Falsifiability is useful, but a matter of judgment

The Black Swan is the state bird of Western Au...
The Black Swan is the state bird of Western Australia (Photo credit: Wikipedia)

Our discussions last week on Jim Baggott’s book, ‘Farewell to Reality’, and Sean Carroll’s Edge response, left me pondering falsifiability, the idea that theories should be falsifiable in order to be considered science.

Falsifiability is a criteria identified by the philosopher Karl Popper.  Popper was arguing against a conception held at the time by logical positivists known as verificationism, the idea that something couldn’t be considered scientific unless it was a verifiable proposition.

To be verifiable, a proposition needed positive empirical evidence for its existence.  If a proposition wasn’t verifiable, the logical positivists relegated it to metaphysics, which they regarded as meaningless literal non-sense (that is literally not of the senses).

Many philosophers saw verificationism as too stringent, noting that it would cut out too much of what was then considered legitimate science.  A number of alternate criteria were proposed, but Popper’s caught on.

Unlike verificationism, falsifiability doesn’t require positive evidence for every assertion, but it does require that the assertion has the possibility of being proven wrong.  This seems like a hair splitting difference when you first hear it, but the distinction is important.

The classic example is black swans.  If we only ever observe white swans, then we might form a theory that all swans are white.  According to verificationism, that theory is not science since we haven’t proven that all swans are white.  However, this could only be done by observing every swan that exists, that has ever existed, or will ever exist.  It is far too stringent a criteria.

Falsifiablity accepts the theory that all swans are white as scientific because it has the possibility of being disproven, when the first black swan is observed.  Note that falsifiability doesn’t mean that we necessarily have control of when the contradictory evidence might arise, only that the possibility exists.

This actually turns out to be a critical part of falsifiability.  Your theory doesn’t have to be falsifiable under controllable experimental conditions (although it’s certainly a good thing if it is), it only has to falsifiable in principle.

Popper argued that if you’re not talking about something falsifiable, then you’re talking about philosophical concepts such as metaphysics.  But unlike the logical positivists, Popper didn’t discount metaphysics, pointing out that what is metaphysics in one century might be science in future centuries.  A good example here is atomism, which was a metaphysical concept for the ancient Greek philosophers, but became a scientific one in the modern age.

The problem, of course, is that what is falsifiable in principle is a matter of judgment.  Popper famously used his criteria to mark Marxism, psychoanalysis, and natural selection as not being scientific, although he later changed his mind about natural selection.  (Note that he was talking about natural selection, not evolution overall.)

Popper discounted Marxism and psychoanalysis because the theories were so flexible that they could be used to explain anything in a post-hoc manner, but couldn’t be used to make predictions.

Falsifiability has a lot going for it, but it’s not a simple criteria.  To understand why, consider what happened when the planet Uranus was discovered.  The planet’s orbit was not found to be in strict accord with Newtonian physics, yet no one at the time declared Newtonian physics falsified.  Instead scientists continued to assume that Newtonian physics were correct and used them to deduce the existence of yet another planet, Neptune.

Of course, eventually phenomena were observed that Newtonian physics couldn’t explain, such as the precession of Mercury’s orbit.  Using the logic that worked for Neptune, some astronomers predicted the existence of another planet closer to the sun, Vulcan (no relation to the Star Trek version), which was never found to exist.

Despite this fact, scientists didn’t abandon Newtonian physics until Albert Einstein formulated a better theory, general relativity.  (It’s worth noting that Newtonian physics remains approximately correct enough that NASA still uses it for most of its spacecraft flight planning.)

This reluctance of scientists to abandon a well established theory until a better one comes along was observed by Thomas Kuhn.  Kuhn noted that the history of science is one of paradigm shifts, where major theories are updated as necessary to accord with new observations, and adhered to until a new theory supplants it in what he termed a paradigm shift, such as the one from a Newtonian universe to an Einsteinian one.

So, where does this leave falsifiability as a criteria for whether or not something is science?  I think as long as we remember that we’re talking about falsifiability in principle, not necessarily in practice, it remains a useful concept.  But, as I mentioned above, falsifiability in principle is a matter of judgment, one that often has to be made by scientists themselves.

However, I think falsifiability remains an important metric.  Without it, we’re left with notions like science being whatever scientists decide it is, a criteria that would only strengthen critics of science who are unhappy about it not accepting things like the paranormal, new age spirituality, and many other ambiguous or ill defined concepts.

Falsifiability has also become important in law, as a principle used to distinguish science from religious or other forms of thought, particularly in cases involving creationism or intelligent design, neither of which pass the falsifiability test.

Does that mean that string theory or related concepts aren’t science?  Again, I think it’s a matter of judgment.  As long as string theorists are striving to find a falsifiable theory, an argument can be made that they’re doing prospective science.  However, the decades long failure to produce such theories are causing many to lose patience with that enterprise.

However, many other ideas such as multiverse which are completely causally disconnected from us, are not falsifiable, even in principle.  They are metaphysics.  As Popper said, exploring the concepts may have value, but its value will be that of the value of philosophical contemplation, rather than empirical science.

So, falsifiability remains useful a useful criteria, but whether or not a theory meets that criteria is a matter of judgment.

11 thoughts on “Falsifiability is useful, but a matter of judgment

  1. The theoretical physicist David Deutsch is a follower of Popper, but if I am correct in interpreting what he says, he argues for a slightly different criterion. He believes that we should accept theories that provide the “best explanation”.

    Any theory that has been falsified would clearly not be the best explanation of a phenomenon, but consider your example of Neptune’s orbit. Strictly this falsifies Newton’s theory of gravity, but it was generally regarded that a better explanation was the existence of another planet. This turned out to be true.

