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A Moment of Science

The Dark Side of the Universe

The curved and expanding universe has no other "side," per se.

The sun, peeking through the thin line of Earth's atmosphere, photographed from the International Space Station.

Photo: NASA's Marshall Space Flight Center (Flickr)

A finite universe is like a ball's SURFACE: It has no edge, and if you're on it, you can't reach the surface's other side.

Do you know what’s on the other side of the universe?

To Infinity and Beyond

There are two ways to think about that question. Either the universe ends, which means it’s finite, or else it’s infinite. If the universe is infinite, then it never ends, so it can’t have an edge or another side. But what if the universe is finite, which it could be, according to Einstein?

The universe is expanding, so there are two options: Either the universe will keep expanding forever, which means space is infinite, or else at some point the universe will stop expanding because the pull of the objects it contains will cause it to start collapsing back on itself. That’s what scientists mean when they say the universe might be finite.

Outer space in 4D

The way to picture it is like a piece of paper that gravity causes to fold back on itself to form a sphere. A finite universe is like a ball’s SURFACE. A ball’s surface has no edge, and if you’re on it, you can’t reach the surface’s other side. Also, the surface of a ball is two-dimensional and the universe is three-dimensional, which means you’d need a four-dimensional space to fully visualize a curved universe.

So the answer to what’s on the other side of the universe is that the universe has no other side. Wrap your brain around that.

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