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July 21, 2015

Space is mostly empty, but some parts of the universe are emptier than others. During the 1970s, astronomers began to discover vast reaches of space that contain almost no galaxies at all.

We don’t live in one of those “voids” ourselves. Instead, we live in a galaxy that’s part of a group of several dozen galaxies. This group and several others make up an even bigger collection of galaxies. When you map them out, they form a long string known as a filament. Most other galaxies belong to similar structures. Between these glowing filaments, though, there’s mostly empty space.

These voids typically measure about 300 million light-years across. That’s an enormous distance — every star and galaxy you can see with the unaided eye is much, much closer to us than that.

One of the greatest astronomers of the 20th century didn’t believe such things existed. Edwin Hubble, who discovered that the universe is expanding, thought that space was much more uniform. He reached that conclusion by counting galaxies in different directions. But Hubble didn’t know how far most of the galaxies were. When astronomers measured the distances and plotted the galaxies on a map, they discovered that the galaxies fell along filaments, with vast voids between them.

Astronomers are fortunate that we’re not in one of these voids, because there’d be few nearby galaxies for them to study. Instead, they have a plethora of them to examine, adding to our understanding of the cosmos.

Script by Ken Croswell, Copyright 2015

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