How A Wave Is Unlike An Armadillo: One Reporter's Summer Puzzle "There's something about waves that can get you into kind of a mental funk," one philosopher says. For NPR's summer science series, Joe Palca tries to answer the big question: What is a wave?

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#### How A Wave Is Unlike An Armadillo: One Reporter's Summer Puzzle

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This summer, NPR's science desk has been obsessing over waves - ocean waves, sound waves, even the wave you sometimes see fans doing at sporting events. Science correspondent Joe Palca steps back and asks the big question. What is a wave anyway?

JOE PALCA, BYLINE: Yes, I know. A scientist can tell you all about waves, but I wasn't sure a scientist could answer my questions about waves because if you think about it, waves are kind of puzzling. At least I think they're kind of puzzling.

Is a wave a thing, or is it the description of a thing? Well, rather than pester a scientist with my somewhat philosophical questions, I decided to pester a philosopher. S. Marc Cohen is emeritus professor of philosophy at the University of Washington. He's sympathetic to my befuddlement.

S MARC COHEN: There's something about waves that can get you into kind of a mental funk because you look at a wave. You can see them. You look out on the water, and the wave moves across the water. Something's moving through space.

PALCA: OK, I get that.

COHEN: But what is the wave exactly? So you'll scurry off to a physics textbook, and it'll say that a wave is a disturbance that moves through a medium from one location to another.

PALCA: OK, I get that, too.

COHEN: So it's really not a thing. It's not made of stuff like a chair is made of wood or a football is made of leather. But when a wave moves through the water, it's not really made of water. It's a wave in the water.

PALCA: Oh, OK. So Cohen says from a philosophical standpoint, you're better off thinking of a wave as a phenomenon, a thing that happens, sort of like an event.

COHEN: Not what we Aristotelians would call a substance like a football or an armadillo.

PALCA: So a wave in the water is not like an armadillo - got it. But hold on a minute. If a wave is a disturbance moving through a medium, what about light waves? They're a disturbance, and they can travel through empty space. Cohen says his explanation only applies to physical waves, not electromagnetic waves or light waves.

COHEN: It's really mysterious how they get to move through empty space where there is no medium. But if you want the answer to that question, you'd better talk to a scientist, not a philosopher.

PALCA: I was afraid it might come to that. But I note in closing that waves have elusive properties that can befuddle philosophers, too. I feel a wave of relief. Joe Palca, NPR News.