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How to challenge a scientific theory, method 1: Evidence that contradicts it

Posted at 09:00 on 19 October 2020

This is the second post in a series of three.

  1. How to challenge a scientific theory
  2. How to challenge a scientific theory, method 1: Evidence that contradicts it
  3. How to challenge a scientific theory, method 2: propose an alternative

So you are faced with a scientific theory, such as evolution, that you do not agree with. There are two ways in which you can challenge it:

  1. You can present some verifiable facts or evidence that contradict it.
  2. You can propose an alternative theory that provides a more accurate and precise explanation for the evidence.

However, as we saw last week, you can't just respond with any old nonsense. Not everything is a verifiable fact, not every verifiable fact contradicts your theory, and not every alternative theory provides a better explanation for the evidence than the one you are trying to argue against. Accordingly, whichever of these two approaches you take, there are rules that you must stick to.

This week, we will look at the first of two ways in which a scientific theory can be challenged: point out a verifiable fact that contradicts it.

What kind of evidence?

Now you may have a few candidates in mind here. Piltdown Man, Nebraska Man, Mount St Helens, the Second Law of Thermodynamics, moon dust, or a hammer from Texas encased in a rock. However, before you start triumphantly waving these things around, you need to make sure that (a) they really are facts, and (b) that they really do contradict the theory.

This means that you need to make sure that you correctly understand what the theory says. Far too many amateur apologists skip this step, and as a consequence end up attempting to debunk nonsensical cartoon caricatures of evolution that look more like something out of Star Trek than anything taught about it in schools and universities.

You must also make sure that the facts that you are bringing to the table concern something that is essential to the theory. In other words, they need to overturn the core fundamentals, and not just one side detail. You don't chop down a tree in its entirety by cutting off leaves, twigs, or even branches.

This is why, for example, Piltdown Man is not a valid argument against evolution. It doesn't address the underlying mechanisms, but only the fine detail of exactly what one particular species did (or, in this case, didn't) evolve into. It may have been famous, but it was still only one data point among millions -- nowhere near being a devastating blow to evolutionary biology. A single data point, or a tiny sample with huge error bars, is rarely if ever enough to overturn a scientific theory. Your standards of rigour and quality control need to match those of the studies in favour of the theory at the very least.

Things that are not contradictory evidence

This brings me to my third point. In order to contradict a scientific theory by presenting evidence against it, you need to understand what does or does not constitute contradictory evidence. Science is not like law, politics or the arts; it does not proceed on the basis of who sounds more convincing, but on the basis of what obeys the rules.

Here are some examples of arguments that are not valid objections to a scientific theory.

1. Politics, opinions or worldviews. Scientific theories are not political narratives. Nobody gets to vote on gravity, Maxwell's Equations, the Second Law of Thermodynamics, or quantum mechanics. Scientific theories stand or fall on whether they accurately explain the available evidence, and on whether they can consistently and accurately make testable predictions. And they work in exactly the same way regardless of whether you are a Christian, a Jew, a Muslim, a Hindu, an atheist, or a Tauri-Hessian tractor worshipper. What you believe about who did or did not evolve from what does not make a whit of difference to who actually did or did not evolve from what, regardless of whether you are Ken Ham or Richard Dawkins, the Dalai Lama or the Pope, Donald Trump or Joe Biden.

Politics, opinions and worldviews may influence how we respond to scientific findings, such as man-made climate change or wearing masks to prevent the spread of covid-19. But they do not challenge the findings themselves. Especially not when they have been established and refined over more than 150 years and have a lot of other scientific research that depends on them.

2. Common sense. Science is not intuitive. It is very mathematical and technical. There are many phenomena that work in ways that you would not expect or that are completely outside of our everyday realm of experience. This is especially true at very small scales (e.g. quantum mechanics) or at very large scales (e.g. general relativity, geologic time). It is also very precise and rigorous. There is a reason why so many people give up maths and science at the first opportunity when they are sixteen. They are subjects that are easy to get wrong and difficult to get right.

For this reason, mathematical arguments require a mathematical response. Attempting to argue against mathematics with appeals to "common sense" is called "hand-waving," and it will just make you sound like a crank.

3. Unanswered questions or gaps in the theory. Scientific theories are not overturned by unanswered questions, but by contradictory evidence. No scientist claims to have all the answers, and no scientific theory is complete, nor ever will be. But that is why people do PhDs. Unanswered questions are only of value in challenging a scientific theory if the lack of an answer is in itself evidence of a contradiction.

4. Answered questions. If you must ignore point 3 and ask unanswered questions anyway, at least make sure that they actually are unanswered. The question "What use is half an eye?" for example is well understood, and was even answered by Darwin himself in On the Origin of Species. If you believe the answer to be inadequate, then by all means go ahead and give a coherent explanation of why it is inadequate, but to act as if the answer does not even exist when in reality it does will just make you look like you haven't a clue what you are talking about.

