The discovery of Neptune and falsifiability

April 29, 2012 • 7:51 pm

by Greg Mayer

Jerry’s post on falsifiability raises interesting questions in the philosophy of science, and I’d like to extend the discussion by referring to a famous incident in the history of science (which is something philosophers of science often do– it’s how they test their ideas). The incident is the discovery of Neptune.

Neptune (NASA photo).

By the end of the 18th century, the orbits of the planets had been fairly well worked out on the basis of observation and Newtonian mechanics. But, by the 1820s, it was evident that Uranus was not following the predicted orbit. The French astronomer Alexis Bouvard perceptively remarked

… I leave it to the future the task of discovering whether the difficulty of reconciling [the data] is connected with the ancient observations, or whether it depends on some foreign and unperceived cause which may have been acting upon the planet.

In the 1840s, two mathematical astronomers took up the challenge, and, hypothesizing that the “foreign and unperceived cause” was an undiscovered planet, attempted to calculate the position of such a hypothetical planet based upon Newton’s laws. They didn’t just speculate about the supposed new planet, though, but also sought to have observatories look for it. The two astronomers were John Couch Adams and Urbain Le Verrier.

Urbain Le Verrier (Wikipedia)
John Couch Adams (Wikipedia)

On 23 September 1846, at the Royal Observatory in Berlin, Johann Galle, looking where La Verrier had directed him, found the undiscovered planet, which we now know as Neptune. He wrote to Le Verrier two days later:

Monsieur, the planet of which you indicated the position really exists.

Since the 1840s, there has been a dispute as to who deserves the most credit for predicting the existence of the new planet– Adams or Le Verrier. It is clear that it is Le Verrier who actually inspired the successful observations. But the dispute need not detain us– it suffices that the planet was discovered on the basis of someone’s calculations.

So what has this to do with falsification? Well, the problems with the orbit of Uranus meant that there was something wrong with a Newtonian understanding of the solar system. To a naive falsificationist, it would seem that we must conclude that Newton was wrong. But this is not what practicing scientists did. Instead, they sought a way to preserve Newton’s laws, by changing the auxiliary hypotheses used to carry out calculations of predictions under the laws. For the problem was not that Newton’s laws were wrong, but rather that Newton’s laws as applied to the known planets were wrong. The problem therefore could have been not with Newton’s laws, but with our conception of how many planets there were. Schematically

(Newton’s Laws + known planets) predict (orbit U for Uranus);  (Uranus does not have orbit U); therefore:

Newton’s Laws, or the known planets, or both, are wrong.

What was falsified was a composite claim– we don’t know which part of the composite is false. (This is an example of what is known as the Duhem-Quine thesis– that hypothese are tested in bundles– mentioned in the comments to Jerry’s piece.)

Why did Adams, Le Verrier, and Galle choose to continue working with Newton’s Laws, rather than abandon them? Because Newtonian mechanics had been a spectacularly successful research program, and it didn’t seem epistemically prudent to throw out the whole thing on the basis of an anomalous orbit, when there were other possible explanations for the anomaly. It seemed reasonable to them (and indeed it was reasonable), to continue with laws that had worked so well in so many circumstances already, rather than concluding they were false.

But isn’t pursuing an escape from falsification a characteristic of pseudoscience? Well, yes it is, if escape from falsification is all your research program consists of. But crucially, Adams and Le Verrier’s escape from falsification was not merely an excuse for the failure of Newton’s Laws to correctly predict the orbit of Uranus. Rather, it was itself an independently testable hypothesis, which, indeed, they (or, more precisely, Galle) tested. This observational test did not depend on the truth or falsity of Newton’s Laws of motion and gravitation, and was thus independent of them. The successful prediction of the existence of Neptune has turned what was potentially a fatal falsification into one of the greatest triumphs of Newtonian mechanics– the discovery of a hitherto unsuspected phenomenon. Newton’s Laws showed what philosophers call “fecundity”.

