I "Dark energy" may be nothing more than baseline curvature

[marcus]

A point that has been clarified in this thread---e.g. think of the John Baez quote in post #41 at the top of this page as a kind of clarifying challenge---is that the choice of how to think of the topic here is NOT A SIMPLE DICHOTOMY. It's not a strict either-or.
What's given is that what we actually measure is the longterm expansion rate which I've called the baseline expansion rate, or baseline curvature of spacetime, but there are several ways to think about this:
1. We can take it as a physical constant and not ask why it is the size it is. The longterm rate being approached as the universe thins out is 1/173 of a percent per million years. Period. That converts by conventional algebra to a spacetime curvature.
2. Or we can study different explanations for the size and different models for how this (effective) physical constant can have arisen. But without prejudice--without assuming that one particular explanation for the effective longterm curvature is right. We have papers by George Ellis and others, by S. Liberati et al, by M. Sakellariadou et al, by Dan Oriti and his co-authors, and many more, that do this. Other names are Saez-Gomez and Sergei Odinstov. Links to some have been given in this thread.
3. Or we can assume that it is somehow obvious that the longterm or baseline expansion rate is caused by a constant vacuum energy density.

That last assumption is what is encouraged when we refer to the baseline curvature as "dark energy". This invokes something which we don't know exists---a mythical energy density, just the right size, present now everywhere and always. But see the John Baez quote in post #44: "In brief: no. It [the vacuum] could have some intrinsic energy, but in most familiar quantum field theories (QED, the Standard Model) the energy is assumed to be zero."
...

Yes, so as I was hoping to convey 2 and 3 are fine,...

I'm glad you like option 2! I like 2 myself. Once it's clear that what we measures when we measure the cosmological constant is the asymptotic (baseline) expansion rate it is an intriguing and natural question to ask how it arises in our universe, why it is the apparent size it seems to be. Several of the authors mentioned have gotten into ideas of quantum cosmology pre-geometry, at this point. Obviously the spacetime manifold of GR is classical---it is an idealization that doesn't embody quantum mechanics. There must be an underlying quantum pre-geometry that it arises from. And in that process the effective constants governing the classical spacetime may also arise.

We see that kind of thing happening in, for example, the papers by Oriti or by Sakellariadou, and their collaborators.

 

[bbbl67]

I know of no scientific reason to suppose that "dark energy" is anything more than the cosmological curvature constant identified by Einstein in 1917 as occurring naturally in the GR equation for spacetime curvature.

I agree with you, but the curvature of the universe wouldn't make any sense if we didn't compare energy levels, right? Space would be nothing but a flat featureless void, if there wasn't energy in it.

Now, my feeling is that Dark Energy is nothing more than the same thing that led to Big Bang Inflation. Except in the case of Inflation, since the universe was so much smaller that even a slight curvature led to runaway faster-than-light expansion for a brief period of time, until the sphere of Inflation became even bigger and then the observable part of the universe went to a modest sub-lightspeed expansion phase. Basically a super version of the Hubble sphere.