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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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marked as duplicate by John Rennie cosmology May 18 at 18:40

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ This moderation feels aggressive/not commensurate with what is appropriate as that linked question is asking something completely different, just objectively speaking. $\endgroup$ – A br May 18 at 18:54
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    $\begingroup$ You clearly seem to think that the Big Bang happened at a point, which is false. As far as I can tell, this is the root of your misunderstanding, so the question John Rennie linked to seems very relevant to me. $\endgroup$ – G. Smith May 18 at 19:06

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.

  • $\begingroup$ Thanks for this, super helpful. $\endgroup$ – A br May 18 at 17:56
  • $\begingroup$ But going back to the idea of the big bang - the big bang dictates that there is an edge to the universe, that the universe originally occupied a singularity of size zero, and it has now expanded. If it has expanded, is it not the case that it must have expanded into something given that at the singularity it did not occupy any space (just one point)? $\endgroup$ – A br May 18 at 17:58
  • $\begingroup$ Perhaps to say it differently, we know that the normal mass and energy in the universe is finite. If the universe itself is infinite ( curious.astro.cornell.edu/physics/104-the-universe/… ) then it seems that dark energy should also be infinite $\endgroup$ – A br May 18 at 18:09
  • $\begingroup$ No, the Big Bang does not dictate that there is an edge to the universe. No modern cosmological models have an edge. There was no space “outside” the singularity for it to expand “into”. We do not know that the mass and energy of the universe are finite. (Although the mass and energy of the observable universe is.) If the universe is flat and therefore infinite, then there is an infinite amount of normal matter, an infinite amount of dark matter, and an infinite amount of dark energy that we cannot see. In any case, the density of these things is finite and decreasing. $\endgroup$ – G. Smith May 18 at 19:01
  • $\begingroup$ Thanks for that. But if there is an infinite amount of normal matter, why are there statistics like these, total mass of the universe = 1.59486 × 10^55 kg? hypertextbook.com/facts/2006/KristineMcPherson.shtml Doesn't it seem unlikely that the universe if infinite in mass/energy? $\endgroup$ – A br May 18 at 19:08

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