So, falsifiability is a useful criterion for evaluating scientific claims. But falsifications is a lot harder than the simple logic of  ‘A implies B; not B; therefore not A”. There’s not a hard and fast line between scientific and nonscientific claims, but rather a gradation from vigorous, successful research programs, such as evolutionary biology, to degenerate pseudosciences, such as creationism, with things like cryptozoology somewhere in the middle. If all your research program does is move from one escape from refutation to another (it isn’t A, then it’s B; not B, alright, let’s try C; no good?, then how about D; not D,…), then your research program is degenerating. All the signs of vigor (falsifiability, independent testability, fecundity, and others) must be examined in evaluating the epistemic status of a claim or research program.

And a final word, on behalf of Popper. Although he was the falsificationist par excellence, he was not naive, and anticipated many of the criticisms of falsification that later arose. Although he, understandably, emphasized his notion of falsifiability, he began the development of “sophisticated” falsificationism himself.


Much of the historical detail is taken from Mathematical discovery of planets on the wonderful website History of Mathematics Archive at the University of St. Andrew’s in Scotland.

54 thoughts on “The discovery of Neptune and falsifiability

  1. The precession of Mercury’s orbit is an actual example of falsification of the Newton’s laws. The discovery of Neptune was a triumphant example of the predictive content of the theory, not an example of its potential falsification. We want theories to predict novel phenomena. If Neptune wouldn’t have been there, then, Houston, we’d have had a problem.

    1. I am glad that you introduced Mercury into the discussion. I agree with your post. I would like to add that Newton’s theory was remarkable for its capacity to unify what had been a disparate set of phenomena. In addition to being undermined by a false prediction, Newton’s theory was undermined by a better successor theory (i.e., one that does a better job of explaining the facts). The failure to find an as yet undiscovered planet in the case of Mercury did not lead to a rejection of Newton’s theory. Mercury’s motion was considered an unexplained anomaly until Einstein’s theory came along and explained it.

      1. Thinking more about this, the best example for the question of falsifying Newton dynamics is the anomalous rotation of galaxies discovered by Vera Rubin. In this case, the alternatives are more mass, in the form of hard-to-detect dark matter, or Modified Newtonian Dynamics (MOND). The latter is a clear example of trying to rig the theory to fit the facts.

        1. On Modified Newtonian Dynamics, I might respond by pointing out a complexity in the issue of a theory “rigged to fit the facts.”

          To begin, Quine would likely argue that there are no “facts” at all outside of the theoretical framework through which they interrelate (much like Churchland’s “hyper-dimensional state-space through which concepts interrelate.)

          To look at the history of science, we know that the periodic table of elements predicted many kinds of elements before they were even discovered. We would take this to be a good example of the “facts fitting the theory.”

          If we look at Russell’s at-at theory of motion, however, the idea of theories fitting facts seems very appealing; to solve Zeno’s Paradox, which held that an arrow would have to somehow move “through” or “during” infinitesimal points of time, Russell purposed that we need not bother ourselves as to “how” the arrow moves from infinitesimal to infinitesimal. Rather, we simply see that the infinitesimal calculus provides us with a position for the arrow derived value of t. The way the arrow moves from A to B is simply by occupying all of the interviewing values for x1 to x2 when given t1 and t2. The arrow moves, that is, by being at x1 at t1, and at x2 at t2, and so on for all values in between.

          What we are left with from Russell is the idea that while the calculus works as a wonderful predictor, it merely charts or maps the motion of the arrow without seeking out some other causal explanation for the motion itself, the way Zeno did (or Hume did in regards to causality per se.)

  2. I think this example illustrates why the bayesian outlook is relevant. Given that the orbital data for uranus wasn’t quite right, the question was whether to reject newtonian mechanics or look for another planet. Since the prior for newtonian mechanics is so high (due to all it’s successes) the posterior probabilities (using “back of the envelope calculations”) pointed to the probable existence of another planet.

    The same reasoning can be used (in reverse) when somebody comes up with “strong evidence” for something like ESP or UFO’s. The prior for ESP is so low, that even the new evidence doesn’t put a dent in it.

  3. What’s this “sophisticated falsification”?

    I don’t understand why the mention of “naive falsification” since it is not something the majority of scientists do. Of course there are exceptions but those tend to be dismissed by other scientists as crazy or stupid – for example, claims that “epigenetics” is going to overthrow the Darwinian theory of evolution.

