class tutorial in how *real* scientists think, and he clearly isn’t listening; instead of saying, if only to himself, “wow, I am really lucky to be having the numerous gaps in my education plugged by a real pro!” he just goes on whining the same old boring story about non-verifiability.

    About inflation: last year I had the pleasure of speaking to one of the True Fathers of Inflation, and I asked him whether,25 years ago, people argued about the potential verifiability of inflation. The result was a peal of Homeric laughter. “Never in our wildest dreams did we expect inflation to be related to actual observations!”

    About multiverses: since late 2006 there has been a stream of papers about possible observational signatures of bubble collisions. Whether this will pan out is of course something that nobody knows yet, but it puts an end to the claim that multiverse theories are not verifiable *in principle*. Horgan can perhaps be excused on the grounds of ignorance, but Peter Woit has no such excuse, since he was informed of this work by Anthony Aguirre. I guess this fact just slipped his memory. I guess.

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  • http://www.stevens.edu/csw John Horgan

    Sean, great followup post to a great chat. As I just acknowledged on my Stevens blog, you do a superb job defending the scientific status of inflation, multiverses, the anthropic principle and so on. The dialogue worked just as I hoped it would. Given the comments here and at Bloggingheads.tv, viewers clearly found your perspective more persuasive than mine. Indeed, you’re so damn reasonable that I find myself doubting my doubt. On the other hand, I often have this same feeling when I’m talking to an extremely intelligent, well-informed person–Francis Collins or Simon Conway Morris or John Barrow–who believes in a God who loves us or in the resurrection of Jesus. I know this is one of my rhetorical cheap shots–comparing multiverse theories to theology–but I mean it. I find myself wondering in both cases, How can this person believe these things that I find so incredible? What am I missing? I have no choice but to cling stubbornly to my skepticism, even though I don’t find it very satisfying. And I hope one day you guys find something to make me a believer.

  • observer

    There’s a difference. There’s a trace of a flimsy theoretical basis for believing in multiverses. But there’s no theoretical basis whatsoever for believing in gods.

  • Lawrence B. Crowell

    Physics has a long history of appealing to things not observable. Newtonian gravity has these 1/r^2 lines of force which are not directly observed. Some physicists in the 18th century got snagged on this issue. Even our first physics equation F = ma equates a dynamical quantity called force with a kinematical (geometric) quantity called acceleration times a scalar quantity determined by a scale, which measures a force. This little equation is curious in some ways, with a circularity to it or which requires some “given” quantity called mass. The hidden variable theories of quantum physics are of a similar vein with hidden lines of force. We only measure the consequences of these things. These are in some sense model systems which are used to compute certain relationships between particles. In some sense epistemology preceeds ontology.

    The interest in pushing beyond the standard model has a number of sources. One is that the theory is a twisted bundle construction which somewhat artificially sews together the electromagnetic and weak interactions. This requires that a wide ranging set of parameters be set or adjusted to fit the data. We also have the little problem that gravity sits outside the picture. I know a couple of people who say that maybe gravity is not quantized. This might be the case if we existed in Fred Hoyle’s steady state universe. Yet if we know anything about cosmology it is this is falsified. So at some early phase in the universe, at the big bang, the fundamental forces of the universe appear to be “folded” together in some way. Further, they are likely folded together within a quantum framework.

    The observable universe gives us information, where as the fundamental structure unravelled it has left certain “clues at the scene of the crime.” We detectives look at these pieces and try to reconstruct the physics of this ultimate scattering experiment. We duplicate small low energy aspects of this with accelerators and detect the “bits and pieces” with hadron calorimeters, and we look out into the distant universe to detect the grand scale result. Ideally we want to put these two pictures together. If the two pictures do not come together then the universe is a symphony orchestra playing Prokofiev and Bach at the same time. It is for this reason that while the standard model SU(3)xSU(2)xU(1) is spectacularly successful at describing TeV physics it clearly is limited.

    Physics will always have epistemological quantities which are not observable, as it always has. A successful theory of physics is likely to be one which requires a minimum of such unobservables and what might be called metaphysical assumptions or postulates.

    Lawrence B. Crowell

  • ike

    Belief: Mental acceptance of and conviction in the truth, actuality, or validity of something.

    Theory: A set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena.

    A big difference between science and religion is that scientists often use the “multiple working theories” approach, while theologians tend not to use “multiple working beliefs.” Some scientists, sadly, develop great emotional and psychological ties to some specific theory that are as fervent as any religious belief, and which they are just as loath to discard.

    This fact, in turn, leads to the common insult that such-and-such a scientist is a fervent true believer, not a “hard-headed empiricist.” This is the kind of genteel trash-talking scientists often engage in, which is less than useless. What’s next? I sure don’t want to start hearing about “liberal science” vs. “conservative science”, any more than I want to hear about “German science” vs. “Jewish science.”

    But enough about that. Consider predictability as the test of a theory – in the era before quantum mechanics, some people (Laplace) predicted that if enough information was known about the current state of the universe, the exact pathway of its future development could be calculated from the laws of motion and forces.

    We now know this to be false. Chaos, or sensitive dependence on initial conditions, is a feature of both mathematics and nature (and is the reason why no one will ever be able to predict the specific weather a month in advance). Quantum mechanics also introduces uncertainties. No one can predict exactly when a specific atom of carbon-14 will emit an electron and an anti-neutrino and turn into a nitrogen atom.

    Thus, the whole notion of what it means for a theory to make “good predictions” has itself changed. What if someone comes up with a set of equations that unify general relativity and quantum mechanics, and finds that the equations are chaotic and are not useful for making any predictions – what then? That’s a bit different than a theory that makes a prediction that can’t be tested except in a black hole-powered particle accelerator.

    (By the way – that beta decay, as in 14C -> 14N, led some scientists of the day to propose that conservation of energy and momentum was wrong – but Fermi then proposed a new particle to account for the missing energy – the neutrino – in 1930 – which was then observed in 1956. Was Fermi a dreamer? Were the experimentalists (Cowan et. al) “hard-headed empiricists”?)

  • snoopy

    I was wondering about theories that may differ in principle (…) but give identical predictions for every conceivable experiment within our technological reach.

    Imagine a theory along which each black hole contains a universe, and our observable universe is itself in a black hole (no communication allowed, nor pink hair).

    Imagine a second version of this theory that gives the same prediction for our universe, but gives no cue on why our universe exist.

    Is that the kind of situation you were thinking about?

  • Elliot

    Gee Sean,

    Now Mr. Horgan is giving equal weight to scientific and theological arguments, as long as they are presented by an intelligent person. Because they are both “almost” convincing.

    As we said in Law school “res ipsa loquitur”

    e.

  • Dany

    Sean,

    When we will have the adequate unified field theory of the fundamental interactions and if we will have at least two apparently different versions, then we will be in a glorious position to discuss whether they are equivalent or not.

