The Nature of Truth

Seed Magazine has a video and transcript up of a discussion between cosmologist Paul Steinhardt and philosopher of science Peter Galison advertised as The physicist and the historian discuss the nature of truth as theoretical models of the universe become increasingly difficult to test.

Steinhardt is no fan of the anthropic landscape and makes a general attack on the idea of eternal inflation, explaining why he prefers his cyclic model:

The original idea — the way it’s often talked about in literature and textbooks, even the way we talk to students — is that inflation makes everything in the universe the same. What we’ve learned is that inflation actually divides the universe up into little sectors that are all different from one another. Some regions of space would be habitable like ours, but others would be inhabitable; still others would be habitable but would not have the same physical laws or the same distributions of matter that we see here…

Because you have an infinite number of everything, you have no rigorous mathematical or statistical way of computing a probability — it’s not even a sensible question to ask. So people are in the process of trying to regulate this infinity. For example, they try to invent a rule for deciding probability that makes what we see likely. But there’s no way of deciding why that rule instead of some other one. They simply keep trying until they’ve found the answer they wanted. Some people are going down that path and are prepared to declare victory if they find something they think works.

Others take a different path. They accept the infinity of infinities and the fact that they can’t find any measure for deciding whether our circumstance is more probable or not. They’ll be satisfied with the fact that at least some patches look like what we see, and will declare victory on that basis.

Personally, I don’t find either of these approaches acceptable, which is why I have developed an alternative picture in which the big bang is not the beginning. A big bang repeats at regular intervals of a trillion years or so, and the evolution of the universe is cyclic.

The two then get into a philosophy and history of science discussion, starting with Steinhardt’s:

We’ve been talking about an example in which you have a complex energy landscape and an infinite number of possibilities for the universe. But we have no real explanation as to why things are the way they are, because it could have been different.

So it has no power. And without real explanatory power, it’s not interesting to me. But I’d be interested to hear how this has played out in the history of science.

and Galison’s response:

We have that sort of split right now among the string theorists. One side says, “Look, what’s really scientific is to say there’s this infinite or very huge number of craters to be imagined in some landscape, each of which carries different physical particles and different physical laws and so on. And we happen to live in one of them.”

But the other says, “You’ve given up! You’ve given up the historical project of science. We went into string theory because we wanted to produce a theory that had one parameter, or very few movable parts. And now instead of a glider you’ve got a helicopter with 10,000 little pieces that have to move exactly the same way. If the slightest thing goes off, it falls to the ground in a heap of burning aluminum.”

It’s really an interesting moment in that way.

Steinhardt describes the current situation as follows:

I think it’s historic. There’s a certain community that feels, “This is an ‘aha’ moment. Science has to change. We have to accept that science has limits. There’s only a certain amount that we’ll be able to predict. Beyond that we’re going to accept that we live in some special corner of space in which seemingly universal laws — including Newton’s law of gravity — are just local environmental laws that aren’t really characteristic of the whole.”

Other groups say, “Hold it, this is failure. We either find ways of fixing the problems in those theories, or we scrap them and replace them with something else.”

The source of the problem here is not actually eternal inflation, but string theory. It is the fact that one needs to postulate a huge landscape in string theory in order to have something complicated and intractable enough to evade conflict with experiment that is the problem. Once one has this, and populates it with eternal inflation, then one has a pseudo-scientific framework with no explanatory or predictive power. Galison notices that string theorists are dividing up into those who follow this path, and those unhappy with it, but it is only Steinhardt who makes the obvious point that what’s going on here is just garden-variety scientific failure. The failure though is not attributable to the general idea of inflation, but rather to the string theory-based assumption that fundamental physical theory involves a hopelessly complicated set of possibilities for low-energy physics.

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25 Responses to The Nature of Truth

  1. srp says:

    Straight up now:

    1) One could argue that it’s too soon to give up looking for “simple” theories that a) unify all of high-energy physics and that b) deduce most of the empirical parameters from just a few, but that string theory isn’t the answer to this problem. (This is my understanding of the Woit position.)

    2) One could argue that someday string theory will become that simpler elegant theory and that it is by far the leading candidate to achieve unification and parameter reduction. (This is my toned-down understanding of the Motl position.)

    3) One could argue that no fruitful approach to unification and parameter reduction has been found after a lot of effort and that there are reasons to think that the task is impossible (e.g. a small cosmological constant that is hard to derive from first principles). Then trying to develop a theory of why the parameters are what they are is like trying to develop a first-principles theory of why the earth has its specific circumference or why Britney Spears is blond–a misguided exercise in futility. (This is my understanding of the Susskind position.)

