5X5 Episode 32

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5X5 Episode 32
Occam's Razor
11th August 2008

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5X5 31 5X5 33
Skeptical Rogues
S: Steven Novella
R: Rebecca Watson
B: Bob Novella
E: Evan Bernstein
M: Mike Lacelle
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Skepticism 101 - Occam's Razor[edit]

Voice-over: 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 this is the first in a series of installments that we're going to do on the 5x5 about skepticism 101. We're going to pick specific skeptical topics and we're going to discuss them – give a thorough definition and discuss the applications of them. We're going to start with Occam's razor. Now, Occam's razor is a heuristic or a principle, a rule of thumb, that is also called the Law of Parsimony, which means that when multiple answers are possible for any hypothesis, that the one that introduces the fewest new assumptions is the one that's most likely to be correct. It doesn't mean that it has to be correct, but it means all other things being equal, the simplest – and by simplest, meaning the one that introduces the few newest bits or newest assumption – is the one that is preferred and is most likely to be true.

E: Occam's razor was named after William of Occam who was a Franciscan theologian, a writer and an influential philosopher from the 14th century. He struggled against the common practice of describing nature using abstractions there were untestable. Of the many quotes that are attributed to him, perhaps his best known one—I won't bore you with the Latin, but it translates as, "Plurality is never to be posited without necessity." It wasn't until many centuries later that the term "Occam's razor" first appeared in 1852 by Sir William Rowan Hamilton, who was a mathematician, a physicist and an astronomer and he was the first to actually coin the actual term "Occam's razor".

B: This isn't just some rule of thumb for debunking wild paranormal claims. One of the canonical examples of Occam's razor occurred over a hundred years ago. The equations of Einstein's theory of relativity were the same as Lorentz's. Lorentz's theory contracted rulers and slowed clocks during movement through the aether; Einstein's theory did the same, but without the aether, since the aether could not be detected, Occam's razor sliced it away.

S: Yeah, it was one assumption more than was absolutely necessary in order to explain everything.

R: But, of course, these days it can be applied to crazy paranormal things, like, for instance, you come across a cow that's had its innards cored out and you can assume either that aliens came down and sucked out its anus, so to speak, or you can assume that small predatory animals fed upon a dead cow and went for the mushy bits first. One of those explanations requires us to re-evaluate everything we know about life in the universe and the other one can be easily explained by what we already know about life on earth. So Occam's razor would suggest we go with the animals.

S: Interestingly, you bring up the UFO mythology. UFO proponents sometimes try to cite Occam's razor in favor of their beliefs: that we are being visited by extraterrestrial aliens. They say that skeptics have a different answer for everything: crop circles are hoaxed; UFO sightings are misidentified objects; alien abductions are waking dreams and they have one explanation for everything. They're all due to alien visitations. Therefore, their explanation is simpler and should be favored by Occam's razor. But here's the mistake they're making: they're misinterpreting Occam's razor as the simplest explanation, rather than the explanation that introduces the fewest new assumptions. We know that people hoax crop circles, that people have waking dreams, that they misidentify objects in the sky. That is not introducing anything new into our knowledge about the world, about ourselves, about the universe, but the introduction of the concept that the earth is being visited by a space-faring extraterrestrial race is a major introduction of a new assumption and therefore Occam's razor does not favor that. But that's a very common abuse or misuse of Occam's razor.

B: So, it could be simpler, but it could be less correct as well. So you've got to watch out for that.

S: If it's simply adding one massive new assumption, that's not favored by Occam's razor.

M: Another classic example would be the heliocentric and geocentric model of the solar system. In order to explain the motion of Mercury relative to Venus, the geocentric model posited the existence of epicycles within the orbit of Mercury. The heliocentric model was able to explain this by putting the sun at the center of the solar system, rather than have the earth at the center of the solar system.

S: And so, even though, initially, the heliocentric system really wasn't anymore accurate than the Ptolemaic system of epicycles, but it was just vastly simpler.

M: Right.

S: And then, of course, eventually it was later verified by more accurate observations, so you still need that. Occam's razor doesn't tell you what must be true, it just tells you what's most likely to be true. At least, the things you need to rule out before you accept a less parsimonious explanation.

E: So it has a role in the scientific method, in that respect.

S: Absolutely. Yeah, it's essentially thought of as a heuristic of scientific thinking. Certainly, it's something that is lacking in many of the paranormal believers' arguments. They often will leap over known and simple explanations to hypothesize completely unknown new realities in blatant violation of the principle of Occam's razor.

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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