Looking twice at the history of science

Thursday, March 21, 2013

Saving the symmetry principle, II: why distinctions matter

The flurry of tweets that followed my last post made it clear that there are quite a few interpretations of the sentence “people believe things just because they are true.” One question that came up was whether or not the distinction between truth and evidence is any use in understanding that sentence. I think it is. But even if it is not, I want to make the broader point that esoteric-seeming distinctions can make a big difference to the success of our interactions with the general public. Expand post.


  1. This reminds me of an episode when I was teaching physics in high-school. My department chair, a biology teacher, asked me if I knew which was faster, light or sound. She meant, are reaction times faster (in humans) to aural or optical stimuli? (As it happens, the answer is aural --- so sound is faster than light in this sense.)

    A third interpretation of the "tree in the forest" question: we mean sound waves, but we are wondering if the laws of physics hold when nobody is observing.

    Of course quantum mechanics stimulated this sort of question: Einstein once asked Bohr if he really believed the moon existed only when someone was watching it. I seem to recall Bishop Berkeley also had some speculations along these lines.

    First one to say that Berkeley anticipated quantum mechanics can scrub out all the stables in the Many Worlds.

    1. Your last sentence in turn reminds me of this:

      "Frank admissions that the [Leyden] jar shattered accepted theory appeared on every hand...Perhaps the powers of frictional and communicated electricity differ, or--as one resourceful commentator supposed, in anticipation of the Copenhagen interpretation of quantum mechanics--electricity expressed itself in contradictory ways according to the experiment tried" (Heilbron, "Elements of Early Modern Physics," 185).

  2. As long as we're being sort of glib, I always find this xkcd a propos in these matters (the mouseover text reveals the applicability is not accidental):

    1. Not bad! I could also have cited John Zammitto's account of "postmodern equivocation," as reported here:

      The same theme comes up in this long but (in my view) informed and reasonable criticism of views labelled "postmodernist":

      The theme recurs in this short but sweet commentary on a 2011 debate in the pages of the NYT:

      Just to be clear, I should add that:

      --I don't think Vanessa's Guardian post on the symmetry principle was guilty of "communicating badly and then acting smug when not understood," as the xkcd comic put it

      --some postmodernists may have been guilty of doing this, but when they do so they strike me less as "smug" than as conceptually confused, and at any rate they have made some good points along the way (the trouble is to sort the wheat from the chaff)

      --I'm not suggesting that anyone should have their hands cut off

  3. That example with the sound seems strange to me. I could spin it a bit further and ask: If a tree fell in a forest and nobody saw it fall, would it in fact have fallen? Yes it would! I could go there and check. It would no longer stand.

    1. I'm not sure what your point is here. The original question was about whether the falling tree made sound, and not about whether or not it had fallen.

  4. I wrote a long comment which it turned out was too long. So I’ve divided it into 2. The main points are coming up in a minute. In this post are just a couple of gripes.

    Firstly - I found Vanessa’s sub-heading (“No-one believes something simply because it is true”) just a tiny bit mischievous and provocative, because I think a lot of people will have interpreted that as a denial of *any* link between the truth of a theory and people’s belief in it, including this one:

    True theory => predictions likely to agree with it => more evidence for than against => people believe in it

    and the replacement of such a link by some other agency such as the social, political and religious circumstances that she mentions, so that this begins to look like just another attempt to stress “externalist” arguments over “internalist” ones.

    I suppose that is no surprise really, because it’s what commercial blogs are there for – the bloggers would be criticised, and maybe even relieved of their duties, if they did not provoke a nice fat wad of responses. So I see “The H Word” as a bit like a tabloid newspaper, hence not perhaps the best forum for serious discussion.

    Secondly – I think Vanessa’s use of the examples of climate change, vaccination and creationism to back up her argument is a little disingenuous, since here we are no longer just talking about belief – it is perfectly possible to believe in the evidence for a particular theory (e.g. AGW or the non-existence of God) but fail to act on that belief because you don’t like its implications (need to change lifestyle, no life after death) and this is well summed up by the contribution of “Frogflydandelion” – to which I would just add that in the case of vaccination, the problem is one of risk assessment – knowing that all treatments have side effects, how on earth do you compare the desirability of giving your child a vaccination where there is a small but serious risk of complications, with that of not giving it and risking a disease that is at least well known and not often fatal? It is not simply a matter of believing or not believing in anything. And while I am sure the various risks have been worked out, it is often difficult to get these across to frightened people, as is the case with nuclear power and the dangers of radiation.

    1. Thanks Jim for these interesting comments. In response to your first point, I think that Vanessa *was* trying to argue that external factors are important, and perhaps even that they are *more* important than internal ones. Sometimes she included "experimental" and "instrumental" factors in the list of things that historians should focus on; but then when she drew lessons about present-day debates she seemed to go back to de-emphasising arguments and evidence.