    Meanwhile, we are in situation that some physicists are doing physics and the others talk that the solution doesn’t exist (or, equivalently, there are infinite amount solutions of the same problem). As an illustration, you may use the collection of papers “The Physics of Quantum Information”, Springer-Verlag,2000, (ch. 4,5) where the results of the investigations of A.Zeilinger et al presented side by side with the single “conceptual” (????”?) paper by D.Deutsch and A.Ekert. The later contains completely wrong description of Mach-Zehnder interferometry. In addition, it is transparent that the writers have no idea what they are talking about (4.1.2; absence of basic knowledge of QM; you will enjoy reading it).

    I guess that the hierarchy of competence in the discussed by you questions is going as following: physicist -> mathematician -> philosopher ->journalist -> computer “science” engineer -> physicist (LQG). I guess that the problem is simpler than as presented by you: it is ignorance vs knowledge and understanding. What I said doesn’t contradict the fact that D. Deutsch is outstanding computer science engineer.

    Regards, Dany.

    P.S. Since D. Deutsch is not a physicist, he doesn’t know that the physics is the infinite set of the solutions of the mathematically “unsolvable” problems.

  • Richard E.

    I must watch the blogging heads thing, but sadly I am in the middle of debugging some codes which are designed to impose observational constraints on a whole class of inflationary models.

    But it certainly sounds interesting!

    R.

  • http://www.crank.net/physics.html Ian B Gibson

    Gee Sean,

    Now Mr. Horgan is giving equal weight to scientific and theological arguments, as long as they are presented by an intelligent person. Because they are both “almost” convincing

    Nope. Read his comment again – he’s saying the arguments in question are not scientific arguments.

    That’s his whole point, in fact.

  • Lawrence B. Crowell

    On the subject of multiverse(s), and God I hate that term, I think these are in the Hawking-Hartle path integral certain configuration variables (metrics) for eigenstates of the wave functional. There is one configuation variable who’s eigenstate amplitude became near unity in a decoherence, where correspondingly the amplitude for the others became zero or “epsilon.” The configuration variable for the amplitude which became unity describes the classical universe we observe. The “other universes” are tiny fluctuations in the spacetime configuration with some small overlap with these other near zero amplitudes.

    I don’t particularly buy this idea there is some plethora of cosmologies. First off I think this is too easy a way out. I think it better to address the question of why our cosmology was einselected from the path integral to have a classical structure. Maybe better put, how is it that the wave functional or path integral for the quantum cosmology entered into a self-decoherence so that one amplitude emerges at near unity with a metric that is einselected as a classical-like configuration variable? What role does the structure of elementary particles play in this selection of a unique quantum state? In this way we are faced with answering the hard problem. In contrast there is too much in the way of multi-cosmological arguments that there is a vast number of them and so ours is an inevitable outcome. This is matched in its intellectual fatuousness by the so called Anthropic principle, which in the weak form really has to be seen as a question. Using the AP as a “solution” in physics is to me begging a question.

    There are two ways of looking at this. One is that a superposition of cosmologies mixes points on manifolds so that there are non-trivial toplogical connections between points, or where a spin field exists. In this way there is in the path integral of possible configurations a combinatorial network of spinor fields, which is what is the “spin-foam” or causal net common to Lopp variable LQG. The metric which is einselected for is that which has the minimal topology or which is simply connected. An alternative approach is to think of a cosmology which is einselected is that which has conformal fields which are commensurate with the conformal AdS infinity. Thus there must exist BZT/BPS black hole structure which provides the additional boundary conditions. The “data” is contained on strings coupled to the dual brane, which I think is isomorphic to the above situation with the spin foam. In other words two spin fields with multiple topologically inequivalent paths attaching them is equivalent to a brane charge determined by the orbifolding of a string.

    I am not biased against either string or LQG, and I suspect the two are different views of the problem. But in what comes I suspect that the “multi-verse” needs to be reduced to a universe, and that how the universe we observe is structured is one which is consistent with the conformal start and endpoints of the HH path integral.

    Lawrence B. Crowell

  • observer

    Define multiverse.

  • Lawrence B. Crowell

    Multiverse: a system which contains many universes. Often these are presumed to exist in the same way our observable universe exist, but with different gauge coupling constants or with entirely different gauge theories depending upon how the E_8xE_8 group is decomposed.

    Lawrence B. Crowell

  • Elliot

    Ian,

    Granted that the multiverse and landscape are highly speculative, but inflation is clearly within the realm of scientific falsifiability. To equate inflation with belief in the resurrection of Jesus is simply nonsense.

    In my entire life, there have only been 2 or 3 books where I felt like I deserved a full refund. “The End of Science” was one of them.

    e.

  • observer

    Elliot

    I found a copy of “The End of Science” in an abandoned box outside a door. I thought it was okay except for the bits where it says Science is coming to an End.

    Lawrence B. Crowell

    That’s a very narrow definition of “multiverse” (and incomplete, since you don’t say how the universes are connected).

    There seem to be so many concepts or multi(or similar prefix)verse. I find most of them to be completely ridiculous, though I’m sure one of them is true. Has anyone classified these concepts, or tried to develop consistent terminology that distinguishes them?

  • http://voicesofreason.info Neil B.

    I am curious about just what sort of “theoretical justification” there might be for other universes in a multiverse. I can imagine a concept like strings, that can underly phenomena and to some extent “explain laws” (well, the strength of gravity and some other things.) But even that foundation has to have something behind it, some properties or principles. If e.g. strings are fundamental, then you can’t explain their properties the way you can the properties of a “real string” made of an elastic material, the latter being made of constituent atoms. You might be tempted to think some properties are just logically natural (?), but no one should be fooled (or fool other people) into thinking the explanatory discussion can simply be borrowed as an analogy. If the laws of strings are taken as a “given” then we have all the wonderful ruminations about why couldn’t they have been otherwise, since other ways to be are “logically possible” etc. In any case, it is not clear how to find the laws of what undergirds laws, how do you get that off the ground?

    Well, the latter train of thought often leads then to the multiverse, given the idea that different ways to be are in fact instantiated (or at least, could be or could have been.) Then I wonder, what rigor or real understanding underlies the notion of the metaspace or whatever that holds the various universes. We have “space-time” and the things we know of are confined within it, per the customary illustrations of bugs on rubber sheets etc. But really, aside from just talking about it that way, what constitutes the bounding of one space within another of more dimensions? I asked Bee how the “skin” of one empty space could be floating inside another space with more dimensions. I wondered how the domain of the lower-d realm was actually demarcated and separated from the other one, since they were both “space” – it isn’t like a bubble of air in water, etc., or is it? Just drawing diagrams and imagining a locus of points doesn’t justify or explain the holding of known phenomena within a limited manifold inside another one, when both are intrinsically “empty” except for any required quantum virtuality. Her answer didn’t really satisfy me, although likely a good shot in terms of what anyone could say given what we know. Below is the question/response, from http://backreaction.blogspot.com/2008/03/talk-like-you-want.html:

    Neil: How can it be like a “skin” IOW when its emptiness within emptiness, so to speak.