    4) One could propose some theory of one’s own that allegedly solves the problem but has been ignored by everybody for various political and sociological reasons. (This is my understanding of the position of some of the commenters on this blog.)

    Other than existential or philosophical commitments, is there any rational basis for choosing amongst 1) – 4)? Because what I mostly see is a lot of foreign tourist syndrome–people repeating their assertions LOUDER and S-L-O-W-E-R in the hopes that their interlocutors will understand the invincible correctness of their view.

  2. Peter Woit says:

    srp,

    Personally, I don’t think this has anything to do with existential or philosophical commitments, rather with the fact that 2) is wishful thinking, 3) is pseudo-science, and 4) are generally being ignored for good scientific reasons. But that’s just me….

  3. srp says:

    I guess I think that objections to 3) ARE purely philosophical or existential (having to do with the definition of science). Further, they rest on a very particular view of science that is really most relevant in physics and chemistry–that science doesn’t study the particular histories of things but seeks only general laws that apply in all times and places.

    I personally find this ideal rather congenial but there is no way to make it a necessary condition for work to be scientific. Otherwise structural geologists who explain how a particular mountain came to be would not be scientists. Not to mention the issue of evolutionary histories in biology.

    In my opinion, the ideal of ahistorical and universal explanations in physics was really placed in danger by two related phenomena: The end of steady-state cosmology and the interpenetration of cosmology and physics. When I was growing up, I just assumed that the universe was eternal and had always existed; talk of “in the beginning” or “the beginning of time” seemed to me nonsensical, poetical, or mythological. In such an eternal universe, we don’t explain “where things came from”–the universe has no history and just IS. In such an environment, it wouldn’t be possible to explain why the particles have the masses they do (or any other empirical parameter) by appealing to historical accident.

    Then came the Big Bang theory, which necessarily opened the door to the possibility of such developmental accidents. “The symmetry just happened to break this way” and similar arguments become ways of saying that “stuff happens” when an explosion happens and creates the universe.

    The impact of the new cosmology on physics was delayed a bit because at first the flow of ideas was mostly from physics to cosmology. But as the Big Bang and its attendant ideas (e.g. inflation) took hold of the imagination, and as physicists started speculating about high-energy regimes beyond the range of their accelerators, they started to use ideas from cosmology to make sense of the physics. I’m not sure this intimate embrace is healthy for either field (I worry that each assures itself that the other has the answers to its deepest problems rather than solving them directly), but it was probably inevitable.

    Now that physicists turn to cosmology to think about things like ultra-high energy regimes where forces are unified, and given that cosmology is historical given the Big Bang, the door is open for thinking that lots of facts about the universe–particle masses, forec strenghts, etc.–are accidents not derivable from first principles or models with fewer parameters. It almost seems natural, even if you don’t believe in multiple universes.

    After all, we turn to historical accident to explain the strength of the Earth’s magnetic field, the size of the Sun, and so on. Yet no one argues that the people studying these things are unscientific because they don’t deduce these facts from basic symmetry principles. So I think that the general discomfort with these ideas is philosophical and existential.

  4. Aleksandar Mikovic says:

    I liked the description of philosophies behind the various proposals for the Theory of Everything given by Srp, and it is good that people are aware of various approaches. Note that even the usual scientific method is based on the beleif that our world can be described in a certain way. However, formulating a TOE is not just another scientific theory, because the domain is the whole Universe and everything in it, and this clearly is not the usual situation. A good analogy is when somebody tries to apply the usual quantum mechanics to the whole universe, and consequently encounters problems of how to define the measurement (no outside observers), how to define probabilities etc. Every scientist has a dream that the Universe can be described by a set of equations which can fit on a t-shirt, but our Universe may not be of this kind. But even if our universe is not described by a simple mathematical structure, I don´t think that would be the end of science. This situation would require a more general way of thinking then the usual scientific way.

  5. thought says:

    I think some people need to realize the difference between everything that can exist, and everything that does exist.

  6. Rick Ryals says:

    It is a historically recorded fact that scientists ignore certain types of theories for political and sociological reasons, and you can bet your last buck that there will be no complete theory of quantum gravity, and no ToE, as long as this remains the case:

    http://dorigo.wordpress.com/2008/06/23/

  7. Zathras says:

    I also like srp’s description of the various options. Peter, could you explain further why you would contend #3 is pseduoscience?