      I think she was right to say that external factors are often important in debates, and that they can be interesting to study. But I do not think the symmetry principle is a very good argument for this conclusion, since the principle only says that we should explain the beliefs of "winners" and "losers" in the same way--it does not say which sorts of explanation we should focus on.

      I agree--and I expect Vanessa would also agree--that something like "the H Word" has a different purpose than an academic journal or even an academically-inclined blog like this one. To look on the bright side, I think Vanessa and Rebecca are doing a service to other historians of science by bringing history of science to the masses. At the same time, it's important to get our message right before we broadcast it publicly.

      I would add that my target in this series of posts is not Vanessa's Guardian article per se, but the current understanding of the symmetry principle among working historians of science (an understanding that Vanessa's article captures quite well, I think).

      I take your second point that the debate about climate change, say, is not just a debate about the correctness of a scientific theory but also about what we should *do* about that theory. And since the question of how to act is (almost by definition) an ethical and political one, it may be a bit tendentious for Vanessa to treat the climate change debate as a model for all debates involving science.

      On the other hand, the debates that attract the most public interest are usually the ones that *do* have an ethical or political dimension. So I see no problem in making the climate change debate an exemplar of *public* debates involving science.

      I expect Vanessa would also say that many past scientific debates had ethical and political dimensions that they have now lost, and that historians ignore at their peril. To take Vanessa's example, the debate between Newton and Leibniz, over the existence or otherwise of absolute space, may seem rather esoteric to us. But at the time it was thought to be closely linked to ethical and religious questions such as the nature of divine providence. So it is not tendentious to compare the Newton/Leibniz debate to the current debate about climate change.

      Of course, the opposite point also holds: presumably there are present-day scientific debates that have ethical and political implications that past scientists could not have anticipated.

  5. Here is my main argument. It should probably have preceded the other one – sorry.

    I am troubled by the preponderance, in both Vanessa’s blog and this one, of references to the “truth” and “falsity” of theories. As one or two of Vanessa’s responders (particularly Ian Love and James Valencia) did point out, these are not the right sort of words to use when talking about scientific theories – and in fact you’d be hard pressed to find a scientist talking about truth and falsity; you’d be far more likely to find statements such as

    “theory X gives predictions which agree with the available data to within the experimental uncertainty”.

    The key words here are “within experimental uncertainty”. Thus we use Newtonian gravity for most everyday situations, including space flight. We wouldn’t say it was “wrong” or “false”. If we are firing a projectile, it is fine to use the constant acceleration equations, even though we know that “g” does actually vary with height – but we don’t take that into account because it would not make a big enough difference to our calculations. We would say these equations give an answer that is within the desired precision. Yet some would say that, because the agreement isn't exact, the equations are "false" when applied to objects moving in the earth's gravity.

    Of course one could justifiably reply that this may be the way we do science nowadays, but in the past it was different. That may be so; but at least by the time of Newton, who was the subject of most of the discussion on Vanessa’s blog, it would appear that the language used was concistent with this description, as the following quote shows:

    “the power of magnetism … decreases not in the duplicate, but almost in the triplicate proportion of the distance, as nearly as I could judge from some rude observations”
    [Newton, Principia, bk III, prop. VI, cor. 5]

    It turns out that there was a great deal of confusion about what exactly was being measured here, at least until the time of Michell (1750) or possibly Coulomb (1785) but the point is that the terms “as nearly as I could judge” and “rude observations” indicate agreement within experimental uncertainty. (There again, since the observations in question were made by Hooke, perhaps Newton was simply having another dig at his old mate here …)

    One could also say, with some justification, that whether or not you talk about truth depends on who is doing the talking. Philosophers tend to talk in terms of truth, falsity and logic; scientists don’t. But since we are talking about the history of science, and about what scientists thought, surely we should adopt scientists’ interpretation of these terms?

    We need to take on board the fact that the probability of perfect numerical agreement between theory and observation is very small; and in the case of theories that give an irrational number as the predicted value of a measurement (as Newtonian mechanics does for the period of a pendulum, for example) it is zero, since all measurements must yield rational numbers. What matters is the difference, *in terms of the uncertainty*. As Henry Kyburg put it, when uncertainties are considered, “being exactly on target is no better than a near miss”.

  6. As for "truth", I think Kuhn started this particular hare. He claimed that we should give up the very idea that our scientific theories are closer and closer approximations to The Truth, and also abandon the notion that there even is such a thing as The Truth (about the laws of the universe). For a forceful rejection of this standpoint by a famous physicist, see Steven Weinberg's essay "The Revolution That Didn't Happen"

    Is it really true that scientists don't believe actual Truth of *any* of their theories? Take two of the foundation stones of biology: the cellular composition of life, and the fact of evolution. As for the first, well, it's just a fact --- look through a microscope! Yes, you could spin some story about mass hallucinations over hundreds of years or bizarre undiscovered optical effects. Any biologist would respond, "Really? You're kidding, right?"