    Bee: Define ‘emptiness’. The brane is a distinguished sub-manifold (the skin) in the higher-dimensional space. It’s where particle interactions (with exception of the graviton) take place if you want to put it this way.

    Well, OK, “distinguished” how?

  • Lawrence B. Crowell

    I never read the end of science, for a number of reasons. I think that science will of course end, and it could well end with the end of the human race. I have some reasons to suspect our existence into the future may be rather short. I also suspect that if our species exists many thousands of years from now people might be living in a sort of neo-stone age, as they come up with stories of gods who built these strange landscapes filled with these odd items made of plastic, steel, wire and glass. Science for all we know may be a sort of passing cultural system or paradigm for civilization, just as cultural motifs from the past eventually come to an end.

    The multi-verse or the landscape is some sort of artifact of how modern physics, in particular string theory, appears unable to constrain itself. Maybe I am wrong or a bit too conservative, but I doubt that there are these other cosmologies which exist in the same way our observable universe does. Further, even if they did exist I doubt they have any measurable consequence within our universe. Given there these cosmologies are achronally connected I doubt we can measure anything about them. With cosmology we have only one scattering experiment from which to detect information. This of course makes quantum cosmology rather different from standard QM, which has various postulates about pure states and identically prepared systems. We likely have no other system from which we can compare data with other than the low energy results we observe from the one great vacuum scattering event called the big bang.

    Lawrence B. Crowell

  • John Ramsden

    observer wrote (#44):
    >
    > There seem to be so many concepts or multi(or similar prefix)verse. I find most of them to be completely ridiculous, though I’m sure one of them is true. Has anyone classified these concepts, or tried to develop consistent terminology that distinguishes them?

    “Universe or Multiverse?”, Bernard Carr (ed), Cambridge, 2007, ISBN 978-0-521-84841-1

  • Michael T

    Thank you for that Lawrence. So much of the dialog on this site is outside most readers experience and education (of course mine). It is a pleasure to read your posts and get some sense as to the fundamental issues at hand in a most comprehensible way. And keeping with the spirit, much gratitude to all of the learned minds at work. You know we just don’t say thanks as much as should.

  • http://www.website.com Amanda

    Horgan said: “Indeed, you’re so damn reasonable that I find myself doubting my doubt.”

    OK, I take it back. He *was* listening. Dare we hope that he will henceforth refrain from referring to the work of brilliant, honest people as “bullshit”?

  • http://www.pipeline.com/~lenornst/index.html Len Ornstein

    Sean:

    I just listened to your conversation with Horgan. Although I’m one who has low expectation that concentration on unobservables (beyond event horizons, superluminal velocities, anthropic landscapes, multiverses and string theories), will contribute to further understanding, I found almost nothing that you said with which to disagree.

    I think the problem is mainly semantic, and levels of emphasis:

    In science, all speculations, hypotheses and theories are ‘only’ models. And science requires that a model must pass observational tests, with some significant degree of confidence, to be useful as a tentative acceptable (useful) description of ‘reality’.

    “Prediction”, “understanding of mechanism” and “explain”, are logical ‘consequences’ of the structure of models. Therefore, in science, all are understood to require the reality checks of some kinds of observations, to be deemed meaningful.

    So the small differences between you and me, you and Horgan and you and Woit, are mainly related to how much patience we each have (based on our different levels of experience and of confidence in the record of experimental and observational science) to wait for the possible coming together of the “larger framework that will hopefully be testable” (your words to Horgan).

    I think we all are ready, at least tentatively, to ‘accept’ unobservable entities, WITHIN models, that none the less ‘make’ previous and/or new observations ‘fit together’ better than they do in previous models.

    What mainly differs are our levels of skepticism – AS TIME GOES BY – that particular unobservables will turn out to be useful.

    Len

  • crustle

    I am an example of the person Sean discusses in his conversation with Horgan – a layperson who finds cosmology fascinating, and who will listen to experts in the field with rapt interest. For what it’s worth, I do not believe in god, and I certainly don’t think cosmology is theology. I appreciated this conversation, however, since I have friends who have had discussions like this one, and it was wonderful to listen to someone as brilliant as Sean break down certain arguments at length. Thanks for the wonderful, provocative post.

  • mathandphysics1

    I think John Horgan can’t read
    from wikipedia article on science

    “Mathematics, which is sometimes classified within a third group of science called formal science, has both similarities and differences with the natural and social sciences. It is similar to empirical sciences in that it involves an objective, careful and systematic study of an area of knowledge; it is different because of its method of verifying its knowledge, using a priori rather than empirical methods. Formal science, which also includes statistics and logic, is vital to the empirical sciences. Major advances in formal science have often led to major advances in the physical and biological sciences. The formal sciences are essential in the formation of hypotheses, theories, and laws, both in discovering and describing how things work (natural sciences) and how people think and act (social sciences).”

    He should really study Dirac

  • Celestial Toymaker

    I was interested in Sean’s view, expressed in the Talking Heads discussion, that the evidence for Inflation isn’t as solid as is often assumed.
    Since he’s not known to be a crackpot, it might be useful to list the main reasons for this mild scepticism.
    Maybe in a separate thread?

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    CT, it’s not that “evidence for inflation” isn’t as solid as is often assumed, it’s that (in my opinion) the underlying theoretical justification isn’t as solid as many people like to think. Roughly, inflation solves the fine-tuning of the early universe by assuming that it was even more finely-tuned. I’ll write more about it if I get the chance.

  • http://countiblis.blogspot.com Count Iblis

    Isn’t fine tuning impossible to avoid given the fact that entropy was much lower in the past and any explanation for low entropy initial conditions in terms of fluctuations in an earlier more typical high entropy state leads to the Boltzmann Brain paradox?

  • WildGhost

    Sean: “… all of these crazy speculations about the multiverses and extra dimensions originate in the attempt to understand phenomena that we observe right here in the nearby world.”

    Alright, I’m going to say it…

    Modern physics evolved from the 4 dimensions that were defined by our experience. None of the additional dimensions that have hitherto been postulated by mainstream physicists in an attempt to explain certain observations have reflected anything that we experience.

    If we are going to start adding dimensions, doesn’t it make sense that they be dimensions in the same sense as the first four – dimensions that reflect experience? And if we are going to try to use those dimensions to solve physics problems, doesn’t it make sense that we first have to understand what it’s like to experience that dimension?

    I’m just saying…

    From wikipedia entry on the 5th dimension – “It has occasionally been stated the Fifth dimension is probability, meaning that the fifth dimension is the full amount of possibilities that could happen or, in other words, alternate realities.”

