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. Haelfix says:

    These comments all miss the following very important point. Namely that the idea of a multiverse IS falsifiable in principle. If you make a collider and create the inflaton particle, you immediately know detailed properties about the physics of the very early universe, like whether it is in the eternal class of potentials or not. From that point on, you likely know whether or not there really is a multiverse of causally separate regions.

    Now this is probably not falsifiable in practice because we can’t create accelerators with that type of energy, but it is falsifiable in principle and that is what Popper was talking about. I dare anyway to come up with an argument that says that this is not science, and then contemplate how silly they sound when faced with all the impossible experiments that latter became possible. Does every idea preceding these experiments not count as science?

  2. Doc C says:

    @ Haelfix, What is different about being falsifiable in principle but not in practice and having no way to provide evidence for a belief? For example, those who believe that God will return to the world at the end of time can say that God is falsifiable because he will be falsified at the end of time if no God actually shows up. We can’t know the facts about the end of time in practice, but we can in principle; we just have to wait for it.

    Humans have acted on non-falsifiable beliefs for millenia, and we are still here. Maybe we don’t always need certainty to successfully interact with our environment. However, falsifiability is the only way we gain certainty by successfully testing our interactions.

  3. DEL says:

    @Doc C:

    “… falsifiability is the only way we gain certainty by successfully testing our interactions.”

    Sorry, but the whole point of falsifiability is that there is no certainty. You can only falsify a wrong theory but you can never be certain of one you failed to falsify.

  4. Doc C says:

    @DEL, Yes, that was sloppy. I should say the only way to gain IN certainty, or become relatively more certain. However, the true lack of certainty of any theory or law, taken to its extreme, is not a useful way to do science, with or without falsifiability.

  5. Bruce Caithness says:

    My reading of Popper is that a falsifiable statement is vulnerable to empirical refutation. Even if it fails a test there might still be debate about whether the theory is actually wrong e.g. due to errors in the test environment.

    Popper has a sophisticated view of the rules of the game of science. The game of science is in principle without end and a practitioner no longer plays the game of science if he or she chooses to evade critical analysis or further empirical testing of theories.

    Certainty is perhaps an over-used word which tends to focus on belief rather than truth, even if truth is hard to find.

  6. Haelfix says:

    The Higgs boson was a theoretical idea that was written down 50 years ago. It was not a falsifiable idea at the time, so according to this silly dogma we must not consider it science. For that matter, all GUT theories, theories of dark matter and for that matter almost all of modern HEP-PH must not be science either.

    Popper knew perfectly well that science didn’t always have to be falsifiable now. Instead he was interested in refuting statements like ‘god is an invisible spaghetti monster that hovers over my room’. The latter statement can never be disproved, even in principle. Conversely, the multiverse might be verified tommorow (for instance by observation of a bubble collision) or alternatively it might be refuted tommorow if strange features appear in the next CMB experiment that shows deviation from inflationary expectations, and certainly if we had a big enough accelerator we would know with almost complete certainty.

    Of course, scientists don’t care one whit about whether or not something adheres or not to one dead philosophers ideas about propriety, instead we have a great deal of mathematical evidence as well as circumstantial evidence for an idea, therefore we are allowed to study it.

  7. Mohammed Patel-Gonzales says:

    Dr. Carroll – I know this is off-topic but I figured you’d get a kick out of this in any event, & that is because I was able to understand something because of what you mentioned on the blog some while back now.

    Anyway, I’m reading an urban fantasy by Tad Williams called The Dirty Streets of Heaven & in it, one angel says to another something like the following: “He even asked me how A & B work, which is kind of like asking a Juggalo to explain magnetism.” The book came out in 2012 but I never would’ve understood what the author was talking about here if it hadn’t been for your earlier comments on the idiotic ignorance of the Insane Clown Posse concerning magnetism & such, which presumably extends to their fans, called Juggalos, as well. Oh, & BTW, the FBI recently deemed the Juggalos to be a criminal gang so presumably now they can be shot on sight by anybody. Good news!

  8. DBachmann says:

    I would humbly suggest that if something “might play a crucial role in how the world works”, it is a fortiori also observable, at least indirectly, and statements relating to it are in principle open to falsification. I seem to remember that even string theory once had a motivation based in observables, specifically the desire to understand gravity, which I assume we are all experiencing as we speak.