    As for evolution, biologists frequently make the distinction between the *fact* of evolution, namely that new species arise out of old ones, and the theory of natural selection, namely the mechanism. They use the word "fact" because they really harbor no doubts on this score. (Nor, IMHO, should they.)

    Eddington once suggested that the second law of thermodynamics should also be treated as certain. His argument: we can calculate the probability of a violation (for example, all the air molecules accidentally ending up in the top corner of the room), and this probability is way less than any reasonable estimate of being mistaken about any other law (say, Maxwell's equations --- the example he gives).

  7. Ah, well … my field is physics, and I am not very conversant with biology, never having studied it. So maybe biologists do talk about truth and falsity. But to me it seems to be a very “fuzzy” subject – I mean, how exactly do you define a species?

    In the physical sciences, theories tend to make quantitative predictions which have to be compared with observation, and since the probability of exact agreement is negligible, this comparison always has to be done in terms of the uncertainty, and an assessment made of whether the agreement is close enough to accept the theory, or far enough out to reject it. Popper wanted this to be a logical procedure with no element of human judgement in it, but that is only possible if you have theories and experiments that deal with qualitative attributes (e.g. black ravens) rather than quantitative ones. In real physical experiments there is always a finite probability that a theory is true whatever the result of the experiment; we have to decide for ourselves how many standard deviations away from the predicted value is acceptable, since there is no point on the error curve where the probability is zero. (However in the mid-19th century, before the normal distribution achieved the universality it enjoys today, Augustus de Morgan suggested a suitable criterion for testing theories as “the value which it would be reasonable to shoot a man for supposing the likelihood of” – but we probably wouldn’t want to sign up to that nowadays).

    I wouldn’t necessarily criticise the idea that we get closer and closer to The Truth, as long as it is also accepted that we will never reach it, and probably shouldn’t waste too much time speculating on what form The Truth might actually take.

  8. I'm not a biologist either. In the 20th C., philosophers of science often acted as though "science" was synonymous with "physics". Not a good practice.

    As for The Truth --- I think this applies in physics as well. Is there a physicist out there today who doubts the reality of atoms? Yet as you know, this was a contested issue around the turn of the 19th century.

    I certainly take your point that, after QM and relativity, physicists no longer claim finality for our current theories. OTOH, it's easy to come up claims from noted physicists (e.g., Feynman, Weinberg) that GR and QM are in some sense correct --- that is, any future theory must incorporate them in some manner, just as they both incorporate classical physics in the manner you've alluded to.

    All this is straying rather far though from the H-word essay...

  9. I agree with your first statement - so perhaps we should not make sweeping statements about "science" as a homogeneous discipline - what is true of physics is not true of biology and vice versa. Not to mention psychology etc!

    Reality of atoms ... well, yes, I'm sure most physicists would agree that atoms exist, but to put meat on that you have to describe what atoms are, and do it without using macroscopic analogies that don't hold at that level. Part of that description will involve quantitative properties (which as you can probably tell is what I'm mainly interested in) and here we cannot be precise, e.g. we can never say we "know" that the charge on the neutron is zero, only that a theory that incorporates that value is our best fit to the observations, which will of necessity only give an interval and not a precise value.

    Yes, straying off the subject ... but then we have to do *something* while we wait for Michael to post Part III! :-)

  10. True enough. You hear that, Michael? Where's that ringing defense of asymmetry? Or of symmetry? Or both at the same time? (Which is what I'd really like to see.)

  11. Thanks to you both for gracing my blog with this very interesting discussion!

    I tend to agree with Michael that it does not make much sense to discard altogether the notions of "truth" and "falsity" in science. One of the aims of science is surely to find out about nature. It is hard to see how scientists can claim to find things out about nature if they are unable to *say* things about nature. And it is hard to see how they could really say anything about nature if every claim about nature was equally true or equally false.

    I take Jim's point that strictly speaking scientific theories should come with at least three caveats: they are probable rather than certain; data can only agree with theory "within experimental error"; and "experimental error" is never zero.

    But this is an argument for qualifying the notions of truth and falsity, not for abandoning them. Indeed, it is hard to make sense of the idea that a theory is "probable" unless this means that the theory is "probably true." And it is hard to understand why anyone would want to compare a theory with the data unless they were interested in assessing the *truth* of the theory (or at least in assessing the truth of the theory's predictions).

    As fascinating as all this is, I think it is independent of what I want to say about the symmetry principle. That is, it would be perfectly consistent for someone to accept what I have to say about the symmetry principle and yet deny that science has anything to do with "truth" and "falsity."

    To show this I need to distinguish between the different things that people can mean by the phrase "people believe things because they are true." In my view, the ambiguity of this phrase does a lot of mischief in both public and academic discussions about the symmetry principle (and about science in general).

    I will make some of these distinctions in my fabled "next post", which should appear on this blog any day now.

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