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I'm curious if there are any theories about the increasing rate of the expansion of the universe that are centered around gravitational pull from matter outside the event horizon of either the observable universe, or the entire universe?

Since observations point to a uniform rate of expansion in all directions, it would make sense (as most theories speculate) that some force is at work. Most theories invoke dark matter/energy, but is it possible that it is simply gravity?

In my thought experiment I considered this in two scenarios:

  1. Finite and Boundless Universe: There is no limit to the size which the universe can expand, but being finite in size and expanding outward, the accumulation of matter at the very edges of the universe is more dense than that in the observable universe. This dense outer boundary is constantly pulling the rest of the universe towards it. As more matter accumulates at the horizon, gravity increases, and the rate of acceleration expands.
  2. Finite and Bounded Universe: The universe is limited in size, as expanding matter and energy reach the event horizon of this limited universe, it is compacted like a black hole that surrounds the entire universe. As the maximum size is limited in this scenario, matter and energy would infinitely accumulate at the horizon; in turn constantly speeding up the expansion of the universe as all matter is pulled outwards towards the ever-growing horizon.

I'm quite the astronomy nerd, and have a good understanding (as much as a non-professional can) of the physical laws governing the universe on a large scale, so I know there are some immediate problems you could pick apart in the above scenarios, this is just an idea I had to jot down before I forgot. I am interested in whether or not any fleshed out theories similar to this idea exist.

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    $\begingroup$ I don't think an event horizon for the entire universe makes much sense, each observer has their own horizon. $\endgroup$
    – PM 2Ring
    Commented Jan 1, 2020 at 13:30
  • $\begingroup$ @PM2Ring After the big bang, as the universe expanded, the "event horizon" as I use the term here would be the outermost boundary of the universe. $\endgroup$
    – jon.bray.eth
    Commented Jan 3, 2020 at 3:29
  • $\begingroup$ But in standard Big Bang theory, the entire universe doesn't have a boundary. Please see physics.stackexchange.com/questions/136860/… $\endgroup$
    – PM 2Ring
    Commented Jan 3, 2020 at 3:32
  • $\begingroup$ True, but we also don't really have any solid models to truly explain the odd phenomenon of a singularity either. $\endgroup$
    – jon.bray.eth
    Commented Jan 3, 2020 at 3:48
  • $\begingroup$ Hopefully, a quantum gravity theory will eliminate the gravitational singularities of black holes, and of the Big Bang... Of course, even when (if) we have such a theory we won't be able to directly verifying its predictions about singularities, which is a bit frustrating. $\endgroup$
    – PM 2Ring
    Commented Jan 3, 2020 at 3:55

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There are no such theories because there is an immediate problem with both scenarios as stated.

It is a fact that a spherical shell of material has no net gravitational influence on material anywhere inside it. https://en.wikipedia.org/wiki/Shell_theorem

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  • $\begingroup$ Interesting, I hadn't thought of that theorem in years. As I understand it there are a few assumptions of uniformity and the spheres existence within the boundaries of space-time. In the context of the question the shell is the boundary of the entire universe - which is likely not completely uniform. As the "outside" of the sphere would be outside our universe, the same physical laws would have to apply there, which may not be the case. Can this theorem be applied to such a scenario? $\endgroup$
    – jon.bray.eth
    Commented Jan 3, 2020 at 3:42
  • $\begingroup$ Also, the theorem is in regards to a point within said sphere. In this scenario the shell is not the only factor, as trillions of other galaxies and objects are also enacting forces on any test point. $\endgroup$
    – jon.bray.eth
    Commented Jan 3, 2020 at 3:45
  • $\begingroup$ @SentientFlesh The shell theorem is the same in GR. Anything that is outside our universe, as you put it, cannot affect the physics in our universe. $\endgroup$
    – ProfRob
    Commented Jan 3, 2020 at 7:53

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