A simulation of the large-scale structure of the Universe. Identifying which regions are dense and massive enough to correspond to star clusters, galaxies, galaxy clusters, and determining when and under which conditions they form, is a challenge that cosmologists are only now just rising to. (DR. ZARIJA LUKIC)

What Was It Like When The Cosmic Web Took Shape?

The Universe began almost perfectly uniform, while today, it’s anything but. Here’s how we grew up.

One of the strangest facts about the Universe is how dramatically its changed over time. Today, we see a Universe filled with large galaxies containing hundreds of billions of stars, clumped and clustered together into a massive cosmic web. Closer back in time to the Big Bang, however, everything was extremely smooth and uniform, with very little clumping or clustering to speak of. Go back far enough, in fact, and you won’t find any galaxies or stars at all.

This makes sense from a qualitative point-of-view. The Universe was born with tiny imperfections, gravitation grows them while the Universe expands, and depending on how and where gravity wins, we get these enormous galaxies and galaxy clusters separated by regions containing nothing: cosmic voids. But structure didn’t form all at once, and the largest structures formed last. This is the cosmic reason why.

The evolution of large-scale structure in the Universe, from an early, uniform state to the clustered Universe we know today. The type and abundance of dark matter would deliver a vastly different Universe if we altered what our Universe possesses. Note the fact that small-scale structure appears early on in all cases, while structure on larger scales does not arise until much later. (ANGULO ET AL. 2008, VIA DURHAM UNIVERSITY)

Imagine the Universe as it was in these early stages. It’s full of matter and radiation that distributed almost perfectly…