What Scientific Ideas Are Ready for Retirement?

Every year we look forward to the Edge Annual Question, and as usual it’s a provocative one: “What scientific idea is ready for retirement?” Part of me agrees with Ian McEwan’s answer, which is to unask the question, and argue that nothing should be retired. Unasking is almost always the right response to questions that beg other questions, but there’s also an argument to be made in favor of playing along, so that’s what I did.

My answer was “Falsifiability.” More of a philosophical idea than a scientific one, but an idea that is bandied about by lazy scientists far more than it is invoked by careful philosophers. Thinking sensibly about the demarcation problem between science and non-science, especially these days, requires a bit more nuance than that.

Modern physics stretches into realms far removed from everyday experience, and sometimes the connection to experiment becomes tenuous at best. String theory and other approaches to quantum gravity involve phenomena that are likely to manifest themselves only at energies enormously higher than anything we have access to here on Earth. The cosmological multiverse and the many-worlds interpretation of quantum mechanics posit other realms that are impossible for us to access directly. Some scientists, leaning on Popper, have suggested that these theories are non-scientific because they are not falsifiable.

The truth is the opposite. Whether or not we can observe them directly, the entities involved in these theories are either real or they are not. Refusing to contemplate their possible existence on the grounds of some a priori principle, even though they might play a crucial role in how the world works, is as non-scientific as it gets.

I’m also partial to Alan Guth’s answer: “The universe began in a low-entropy state.” Of course we all know that our observable universe had a relatively low entropy at the Big Bang; Alan is making the point that the observable universe might not be the whole thing, and the Big Bang might not have been the beginning, so it’s completely possible that the universe as a whole was never in what one might call a “low-entropy” state. Instead, starting from a generic state, entropy could increase in both directions, leading to a two-sided arrow of time. This has been one of my favorite ideas for a while now, and Alan and I are writing a paper with Chien-Yao Tseng that examines toy models with such behavior.

Here are some other interesting/provocative answers, picked unsystematically out of over 100,000 words overall. Remember that the titles are what the person wants to retire, not something they’re in favor of.

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81 Responses to What Scientific Ideas Are Ready for Retirement?

  1. Neil says:

    I doubt that you want to retire falsifiability. You just don’t think it is a requirement for an idea to be science.

  2. Adam H says:

    I am not bothered by falsifiability. It is one solid criterion but not the only one. I am more concerned of this blatant gimmick to redefine the scientific method to suit theories which fail to meet any of its criteria. It’s not going to fool anybody. If we reach a point where the scientific method fails, then we say the scientific method can not tell us anything beyond this point here. At that point, we can use other means to explain what’s going on but we don’t pretend that we are conducting scientific inquiry because we’ve cleverly just redefined what we mean by science.

  3. Mike D says:

    I’m reminded of Stephen Hawking: “It’s meaningless to ask what is real, only what agrees with observation.”

  4. CPV says:

    “Amanda Gefter, Andrei Linde, and Seth Lloyd all suggest that we get rid of the idea of a unique universe, each from a slightly different perspective. Sorry, universe: the tide is turning against you.”

    I suspect the universe is still sleeping quite well at night with such weak arguments arrayed against it.

  5. Reginald Selkirk says:

    Whether or not we can observe them directly, the entities involved in these theories are either real or they are not.

    That’s setting the bar very low. Santa Claus is real or he is not. The easter bunny is real or it is not. Invisible pink unicorns are real or they are not.

    Does science tell us anything about whether these things are real?

  6. Doc C says:

    So if we can’t touch it it can’t be real? If ‘Santa Claus” inspires a child to buy a toy for an indigent child (because Santa can bring that child toys, but his family can’t, so the first wants to help Santa), is Santa real? He has a real effect.

  7. Jens says:

    If you drop falsifiability, an infinite number of theories will all be right. On what new basis will you know the right one?

    “Darkness gathers. The demons begin to stir.”

  8. Ken Gayley says:

    Sean Carroll is an excellent theorist, and I wish I had his deep understanding of string theory and most of the rest of physics for that matter, but he’s really wrong here. And it’s quite clear why he’s really wrong– what does he think is the actual process whereby “nature is the ultimate guide”? Falsifiability, obviously! Seriously, we have a huge body of evidence from which to answer that question, it is called the history of physics. In that history, it is completely demonstrable that the process for discarding theories is not coming up with ones that a consensus of people like Sean Carroll prefer for personal reasons, they get discarded for only one reason: they got falsified, because they were falsifiable. What happens to what is unfalsifiable is also a matter of record: it becomes folklore.

