Ask Ethan: Is it all-or-nothing for the expanding Universe? | by Ethan Siegel | Starts With A Bang! | Jul, 2024

On the largest of cosmic scales, the Universe is expanding. But it isn’t all-or-nothing everywhere, as “collapse” is also part of the story.

One of the most remarkable revelations in our understanding of the cosmos is the fact that the Universe is expanding. Distant galaxies, on average, all appear to recede from us, with faster and faster recession speeds for galaxies that exist at greater distances. While individual objects and systems may be gravitationally bound together — stars and planets, galaxies, plus galaxy groups and clusters — the space between these structures is not only expanding today, but has been expanding for all 13.8 billion years of cosmic history, and will continue to expand indefinitely far into the future as well.

But is the expanding Universe truly an all-or-nothing proposition? Are there exceptions to the expanding Universe, and is “collapse” a scenario that’s been ruled out entirely? That’s the question plaguing the mind of Patreon supporter Brent Minder, who wants to know:

“Does the universe’s current state have to be all or nothing in terms of expanding or collapsing? Is there a theory that the universe is in a mid-state of collapse and expanse? That is: what if the…