    How about it, Sean? What about the idea of another dimension that can actually be experienced?

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    Modern physics evolved from the 4 dimensions that were defined by our experience.

    Have you ever experienced an atom?
    Have you ever experienced noncommutativity of observations?
    How about spacetime curvature?
    Vacuum polarization?
    Quark confinement?

    Modern physics is almost entirely about stuff that is not part of your experience.

    Quantum mechanics, relativity, quantum field theory, … are all subjects which are tremendously counterintuitive, precisely because they deal with phenomena far removed from our ordinary experience (and hence our intuition, built on that experience, fails miserably when applied to them).

    None of the additional dimensions that have hitherto been postulated by mainstream physicists in an attempt to explain certain observations have reflected anything that we experience.

    Expecting Modern Physics to reflect things that we experience is to entirely miss the point.

  • Lawrence B. Crowell

    Sean on Mar 17th, 2008 at 2:39 pm

    CT, it’s not that “evidence for inflation” isn’t as solid as is often assumed, it’s that (in my opinion) the underlying theoretical justification isn’t as solid as many people like to think. Roughly, inflation solves the fine-tuning of the early universe by assuming that it was even more finely-tuned. I’ll write more about it if I get the chance.

    ——————

    I’d tend to second this. The exact model is unknown, but the basic scheme is approximately correct. The inflation of the early cosmos by a Higgsian inflaton that shoved the universe from a false vacuum to a real vacuum appears to fit within astronomical data. What we don’t know is what model this works within, what this has to do with quantum gravity and so forth. It is like Darwin, he got the evolutionary scheme more or less on the mark, but lacked the biological underpinning of it called the genetic code.

    Lawrence B. Crowell

  • Elliot

    Random Speculation: Since the mechanism(s) for inflation and dark energy are both unknown but both cause what appears to be an expansion in the cosmos, is there a possibility that they are phenomenologically related or is this ruled out by the data?

    e.

  • Thomas Larsson

    Quantum mechanics, relativity, quantum field theory, … are all subjects which are tremendously counterintuitive

    but necessary to explain experiments. Contrast this to supersymmetry, which get increasingly disfavored by experiments as time goes by.

    Interestingly enough, Paul Steinhardt seems to think that inflation is incompatible with string theory. Since Steinhardt is a world-class scientist, maybe one should pay attention.

  • mathandphysics1

    “Since Steinhardt is a world-class scientist, maybe one should pay attention”

    Note: The following comment isn’t intended to pick on Dr Steinhardt.

    Their is an elitist fallacy that seems to continuously permeate academia as well as physics that if you don’t have a Ph.D. or tenure (or a bunch of papers that have been cited in other work); that you are an imbecilic cretan.

    There are a lot of smart people that have full comprehension of the issues involved in physics (and other fields of science) but for various reasons have either chosen not to pursue a Ph.D. in physics, or were not allowed to by circumstance.

    Now, my previous comment aimed at Mr Horgan hopefully was taken in jest (if not, then now you know to take it in jest); and although I disagree with the man, he obviously is intelligent enough to participate in a legitimate way and highlights a significant point.

    The point is that most people, including many naive “scientists”, are not what they think they are. Karl Popper is perhaps the person who has best described the current popular philosophical approach as “critical rationalism”; and is the point of view of supported by John Horgan’s arguments.

    http://en.wikipedia.org/wiki/Karl_Popper
    http://en.wikipedia.org/wiki/Critical_rationalism

    Sean, on the other hand, is promoting “logical positivism”; which was the philosophy advocated by the Vienna Circle, and is the dominant view enshrined in theoretical physics (and string theory).

    http://en.wikipedia.org/wiki/Logical_positivism
    http://en.wikipedia.org/wiki/Vienna_Circle

    Personally, if forced to choose, I would consider myself a “logical positivist”; however, I don’t think I am required to adhere to any one philosophy at any one time, and I will choose whichever is convenient to support whatever particular argument I choose to make.

  • http://smearland.blogspot.com/ WildGhost

    #57 – I think you missed my use of the words ‘evolved from’. No one disputes what modern physics is now.

    “Expecting Modern Physics to reflect things that we experience is to entirely miss the point.”

    Except that it’s not. Too many aspects of human experience are unsatisfactorily explained by modern physics. If anything, human experiences points to things that call the current interpretations of modern physics into question. (Don’t get me wrong; right now, I’m really picking at only two points – the idea that the collapse of the wave function reflects something permanent and irreversible, and the idea that state selection is random. I think that there is a range of human experiences that shows us that it’s not.)

    One more thing before I duck and run for cover… I think this is, at least somewhat, Horgan’s point – modern physics, for the most part, is not adding to our understanding of our experiences. If we cannot add to that, then perhaps science really is ending.

  • Lawrence B. Crowell

    Elliot on Mar 18th, 2008 at 12:25 am
    Random Speculation: Since the mechanism(s) for inflation and dark energy are both unknown but both cause what appears to be an expansion in the cosmos, is there a possibility that they are phenomenologically related or is this ruled out by the data?

    e.

    The early inflation of the universe and the current “eternal inflation” of the slow acceleration of the universe are obviously related in some way. They are likely due to a dilaton, say in conformal gravity SU(2,2) (or SU(4) ), which both contain the deSitter SO(4,1) and Anti-deSitter SO(3,2) groups. The deSitter cosmology has an event horizon at

    $latex
    r~=~sqrt{Lambda/3}
    $

    for the cosmological constant Lambda about 10^{-54}cm^{-2}. This is inducing the acceleration in a way analogous to a black hole horizon. The very early universe had this cosmological constant vary according to some scalar field so that

    $latex
    Lambda~=~Lambda(phi,~{dotphi})
    $

    and this scalar field is probably somehow related to the dilaton field of the current eternal inflation. In fact the inflationary universe was deSitter-like in all probability. So there must be some set of scalar, Higgian fields that act as dilatons and inflatons.

    Lawrence B. Crowell

  • http://golem.ph.utexas.edu/~distler/blog/ Jacques Distler

    the idea that the collapse of the wave function reflects something permanent and irreversible, and the idea that state selection is random. I think that there is a range of human experiences that shows us that it’s not.)

    I can’t think of any human experiences that involve quantum superposition. So I’m not sure we can trust any intuition from our experience about the proper interpretation of such phenomena.

    (The whole reason why “Schrœdinger’s cat” sounds so paradoxical is that quantum superposition is totally alien to our, and our feline friends’, experience.)

    One more thing before I duck and run for cover… I think this is, at least somewhat, Horgan’s point – modern physics, for the most part, is not adding to our understanding of our experiences. If we cannot add to that, then perhaps science really is ending.

    That’s a logically defensible position. I just think it’s wrong. The purpose of science is to understand how the natural world works, not just that small bit of it that is directly the subject of our experience.

