Extraordinary Physics

In January Eliezer warned:

Our own eyes can deceive us.  People can fool themselves, hallucinate, and even go insane.  The controls on publication in major journals are more trustworthy than the very fabric of your brain.  If you see with your own eyes that the sky is blue, and Science says it is green, then sir, I advise that you trust in Science.

If you trust the scientific establishment enough, you should explain odd personal experiences via odd arrangements of familiar science, rather than rejecting established science claims.   In cosmology today, physicists seem to face a related choice.

For 35 years, the standard model in particle physics has passed every test with flying colors.  Yet we see some odd phenomena in cosmology — how willing should physicists be to invoke radically new physics to explain this phenomena, rather than looking to odd arrangements within or close to the standard model?  For example:

  • The flat uniform universe we see, as well as its small initial deviations, could come from adding one more scalar (the simplest possible particle type).
  • The universe of matter see, with almost no anti-matter, could be explained by a small change to the way the electroweak force violates C and CP symmetries.
  • Dark matter could be axions, scalar particles predicted by a small change to the standard model introduced to explain how the strong force respects CP, while the electroweak violates it.
  • Dark energy could be just ordinary large magnetic fields, which stretch as the universe expands.

It is striking to me, and somewhat puzzling, that physicists seem to prefer to explain these odd facts via more radical changes to the standard model, such as string theory with extra dimensions.  I understand that radical changes would be more interesting to learn about, but it seems to me that the least radical changes should be the most likely explanations.

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  • Ambitwistor

    String theorists prefer radical changes involving string theory, but that doesn’t mean that “physicists” do. And there are many proposals for physics beyond the Standard Model which were invented to solve problems with the Standard Model itself, e.g. the hierarchy problem; that they may solve cosmological problems too is just a bonus.

  • http://amnap.blogspot.com/ Matthew C


    Our own eyes can deceive us. People can fool themselves, hallucinate, and even go insane. The controls on publication in major journals are more trustworthy than the very fabric of your brain. If you see with your own eyes that the sky is blue, and Science says it is green, then sir, I advise that you trust in Science.

    Ahh, yes, the “witnesses are crazy, lying, or misremembering” axiom. That used to be the preferred official “Science” explanation to dismiss witnesses of ball lightning, meteorite falls and even gorillas and okapi.

    When one’s worldview depends on throwing out observations that do not fit within it, or spinning them away, one is practicing a sort of religion not so very far removed from “Jesus Camp”. In both cases, one is deliberately seeking intellectual refuge from uncomfortable facts and observations in our natural tendency for confirmation bias. I think Rupert Sheldrake hits the nail on the head here:


    I am skeptical of people who believe they know what is possible and what is not. This belief leads to dogmatism, and to the dismissal of ideas and evidence that do not fit in. Genuine skepticism involves an attitude of open-minded enquiry into what we do not understand, and this is the approach I try to follow.

  • http://libertarianhawk.livejournal.com Karl Gallagher

    Minor changes get a one-year extention of a post-doc grant. Radical changes get tenure.

  • conchis

    “it seems to me that the least radical changes should be the most likely explanations.”

    To be honest, the more I think about this, the less sure I am why it should be true.

  • Me

    People seem to forget that radical changes are made on models of the reality. Reality remains the same. The models are the ones that change. (…and there is nothing wrong with updating an existing model OR proposing a radical new one)

  • http://profile.typekey.com/robinhanson/ Robin Hanson

    Ambi, it would be interesting to see a survey on your claim about wider physics opinion.

    Conchis, I agree we have work still to do to say more clearly why more radical changes are less likely.

  • Ambitwistor

    It would be interesting, but from my experience as a physicist, I find your claim rather extreme. Honestly, I don’t see physicists running out and embracing every string-derived model over more prosaic explanations that have been around for much longer. As you note, scalar inflatons, axions, etc. have been accepted as strong candidates for a long time. I don’t even think most string theorists insist that a lot of the stringy cosmology scenarios are the most likely; they’re too new and too little is known about the string landscape to tell which proposals are really plausible. When you get outside of high energy theory and talk to the hard-nosed particle experimentalists (let alone the condensed matter folks who make up most of the physics community), you will find even fewer people jumping on the “radically different physics” bandwagon.

    In short, I am surprised by your claim, “Physicists seem to prefer to explain these odd facts via more radical changes to the standard model”? What is your basis for making it? Sure, radical changes to particle physics are exciting to high energy theorists, and they get a lot of trendy attention within that community for coming up with a novel proposal. But that doesn’t mean that they are widely believed to be the most plausible explanations of various cosmological conundrums (even among HEP theorists), which is what I think you are implying.

  • http://profile.typekey.com/robinhanson/ Robin Hanson

    Ambi, I’m describing the impression one gets from reading popular media articles – a survey showing that impression to be misleading would be quite newsworthy.

