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# The Fourth Dimension

The Fourth Dimension

A line has one dimension, a square has two, and a cube has three. But to describe a melting ice cube, you'd need four dimensions. We'll talk with a mathematician about the fourth dimension - time - after this on Earth and Sky.

Date

JB: This is Earth and Sky, on the subject of time - often called the "fourth dimension." Mathematicians talk about a line as one-dimensional, a square as two-dimensional, and a cube as three-dimensional. But if you wanted a precise description of say, an ice cube melting, you'd need four dimensions - length, width, depth, and time. We spoke with Dr. David Eisenbud, the director of Berkeley's Mathematical Sciences Research Institute, about time as the fourth dimension:

(Tape 0:08:44-0:08:49) People often furrow their brow and try to think about, what is the fourth dimension? Where is it anyway? (Tape 0:08:56-0:09:37) Really, the way mathematicians think about it, four dimensions is a simple idea. If you have something one-dimensional, like a line, the reason it's one-dimensional is you can say where you are on the line by telling one number, how far you are from a certain point. If you want to say where you are on a plane, you need two numbers. If you want to say where you are in three-space, where we live, you need three numbers. But if you want to say where/WHEN you are -- that is to say where you are in space and what time it is, you need four numbers - three space dimensions, and you have to tell what time it is, that's a fourth number. So we say that's four dimensions.

JB: Thanks to Dr. David Eisenbud of Berkeley's Mathematical Sciences Research Institute for speaking with us. And with thanks to the National Science Foundation, I'm Joel Block, for Deborah Byrd, for Earth and Sky.

Author: Beverly Wachtel

Thanks to the following individual for aiding in the preparation of this script: Dr. David Eisenbud
Director, Mathematical Sciences Research Institute
Berkeley, CA
de@msri.org

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