  • Elliot

    Lawrence,

    Thank you for taking the time to characterize this is more a more precise scientific description.

    e.

  • John Ramsden

    Lawrence B Crowell wrote (#40) :
    >
    > I don’t particularly buy this idea there is some plethora
    > of cosmologies. First off I think this is too easy a way out.

    Yes, it seems to go against Occam’s Razor. But it is more in keeping with an infinitely recursive structure, and many find this “no first causes” idea more satisfying than a single large cosmos popping out of essentially nothing purely by chance.

    It’s fairly clear in general terms how dark energy might drive a cyclic cosmic evolution, in conjunction with the mysterious opposing force discussed on this very forum only a week or two ago (the “sideways vector field” Sean described).

    I’ll summarize this briefly below, *and* suggest how the fine tuning required for it to work could constrain constants in existing models and thus make it accessible to experiment.

    First a crude analogy of waves breaking on a flat beach. Please don’t take it too literally, or fear I may! We all know how this works – The wave rears up and over in shallow water, is accelerated downward by gravity and after breaking continues up the beach getting flatter and slower until it stops and then draws back. Note that this undertow, which helps shape the next wave, is in a sense tangential or “dual” to it. Note also that in racing up a stony beach and then receding, a wave “grades” the pebbles, in decreasing size toward the shore.

    In the distant future, most mass-energy will end up in black holes, and those surviving will over vast times have evaporated until their temperatures are comparable to the ambient temperature and are therefore equal in mass.

    The model I sketch requires that the expansion eventually slows to a stop and goes into reverse, and the fine tuning referred to above demands that some black holes survive intact until this stage (see below).

    Once the universe starts contracting, the background temperature rises and the continued survival of black holes is thus assured. Also, to reset the entropy clock for the next cycle, the black holes reduce their collective degrees of freedom by joining in symmetrical open and closed chains, which I identify with strings.

    (The work of Douglas, http://arxiv.org/abs/hep-th/9608024 if I haven’t misunderstood it, suggests that branes comprise compacted strings. That being so, why can’t a string be a chain of branes, identifying the black holes’ event horizon as a brane? Believing in an infinite heirarchy of structure, I don’t buy the notion of strings being fundamental objects! For example, in some respects a crystal fracture boundary behaves like a string; but that isn’t fundamental is it?)

    Anyway, if anyone is interested, I have a paper proposing exactly how black holes could form and maintain these symmetric assemblies, without either combining or falling apart. I propose this works by a combination of frame dragging, and the holes ejecting via polar jets a portion of the energy made available by the shrinking universe. Of course the energies involved are miniscule, but this works over vast timescales.

    During the contracting stage, the next Big Bang takes shape by duality which by some means combines AdS/CFT, Scale Factor, and Time-Temperature dualities. Assuming this is akin to a Fourier transform between suitable domains, an uncertainty principle follows naturally. (So we are not in kooksville, with black hole assemblies directly playing the part of atoms in a “larger” universe and so on!)

    Specifically, the AdS/CFT aspect of the duality means that energy quanta in the emergent universe correspond to equal-mass black holes in the contracting universe, and mass in the emergent universe corresponds by duality to radiation. Also, one assumes the duality accounts for the discrete spectrum of possible fermion rest masses (perhaps corresponding to a discrete spectrum of possible closed black hole assemblies?)

    Clearly this model is driven in part by exterior forces, and is thus not a perpetual motion engine: dark energy corresponds to gravity on our abstract higher dimensional “sea shore”, and the sideways vector field Sean recently discussed corresponds to the opposing force of the “shore” itself.

    One obvious objection to the model is that in each cycle essentially all mass-energy is packaged into units many orders of magnitude larger than the Planck units the mass-energy originally comprised, probably hundreds of billions of solar masses, which suggests the cycle must soon “run out of steam”.

    There are at least two ways round this – Firstly if the number of Planck units is infinite, then dividing that number by a finite scaling factor still leaves an infinite number of black holes. I must say for various reasons I don’t find that explanation at all satisfying, especially the assumption of an infinite number of Planck units.

    However, I was amazed when two or three people in this thread have mentioned that the Many Worlds interpretation is respectable, and actually equivalent to QM. I had somehow previously formed the impression it was generally considered a marginal idea at best, and it always seemed to me an absurdly extravagent way for the Universe to behave!

    But a Many Worlds interpretation could be just what is needed to keep the supply of black holes steady between alternating dual cosmic generations, although the vast numbers involved defy the imagination.

    Every parallel universe that, loosely speaking, forks off “ours” must evolve in the same way to little more than a collection of remnant black holes, and in the asymptotic stages where everything flattens out who is to say that the parallel universes might not reconverge?

    Note also that in the extended stage each black hole may be causally disconnected from any others, so no observer at any given location seeing a neighbouring hole come back into view as the recollapse got underway could be sure that this hole had always been in the same cosmos! Related to this is the question of more than 3 space dimensions, which for lack of space I haven’t discussed (along with several other considerations).

    But in parting here’s one more thing to ponder. The alert reader may have noticed a similarity of this alternating dual model with none other than photons. And who knows, although photons can be adequately modelled by dual electric and magnetic fields or “sum over histories” integrals, perhaps intrinsically (and of course far beyond our ability ever to observe even in principle) they have a more fractal structure and evolve internally in a manner somewhat resembling the model we have described.

    One final note, for fellow amateurs reading this and who may not be exactly clear on what “duality” means: It is an alternative consistent arrangement of the whole, rather like those ingenious pictures that show, say, a bowl of flowers and are then seen to show at the same time an old man’s face. Al Seckel has a website devoted to these at http://www.illusionworks.com/ .

    Regards

    John R Ramsden (jhnrmsdn at yahoo co uk)

    2008-03-19

    P.S. I was very sorry to read that Arthur C Clarke died this morning, at the age of 90.

    Among other things, it means he’ll miss the forthcoming film of his book “Rendezvous with Rama”, due out next year.
    ( http://www.rendezvouswithrama.com/ )

  • http://www.website.com Amanda

    Sean C rashly said: “I’ll write more about it if I get the chance.”

    PLEASE DO SO!!!!! I think that this is one of the most important misunderstandings in the community: that inflation somehow solves the problem of initial conditions. A lot of people find this belief very comforting, and refuse to examine it despite the fact that it is such a bizarre claim. It’s high time they were disabused.

  • John Merryman

    Wild Ghost,

    If anything, human experiences points to things that call the current interpretations of modern physics into question. (Don’t get me wrong; right now, I’m really picking at only two points – the idea that the collapse of the wave function reflects something permanent and irreversible,

    Not if time is a consequence of motion, rather than the dimensional basis for it. If it is motion causing events, such as the rotation of the earth causing days, then the arrow of time goes from future to past, so the wave function is future potential collapsing into past circumstance.

