system
Given the following post, respond as if you're commenting on Reddit:
human
Eridanus Supervoid, how is it that something that large can be completely empty?

Also, is it possible for galaxies to move inside the supervoid and fill it out?
gpt
1. It's not completely empty. There's still stuff there, just a lot less than the average of the universe. One principle of cosmology is the idea that at very large distances, the universe "looks the same" in any direction. Imagine you have a jar. You carefully lay a layer of blue marbles on the bottom, then a layer of yellow on the blue, and white on the yellow. Now you shake the jar up. Things should get pretty mixed up. It's still *possible* to find areas in the jar where you have a bunch of blue marbles and nothing else, but it's just not very likely. This is something similar. It's odd to have a void that big, but not *impossible* based on our current models of how the universe came about.

2. Yes, there is nothing technically preventing anything from filling that void, but since matter has gravity associated with it, it means things that are clumped together exert more gravity towards each other and that makes them clump even more. It's basically not likely that anything will ever fill that void.