5. An absence of unnecessary evidence. Absence of one particular line of evidence is only a legitimate argument against a scientific theory if the missing evidence is something that the theory tells us we should expect to see. For example, the fact that we haven't made direct observations of the Oort Cloud, when we do not have the technology to do so, does not prove that it does not exist, especially when it is supported by indirect evidence. On the other hand, we would expect to find vast swathes of easily sequenceable dinosaur DNA if the earth really were six thousand years old. But we don't.

For what we should expect to see in the fossil record, Scott Buchanan has a fairly comprehensive article on his site, Letters to Creationists: Realistic Expectations for Transitional Fossils.

6. Assumptions or interpretations. A scientific theory is not falsified merely by the fact that it makes assumptions or interpretations. In order to falsify a scientific theory by attacking its assumptions, you must (a) state what those assumptions are, (b) make sure that the theory really does make those assumptions in the first place, and (c) provide evidence that the assumptions are invalid.

However, it is important to remember that there is a difference between "doesn't always work" and "never works." Just because an assumption breaks down in specific situations does not mean that it is invalid everywhere else. For example, we know that carbon-14 dating doesn't work on marine life due to the marine reservoir effect. But that does not mean that it doesn't work on terrestrial plant and animal remains. And it certainly does not mean that uranium-lead dating does not work on zircon crystals in granites.

Assumptions and interpretations may indicate that other alternatives are possible, but only if those alternatives are mathematically coherent and consistent with the evidence. We will look at this possibility next week.

7. Ambiguous evidence. Evidence does not falsify a theory merely because it is consistent with another, alternative hypothesis. For example, just because some things (such as oil or apparently fossilised teddy bears) can form quickly, that does not mean that everything actually did form quickly. Especially when there are other things that can not, such as lead in zircons, or Widmanst├Ątten patterns in meteorites.

8. The fact that it is a theory. The word "theory" does not mean the same in science as its colloquial everyday use. A scientific theory is not a guess, it is not a just-so story, and it is not something that someone just pulled out of their backside. On the contrary, it is an explanatory framework that is well supported by evidence and that has a successful track record of making accurate testable predictions. In other words, it is, to all intents and purposes, an established fact.

The scientific term for something that has not yet been established by evidence is a "hypothesis." And no, something doesn't get downgraded from a theory to a hypothesis just because you, as a non-scientist, call it that. Calling something a hypothesis when it is, in fact, a theory, is not getting your facts straight.

9. Occasional acts of scientific misconduct or fraud, unless you can demonstrate that either (a) the fraud is pervasive and systematic across the entire discipline, or (b) the fraudulent material is essential to the theory. There are millions of scientists in the world, and inevitably there will be a few bad eggs among them. But that doesn't mean that the entire discipline is rotten to the core.

10. Undesirable consequences. We don't claim that gravity is wrong just because someone falls off a ladder and ends up in a wheelchair, and we don't claim that atomic theory is wrong just because Kim Jong-Un is building nuclear weapons. In the same way, the fact that some people have cited evolution as justification for eugenics, human extinction, or other bad behaviour, does not call into question the fact that biological populations change over time, and have been doing so for millions of years.

11. Character flaws of famous scientists. Facts do not change just because the person who discovered them was a socialist (like Albert Einstein), or a eugenicist (like Francis Crick), or a generally abrasive person (like Isaac Newton). In the same way, allegations that Darwin was a racist, even if true, are not valid arguments against the theory of evolution.

12. "Science changes." You can't just dismiss anything and everything about science that you don't like by glibly saying "facts change" or "science changes" or "scientists are always changing their minds." Scientists only change their minds about things if evidence demands it, and even then only in a controlled and methodical manner. In the same way, if you want to effect a change to the scientific consensus yourself, you must provide evidence to support the change that you want to see, and make sure that you follow the rules when making your case.

13. "Were you there?" There are ways of testing things that do not require you to have "been there." Repeatability does not require you to control and observe a process all the way from start to finish. In any case, to the extent that it does have any merit, "were you there?" is nothing more than an unanswered question, which brings us back to point 3 above: scientific theories are not refuted by unanswered questions, but by contradictory evidence.

14. Magic shibboleths. More generally, if you think a clever-sounding one-liner (for example: "it's just an assumption", "it's just an interpretation" or "were you there?") refutes any and every argument that you haven't otherwise thought of, it almost certainly doesn't. I'm sorry, but there are no shortcuts for doing your homework.

15. One single data point. Reproducibility is fundamental to science, and scientific theories are never established or overturned on the basis of a single study by a single research team, especially not if the "other side" has hundreds or even thousands of other data points in its support. In such cases, the single data point is almost certainly a result of experimental error rather than a radical new law of physics. And if you only have a tiny minority of anomalous data points, the chances are that you have only discovered a corner case, for which the correct response is to refine the theory, not to throw it out altogether. Especially if the anomalies are relatively small.

Next week I will look at another option that you have when faced with a scientific theory that you disagree with: proposing an alternative. But just as with providing contradictory data, that too needs to stick to the rules.

Featured image: Folded Precambrian rock formation in the Grand Canyon, showing clear evidence of fracturing in the fold of the rock. Photograph by the US Geological Survey.