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.
- Time to ditch falsifiability? (selfawarepatterns.com)
- Scientific theories need to be falsifiable (motls.blogspot.com)
- Wittgenstein (and falsifiability, Popper and Snakes) (ausomeawestin.wordpress.com)
- Karl Popper (blkbx.wordpress.com)
- Retiring falsifiability? A storm in Russell’s teacup (scottaaronson.com)
- 9th EDITION SERF UNDER_GROUND JOURNAL. (beththeserf.wordpress.com)
- Science, philosophy, and caution about what we think we know (selfawarepatterns.com)