  8. Peter Woit says:

    Zathras,

    I think I’ve already done this ad nauseam on this blog. There’s nothing wrong with the idea that some things are just an accident of history and you can’t compute them. But if you want to do promote a theory and claim that it is science, it has to have some predictive power. If your theory is nothing but an elaborate excuse for not being able to predict things, then it isn’t science. If you look into what is going on with the string theory landscape, that’s what you find.

  9. Zathras says:

    Peter, I agree with your stand on Susskind’s view on string theory here. This, however, is not what #3 says (although it is part of what Susskind says; there is a discrepancy here). Susskind has two points; one negative (described in #3) and one positive (effectively demolished by you). My question was what do you think of the negative theory described in #3, and why is it pseudoscience?

  10. Joey Ramone says:

    String theory is pseudoscience.

    It will be around for a decade or so yet, mostly promoted by physicists in their 70s, some of their past postdocs yet writing grant proposals, and journalists who will slowly realize that it no longer sells magazines like it used to, as it just isn’t “cool” anymore, due to the old men hyping it. Brian Greene wore a cool black leather jacket much like mine in an Elegant Universe, and the DVD sold very well, but he probably won’t be inducted in the Rock’n'Roll Hall of Fame. He might yet win a Nobel, but in literature or maybe even economics, for mining higher dimensions for millions.

  11. Peter Woit says:

    Zathras,

    It seems to me that I’m just repeating myself, but again, the point is that a theory has to have some conventional predictive power about something or else it’s not science. If you can’t even in principle test it and find out if it’s wrong, it’s not science. The theory that the fundamental constants were chosen on a whim by the Jolly Green Giant has a great deal of explanatory power but predicts nothing.

    It’s bad enough to promote pseudo-scientific explanations, worse to do so as a bald-faced attempt to evade the consequences of failure.

  12. Zathras says:

    Peter,

    I understand what you’re saying. The underlying assumption you are using, however, is that a predictive theory to find these constant (a) exists and (b) can be found. This kind of assumption does not seem to me to be scientifically based, since no such theory of everything has been found.

    The inherent problem in the debate is that science self-selects those people who believe the assumption above. If someone did not believe it, they probably would not go into, or stay in, science. I know this from personal experience. I left graduate school at Caltech for mainly these reasons. I lost my faith that such theories could be found, and so I left science.

    Again, I am not defending Susskind’s defense of string theory. It is not defensible. The lack of an ability to find a testable theory does not allow one to ironically spin out elaborate B.S. and call it science. The negative theory stands on its own. It can be falsified by the finding of such a theory. Since this has not occurred, and I doubt it ever will, the negative theory is what I will place my stake in.

  13. thought says:

    I don’t see what people like in srp’s classification of possibilities into cases 1)-4). The cases are not mutually exclusive and don’t even come remotely close to covering the possibilities.

    On the other hand they have the interesting recursive characteristic that srp’s classification itself clearly falls into case 4).

  14. Peter Woit says:

    Zathras,

    I honestly have no idea which if any of the parameters in the SM can be computed from first principles, and which are historical accidents. I’m not making any assumptions about that at all. I do believe though that the SM is not a final theory and we can do better. That’s a working assumption based on history, looking at the problems of the SM, and having some very general ideas about what a better theory might look like that I think are worth pursuing. People who think the SM can be improved upon and who want to try should work on this, those who think it’s hopeless should do something else, just not invoke the failure of one idea as proof of hopelessness.

  15. anon. says:

    ‘The underlying assumption you are using, however, is that a predictive theory … (a) exists and (b) can be found. This kind of assumption does not seem to me to be scientifically based, since no such theory of everything has been found.’ – Zathras

    You only know what exists and what can be found once you’ve found them. Scientific research is exploration, and no explorer ever knows in advance for certain what will or can be found. You try to find things. If you stop science because you are uncertain whether you will make progress, you’re finished straight off.

    I don’t think that Woit is implicitly assuming that a theory of everything that makes falsifiable predictions exists and can be found; merely that science is about searching for such things.

    If you find a road turns out a dead end, you should admit failure, and try to find a new pathway. You can’t know what you are going to find in advance. That’s the point of science. Religion is about believing claims that can’t make falsifiable predictions.

    Scientists should pursue ideas they find interesting, but they shouldn’t believe in their validity until they have solid evidence.

    Some guy essentially discovered X-rays (causing fluorescence outside a cathode ray vacuum tube) before Roentgen, but he didn’t bother to publish (or feared censorship?) because it seemed to contradict the reigning theory of solid impenetrable atoms! That’s what you get from believing unproved orthodoxy.