    I still don’t see any evidence that science is somehow in any way dependent on philosophy.

    1. Jerry is making the point that some science philosophy has over-simplified and in practice science is often more subtle than its given credit for. I agree with that, and I also agree that science is not dependent on philosophy. Further, philosophy has sometimes held science back by trying to impose bad ideas such as restrictions on what areas science might apply itself to.

      However, in defence of philosophers, scientists have also benefited from and incorporated into their practice ideas that came from philosophers. This was particularly clear in the early days of quantum mechanics as physicists struggled with the implications of their theories.

      1. But what are these ideas which came from philosophers and influenced the formulation of quantum mechanics?

        1. I don’t know enough of the history, but Bohr and Einstein were themselves vigorous participants in philosophical debates and I don’t know how you’d even go about starting separating that from their contributions to physics.

          1. If we understand science as ‘natural philosophy’ as it used to be called, then maybe the ego wars between science and philosophy can end, or at least raise awareness that natural philosophy is a good philosophy that works.

            1. OK, I read it and I don’t see how philosophy is in the least bit relevant to science. I see the rather trivial fact that Einstein writes that he believes a philosophy of science is of value but who but Einstein knew what he meant by that. What is clear is that Einstein believes that scientists must not become complacent and set in their views about what is right and wrong and the right and wrong way to do things, and that’s about it.

              Perhaps an analogy would help (though I hate analogies). The sun shines and for 100 years now scientists have understood why it shines. However, what scientists understand is absolutely irrelevant to whether the sun shines or not. If science is right then humans have a fair approximate idea of how long the sun will shine, and if science is wrong that doesn’t really matter because the sun will do what it will do. The case is similar for any philosophy of science – it is entirely irrelevant to science. It can only possibly be of value if it can actually guide science somehow – that is, offer something which scientists don’t already know and which helps to make new discoveries and improve our understanding of the world. Since the philosophy of science is either disjoint from reality as in the methods of Plato and Aristotle, or is merely post-hoc rationalization and rumination as in the case of Popper, the philosophy of science has absolutely no real value to science. Philosophy is mired in dead ends and that is why it was abandoned by scientists hundreds of years ago. It creates conjectures but does not advance anything. I would go so far as to say that most of philosophy is merely a delusion of rational thought akin to the delusion of the existence of gods. (And sure many contemporary philosophers say there is no god, but one doesn’t need philosophy to arrive at that conclusion.)

              1. It’s conceivable that science as a sociological phenomenon could work itself into corners or local maxima, and that such events could ultimately constrain the output of such scientific communities. In such cases, philosophers of science could conceivably help scientists “repair” their fields. I’m imagining a situation in which a field’s pedagogical methods end up better at instilling dogmatism than skepticism, or something like that.

                I say it’s conceivable because I don’t think it’s likely at all. I’m essentially of the same opinion as you; science seems to work whether or not we understand precisely why, and that this fact is analogical to the sun shining whether or not we know why, or the fact that birds would be the way they are whether or not ornithologists go around observing and describing them.

                And even if scientific communities were ending up in my hypothetical scenario from my initial para, I don’t think philosophy of science is currently in a position to diagnose and repair the problem so the argument is moot. But I wanted to at least mention the possibility.

          2. It’s not a matter of trying to separate their philosophical debates from their science but showing how the philosophical debates may have contributed to the science as claimed.

            1. For all the faults of the paper (there are many), Arthur Fine has a great discussion of the impact that Bohr’s and Einstein’s philosophical disagreements had on the development of 20th century physics in his paper “The Natural Ontological Attitude”. The short of it (unfortunately, I can’t find a PDF online—it’s in his book The Shaky Game if you’d like to look it up): Bohr’s anti-realism led him and his followers to pursue a different research program than Einstein’s realism, and Bohr’s was by any reasonable measure more successful.

              If you’d like, I can re-read it tomorrow and type up a more in-depth summary. Bedtime now.