  • Dany

    Paradoxically, the discussion here focuses on the area of the research in physics where the tremendous progress had place in last 30 years. It was triggered by R.P. Feynman (as usual) at 1982. The main difference compare with the “fathers” was the real life realization of the gedankenexperiments. It allows us to experience not only single atoms (known about 100 years) but to see a picture of the single electron. Moreover, we may not only to see the final result but to follow the process of the acquisition of the knowledge.

    With respect to observables I don’t know how to present content of J.A. Wheeler & W.H. Zurek to grandmother. Roughly (oversimplification), we have two aspects:

    1)Bandwidth; if it is too wide, you don’t know where to find the signal and how to extract it out of noise (you may use psy family story as illustration). For the same reason our natural sensors (eyes) are narrow bandwidth devices. That is about the variables observable in principle.
    2)Gauge dependent variables connected with the internal symmetries; these are not observable in principle. Only Noether related quantities are observables. Apparently, it is enough (in some Ockham analogy with the bandwidth).

    Regards, Dany.

  • Lawrence B. Crowell

    John Ramsden on Mar 19th, 2008 at 1:49 am

    Yes, it seems to go against Occam’s Razor. But it is more in keeping with an infinitely recursive structure, and many find this “no first causes” idea more satisfying than a single large cosmos popping out of essentially nothing purely by chance.

    ——————

    This of course has that “it’s turtles all the way down” sort of logic to it. I think the “other cosmologies” are configuration variables for various amplitudes in the grand path integral. These amplitudes are “eiselected out,” and so their overlap with the amplitude for the observable is decoherently reduced to zero. This grand path integral is from a set of inequivalent vacua states to the Minkowski spacetime at conformal AdS infinity. From a “timeless” perspective the path integral is “all there is,” where this exists in a “bulk,” such as in 11-dimensional M-theory. The observable universe is a process which takes one nothing, the set of unitarily inequivalent vacua, to another nothing which is the Minkowski void at conformal infinity.

    Lawrence B. Crowell

  • John Merryman

    John, Lawrence,

    Wouldn’t a many worlds scenario, branching off an infinite series of universes eventually dissolve into total chaos? If they interact at initiation, then it seems likely they might interact over time. Solving one problem can’t create more problems for it to be an effective solution.

  • John R Ramsden

    Lawrence B Crowell wrote (#70)
    >
    > This of course has that “it’s turtles all the way down”
    > sort of logic to it. I think the “other cosmologies” are
    > configuration variables for various amplitudes in the
    > grand path integral. [..]

    Many thanks for your comments on my post #66 Lawrence. (That post was possibly longer than some might think proper here, and if so I apologise.)

    Although your explanations in #40 and #70 certainly make sense, they do raise further questions. As these are doubtless due in part to my faulty understanding, please don’t think of this reply as solely an attempt at rebuttal by an obstinate amateur blundering on with their misconceptions and heedless
    of expert input, even if it may seem so.

    Firstly, your explanation in #40 involves boundary conditions at infinity, and in the context of this discussion my impression (perhaps reading to much into what is after all a routine assumption) was that you meant this to hint at excluding the possibility of anything “beyond”.

    However, what is infinite in one metric may become finite in other useful metrics (even if new infinities may pop up in place of the old). But if in this way infinite boundaries are ambivalent in formal models, does that not suggest a possible ambivalence in what appear to us unbounded aspects of nature
    itself, especially one causally connected patch? In particular, doesn’t it challenge the very idea of a single all-embracing infinity even existing?

    This leads to my next question. You mention “turtles all the way down”; but in a multiverse model, assuming we have no special place, one can add “turtles all the way up”, in other words not exclude the possibility of “force majeure”.

    The very appearance of an apparently uniform influence throughout the Universe strongly suggests exactly that, and is how dark energy helps drive the “alternating dual” dynamics in the model I proposed.

    But the words “up” and “down” here (not to mention “turtles”!) can be misleading, if they suggest a crude picture of “bubbles within bubbles” and so on.

    Duality seems a more flexible concept because it allows one more readily to think of everything being on the same footing, even if at any given scale and standpoint some phenomena come to the fore and others are imperceptably small or large or, generally speaking, unobservable in one’s current intrinsic
    setting.

    You also mention a “grand path integral”, as representing the totality of reality. Although the dynamics you describe looks sound isn’t every photon, also modelable by a path integral, it’s own master so to speak despite the existence
    of other photons? Surely that in itself is circumstantial evidence for the view that everything is relative, and no one dynamic process can be said to directly control all else.

    All that said though, it’s obvious your explanation is a good example of how dynamics should be formally considered. So I’ve saved your posts and will re-read them now and then until they too become an almost unconscious part of my way of thinking.

  • John R Ramsden

    John Merryman wrote (#71)
    >
    > Wouldn’t a many worlds scenario, branching off an infinite
    > series of universes eventually dissolve into total chaos?

    What counts overall is the small residual “structure” that remains at the boundaries of these worlds (or “arenas” as some prefer to call them in multiverse studies) and interacts between them.

    In fact, arguably one can think of an arena as comprising nothing *but* boundaries, both large and small, and its dynamic evolution as merely the recombination or reconfiguration of these.

    I think Lawrence alluded to something like this in referring to boundary conditions at black hole event horizons and the AdS (Anti-de Sitter) horizon at infinity.

    > If they interact at initiation, then it seems likely they might
    > interact over time.

    Correct – In the dual model I summarized “they” are simply two views of one and the same thing but with various characteristics such as mass, temperature, and time all rearranged, or scales “inverted”.

    Remember the clever pictures I mentioned, which show two different things at once (You *did* read all my post didn’t you, and not wimp out half way through ;-)

    All the dualities I listed have been known about for years. They can be useful “dictionaries”, by which one can convert a problem hard in one setting into an equivalent form tractable in another.

    One of my basic points is that knowing in detail about late evolution, by using general relativity, a sound grasp of the duality would allow one to make deductions about the early stages of the dual early evolution, i.e. the Big Bang.

    (Veneziano and Gasperini have been studying these pre-Big Bang scenarios for years, and I think it was Veneziano wyho discovered scale factor duality. Gasperini’s web site seems to indicate that work has tailed off somewhat recently, but it may just be the baton has passed to others.)

  • John Merryman

    John,

    I definitely read all posts here. Understanding them is another matter.

