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

Aug 8, 2016
Originally published on August 30, 2016 10:44 am

This summer, NPR's science desk is thinking about waves, of all kinds — ocean, gravitational, even stadium waves. But what is a wave, anyway? My editor asked me to puzzle that one out. And, to be honest, I was puzzled.

Is a wave a thing? Or is it the description of a thing? Or is it a mathematical formula that produces a curve that gives you the description of a thing?

Rather than pester a scientist with my somewhat philosophical questions, I decided to pester a philosopher. Marc Cohen is emeritus professor of philosophy at the University of Washington. He's sympathetic to my befuddlement.

"There's something about waves that can get you into kind of a mental funk," Cohen acknowledges. "Because you look at a wave — you can see them out on the water, and the wave moves across the water. Something's moving through space."

OK, I get that.

"But what is the wave exactly?" asks Cohen. "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."

OK, I think I get that, too.

"So it's really not a thing," Cohen says. "It's not made of stuff, like a chair is made of wood, or a football is made of leather.

"When a wave moves through the water, it's not really made of water," he says. "It's a wave in the water."

From a philosophical standpoint, Cohen says, you're better off thinking of a wave as a phenomenon, a thing that happens, like an event.

"Not what we Aristotelians would call a substance — like a football," Cohen says, "or an armadillo."

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, then what about lightwaves? They're a disturbance, and they don't need a medium to travel through. Cohen says his explanation only applies to physical waves — not electromagnetic waves or lightwaves.

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

I was afraid it might come to that.

But I note, in closing, that Cohen admits that waves have elusive properties that befuddle philosophers, too.

And that provides me with a wave of relief.

Science reporters at NPR are exploring all sorts of waves this summer. Find more of our favorites here.

Copyright 2018 NPR. To see more, visit http://www.npr.org/.

AUDIE CORNISH, HOST:

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. Transcript provided by NPR, Copyright NPR.