  4. The attacks on Popper, and the Logical Positivists in general all seem to have been predicated on the view that they were laying down logical axioms — “do this and you must achieve truth”. But if we regard their writings in the same light as the Pirate’s Code — “…more what you’d call ‘guidelines’ than actual rules..” — I think they still hold up extremely well: at least, I haven’t encountered any remotely convincing alternatives. Following Popper won’t necessarily yield truth, but not following Popper is unlikely to yield anything but nonsense.

    1. Oh dear, Popper would have been very annoyed by your lumping him together with the Logical Positivists. His 1934 book Logik der Forschung was widely seen as an attack on not just the LP’s verification principle but LP itself.

    2. Oh dear, here we go again with the false equivalences. What do you mean by “not following Popper”? Most scientists I know are either unfamiliar with Popper’s work or couldn’t care less about his work – and yet they do not produce nonsense. You may imagine that what the scientists do fits into Popper’s description – but that is of no relevance whatsoever to science.

      1. A scientist can ‘follow’ someone’s ideas without being aware of the originator of the idea nor their actual writings. If most scientists you know have not heard of or are aware of falsification, then you probably hang around with a lot of elementary school aged scientists.

        A lot of Christian thought and ideas are based on the writings of St. Augustine and Aquinus, but most Christians are unaware of them or could care less. Using your logic, these two didn’t affect Christian thought.

        1. See, that is the problem with philosophy – it is worthless because it is so ass-backwards. It claims to be important and relevant to science when it is not. Even your analogy here is so obviously wrong for many reasons.

          1. whether philosopher’s ideas about science are right or wrong don’t matter at all – science goes and does its thing anyway. Philosophy can only be relevant if it contributes somehow to science rather than simply making claims about science as it does. Making claims about science then claiming to be of relevance to science because of those claims is just so backwards. It’s like taking a yoyo apart, describing its construction, then claiming that yoyos owe their function to your description. Backwards. To say that scientist “follow” some goddamned philosopher because some philosopher made some generalizations is simply a lie – the sort of lie perpetuated by philosophy for over 2000 years and why philosophy is so utterly worthless in understanding the universe. Philosophy is a long-running failed attempt at learning which is entirely unaware of its own irrelevance.

          2. You have an extremely naive view of things or you are deliberately attempting to deceive by claiming that “Christian thought” would not be affected by Augustine and Aquinas if one used “my logic”. You have a deceitful representation of my position.

    3. Most scientists do not follow Popper, even in ‘guideline’ form. Don’t believe me? Go out and count the number of publications that focus on confirmatory rather than falsifying evidence.

      Or better yet (but much harder to do), try and count proposals for those things. I bet if you did that, you’d find that the overwhelming majority of time, scientists plan experiments that do not have falsification as a primary goal. It may be a minor goal or surprising discovery, but it’s rarely the point of the research.

  5. Why would you consider the use of Newtonian physics to explain the problems with the orbit of Uranus as an escape from falsification. Falsification works differently for established (well tested) sciences than untested ones. At some point a theory does stop being falsifiable because finding one failure in a theory does not negate all it’s previous successes and so does not negate all of it. A good example is the problem Newtonian physic had with the anomalous perihelion advance of mercury until Einstein’s General relativity. I suspect that if we don’t find the Higggs boson it won’t negate the standard model as a means of explaining the universe but rather it will lead to a quest to find out why and will either lead us to modify the SM theory or come to an understanding of the limits which would require new theories to fill it.

    1. Actually, the Neptune example is pretty much a standard in philosophy of science for demonstrating why strict(/naive/etc.) falsificationism doesn’t work.

      Basically, the discovery of Neptune shows how any theory can be defended against any sort of falsification.

      Experimentalist: “The results of the experiment do not match the predictions of the theory.”

      Theorist: “Then there must be some other cause at work which is unaccounted for by experimental assumptions.”

      This doesn’t just work for “established theories,” you can use this to defend any theory. It’s just like Sagan’s invisible dragon; every time you find a new argument against the dragon’s existence Sagan produces a post-hoc excuse for why that test shouldn’t work.