    My deeper ambivalence about the many worlds concept concerns one of the points I’ve made about time. The many worlds model says that nature doesn’t decide between potentials and at every fork in the road, all alternatives happen as different realities. This presumes that information, as well as the energy manifesting it, goes from past to future, so that at every current and past circumstance, the potential alternatives branch out to all possible subsequent events. My point about time is that while the energy goes from past to future events, the information that is these events goes from being in the future to being in the past, whether it’s the rotation of the earth forming specific days, or strings manifesting as specific vibrations. The information that is any particular day or vibration, is first in the future and then in the past. The result is the collapsing wave model, where all potentials come together and what prevails, as the energy input collides, is the actual. Consider Schrodinger’s cat: Rather than just view it from the perspective of the observer, where the cat is both dead and alive until it’s revealed, consider it also from the perspective of the wave of events. First the quantum event, then the poison, then the cat, then the opening of the box. As these events occur, the wave collapses, but the information doesn’t travel any faster then the wave collapses. It’s like a star exploding right now, about ten thousand lightyears away. We have no way of knowing until the wave of energy reaches us, because it is still ten thousand years in our future. The timeline for the information of this event is from our subjective future, to present to past, as the arrow of time goes from what comes first(events being in the future) to what comes next(these events being in the past).
    So since time is not a fundamental dimension, where both energy and information go one direction, we don’t need to assume every potential must imply an actual.

  • John Ramsden

    One more comment, basically a continuation of #73, to explain how the duality picture seems similar in a way to Lawrence’s explanation. Then I really must give it a rest, or Sean will be on my case for hogging the discussion!

    In #40 Lawrence sketched a picture of (if I understand it) one eigenstate dominating the others, which then cancel out and fade into the background. Now eigenvectors are basically symmetric or “stable” solutions, a classical example being the way a rotating rigid body evolves to rotate about a principle axis, and this symmetry is also a key aspect of my proposal.

    A non-trivial duality of the kind I envisage is a generally a many-to-one transformation, something like a Fourier transform, which therefore “mixes” configuration values of one space to form discernable structures such as particles and fields in the dual space.

    That means randomness in a space is transformed to dual randomness. In particular an empty space is dual to another empty one. Likewise a space containing randomly arranged structures also maps, for all practical intents, to an empty one because those structures are jumbled up throughout the dual space. Similar to Lawrence’s eigenstates that don’t make the grade, their dual images are simply lost in the background.

    Now everyone agrees that black holes will one day be the only surviving structures in our intrinsic arena (i.e. the universe we percieve directly), aside from random radiation. So it follows that if an arena dual to it is to evolve to contain any interesting structures then the black holes in ours must be arranged symmetrically WRT the dual transform.

    It’s true they are symmetric in time, by simply lasting so long, and their shape in space is also obviously pretty symmetric. But it seems to me that even more symmetry, collective symmetry if you like, may well be required to produce “compact” dual images, and that means it isn’t good enough for them to be scattered through their intrinsic space at random – They must somehow arrange themselves in symmetric chains almost like molecules.

    As luck would have it, another benefit of black holes collecting and held in symmetric chains is that their degrees of freedom are thereby reduced. This I argue reduces the collective entropy of their dual structures, which is what I meant by “resetting the entropy clock” in the emergent dual arena.

    Also, although the dual emergent structures may be intrinsically Planck-sized strings as conventionally understood, and behave as such, they are derived from vast macroscopic strings in the original arena. These latter beasts aren’t the exotic long strings one occasionally reads about in New Scientist, but are precisely the chains of black holes held in place by familiar forces (see my post #70), which cause these strings to “vibrate” over intrinsic eons and generally behave just like a conventional string – because in effect that is what they are!

    Finally, the fine tuning I referred to is the condition that black holes in late evolution hang around long enough to form these supposed strings. If not
    then no interesting dual arena emerges. But turning the argument round, one assumes in this rubric that our arena started out (and of course still is) dual to a later-stage arena, which in turn means that enough black holes *did* survive in that.

    If we’re *really* lucky, and happen to live in one of stable sequence of duals, then that might (with a sound understanding of the dual transform) allow even more delicate fine tuning, which could one hopes be confirmed experimentally by the values of physical constants.

    (I’m skeptical of the notion that fundamental constants can differ between dual arenas. But then until the nature of the dual transform is clarified, who can say which constants *are* fundamental?)

    Anyway, I’ve rambled on quite long enough and will call it a day.

  • Lawrence B. Crowell

    John Ramsden on Mar 20th, 2008 at 7:16 pm

    In #40 Lawrence sketched a picture of (if I understand it) one eigenstate dominating the others, which then cancel out and fade into the background.

    ————–

    The decoherence is related to the unitary inequivalence of vacua. Hawking radiation from black holes and the related Unruh radiation result in thermal states due to this. Technically it is a Bogoliubov transformation. As a result there is a coarse grained thermalization of states and decoherence.

    Lawrence B. Crowell

  • John Merryman

    John,

    I suppose my point about two arrows of time, with energy and information going opposite directions, amounts to a duality, that, as you point out about dualities, seems whole from either perspective, but like a coin can be turned over and seen from the other side as equally whole. Such as why relativity treats it as a linear dimension, yet it functions as a quality of relative motion.

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  • John Merryman

    Lawrence, John,

    Question about string theory; Can strings essentially vibrate away and form at the intersection of vibrations? This would accord with the macrocosmic relationship of process and product, form and function, nodes and networks, nouns and verbs, etc.

  • http://tyrannogenius.blogspot.com Neil B.

    “Probability” is not falsifiable per Popperian constructs! I wish I had thought to mention this related issuee arlier, since verification and observability are related. Probability is a very important parameter but “meaningless” by strict construction of the standard of falsifiability! For example, given a claimed 50/50 chance, no particular run of heads or tails could be given as dispositive of that claim – it would just have 1/2^n chance of happening, along a continuum of lesser chance. You could make an arbitrary decision that you couldn’t find the claim credible anymore, but you couldn’t justify drawing the line just there (or at all really, as I explained.) Tough luck! So I don’t want to hear anyone say, “If it’s not falsifiable, it isn’t science” without acknowledging this big fly in the ointment.

  • Lawrence B. Crowell

    John Merryman on Mar 22nd, 2008 at 11:08 am

    Question about string theory; Can strings essentially vibrate away and form at the intersection of vibrations? This would accord with the macrocosmic relationship of process and product, form and function, nodes and networks, nouns and verbs, etc.

    —————–

    There is the M-theory due to Ed Witten, which accounts for various string types according to how they couple to higher dimensional vibrating objects called p-branes. We have vibrating strings, but we can put them on a sound board or instrument which has dimension = 2, such as a violin, piano or guitar. Then the modes of one type of string are compatible with the vibrations on the p-brane, and since these are compatible with vibrations of another string type these p-branes define S or T duality relationships between strings.

    There is an interesting comparison between music and strings. A music theorist a couple of years ago found that cord progressions were mathematically isomorphic to orbifolds, which are the manifold of compactified strings. I’d have to dig the reference. I sat down at a piano and played through some of the constructions. Yes I am one of those ever rarer “birds” who has a piano at home.

