SGU Episode 553

From SGUTranscripts
(Redirected from Pleochroism (553 WTW))
Jump to: navigation, search
  Emblem-pen-orange.png This episode needs:  transcription,  proof-reading,  formatting,  links,  'Today I Learned' list,  categories,  segment redirects. How to Contribute

SGU Episode 553
February 13th 2016
SGU 552 SGU 554
Skeptical Rogues
S: Steven Novella
B: Bob Novella
J: Jay Novella
E: Evan Bernstein
C: Cara Santa Maria

Quote of the Week
Education has failed in a very serious way to convey the most important lesson science can teach: skepticism.
David Suzuki
Download Podcast
Show Notes
Forum Topic


  • Tax season, and tax scams

VO: You're listening to the Skeptics' Guide to the Universe, your escape to reality.

What's the Word (5:00)[edit]


S: We're gonna start with What's the Word, Cara?

E: Yeah

C: Yes! We are starting with What's the Word. And the word this week was actually submitted by @USCWaller on Twitter. The word is Pleochroism.

B: Ooh

C: And yes, again, I looked up how to pronounce it because I would say plee-oh-crow-ism

J: Huh! Me too!

C: Of course, if you are using it as an adjective, it would be plee—oh-crow-ick, and I'm assuming it's not incorrect to say plee-oh-crow-ism, but most sources online say plee-ock-romism. So, listening to that word,

B: I don't like it

C: Any guesses? (Laughs) All right, Bob, any guesses of what you think it might mean?

B: Something to do with light, I would think.

C: Um-hmm, from the “croism” aspect of it?

E: You're right, cro ...

C: Yeah, so it's a term

B: And then “rocks.”

C: And rocks - actually, no rocks in that word, but (laughs)

E: (Chuckles) I think you're thinking of “litho.”

C: But it is true, it is true, it is a word that you often hear in optics and geologies, specifically minerology.

B: Ah! Rocks! There you go!

C: Yeah, rocks! There you go! Referring to the property specifically of crystals to exhibit different colors when they're viewed from different directions under light. And notably, you'll see this when the light is polarized. So looking at specific directions of light, the crystal will look one color; and then when you look at the other direction of the wavelengths, it will look a totally different color.

So, pleochroism comes from the Greek “pleo,” meaning “more;” and “chros,” meaning the color of some sort of exterior coating, like a skin. And its first scientific use in the literature was in 1857. And, yeah, @USCWaller sent this in, because he said that it was his favorite geology word that he's come across. It's a good word.

S: Yeah, that's cool.

C: I feel like I could use it in life, like I have some nail polishes, that when you look at them under different lights, they sometimes look green, and sometimes look purple. Pleochromic nails there.

J: Cool!

C: I know, I want to try and work it into my daily vocabulary.

S: What is the, on a molecular level, do we know what the mechanism of that is?

C: It has to do with double refraction. So, because of the actual structure of the crystal, when, just like in a prism, light will pass through, and it will break it into different wavelengths. In a crystal, that exhibits this double refraction property, it splits the light into two different polarized components. There's an ordinary ray that comes out of it, and then there's an extraordinary ray, which I love that that's what it's called.

(Evan laughs)

(Bob laughs)

C: And they come out in perpendicular planes. So, there are different substances, like a dichroic substances, that only transmit one type of ray. But pleochromic substances transmit both. And so, if you use a polarizing filter over your light, you will see two different

S: Cool

C: colors. Yeah, it's really interesting.

J: Cool

E: That is

S: Let's go on to some news items.

News Items[edit]

Robotic Chef (8:04)[edit]

(Commercial at 25:53)

Brain Electrodes (27:41)[edit]

Diagnosing Cancer (39:32)[edit]

Gravitational Waves (50:27)[edit]

Who's That Noisy (1:02:04)[edit]

Answer to last week: Ice

Questions and Emails[edit]

Question #1: RFID (1:05:18)[edit]

  • Corrections

(Commercial at 1:06:48)

Science or Fiction (1:08:10)[edit]

Item #1: Scientists have identified a new bacterial species capable of causing Lyme disease, the first new such species in North America. Item #2: New research finds that sustained aerobic exercise, but not resistance or intermittent training, increases neurogenesis in the hippocampus of rats. Item #3: Researchers find that over the last 1000 years cultivation has created crops that are far more hardy and resistant than their wild counterparts.

Skeptical Quote of the Week (1:24:48)[edit]

Education has failed in a very serious way to convey the most important lesson science can teach: skepticism. - David Suzuki

S: The Skeptics' Guide to the Universe is produced by SGU Productions, dedicated to promoting science and critical thinking. For more information on this and other episodes, please visit our website at, where you will find the show notes as well as links to our blogs, videos, online forum, and other content. You can send us feedback or questions to Also, please consider supporting the SGU by visiting the store page on our website, where you will find merchandise, premium content, and subscription information. Our listeners are what make SGU possible.


Navi-previous.png Back to top of page Navi-next.png