  16. Peter Shor says:

    My opinion (which probably shouldn’t count for too much): It’s clear that the Standard Model isn’t the final theory because it doesn’t account for gravity. Previously, any time we’ve unified two existing theories, this has increased our predictive power – think of Maxwell’s equations, special relativity, general relativity, the SM. It would be very disappointing if that didn’t happen with the unification of the SM with gravity.

  17. milkshake says:

    There is just not enough to go on. If they cannot propose any signature of the multiverse spawning business then they should say so (and try to do something about the problem).

    Not too long ago geologists used to argue whether the continents are moving and whether meteorites produce craters. These things are hard to watch in action but the indirect evidence got pretty good eventually.

  18. neo says:

    The issue is no doubt philosophical–that is why it is not science. As a committed Copernican, I recognize that I live in a privileged environment (the inhabitable zone of a star), and I have no problem with the Anthropic principle as an explanation. So what is wrong with the landscape? the difference is that I know that the (much greater) nonhabitable zone exists–I can observe it. Those who invoke the landscape assert non-habitable universes that we cannot observe, nor have any hope to observe. That is why it is not science. The question is whether Steinhardt’s cyclic universe theory is any different.

  19. Artful Codger says:

    [a] Inflation is well-supported observationally
    [b] Many models of Inflation are eternal
    [c] It is therefore perfectly “scientific” [in the sense that it flows from a theory with observational support] to believe in the existence of large numbers of other ["Coleman-De Luccia"] universes.
    [d] Standard QFT makes the *observed* value of the cosmological constant seem utterly bizarre [See Polchinski's 2006 article on the arxiv].
    [e] I conclude that the anthropic explanation of this particular number is very plausible.

    What I find strange is this: detractors of the anthropic explanation of the CC never seem to be able to propose an alternative. Dear Peter: would I be correct in assuming that you believe that one day somebody will come up with a physical theory that allows one to *compute* the value of the CC from mathematics? This means that *mathematics* is “designed” to allow our existence. This is far more bizarre than the anthropic explanation.

    I have sympathy for your points about the role of string theory here, *though* as you can see above, string theory really doesn’t have much to do with it at all! What I mean is: if *anyone else* had invoked the anthropic principle, say the LQG people, then certainly the macho string types would have started testiculating about the flabby philosophizing of their opponents. But one should not allow these sociological phenomena, striking though they may be, to obscure the fact that the anthropic explanation of the facts is actually the *least* weird alternative.

  20. Peter Woit says:

    Artful Codger,

    No, I have no idea whether the CC is the kind of thing computable from first principles. Maybe the anthropic explanation of its size is correct, who knows? But if you want to claim scientific evidence of an eternal inflation scenario producing a multiverse with a distribution of CCs that allows such an anthropic explanation, you have to come up with a conventional scientific prediction. If this is science, there has to be some way, at least in principle, to put it to a convincing experimental test. Tell me some measurement that someone will someday be able to go out and make that your theory gives a distinctive prediction for. If you can’t do this, what you are doing is just making up untestable speculative scenarios, with no way to ever find out which corresponds to reality. That’s not science, it’s pseudo-science.

    And, like any pseudo-science, it’s harmless as long as it’s ignored by most of the scientific community, which so far seems to be the case (do you have any idea how idiotic most physicists think this kind of thing is?). It’s not harmless if it becomes a dominant ideology, used to prop up a failed research program.

  21. Artful Codger says:

    “And, like any pseudo-science, it’s harmless as long as it’s ignored by most of the scientific community, which so far seems to be the case (do you have any idea how idiotic most physicists think this kind of thing is?).”

    Sure, “most physicists” think, or pretend to think, that this kind of work is idiotic. That means nothing. Phil Anderson seems to think that *all* fundamental physics research is idiotic, and I guess that most condensed matter physicists agree. So what? If we allow physics research to be directed by the inferiority complexes of the collective, then we really are doomed. By the way, these same physicists whose help you are enlisting might apply the same words to the kind of research *you* favor. In fact, I’m pretty certain they would.

    Calling something idiotic is not terribly scientific. Coleman certainly was no idiot. The fact that our best theory of the early universe [Inflation] leads to unpleasant consequences is not something we should ignore.

    Experience suggests that suspending judgement on such matters is not a productive way to go. It’s better to identify the most plausible explanation of the facts, and then push it until it works or something better comes along.

