'We Don't Planet' Episode 7: The Vast Cosmic Web

At the very largest scales — larger than solar systems, galaxies, and even clusters of galaxies — the cosmos reveals a surprising structure. Instead of being scattered around randomly, galaxies are arranged in a vast web-like pattern. In this cosmic web, there are long thin strands, walls and sheets, dense clumps, and enormous voids of almost nothing.

This entire structure is made of galaxies, in the same way that your boy is made of cells. Except that comparatively, the galaxies are more than 100 times smaller than your calls are compared to your body. This pattern fills up the observable universe — indeed, it is the very largest pattern found in nature.

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Despite its impressive size, the cosmic web has humble origins. In the earliest epoch of the universe, quantum fluctuations in space-time itself imprinted themselves in the distribution of matter, appearing as slight differences in density. We can see the influence of these processes in the cosmic microwave background, the "baby picture” of the universe, made from light that was released just 300,000 years into the Big Bang.

Those tiny differences were unstable: small pockets of higher-than-average density attracted more matter, and the lower-than-average density regions began to empty out. Over the course of billions of years, the action of simple gravity built dwarfs, galaxies, groups, and clusters. 

Galaxies stream along the thin filaments, heading toward the nexus points — the clusters. Meanwhile, the voids continue to expand, slowly dissolving the walls between them. This pattern is full of rich cosmological information, since its structure was seeded more than 13 billion years ago.

"We Don't Planet" is hosted by Ohio State University astrophysicist and COSI chief scientist Paul Sutter with undergraduate student Anna Voelker. Produced by Doug Dangler, ASC Technology Services. Supported by The Ohio State University Department of Astronomyand Center for Cosmology and AstroParticle Physics. You can follow Paul on Twitter and Facebook.

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Paul Sutter
Space.com Contributor

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute in New York City. Paul received his PhD in Physics from the University of Illinois at Urbana-Champaign in 2011, and spent three years at the Paris Institute of Astrophysics, followed by a research fellowship in Trieste, Italy, His research focuses on many diverse topics, from the emptiest regions of the universe to the earliest moments of the Big Bang to the hunt for the first stars. As an "Agent to the Stars," Paul has passionately engaged the public in science outreach for several years. He is the host of the popular "Ask a Spaceman!" podcast, author of "Your Place in the Universe" and "How to Die in Space" and he frequently appears on TV — including on The Weather Channel, for which he serves as Official Space Specialist.