“To be loyal to myself is to allow myself to grow and change, and challenge who I am and what I think. The only thing I am for sure is unsure, and this means I’m growing, and not stagnant or shrinking.” ‐Jarod Kintz
But for the Universe, although it's constantly changing, growing in a gravitational sense is a thing of its past. Sure, we continue to form new stars, galaxies continue to merge, and the structure we see on the largest scales continues to evolve.
Image credit: Bob Franke, via http://bf-astro.com/.
But there once was a time when there were no stars, no galaxies, and no groups or clusters. These all formed, so at some point, the Universe was able to build these structures where there were none before. But today, everything that isn't already gravitationally bound to itself never will be.
Image credit: Boylan-Kolchin et al. (2009) for the Millenium-II simulation; MPA Garching.
How did the Universe grow up, and why did it stop doing so? Come and read the whole story.
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Thanks, Ethan
I know you've covered this before, but this article neatly wraps it all up, and has greatly clarified my understanding.
Very cool article. And the accompanying images really add to the story. Thanks!