    A classic example of this is the geocentric model of the solar system. For millennia, that model was adopted because the consensus of the Sean Carrolls of the day was that the stars could not be so far away that they would not appear to move, it just didn’t make sense to them for the universe to be built that way. So if personal preferences, rather than falsifiability, ruled the day, we’d still be teaching the geocentric model. But when Galileo saw that Venus went through phases, it meant Venus had to orbit the Sun, period, end of debate. Thank goodness for falsifiability!

  9. mike says:

    Dear Mr. Carroll
    I was wondering if you can answer the question or consider writing an article on the subject:

    Has dark energy or dark matter changed in the life of the universe?
    Is it possible for one to slowly change into the other over the life of the universe?
    For instance, if dark energy can change into dark matter, then perhaps the universe will slow it’s expansion, perhaps even stop it’s expansion, reverse and a big crunch will occur.

    Is there any evidence or reason (beyond my pure conjecture and perhaps wishful thinking) for this to be?

    Yours truly

  10. AI says:

    Sean your answer is bad and you should feel bad.

  11. C.Takacs says:

    Mr. Carroll,
    You might seriously consider writing a retraction, or something that perhaps clarifies your position to some degree better than you have. Your position on jettisoning falsifiability from science is not logically sound, namely because you are abandoning the underpinnings of logical argument itself, without which there is no science.

  12. Jesper says:

    Dear Sean Carroll

    In your ‘Edge’ piece you advocate for the retirement of ‘falsifiability’ and yet you end your piece with declaring Nature our ultimate guide. To me, this is completely self-contradictory. If Nature has no way of saying “you are wrong!” – which is falsifiability – then to me it appears you’re taking it along, not as a guide, but more like a Teddybear to hold your hand.

    As a physicist I’m deeply troubled by seeing someone in a significant position advocating the abandonment of falsifiability. Yes, it might be that string theory is correct without being falsifiable. Yes, it might be true about the multiverse too. And it might be true about God and about the giant teacup theory. But for Science to have any value, we have to stick to the perhaps limited position of only accepting statements and theories, where Nature is left a right of veto. Otherwise we’re not doing Science anymore.


  13. DEL says:

    Falsifiability is just one in a whole set of requirements. Others are, e.g., internal consistency, mathematical distinction, Occam’s Razor compliance and, lest some priviledged Edger might suggest to retire it, agreement with the complete existing body of experimental and observational results to within their respective error bars.

  14. Pingback: Shtetl-Optimized » Blog Archive » Retiring falsifiability? A storm in Russell’s teacup

  15. Hi Sean,

    It’s been long time since I publicly, sort of, insulted you—I mean, online. (I vaguely remember the development of a facility to shuttle in between the universe(s (!)) of multi-verses. … Come to think of it, I got it almost right.)

    Never mind.

    With that (Marathi) “namanaalaa ghaDibhar tel” [rough English sense of the term even if not the translation: When you pour a pound of oil to the lamp of the God right before the beginning of a prayer… [meaning: you are so stupid, such a newcomer, you wouldn’t even know how to make a candle burn *all* through the night at a church]], even without the full of your post or your readers’ replies, let me answer in brief:

    Instantaneous Action at a Distance.

    We could do without it.


  16. Bruce Caithness says:

    Maybe it is worth recognising that Popper’s idea of falsifiability was a vast improvement on the positivist attempt to separate science from non-science in terms of sense or meaning. Popper is not saying that non-falsifiable statements are meaningless nor even less true than scientific statements. For instance realism and anti-realism are metaphysical and cannot be refuted. This does not mean they are beyond argument. Popper liberated metaphysics from a narrow positivist treatment.

    Popper would say: We explore the universe by conjecture and we explore our conjectures through logic (rationality filters our guesses). Falsifiability is a logical property of scientific statements.