    Also, I see nothing wrong with the statement that “the universe began in a low entropy state”, as you say yourself in the linked post, “the fact that entropy increases defines the arrow of time”. The statement is true to the point of being tautological, so I suppose you could argue it is unhelpful based on that. But arguing against it devolves into a semantic game on the meaning of “beginning”.

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  10. There are category issues here. I would say that “nonfalsifiable physics” is really “mathematics”.

  11. Sean, I strongly disagree with your position on falsifiability, for many of the same reasons that others have mentioned before. Two things I would like to point out though:

    – The criteria you suggest as replacements, that a theory should be only “definite” and “empirical”, are not enough to exclude a vast swathe of creationist ideas that I’m sure you would agree are not scientific. Therefore falsifiability is still necessary.

    – I think the point you were getting close to making, but did not quite articulate, is that the definition of the word “falsifiability” should be slightly expanded to incorporate the notion of Bayesian probabilities rather than simple yes/no rejections. In this case the multiverse may yet turn out be (but is not guaranteed to be) a “falsifiable” idea. But if it doesn’t, it is still not science.

    I can’t fit much more than that summary in this comment box, but I’ve fleshed out these ideas a bit more here if anyone is interested.

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  13. colnago80 says:

    Speaking of ideas that should be retired, does Prof. Carroll have any comment on the latest from Steven Hawking that black holes don’t exist?


  14. DEL says:

    Colnago80’s point does bear on the issue of falsifiability discussed here. Specifically, we may ask whether Steven Hawking’s kind of work is or is not science. Surely, by mathematically fiddling with the equations of GR and QM, doing it in an academic setting and on Isaac Newton’s chair, uploading papers to arXiv, etc. etc., the most celebrated physicist of our time must be doing something scientific, mustn’t he? I’d say yes, of course, but these are only superficial, social-cultural hallmarks of science.

    Here’s what I understood of the problem Hawking is nowadays dealing with: what does a free-falling object encounter just past a black hole’s event horizon, a blissful continuous glide down or a sudden violent incineration?

    By definition, what happens beyond the event horizon is in-principle a secret. However, the behavior of matter and radiation just outside the event horizon might be linked by theory to the answer to that problem. So, to decide whether Hawking is a scientist or a science artist—a noble-enough occupation, in my view—I would like to know whether there might exist some unique observable prediction associated with the sought answer or with some spin-off result. If there is, and if it is observed, then Hawking might even be noticed, at long last, by the physics Nobel prize committee.

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  16. Marcos Hardy says:

    Popper’s “falsifiability” is obsolete only if you apply it indiscriminately to determine Science from non-Science instead of use the concept to understand the workings of scientists in the real world. Every time a scientist experimentally tests an hypothesis he is falsifying a scientific idea, once the hypothesis has been successfully tested and published, then other scientists will attempt to falsify it through replication, and so forth, until a theory is established, which in turn will be tested (falsified) ad infinitum. Examples of this type of falsification abounds, from cold-fusion to the memory of water to cite extremes. Freud did not “discover” the unconscious but in his research of the operations of the mind produced a testable model of its dynamics in shaping our behaviors, thus questioning the reality of “free will.” Today, neuroscientists are producing increasingly reliable experimental tests of Freud’s models; i.e. Freud’s model, one of Popper’s examples of “unfalsifiability,” is now becoming amenable to falsification. And, please, do not confuse Freud’s scientific research efforts with the corrupt voodoo clinical work of the psychoanalysts. Einstein’s theory of gravity was successfully tested through Eddington’s 1911 measurements of starlight deviation during a total solar eclipse. Nonetheless, astrophysicists are getting ready to test it (falsify it) once more with a pulsar and two stars (cf. Adrian Cho in Science (2014) vol. 343 pp 126.) Has not Einstein’s theory of gravity achieved total “truthiness” already? Why does it need constant testing (falsification)? Well, Science advances, also, through falsifiability. That “string theory” (is it a theory already?) and “multiverses” (typical examples of what Horgan called “ironic Science”) are not currently amenable to falsifiability speaks of technological shortcomings in our current state of development but not necessarily in the future and scientists might become able to eventually falsify them. Dark matter and energy are conveniences (as was the flogiston once) to explain cosmic phenomena but scientists are putting an extraordinary effort to test (falsify) the hypothesis. One might even say that Marxism, another of Popper’s bête noirs, was falsified through the social experiments of the post-war. I believe that the concept of falsifiability is an extremely useful epistemological concept to understand the developmental operations of the Sciences in the real world. The problem does not lie with Popper’s falsifiabilty but that, like Kuhn’s “paradigm,” it has been horribly misused and mangled. To apply an unfalsifiable cliché, keep the baby and start discarding the dirty bathwater. Keep falsifiability current and apply it correctly.

