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As I understand it, Dark Energy is believed to reside in empty space. As the Universe exapnds, more empty space exists inside the Universe and so the small energy per unit of empty space adds up to a greater total, thus causing an accelerated expansion.

But if this were true, what about all of the empty space outside the edge of the universe? This theory appears to take into account the "interior space" of the universe, but not the presumably infinite amount of exterior space outside the farthest reaches of the universe.

Indeed, if empty space has energy, would not the infinite amount of empty space past the edge of the expanding universe thus exert infinite inward force, crushing the universe?

Said differently, isn't it the case that the amount of empty space is actually not finite - it is infinite, and most of it is outside the edge of the universe, and if dark energy were real, this wouldn't this result in an infinite inward force?

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Qmechanic
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There is no exterior space. The universe is not expanding into anything. Space is simply expanding between galaxies. There is no “edge of the universe”, so your diagram is misleading.

The simplest model to understand, consistent with observations, is that space is flat, infinite, and expanding. As far as you care to go in any direction, there are still galaxies. But they are getting farther apart from each other because space is expanding between them, and it is expanding faster and faster.

It is also possible that the universe has a finite and increasing spatial volume, but there is still no edge and no exterior space in this model. Visualizing how this could be is harder without understanding differential geometry. But imagine setting out in a spaceship, going straight away from Earth in any direction, and discovering that you eventually come back to where you started. Space might be like the three-dimensional equivalent of the 2D surface of an expanding sphere.

G. Smith
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