  17. Pingback: Methods: testing an idea

  18. DEL says:

    For many years I have been an e-mail subscriber to Edge and I usually read most of the monthly conversations there. I made it a rule, however, to skip the annual question and all the answers given to it, for three main reasons: 1) The sheer volume of them. 2) The mostly mediocre quality of the answers, which reafirms what Buddhini Samarasinghe wants to get rid of:

    ◾Buddhini Samarasinghe, Scientists Should Stick to Science.

    3) If I’m technically prevented from even proposing an interesting answer, since Edge excludes mortals such as I, (i.e., those that do not cater to Mr. Brockman’s publishing business,) then I’m not interested in their tedious answers—let them read one another ad nauseam.

    Several years ago I attended a Nobel laureates seminar in the Technion, Haifa. One of the speakers was a co-winner of the 1991 prize for the invention of the patch clamp neuroscience lab technique. He told the audience that, being a rather shy person, he had hesitated whether to accept the invitation. Consulting his mentor, the latter had told him briskly: “A shoemaker should be making shoes.” (But he had accepted anyway.)

    Take, for example, the first answer, by

    ◾Danny Hillis, Cause and Effect.

    As an example for the unsoundness of the cause-and-effect concept, even in classical mechanics, he brings up the case of Newton’s 2nd law, F=ma, where one cannot say which of the three quantities is cause and which are the effects. But this only shows a misunderstanding of that law, which is nothing but a definition of inertial force (mass being defined, as by Newton himself, to be “the quantity of matter,” [Principia, Book 1, Definition 1]), and a failure to realize that causality entails that the events involved be time-sorted. Incidentally, in the LHC, which is the cause and which is the effect, the hadrons colliding or the Higgs boson signature detected? If you know the answer to that you know also what to think of Hillis’ suggestion.

    Yes, shoemakers should be making shoes and scientists should stick to science.

  19. policrit says:

    I am troubled by the treatment of falsifiability as a single theory. There are strong and weak versions with many gradations. Is the theory not falsifiable right now with present methods? In the near future with plausible methods? Eventually with purely theoretical methods? Probably unattainable methods? Not falsifiable with any conceivable test? I would submit that at least the last is certainly a valid notion.

  20. From reading the enlightening comments, the post are against your idea of rejecting the idea of falsifiability as a scientific concept to reject. The posts give excellent arguments against your proposed idea. Floating out such ideas is a wonderful way to learn.

    Science is based on experimental data. Theoretical and experimental physics ultimately make their advancements based upon data. Theories need to be tested with data. If a theory cannot be tested against data it is not science, it is philosophy. A scientific theory must have the ability to be shown wrong with experimental data.

  21. The practice of Science has always been ad hoc, a gradual groping
    for a way of proceeding that seems reasonable– “falsifiability”
    is one an attempt at firming this up, and it seems funny to me
    that so many people here are trying to treat it as though it’s
    some sort of primary revealed doctrine.

    Falsifiability itself isn’t a scientific idea, right? Most of us
    would call it a philosophic principle (after all: “Is
    falsifiability falsifiable?”). So if it strikes you as a
    critically important idea, you’ve already conceeded that there
    are things outside of science that matter.

    An attempt at advancing science like “string theory” might not be
    precisely “scientific” (as of yet) if you’re a true believer in
    falsifiability, but in that case you could just put string theory
    in another category (“proto-scientific”?). String theory need
    not be abandoned as Unscientific and Unclean.

  22. Jesper says:

    @ Joseph Brenner.

    “… So if it strikes you as a critically important idea, you’ve already conceeded that there are things outside of science that matter.”

    – yes, of course! The concept of falsifiability – which simply means that you’re giving Nature a right of veto – does not mean that only falsifiable statements are worth while considering. It simply means that only (in principle) falsifiable statements can be called scientific theories.

    Most things that matter is outside of science – obviously.

  23. Richard says:

    If you have a (mathematically) complex theory which currently does not make predictions, but you think it will after 1 year of research, is it scientific? What about 5, 10, 50, 100 years? At what point does it become nonscientific?

  24. Bob Iles says:

    For further info on this exciting topic cf. arXiv:1210.8144v1.

  25. Jesper says:

    @ Richard. In my opinion, to call a mathematical framework (or something else) a theory requires predictions (they may not be practically verifiable). If your framework doesn’t make predictions, then it may of course still be very interesting and worthwhile pursuing, and it is still scientific – its just not a theory.