ARI SHAPIRO, HOST:
We are all trapped in space, the space of three dimensions. Sounds abstract, but NPR blogger and astrophysicist Adam Frank can explain. First he says imagine a bear right in front of you.
ADAM FRANK, BYLINE: To escape this angry bear, which direction would you run? You could bolt to the left or right. That would be a good idea. You could also run straight ahead into the bear, which would be dumb, or you could run straight away in the other direction. If there was a cliff nearby, you could jump off it and escape by falling downward. And finally, if you had a jetpack, you could fly straight upward, which would be totally awesome.
So there you go - left, right, forward, back, up, down. For physicists, each of these pairs constitutes a dimension. If forward and back were all that existed, you'd be living in a one-dimensional world. In a 1D universe, everyone lives along a single line.
But if you added left and right to that line, suddenly everybody gets more room. There would literally be more space to inhabit. This expanded 2D world would be planar, kind of like an infinite sheet of paper. But up and down still wouldn't exist for inhabitants of this 2D world. In fact, it would take a pretty creative 2D citizen to even imagine the possibility of the third dimension. We, of course, know all about up and down because we inhabit a 3D world. Maybe just like those 2D planar creatures, we're trapped in our 3D space and can't even picture the other dimensions.
It was Einstein who showed us that time can be thought of as a fourth dimension. Just like you can drive from west to east along Interstate 80, all of us are constantly traveling from the past to the future through time. Of course the weird thing about time as a dimension is you can only travel one way.
These days, a lot of physicists are going beyond Einstein and think there might be extra dimensions of space that we just don't experience. If we found them, suddenly there'd be extra directions to travel in and more space to fill. But for now we're all just stuck in 3D.
SHAPIRO: That's NPR blogger Adam Frank.
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