    Consider dark matter. It’s never been observed, but our existing models of the universe appear to be falsified in that they cannot account for the observed rotation of galaxies. We could say that our theory of gravity is wrong, or we could postulate the existence of dark matter. For various reasons, cosmologists have decided that dark matter is the better explanation, even though attempts to observe it directly have so far failed.

    What about string theory / multiverses, etc? These theories may not be falsifiable (let alone provable) and yet one day scientists may decide that they provide the best possible explanation for the subatomic world and choose to accept them. (Or they may not.)

    I think that while many scientists will say that falsifiability is the criterion for accepting a scientific theory, in reality it’s that the theory provides the best possible explanation. This is like when we buy a car. We choose the one that looks best in the showroom, then find ways of rationalizing why it’s the right choice.


    1. Thomas Kuhn would have agreed, and I think I do as well, for choosing among prospective scientific theories. It appears to be what actually happens in science.

      Where falsifiability becomes useful is in deciding whether or not a proposition is a scientific one, albeit with informed judgment. If science is allowed to be whatever scientists happen to think up, then it’s credibility may suffer. It’s worth studying the history of philosophy in late antiquity to see what can result.


    2. On the other hand, following the best fit can lead to claims of unfalsifiability. If evolution can twist just a little bit to accommodate any unusual observation, it will never be false. Falsifiability must remain some kind of factor, otherwise a person can come along and say that creationism is a best fit. I think the question is, how much twist is acceptable?


  2. Wonderful post, as usual – this is a great overview, and so well explained. Also, incredibly timely – I just posted something about metaphysics and math, and Neptune got a brief mention from me as well!


  3. Your points are certainly valid, in that falsifiability is effected and ruled over by human error. However, that is the part of science that falsifiability meant to account for. From my (possibly lacking) knowledge, science must try its hardest to keep to the facts. This includes reducing the amount of human error. While falsifiability allows for what seems to be a ridiculous outreach into impossible ideas, it accounts for it by allowing much to be stricken down when shown otherwise.

    The other part, of which is brought up in the Neptune example, is how current models are discarded. While Neptune’s orbit did not fit what was originally anticipated, its movements did not seem impossible in a mathematical sense of Newtonian physics. While I’m sure that some argued that Neptune had shown a hole in the current model, it wasn’t enough to be a complete hole. Just enough to change the current calculations. As you’ve said, the change in calculations was shown to have credibility. Also, since they have found that Vulcan had clear evidence that it did not exist, it was dropped.

    Yes, quantum physics seems like the crazy cousin of good old classical physics. Full of disappearing particles, particles that are directly linked to others, and even particles that mess with freaking time, it’s no wonder people are skeptical. However, these ideas are not based on simple whims that would seem to strike a sci-fi author. Rather, most are based on basic observation and some extremely complex math. String theory is based off of calculations, quantum entanglement has been thoroughly used in experiments, and particle-wave duality has become a solid part of understanding the universe through constant testing.

    Finally, I would suggest reading Issac Asimov’s great essay ‘The Relativity of Wrong'(http://chem.tufts.edu/answersinscience/relativityofwrong.htm). You’ve suggested that previous models of science have been thrown out given that a new model has been discovered to be closer. Asimov addresses how science has been ‘wrong’ in the past, and how we should approach the idea of holes in current models. Greatly has to do with falsifiability.


    1. Thanks for the Asimov link! I hadn’t read that before (although I’ve seen the quote about wrongness and the shape of the Earth around the web). It’s always great to read something of his I hadn’t seen before. He’s right, which is why I noted that Newtonian mechanics are still useful for NASA.

      I think quantum mechanics is actually an excellent example of why we should be cautious of getting too far in advance of empirical knowledge. Who could have logically predicted QM until the bizarre evidence demonstrated it? Who’s to say that the bizarreness we currently understand about can be used to logically predict the bizarreness at lower levels.

      Each assumption beyond empirical adds a degree of uncertainty, and multiple layered assumptions make that uncertainty climb until, at some point, there’s so much uncertainty that we’re just speculating. There’s nothing wrong with speculation, but we should understand it for what it is.


      1. Were these simply assumptions, I would whole heartedly agree with you. Assumptions(or even most claims) should be approached with a healthy degree of skepticism. However, most of the ideas that have come out of quantum mechanics have more than just bizarre ideas to back them up. To get a good example, I would recommend going to your local college library, and browsing the journal section. Find anything dealing with theoretical physics and get ready to read some Greek. For quick access, here is a few papers I found online that detail some ideas that link black hole properties with string theory.

        Notice how concise they are in what they are saying, allowing for anybody to double check the mathematics and concepts inside. Indeed, that is the very thing that makes falsifiability so great. Anybody can try to prove you wrong. If they succeed in doing so, and their math is concrete, then we have a winner.

        Now, all of this requires much more knowledge than I have, and I will not try to pretend like I understand the math and terminology that is presented here. However, there are many who do, and would be more than willing to call out a mistake. Thus, I’m sure that our system of presenting and refuting metaphysics is quite secure. Skepticism is a great thing to have on ideas that seem like they came out of B-movie. However, the process requires more than skepticism to refute an idea.


        1. Thanks for the links. I think you and I are basically on the same page here. I never meant to imply that quantum mechanics are just bizarre ideas. The standard model is well attested empirically (more so now with the Higgs having been confirmed).

          But I’m also aware that string theory, and the holographic principle, haven’t been empirically attested yet. In my mind, they should be held in our minds with a question mark until there are observations for them, or observations that contradict them.


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