  • Pseudonymous

    Ahh, yes, the “witnesses are crazy, lying, or misremembering” axiom. That used to be the preferred official “Science” explanation to dismiss witnesses of ball lightning, meteorite falls and even gorillas and okapi.

    Also to dismiss witnesses of mermaids, UFOs and ghosts.

    Extraordinary claims require extraordinary evidense.

  • Nick Tarleton

    Also to dismiss witnesses of mermaids, UFOs and ghosts.

    Which shows that, no matter how often science is wrong, on any randomly-chosen question it’s very likely right.

  • http://www.acceleratingfuture.com/michael/blog Michael Anissimov

    Actually, extraordinary claims only require normal evidence… I believe Robin went over this in an earlier post. Why should extraordinary claims require more evidence than normal claims? It’s not fair to hold a double standard.

  • http://www.amara.com Amara

    Physicists seek testable predictions in their theories. Maybe what you are seeing are cases where the testable predictions are easier with a new theory than with an extension of existing one. (I am not sure what to say about Strings community, however)

  • http://quantumreallity.blogspot.com/ bob eldritch

    It is striking to me, and somewhat puzzling, that physicists seem to prefer to explain these odd facts via more radical changes to the standard model, such as string theory with extra dimensions. I understand that radical changes would be more interesting to learn about, but it seems to me that the least radical changes should be the most likely explanations.

    But then the history of science shows that, just occaisionally, very radical theoretical changes are needed to to explain the natural evidence. Two outstanding examples are the change from the Ptolemaic Earth centred universe to the Copernican theorry of a spinning Earth as one amongst the other planets orbiting the sun, and Planck’s theory of quanta, which at least appeared to contradict the existing wave theory of radiant energy and led to the development of the quantum theory of the standard model.

    So that one could think, perhaps, that the general problem of developing any experimetally testable theory of quantum gravity like superstring theory is that this approach to finding a successful ‘theory of everything’ is not radical enough.

  • http://profile.typekey.com/sentience/ Eliezer Yudkowsky

    If you think your theory is too complicated, it makes sense to look for a simpler theory even if this requires radical revision. You wouldn’t want to be prejudiced against a simpler theory that explained the same evidence just because it was invented later – things presumably could have been the other way around, and then nobody would even look at the more complex theory. As I understand it, the big problem with string theory is that it is not simpler and cannot even be shown to explain the same evidence.

  • Hopefully Anonymous

    Bob,
    One could extrapolate from that (and the general note that we evolved brains for functional, not optimal purposes of modeling reality) that numerous radical revisions of theory are more likely necessary or not if we want to get substantially better at modeling “actual” reality.

  • Ambitwistor

    Robin,
    I’m not sure why you are counting on the popular media, which has a known bias in emphasizing the newest and most radical hypotheses, to give you an accurate depiction of what any community of scientists actually thinks about the relative likelihood of those hypotheses.

    For that matter, I don’t know any popular media which actually cites physicists as preferring the most exotic scenarios; at best, there is simply more coverage of such topics. Pay attention to how often the quotes from physicists other than the inventors of the new theories say things like, “It’s an interesting idea but it’s far too new to properly evaluate” as opposed to “It’s one of the best and most plausible scenarios out there”.

    Instead of shifting the burden to a survey which disproves “the impression [Robin Hansen] gets from the popular media”, I wonder how you justify holding that position in the first place.

    String theory in particular has yet to take over high energy phenomenology; explanations for particle physics and cosmological conundrums, when they go beyond the Standard Model, are still more likely to be framed within the context of supersymmetry or grand unified theories. (Of course, both are part of string theory too, as is arguably the Standard Model itself, but they are not as radical as extra dimensions or braneworlds.)

    Regarding your specific points, my short answers are:

    1. There are so many inflaton candidates that none are really “preferred”, although candidates which solve problems with the Standard Model in addition to solving inflation are preferred to those which only solve inflation.

    2. Electroweak CP violation exists but is difficult to use to explain matter-antimatter asymmetry, so there is a legitimate reason to go beyond the Standard Model in that case.

    3. Axions are still important dark matter candidates.

    4. I don’t buy “dark energy is magnetic fields” at all.

    Elaborating on point 1: Scalar inflatons have been the preferred mechanism for inflation for decades, although string theory gives you some exotic new possibilities for what those scalars could be. Actually, most inflation theories simply require an inflaton potential with a particular shape; whether you get that potential from an appropriately chosen new particle added to the Standard Model or from some string theory model is up to you.

    I will note, though, that there is certainly a push to propose new inflaton candidates that are “natural” within some theoretical framework, as opposed to a random particle with ad hoc properties glued onto the Standard Model. So those scalars which appear naturally in supersymmetric theories, grand unified theories, string theories, etc. are popular.