    Lawrence B. Crowell

  • John Merryman

    Lawrence,

    It is interesting that String Theory would reflect the relationships of musical chords, though my question is more basic; Are the vibrations a function of the strings, or the other way around? It’s obvious that any particular musical rendition is a consequence of the instrument(and its player) but the creation of that instrument is a consequence of the interest in playing the music and when it is worn out, it will be retired and replaced. So the instrument is equally a consequence of the music. My sense of string threory is that it’s an effort to get beyond the particular focus on particles as the basis of physics and emphasize their activity equally. That the noun is as much a function of the verb, as the verb is of the noun. That there is an institutional bias against this seems to be the elephant in the room. Obviously science is inherently reductionistic, so focusing on the hard parts, rather then the fuzzy stuff, poses a problem, since everything becomes fuzzy if you look hard enough, thus the tendency is to look harder at smaller parts, not accept that in the relationship between being and doing is fuzzy all the way down.

  • Lawrence B. Crowell

    String theory within the context of M-theory is a theory of n-branes for the dimension n = 0, 1, 2, … 11. So what has transpired is that there is now the 0-brane, which is a field at a point. This is a particle. These come about from Chan-Paton factors for open strings “tied” to higher dimensional branes. These endpoints define 0-branes, and there are some ideas that the whole of M- theory can be reduced to sigma models or soliton field theories of these point-like particles. So, … we might in some ways be back to particles.

    Strings have an interesting history. The started out as a model for hadrons, and they had a spectrum given by Regge poles. The competing idea was gauge field theory and QCD — it was California’s physics war between Cal Tech and UC Berkeley. Cal Tech generally won, but they did not smash the idea. Two quarks in a meson are bound by QCD gauge fields termed gluons. Gluons carry the “charge” or color for the QCD force and thus attract each other. Hence two quarks in a meson are connected by this gluon-chromo-flux tube. At a distance this looks remarkably like a string. With the Regge trajectories there was this spin = 2 field with stringy properties. Thus the old hadron bootstrap theory was resurrected in string theory.

    So what is going on? It almost appears that the same thing is taking place. I also think that the 0-branes and their spinor field content define the spin networks of Smolin and the rest of the LQG mafia, where by the way some of their developments of late involve ribbons and stringy like things. So the 1960s armwrestling match between Cal Tech and Berkeley has in some recherche manner been resurrected and it will be curious to see how this ultimately transpires.

    Lawrence B. Crowell

  • John Merryman

    Lawrence,

    Through all the details, it still seems as though the intention is to give form to function, to explain the network as extensions of the nodes.

    So what has transpired is that there is now the 0-brane, which is a field at a point. This is a particle.

    Two quarks in a meson are bound by QCD gauge fields termed gluons. Gluons carry the “charge” or color for the QCD force and thus attract each other. Hence two quarks in a meson are connected by this gluon-chromo-flux tube. At a distance this looks remarkably like a string. With the Regge trajectories there was this spin = 2 field with stringy properties. Thus the old hadron bootstrap theory was resurrected in string theory.

    I still think it is a consequence of assuming the linear narrative of time is a physical dimension and any point on it is as subjective as any point in space. The result being higher dimensional strings of process as physical reality, rather than real change.

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  • John Merryman

    Lawrence,

    Another example of the issue would be with the dichotomy of the Uncertainty Principle, that you can’t measure both position and momentum of quanta. I would say the notion of position is a fallacy, for if any such particle had an absolute position, its temperature would be absolute zero, so it would esstentially not exist, since measuring it requires some degree of motion. While I’m not an expert on the methods used, it would seem that measuring position actually means measuring force, since by actually stopping the particle, you measure the amount of resistance required to do so. While measuring momentum measures the direction of resistance.
    So my argument is the reason reality is fuzzy is because there is no clear distinction between object and action and this applies at all scales. Describing time as a dimension, rather than a measurement, simply tries to make all action a series of objects.

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  • John Merryman

    Fascinating article by a neuroscientist about her experience as victim of a stroke and the insights it gave on the relationship between the left and right hemispheres of the brain and how they process energy and information.

    http://blog.ted.com/2008/03/jill_bolte_tayl.php#more

  • http://noahpinionblog.blogspot.com Mr. Noah

    Of course making accurate predictions is not sufficient for a theory to be a good one. But it is necessary. A theory that makes predictions without giving us understanding of the mechanisms involved is far inferior to one that delivers both predictions and understanding. But a theory that makes no predictions is of no use at all. That is simple and should be obvious.

  • http://quantumnonsense.blogspot.com/ Qubits

    We don’t even have one theory that reconciles gravity and quantum mechanics while matching cleanly onto our low-energy world, or a comprehensive model of the early universe that explains our initial conditions.

    I am positive, that you do have such a theory. An observable object over a certain size simply is not effected by quantum physics, because a quantum field is weaker than gravity field. Where’s the link in that?

    Qubit

  • Lawrence B. Crowell

    In what Qubit writes above this assumes certain things about the quantum/classical correspondence. Zurek demonstrates that quantum effects have resulted in certain changes in the motion of the Saturnian moon Iapitus. Quantum fluctuations can be amplified by classical effects with Lyapunov exponents.

    Lawrence B. Crowell

  • Naraian, A

    Neil (Post 80):

    Disclaimer#1. I have not read all the posts here so if anyone has already made this point, I apologize for repeating).
    Disclaimer#2. I left physics decades ago early in my career for many reasons, but I now conduct clinical work in inflammatory diseases and cancer, so I encounter similar problems in my field. Many people put out both testable and un-testable speculations, but in our case the regulatory environment limits us from going too far. Despite this, some really unlikely speculations are entertained and studies conducted, all due to the influence of a few well known and powerful people. They are bright and honest, yet end up producing what some would uncharitably call “bullshit.” I for one, see it in terms of human fallibility, nothing else.
    The Popperian construct (at least these days) refers to actual experiment that can be conducted to prove or disprove something. In other words, it is not just about a mathematical abstraction like “probability”. Mathematics is a tool or a means to an end in the physical sciences, something you imply as well. If probability simply refers to the likelihood of an event from happening and nothing more, a Popperian analysis should not apply to the abstraction itself. Taking this a step further, anything goes as long as it has a non-zero probability. Could you imagine the number of crackpot contentions that will demand attention? I am not implying that String Theorists are cranks, just that they have badly oversold it. In that sense, both Woit and Horgan are right. Nonsensical theories can sometimes produce occasional predictions that come out true, but that is no reason to go after it. This where Truzzi and his band go off in their Zetetic discussions and end up entertaining ESP, Homoeopathy, paranormal, Velikoskian stuff etc., all in an attempt to be neutral or agnostic as he calls it. And the rest of us are called pseudo skeptics to boot. Some things have to be rejected outright, because they don’t fit in with elementary logic and reason i.e., what we call science. In that sense, I don’t see any fly in the ointment.

  • Anthony A. Aiya-Oba

    Every hardware has its definite software:
    Cosmic Equator of self-contradiction (pair of everything), is the Absolute Logic of self-creation and Gluon of All in all. – Aiya-Oba.

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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .

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