Space Walk Image Gallery
Space Walk Image Gallery

A diagram from the work of Copernicus showing how planets in our solar system move in relation to the sun. See more space walk pictures.

Hulton Archive/Getty Images

Centuries ago, human beings looked up at the night sky and imagined that a black globe enveloped the Earth. They believed the stars were simply pinpoints of light. The sun, moon and other planets circled the Earth in a regular, perfect pattern. In their minds, the universe was small, centered on Earth and organized into perfect spheres.

­­Scien­tists like Copernicus and Galileo discovered flaws in this philosophy. It took more than a century after Galileo's discoveries for the world to accept that the Earth wasn't the center of the universe. As time passed, we began to learn more about the universe. Today, we study the cosmos through advanced telescopes, satellites and probes.

Now we have images of galaxies millions of light years away from Earth. Scientists study distant stars on a regular basis. They've even detected planets in solar systems far beyond our own.

But what about the big picture? What do we know about the universe as a whole? Is it expanding? Is it infinite? If it isn't infinite, what lies beyond the boundary of space? And what exactly does space look like?

These questions fall under the category of cosmology, the study of the universe. People have tried many different approaches to study the universe. Some concentrated on mathematics. Others preferred using physics. And quite a few took a philosophical approach.

There's no consensus among cosmologists about what space looks like, but there are plenty of theories. Part of the challenge of describing space is that it's very difficult to visualize. We're used to thinking about locations in two dimensions. For example, you can determine your location on a map using longitude and latitude. But space has four dimensions. Not only do you have to add depth to the dimensions of length and width, you also must add time. In fact, many cosmologists refer to this collection of dimensions as space-time.

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What are some of the major theories that could help us figure out the shape of space? Read on to find out.