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Is there anything to suggest why the density wasn't uniform? For example if we consider having particle-antiparticle pairs constantly popping into and out of existence could something like that have been enough perturbation to start things moving?

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Please say more about dark matter- in its universe, why would that be true?

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Yes thank you. The concept is much clearer now.

Perhaps I'm looking at it wrong. And these concepts are a big stretch to my ability to comprehend.

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Thank you.

Superclusters are still expanding, they are just overdense regions that would eventually collapse if there were no dark energy. Assuming dark energy persists, only our Local Group will remain nearby.

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The speed of light is fixed. So when we look at light that is emitted from something that is moving away from us very fast it gets red shifted. When it’s moving towards us it gets blue shifted. Same idea if we’re the ones moving and seeing.

Also because light moves at fixed speed the light we see that’s far away was emitted a very long time ago. So we see things as they were when the light was emitted.

We can’t see infra red, but our cameras can. And we can make sensors that can see much lower frequencies than that. However some stuff is so far/long ago away that it gets shifted beyond any ability to measure and becomes cosmic background radiation that essentially acts as noise.

Some things will simply never reach us as long as the universe is expanding, and somethings are so shifted that they cannot be observed meaningfully.

We can infer a lot about the parts we cannot observe because there is a general spherical symmetry to the Big Bang.

But the edge is just the farthest anything from the Big Bang has gone that we can observe . We haven’t seen/understood evidence that there are things that weren’t from the Big Bang yet.

This reinforces my belief that there is life beyond Earth. And also dismally displays how small we are to the universe.

I'm not sure actually! They look like they could be indicating the "virial radius" of each dark matter halo, which is a common way of approximating the system's size. As context, the virial radius of the Milky Way's halo is something like 700000 light years in radius, over ten times larger than its galactic disk. So these spheres would be much larger than galaxies, but they would generally contain galaxies at their centers.

The precise definition of the virial radius varies, but a typical definition is that it's the radius inside which the average density is 200 times the cosmological mean. That would mean that each sphere is exactly 200 times denser than the cosmological mean.

The basic idea of the virial radius is that the material inside this radius should be orbiting stably. There's a theoretical reason for the factor of 200 (technically the theory suggests 178, but it's approximate enough that people usually round it), and its derivation uses the idea that stably orbiting material should obey the virial theorem. That's where the name comes from.

In addition to what others have said, "nothing" doesn't have dimension.

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There’s probably an infinite number of areas of space like what we call “the universe” for trillions of light years in every direction, some expanding, some colliding, some contracting. This is one idea some people have.