    (It is harder to get an inflaton to appear as a “natural” addition to the Standard Model, because the Standard Model doesn’t really explain how you can get the high energy field values necessary for a sufficiently flat inflaton potential. You can just add such a particle in by hand, but it doesn’t really “fit” with the rest of the theory, which operates at a very different energy scale.)

    Note also that many of those theoretical frameworks (SUSY, GUTs, etc.) were themselves proposed in order to solve some long-standing issue with the Standard Model, such as the hierarchy problem, or explaining the extrapolated convergence of running coupling constants — in other words, there are legitimate reasons for going beyond the Standard Model.

    That being said, I will return to my earlier point that there is an enormous collection of inflaton candidates coming from practically every source you can imagine, including simple additions to the Standard Model, and that people have mostly retreated from promoting specific scenarios to trying to phenomenologically characterize the parameter space of inflation theories. There are simply too many workable proposals out there.

    On point 2: CP-violating interactions are certainly part of the explanation of matter-antimatter asymmetry, but the question is what mechanism is at work. Ordinary electroweak interactions don’t provide a large enough asymmetry. You can extend the Standard Model in various minimal ways to get the required asymmetry, but there are not too many parameter values which work there either. See this review.

    On point 3: Axions are a very nice solution to dark matter, and there are good independent reasons to believe they exist. But it’s tricky to get them to have the right mass to serve all the necessary roles of dark matter (see here). Dark matter needs to be compatible with galactic rotation curves, early universe structure formation, and CMBR anisotropies, among others. It’s hard to satisfy all of those constraints at once. It’s hard (but not impossible) to get axions to satisfy them all, but it’s also possible that axions are just one kind of dark matter and that others exist too.

    On 4: Dark energy as magnetic fields doesn’t seem at all plausible to me, but I will defer to experts in the field (none of whom have weighed in on this subject). It doesn’t help that it has been covered by New Scientist — judging from their coverage in fields in which I am qualified, NS has descended to near-crackpot status in the last few years, and I automatically downweight almost everything they publish nowadays. (Witness their recent sad promotion of research which purports to violate the conservation of momentum, incorrectly claiming that this is theoretically permitted by special relativity.)

  • http://profile.typekey.com/robinhanson/ Robin Hanson

    Ambitwistor, the subject of when one can rely on media impressions is interesting; I think I’ll post on it soon. I consider supersymmetry and GUTs to also be “extraordinary” theories, compared to minimal modifications of the standard model.

  • Ambitwistor

    Supersymmetry and GUTs may be “extraordinary” compared to minimal modifications of the Standard Model, though not when compared to full blown string theory. However, the problem with solving the aforementioned cosmological problems with “minimal modifications of the Standard Model” is that (1) it’s often difficult or not impossible to do (see matter/antimatter asymmetry), (2) when it is possible, it’s often ad hoc and does not naturally fit in with the rest of the Standard Model, and (3) when it is possible and natural, it doesn’t solve any of the known problems with the Standard Model, unlike some more supposedly “extraordinary” alternatives.

    There are real reasons to take, say, supersymmetry or grand unification seriously other than their usefulness in solving the cosmological questions you’ve mentioned. As I alluded to before: despite its experimental success, the Standard Model has known theoretical inadequacies (doesn’t account for the particle hierarchy without fine tuning, doesn’t explain apparent coincidences in the running coupling constants, is inconsistent with the gravitational interaction, etc.) Thus, appealing to “minimal modifications of the Standard Model” isn’t necessarily the conservative choice, as it retains all those problems or makes them worse. For that reason, those theories, while speculative, are often not regarded as particularly extraordinary nowadays: after being around for decades, they remain the most conservative modifications to the Standard Model which resolve some of these problems. One may appeal to cosmological solutions within the “extraordinary” frameworks of SUSY or GUTs or whatnot not merely because they are radical or new or “sexy”, but because they kill two birds with one stone (solving a cosmological problem and fixing the Standard Model).

    (One can also argue whether “theoretical inadequacies”, as opposed to disagreement with experimental evidence, is a valid scientific reason to discount proposals which retain those inadequacies.)

    A defense of not-so-extraordinary extraordinariness out of the way, I don’t want to lose sight of the fact that, as I have mentioned, there are a number of long-standing and plausible solutions to these cosmological problems along the “minimal modification” lines you listed. Nor is it the case that “radical” solutions are preferred for the sake of merely being radical: the merely “extraordinary” proposals such as SUSY or GUTs, which have been around for a long time, still have far more mainstream acceptance than the newest and more radical proposals such as large extra dimensions, braneworlds, etc.

    I’m looking forward to your discussion of media impressions. I suspect their validity varies between sources (e.g., Scientific American vs. New Scientist) and from field to field.

  • http://www.componentx.com Brad Hutchings

    I’m with “Me”. These are radical changes to models, not radical changes to reality. By sticking with standard models, we may be preventing ourselves from understanding the extent of our reality. There is no better illustration of this than Edwin Abbott’s Flatland.