      Instead trying to logically establish that there’s no dragon, we just calculate the probability that an invisible, flying, odorless, silent dragon ever lived in Carl Sagan’s garage and the probability is low enough that we can safely ignore it. It has nothing to do with some theories “earning” reprieve from anomalies, as that idea is even more problematic than strict falsificationism.

  6. It would have to *very* naive falsificationists: in particular ones who never heard of experimental error.

    In the case of Uranus, there could have been errors in the observations, errors in the computation, or errors in their assumptions (i.e. the # of planets). Only by elimination of the possibility of such errors to a reasonable certainty could the theory be said to be falsified. That is simple logic.

    What this case really illustrates is that the scientific community tends to apply different thresholds of ‘reasonable certainty’ depending on the pedigree of the theory. For theories that are well accepted (hopefully because they have a large set successful experimental verification already), the threshold of reasonable certainty is set very high. But this is just another way of saying ‘extraordinary claims require extraordinary evidence’

    I think a stronger example is the prediction of the neutrino: to explain a seeming violation of the conservation of energy and momentum, they posited a massless, chargeless particle with almost no interaction with normal matter. It took 26 years before that predicted particle could be confirmed.

  7. The contrast between Mercury and Uranus is instructive. Le Verrier also postulated a planet, Vulcan, to explain the orbit of Mercury. Here, convincing falsification of the prediction was, at that time, at the limits of observation, because Vulcan would have been small, and very close to the Sun. Some astronomers persisted in the search, even after 1915, when Einstein had explained the anomaly in terms of General Relativity.

    Did Mercury falsify Newtonian planetary mechanics? Up to a point. I would rather say, given the successes of Newton’s theory, that it showed that the theory would break down under certain circumstances, which General Relativity correctly predicted. Outright falsification of an established theory is unusual, because it would be unlikely for a theory to be established, unless it had some zone of applicability.

    We even have cases where the formal development of the theory includes the prediction of the limitations of this zone. For example, ideal gas theory depends on the assumption that the physical volume of the gas molecules, and the energy of their interactions, are small compared with the volume of the container, and the kinetic energy available. If the theory had NOT broken down at high pressures and low temperatures, that would have seemed extremely strange.

      1. Not only that, but even if Neptune was not spotted that wouldn’t have meant that Neptune wasn’t there – the astronomers were well aware of that but were hoping for positive confirmation of another celestial body and fortunately Nature obliged in this instance.

  8. It’s interesting that the OP uses Newtonian physics (as others have pointed out) when that physics has been superseded by Einstein’s theories.

    Of course, that doesn’t stop Newtonian physics being useful and that’s the point. A scientific theory is not only about truth, but about how useful it is.

    Bohr’s atomic model is unlikely to be ‘true’ but it’s incredibly useful in understanding what’s going on.

    1. At the time of the discovery, Einstein had not yet invented the time machine and traveled back to inform the astronomers that Newton was wrong.

  9. Historical comment: A recent biography of Galileo suggests that Galileo actually saw Neptune (through a telescope, of course), but gave it no notice.

    In any case, this situation illustrates what Bunge calls the difference between male fide and bone fide ad hoc hypotheses. The postulation of a planet beyond Uranus is an example of the latter: it is independently testable, etc. See _Finding Philosophy in Social Science_.

    As for falsificationism period, it is vital to distinguish between “being able to be falsified” as *the* criterion of science, which is very wrong (way too permissive on the one hand and way too restrictive on others) and falsification as a merit of science, that is, as one potential characteristic amongst many. Bunge’s work is interesting partially because his explanation of scientificity comes in degrees – different components of a vector.

    1. That claim is a frequently repeated lie. The telescopes of Galileo’s era weren’t good enough. In Isaac Newton’s era telescopes *could* be made good enough (using reflectors rather than refractors a large enough telescope could be built to collect enough light). The art of lens making did improve over the years; Galle observed Neptune with a large refracting telescope (24.4cm, f/17.7 equatorial refractor) manufactured by the famous Joseph Fraunhofer. Galileo’s telescope was a mere child’s toy compared to Fraunhofer’s instrument. Come to think of it, the “Galileo Telescope” created and sold a few years ago was a nice cheap child’s toy and it was *better* than any telescope Galileo ever used simply because the lens was far superior – and even with that superior toy and the dark skies of, say, the south island of New Zealand, you wouldn’t be able to spot Neptune.