  17. Michael Allen says:

    How does one go about showing a statement is falsifiable anyway? Wouldn’t that in itself be fundamentally unfalsifiable?

  18. Bruce Caithness says:

    Falsifiability is but a logical property of a statement. The practical attempt to refute a universal statement by showing a basic statement to be wrong is called falsification.

    The propositions of concern to Popper were universal statements with a form such as “all swans are white”. This is in a falsifiable form in as much it would be nullified by the statement (if true): here is a black swan.

    Whether the basic statement “here is a black swan” is true requires a decision which, to forgive the pun, may not be black or white.

    Popper was not talking about “naive” falsification. Whether a statement is decidable (whether we believe we can prove it true or false) differs from the question of its truth.

    “I mean by ‘rationality’ simply a critical attitude towards problems – the attitude of conscious, critical, error elimination” (Popper)

  19. mpc755 says:

    The whole notion of “falsifiability” is meaningless in mainstream physics.

    The particle does not always travel through a single slit in a double slit experiment.

    How do you falsify the above statement? You place detectors at the entrances, throughout or at the exits to the slits.

    When you do this the particle is always detected entering, traveling through and exiting a single slit.

    The notion the particle does not travel through a single slit is refuted by the evidence. It’s been falsified.

    So, what does mainstream physics do? They ignore the physical evidence which refutes the notion the particle does not travel through a single slit and state that something else occurs when you don’t detect the particle.

    What is that something else? Well, now mainstream physics can make up all sorts of stuff about a multiverse or many worlds or whatever nonsense it wants because you can’t falsify made up nonsense.

    The notion the particle does not travel through a single slit is falsified by the physical evidence.

    However, mainstream physics is so fucked up it can’t understand something as simple as the particle always being detected entering, traveling through and exiting a single slit in a double slit experiment is evidence the particle always travels through a single slit. It is the associated physical wave in the aether which passes through both.

  20. DEL says:

    You don’t understand: one doesn’t try to falsify an isolated statement such as “The particle does not always travel through a single slit in a double slit experiment.” The statement F=ma, in isolation, is also unfalsifiable.

    The complete system of statements, explaining the outcome of both the free and obstructed double-slit experiments, of which the statement ‘the particle travels through both slits at the same time’ is just one component, is the falsifiable content. Similarly, the complete system of Newton’s laws is falsifiable, not any one of them in isolation.

    And you don’t understand: foul language won’t make your arguments more persuasive.

  21. mpc755 says:

    Physics is supposed to be about understanding what occurs physically in nature and the evidence which supports what we think is occurring physically in nature.

    In a boat double slit experiment the boat travels through a single slit and the bow wave passes through both. If the boat is moving fast enough the bow wave will create wave interference upon exiting the slits which will alter the direction the boat travels. If you place pilings at the exits to the slits in order to detect the boat the boat will get knocked around by the pilings, lose its cohesion with its bow wave, and continue on the path it was traveling.

    Is the question the boat does not always travel through a single slit falsifiable?

    When you place pilings at the entrances to the slits the boat is always detected entering a single slit. When you placing pilings anywhere within the slits the boat is always detected within a single slit. When you place pilings at the exits to the slits the boat is always detected exiting a single slit.

    The question the boat does not always travel through a single slit has been falsified.

    Now, just because when you place a screen in front of you so you can’t see the boat double slit experiment and the boat makes an interference pattern on the shore when it is not detected is not evidence the boat did not travel through a single slit. It is indirect evidence it is the bow wave which passes through both slits.

    The fact that mainstream physics is so screwed up it can’t understand the particle always travels through a single slit is the reason for the strong language. Sometimes strong language is appropriate.

    Doing away with falsifiability because mainstream physics is in denial of understanding it is the aether which waves in a double slit experiment is one of those times.

    Do you realize most of the nonsense associated with mainstream physics goes away when you understand aether has mass which physically occupies three dimensional space and is physically displaced by the particles of matter which exist in it and move through it?

  22. mpc755 says:

    The idea which is ready for retirement is the notion of, “in truth, only atoms and the void”.

    In truth, not only is there an aether, it has mass.

    There is no such thing as non-baryonic dark matter anchored to matter. Matter moves through and displaces the aether.

    What is referred to as the the Milky Way’s dark matter halo is the state of displacement of the aether.

