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The simplest answer is that Milne's explanation requires a non-uniform cosmos, with a formerly crowded "starting area" that expands into empty space. Observations indicate that the cosmos is nearly uniform at very large scales. With Milne's model of a non-expanding space and uniform cosmos, galaxies that started near to us with high velocities that ended ...


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.


(My answer here isn't correct, as pointed out by the first comment on this post, please refer to it.) Yes, it certainly is possible - and it already has happened. The age of the universe is 13.8 billion years, yet it is something like 90 to 100 billion light-years in diameter. This means that we definitely can't see all of it, not because of our own ...


Expansion depends on the amount of mass Yes, space expands more in regions with less matter — in fact this has been proposed as an alternative explanation to dark energy as the cause of the observed accelerated expansion: If by chance we happen to be located near the center of a "cosmic void", then nearby space expands faster than distant space, and since ...

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