      1. Hmmm … I may have to eat my shorts. E. Myles Standish and Anna Nobili in 1997 wrote “Galileo’s Observations of Neptune” which followed up on the earlier claim by Drake and Kowal. The paper still leaves me with lingering suspicions (there is still a sense that people may be wishing too hard to confirm the claim) but I have no strong reason to reject the claim outright.

  10. So how exactly did Popper revolutionize science in the 19th century? How did he revolutionize science in the 20th or 21st century? Did anything change because of Popper? We can, with the dogma of Popperian falsifiability, establish non-overlapping magesteria and leave it at that. That is to say, we can use falsifiability as an a priori justification to stop pursuing a question because it seems unfalsifiable at a particular instant in time. But that doesn’t seem useful at all to scientific endeavor, certainly not revolutionary.

    1. Popper’s arguments are responsible for the switch from looking for confirmatory evidence to looking for falsificatory evidence. This isn’t 100% true — people paid attention to evidence against theories before Popper. But Popper was the one who really pushed the idea that there’s an asymmetry between confirmation and falsification and that falsification is more useful to scientists.

      More on this below.

    2. Dude – Popper was born in the 20th century; even I wouldn’t expect him to influence 19th century science.

  11. Well said! Popper is characterized, heck sometimes criticized or lampooned, for calling on scientists to make Bold conjectures just like the above; to come up with fatal falsifications like in the above, and I /think/ it was his student Lakatos who came up with the phrasing of ‘naive’ falsificationism, and applied it to Popper’s critics, whereas today people often consider Popper naive, this is perverse, in the old sense.

    1. There’s a collection of papers from a conference in the 70’s, the volume is called “Criticism and the Growth of Knowledge.” Papers are by Kuhn, Popper, Lakatos, Feyerabend, and a few others (but those are the more worthwhile papers). Lakatos’ paper was an extended analysis of falsificationism: naive, sophisticated, etc. I don’t remember all his terminology.

      But what he (and Kuhn) end up with is something drifting pretty far from falsificationism. Lakatos does a great job of showing why no version of falsificationism really works. Both he and Kuhn point out that, contra falsificationism, confirmatory evidence is actually taken very seriously in science. For example, the discovery of Neptune was taken as important evidence for the truth of Newtonian gravity; a no-no from Popper’s perspective.

      Instead, they advocate something Lakatos referred to as “fallibilism”, where you cannot disprove a theory outright but you can adduce evidence to make its truth improbable. It’s the probability version of falsificationism, but it’s also a form of verificationism as it allows evidence to increase the probability of a theory’s truth as well.

      I didn’t think much of Kuhn until I read his paper that concluded this conference; now I think he was right on about some of his “criticisms” of science. Though he makes it clear in this paper that he thought of himself as an observer of science rather than as a critic.

      1. Yes, I have that collection! I agree about Kuhn there, came away from C&GoK understanding his work better.

  12. It’s worth stating that Popper was never a ‘naive falsificationist’–it’s just a strawman.

    Popper anticipated objections raised by the Duhem-Quine thesis in at least the first English editions of LoSD. In fact, Popper’s whole discussion of ‘conventionalist stratagems’ presupposes exactly what Popper’s critics have later claimed he ignored–that one can always save a hypothesis from falsification by instead falsifying some auxiliary assumption. He even discusses methodological rules for how to deal with that; particularly, he stresses that experimental results should be repeatable and that ad hoc explanations of recalcitrant should themselves be empirically testable.

    Whatever the details, the background to Popper’s philosophy was one of radical fallibilism. Thus, he was not trying to provide a set of rules for science that would ineluctably lead to true theories; his problem was not ‘how can I be more certain that science is right?’; basically, Popper believed there was always some incalculable risk that we are wrong, even, or especially, about our most celebrated intellectual achievements. Hopefully, these remarks might provide an antidote to misleading criticism that supposes Popper shared similar goals as his logical positivist contemporaries.