  22. srp says:

    Kepler attempted at one point to explain the structure of the solar system by mapping it to nested Platonic solids. Thus the sizes of the various planetary orbits would be a consequence of fundamental mathematics.

    Today we think that is crazy, not just because the particular geometric model is unmotivated but because the entire category of explanation is believed to be impossible and misguided. There IS no fundamental, ahistorical explanation for the sizes of the particular planetary orbits in the solar system and nobody sensible wastes his time trying to find one.

    We understood this for centuries not because we had data about other stars’ planets (we didn’t) but from general principles about Newtonian theory and what it could or could not do. The assertion that there is no way to derive specific planetary orbits from first principles is not pseudo-science at all, even if it generates no empirical predictions.

    So, since we don’t need to rely at all on string theory or multiverse ideas to do it, it can’t be pseudo-science to tell people to stop looking for ahistorical explanations of things that are, on theoretical examination, very unlikely to be derivable from first principles. It may be bad advice, in that a clever or lucky person might actually stumble upon some deeper structure, but the argument against such a quest can be made using evidence. That evidence is the nature of existing theory and the nature of the phenomenon in question. It may even be possible to prove that a given class of theories cannot deduce the phenomenon.

    I agree that “explaining” an accidental fact by reference to unobservable other universes doesn’t add much to our understanding of anything. The urge to do so, I believe, stems from the psychological conflict between physics’s deep ambition to explain everything with ahistorical laws and the advent of Big Bang cosmology which gives the universe an unavoidable history. The multiverse and evolutionary universe ideas are halfway houses between historical (accidental) and ahistorical (lawful) explanations–we can imagine a structure or process that makes local accidents part of a broader lawful scheme, which makes some people feel better even if it has no additional scientific payoff.

  23. anon. says:

    ‘Today we think that [Kepler's nested solids solar system] is crazy, not just because the particular geometric model is unmotivated but because the entire category of explanation is believed to be impossible and misguided. There IS no fundamental, ahistorical explanation for the sizes of the particular planetary orbits in the solar system and nobody sensible wastes his time trying to find one.’ – srp

    The Titius-Bode law was formulated to predict planetary radii in the solar system and lots of people tried to make sense of it theoretically. Theories of the solar system have been formulated which attempt to model the planets condensing out of a contracting, rotating cloud of gas, and one thing such models try to predict is that empirical law.

    Kepler tried all kinds of data-fitting explanations before formulating the three laws of planetary motion, which served Newton so well. I don’t think that we need to be biased ‘believe’ that any approach is impossible and misguided: either it works and is useful, or it doesn’t. The whole solar system idea of Aristarchus (250 BC) with the earth rotating daily and orbiting the sun was believed by the mainstream to be impossible and misguided for 17 centuries. Thus there is no science in being prejudiced and disbelieving ideas without evidence, any more than in believing string theory without evidence. What you believe or disbelieve is not relevant for science, which isn’t about beliefs.

  24. theoreticalminimum says:

    I just stumbled upon this by accident. The list of participants, and the mention of “God” are somewhat intriguing.

  25. stringph says:

    If Steinhardt’s ‘cyclic’ model – whatever its exact guise is nowadays – were scrutinized with the same rigour as he spends on inflation (or eternal inflation or landscape/eternal inflation) he would never have proposed it in the first place.

    It relies on a mathematically unsound concept of infinite past time to a much greater extent than eternal inflation does. (What is the number of our current cycle?) Steinhardt likes to claim there is an ‘attractor’ behaviour from one cycle to the next – but attractors only attract in one direction: either the behaviour diverges in the past or the future. A past- and future-infinite number of cycles, of which we inhabit a specific one, is not only mathematically problematic, it is dynamically unrealizable.

    The scalar potential necessary for the ‘cyclic’ model to work is even more complicated and absurdly fine-tuned than most inflation or dark energy models. I don’t know of any paper where it is written down algebraically. Steinhardt likes to criticize inflation models based on the form of their scalar potentials, but if you never write down your own model in closed form this criticism can be evaded…

    And to get a hot Big Bang and restart the cycle one needs a process that (unlike inflation) cannot even be modelled meaningfully in field theory. They call it ‘brane collision’ and like to send the field value off to infinity while it is occurring, hoping that it will somehow spring back for a fresh new day.

    If one compares string theory/ eternal inflation/ landscape ideas to a certain US car manufacturer, Steinhardt’s logic seems to be ‘GM cars are disappointing and unreliable, therefore I prefer to travel by camel’.