5X5 Episode 66

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5X5 Episode 66
Plausibility in Science
22nd April 2009

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5X5 65 5X5 67
Skeptical Rogues
S: Steven Novella
R: Rebecca Watson
B: Bob Novella
J: Jay Novella
E: Evan Bernstein
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Plausibility in Science[edit]

You're listening to the Skeptics' Guide 5x5, five minutes with five skeptics, with Steve, Jay, Rebecca, Bob and Evan.


S: This is the SGU 5X5 and tonight we're talking about plausibility in science. Science is a cumulative effort, which means that all the things that we come up with in science, because it's describing the same reality, the same universe, must agree internally; must agree with itself; therefore, as we build an ever more sophisticated model of how the universe works, we can use that model—those ideas that have panned out, in order to test the plausibility of any new ideas in science.

E: And it gives us a starting point or, as it were, a point where we can go ahead and begin new sets of experiments based on the principles of plausibility so that we can avoid having to do the otherwise limitless number of experiments that would otherwise be required. It gives us a place to start.

B: How do you determine prior plausibility, then? One way is to look at the best, strongest evidence for a given topic. Is the new claim in line with that evidence? If it is, then prior plausibility is high. The threshold of evidence is therefore lower for this claim even though it still may be incorrect. Does the new claim disagree with the current accepted body of evidence? Prior plausibility is then lower and the old axiom kicks in: extraordinary claims require extraordinary evidence.

S: And what that means practically is that any evidence for the new claim has to be at least as great as all of the previous evidence that says that it shouldn't be true or that it's highly implausible. So you're still comparing evidence to evidence at the end of the day.

J: A really good example of applying the idea of plausibility would be if you think about homeopathy. Homeopathy, as many of you already know, is the belief that by diluting something in water enough that you can get some type of medicinal effect out of it. There is nothing in science today that we would consider homeopathy to be plausible. There's no way that we can see, so far with our current science, to prove homeopathy or even give it a mechanism for it to work with the way that it's described.

S: That's right; so therefore we would say that homeopathy is an extraordinary claim. Water that doesn't have any active ingredient left in it, can not have a complex chemical action. For example, homeopaths would—trying to rescue the plausibility of homeopathy—would say, "well, the water retains the memory of what was diluted in it", but that's just replacing one magic for another because there's no way; there's no mechanism for that, for the water to have quote-unquote "memory" or to retain it as it gets put onto a sugar pill and then eaten and digested and then absorbed into the bloodstream and then... what, this water is still holding together its memory even enough to have a physiological effect? It's so implausible that from a practical point of view, we could say that the probability that homeopathy can work is... it's as close to zero as we can have in science.

R: Of course though, it's important to keep in mind that plausibility or implausibility in and of themselves is not enough to debunk or confirm an idea. It's just a sniff test to kind of give you the heads-up that maybe something needs to be investigated more.

S: That's right, so like again with homeopathy we would need a mountain of evidence that it worked. It would have to be a very clear effect, reproducible, statistically significant and large physiological effect that nobody could doubt that there was some effect happening. Then we would go back and say "all right, there was obviously something wrong with our plausibility argument so there's some new effect in nature that we haven't discovered before." That's fine, as long as the evidence for a new effect or rewriting the physics or the chemistry textbooks is equal to the evidence that says it shouldn't be possible in the first place. So plausibility plays an absolutely essential role in science. Without consideration of plausibility, it's as if we're starting from square one with every new thought or idea that people come up with and that goes against the cumulative nature of science.

S: SGU 5x5 is a companion podcast to the Skeptics' Guide to the Universe, a weekly science podcast brought to you by the New England Skeptical Society in association with skepchick.org. For more information on this and other episodes, visit our website at www.theskepticsguide.org. Music is provided by Jake Wilson.


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