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.
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.
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.
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?
“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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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.
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.
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
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”?)
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?
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.
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.
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.
Nope. Read his comment again – he’s saying the arguments in question are not scientific arguments.
That’s his whole point, in fact.
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
Define multiverse.
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
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.
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?
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?
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
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
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.
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”?
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