    What ripples when galaxy clusters collide is what waves in a double slit experiment; the aether.

    Einstein’s gravitational wave is de Broglie’s pilot-wave; both are waves in the aether.

  23. DrDave says:

    This is a sort of high-tech “lobbying” where one puts the best spin on something, in this case, the spin is applied to a set of ideas that has some serious problems. Part of the process is to exclude valid rebuttal, and to slyly insult those who have a different viewpoint (calling good scientists and thinkers “lazy” and that their ideas are “bandied about” is the worst sort of laziness, the slur).
    The reality is that there are a lot of entrenched academics that currently are not pursuing all avenues of science. This then becomes a story about raw political power, not ideas. Regardless of whether you believe that strings and SUSY are just another form of dreaming (after all, in another universe dreaming might be reality), the result, the plain, hard, cold, light-of-day truth is that other areas of physics, mathematics, philosophy and science have been permanently back-burnered as a result of the successful lobbying of an activist, well-positioned group with an entrenched mindset. This post shows the defense mechanism of this Borg-like structure–or perhaps NOMAD, saying: “I am SUSY, I created the Multiverse”, on a loop (a gravity loop, of course).
    So truth isn’t beauty, and beauty isn’t truth; in this universe, beauty and truth means freeing the system. Free it, and share your theories with others; let others share their theories as well.

  24. mpc755 says:

    Does a tag line of, “in truth, only atoms and the void” mean you do not believe dark matter and dark energy exist?

    Are you suggesting light waves propagate through an empty void?

  25. mpc755 says:

    How do you know the particle does not always travel through a single slit in a double slit experiment?

    You don’t.

    You choose to believe the particle does not always travel through a single slit so you can make stuff up like ‘many worlds’.

    There is evidence of the aether every time a double slit experiment is performed; it’s what waves.

  26. Marcos Hardy says:

    mpc755: you are exhausting everybody’s patience. Call it a day, please.

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  28. Bruce Caithness says:

    “Myth and Metaphysics.

    In his books Objective Knowledge and Conjectures and Refutations, Popper demonstrates brilliantly the roles of myth and metaphysics in the scientific enterprise. Myths represent our human need to expand the horizon of explanation and to find our place in the vast scheme of things. Emphasizing the importance of boldness of imagination in fulfilling this need, Popper suggests that Democritus’ early theory of atoms began as a myth born of a daring imagination.

    Myths sometimes graduate to the status of metaphysics when subjected to sustained and rigorous criticism. Metaphysics is the work we do when we carry out comparative analysis of our cosmological myths and theories. It is our drive to eliminate inconsistencies, to broaden the scope of our explanations, and to provide depth of detail. If there are priests of myth who insist on perpetuating the myths without correction or revision, there are others among us who both subject the myths to criticism and offer rival theoretical explanations. Of late, the term metaphysics has been adopted and used to propagate the uncritical and highly anthropomorphic notions of pop culture. This is not the tradition of rigorous metaphysics of which Popper speaks.

    Far from being meaningless, critical metaphysics and cosmology provide the cognitive background for the growth of scientific theory. Logical positivists failed to see that, without metaphysics to work upon and to refine, science would stagnate. In some ways, science is the metaphysics that succeeded in spawning bold theories which are not only well articulated and critically debated but also observably testable–and by testable, Popper means falsifiable.”

    Joe Barnhart, American humanist (1920-1993)


  29. Marcos Hardy says:

    As much as I admire Popper, let us not forget that he was a dualist “a la Cartessiane.” He did not believe that mind could be the product of matter. Let us keep Popper’s vision of how Science develops and the workings of scientists. His metaphysics have no scientific value, as they are not falsifiable. (Last comment is tongue in cheek.)

  30. Bruce Caithness says:


    One theme of Popper’s output is evolutionary epistemology. Evolution is trial and error. From this perspective, mind emerges from matter but can hardly be reduced to matter. He is an interactionist.

    I have returned to Popper’s name in my comments because falsifiability is one of his themes that has often been distorted in philosophy of science textbooks.

    It is usually overlooked that there were at least six themes in his work. These are succinctly summarized in Rafe Champion’s “A Guide to the Logic of Scientific Discovery” (Kindle).

    Yes, I notice the irony in your last sentence.

  31. Abhishek Khanal says:

    I’m reminded of Richard Feynman,” For those who want some proof that physicists are human, the proof is in the idiocy of all the different units which they use for measuring energy.”