    1. I think your last sentence brings up an important note, that Popper was doing all this in the context of Logical Positivism. People still debate Popper, but they, as far as I have seen, don’t really debate positivism anymore.

  13. In the case of Neptune’s discovery, it’s also worth noting how the initial conditions of system being modeled were notoriously difficult to observe–an entire solar system. It’s a bit like trying to observe how many ants are in a garden; it’s something you do very slowly and in little pieces, and the initial conditions may even be changing in the time it takes to make all the observation. In these situations, people are usually quite cognizant of the possibility that their ‘auxiliary assumptions’ may be at fault. Hence, scientists weren’t even pretending to test Newtonian physics when observing the orbit of Neptune. Moreover, Uranus’s wonky orbit can be easily explained by positing another planet, an entirely ordinary Newtonian object. This is quite unlike, for example, the observation of light bending around the sun; while it would no doubt be possible to explain away such an experiment, attempts to do so strained the existing theory and explanations to a much greater extent than Uranus’s funny orbit ever did.

    On a related note, and to drive home the naive-falsificationism-has-nothing-to-do-with-anything point, Popper is also know to have said that a little dogmatism may be a good thing in the scientific community. What he meant by that was that people who refuse to give up on an apparently falsified theory perform a useful service, since they are motivated to give their theory the best defence possible. In this way, they may help guard against scientists dismissing a theory before it has had time to develop and mature into something worthy of being wrong.

  14. My understanding of Popper is that the goal of hypothesis testing is not finding truth, but eliminating error. I suppose, the more errors you eliminate, the closer to the truth you can get. However, Kuhn made the argument that moving away from ignorance did not necessarily move your thinking in the direction of truth.

    I think the Neptune example falls into the area of what Popper and Kuhn called ordinary or normal science (don’t remember which was which) where one is using theories in applications where they are known (or expected) to work. I think the proper reaction to the Neptune anomalies is just what happened. Newton works, and here it has found an anomaly. Let’s look for the cause of the anomaly.

    As mentioned elsewhere, in the late 1960s, evolutionary biologists did a lot of soulsearching, and many, me included, became familiar with Popper. It does surprise me, in talking with non evolutionary scientists, how little they think about why they do what they do. I think, for many scientists, philosophy of science means Monkey see, Monkey do.

    By the by, hypotheses are never confirmed, at best they can only be supported.

  15. This, and Mercury, are standard examples trotted out when someone wants to argue that testing doesn’t work. But that is based on an insufficient understanding of testing as applied to theories IMO.

    Neptune first:
    To test Newton’s theory of gravitation you would make a prediction to test. Such a test is based on the same observational data that is tested with it.

    I noted on the earlier thread how the circumstances of the experiment needs to be resolved, and can be resolved as shown here. Until such a resolution happens, unambiguously, there is no firm test. Hence the D-Q thesis can be rejected. (A nitpick here would be that the known planets were, well, _known_. That helped.)

    I think the term “escape from falsification” here refer to a theory somehow being modified in parameters. It seems the article claims that inserting a new planet is a modified theory. It is certainly a new model, since Newton’s theory was kept in the test, and it is this that is tested. From a testing viewpoint this is the same test, it tests the parameters including Newton’s theory.

    The relation between this and pseudoscience is unclear. Pseudoscience isn’t characterized by testing specific parameter sets which can change as you go. It is characterized by never going to rigidify enough for an unambiguous test. Which gets us back to what was described above.

    It rejected Newton’s theory of gravitation as a full theory of gravity. It also clarified when we can use it as an effective theory, a good approximation in most cases.

    Finally, the notion that philosophers ‘test’ ideas when they do postdiction is arguable.

    Compare to new theories, that needs to do postdiction well enough _and_ predict new phenomena to be tested on. The consistency test on old data and theory is taken as given when you work out something new to test on.

    More importantly, philosopher ideas never predict new phenomena to be tested on. If you don’t do that, it is neither eliminating erroneous ideas (theories) nor giving fruitful results. By postdiction you can do exactly the same as pseudoscience, making up “just so” stories that are internally consistent, sometimes externally consistent, but nevertheless unlikely to be factual.

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