I want to create a universe where the visible universe is much smaller than that of our own. The idea is to create a sort of "fog of war" around every star system. In our universe, you can see pretty much every other star, even if, due to the extreme distances, you may only be able to see the "present" of those stars a few years after it happens. I want it to be such that some residents of my universe can only really see a few stars outside of their own, and maybe a few more with technology. In order to see more stars, my universe's residents would have to go expand to other stars. This is in order to create a dynamic similar to how we explore earth; areas that were before completely unknown would then be discovered and charted, and then reported back to be acted upon. I've considered:
Changing the speed of light, or the size of atoms, or some other fundamental constant — this changes so many other things about the universe as to make it completely unrecognizable. so I've ruled out this.
A viscous luminiferous aether — the idea here is that light will get redshifted extremely quickly, therefore creating the fog of war effect I want. The cloud of vision so-to-speak will be slightly nonspherical due to aether winds, but I'm fine with that. The main problem here I believe is that light would be rather slow, and I sort of want to keep it at the speed it is now (or faster)
A 4+0D aka Riemannian universe — This sort of universe has no defined speed of light, so I could make it as slow as I want it to be, and hence would allow it to redshift faster. This has the same problem is the luminiferous aether though, I ideally would not want to slow down the speed of light. It also introduces many other weird artifacts such as negative kinetic energy, which I would prefer to avoid.
A literal "fog" of war. There could be very numerous gas particles that exist everywhere, dispersing light, and generally making looking far hard. The problem is, of course, gravity. It's sort of hard to make anything not affected by gravity, since it's literally just how space is curved. I guess I could handwave a particle that isn't affected by gravity to make this work, but there's more issues with this. Because of the abundance of this particle, there would probably be a lot of interactions between it and "ordinary" matter, which would probably create a lot of new implications for chemistry. While that's interesting, I would rather just have something that doesn't completely change the way our universe operates.
So, what could I even use to justify a universal "fog of war"?