Now that summer vacations are generally over, it is time to dust off this forum...

There's a new study out by Temple & Smoller: Expanding wave solutions of the Einstein equations that induce an anomalous acceleration into the Standard Model of Cosmology

Since nonlinearities alone could actuate dissipation and decay in the conservation laws associated with the highly nonlinear radiation phase and since noninteracting expanding waves represent possible time-asymptotic wave patterns that could result, we propose to further investigate the possibility that these corrections to the Standard Model might be the source of the anomalous acceleration of the galaxies, an explanation not requiring the cosmological constant or dark energy.

This might be the preprint of the paper, but I'm not sure.

Ari said:

Now that summer vacations are generally over, it is time to dust off this forum...

The inches of regolith, you mean :) How was your summer?

There are a couple of things in that paper I find a bit odd. I think they are trying to say that the strange accelerations we "see" happen when a ≠ 1, but later say:

Temple & Smoller said:

Of course, if a ≠ 1, then the spacetime has a center, and this would violate the so-called Copernican Principle, a simplifying assumption generally accepted in cosmology, (c.f. the discussions in [10] and [1]). As a consequence, if the earth did not lie within some threshold of the center of expansion, the expanding wave theory would imply large angular variations in the observed expansion rate.⁸

The footnote was even more mystifying:

⁸The size of the center, consistent with the angular dependence that has been observed in the actual supernova and microwave data, has been estimated to be about 15
megaparsecs, approximately the distance between clusters of galaxies, roughly 1/200 the distance across the visible universe, c.f. [1, 11].

So the earth has to be fairly near the center of expansion in this theory and that's okay because that's the way it seems to be? Have I got that right?

Ritchie said:

The inches of regolith, you mean :)

Well, yes, but we need to watch out for fossils, which is why I suggested only "dusting off" so that we don't break them... ;)

Ritchie said:

How was your summer?

Fast, as usual. It's the curse we northeners have to face; the summers are just too damn short.

Ritchie said:

So the earth has to be fairly near the center of expansion in this theory and that's okay because that's the way it seems to be? Have I got that right?

Well, I think they are saying that Earth would need to be at the center and if so, then the center would have the size given in the note.

By the way, I now think that the arXiv preprint I linked to is not the paper published now. The arXiv preprint says at the end of the introduction: "Details will appear in a forthcoming article". I assume that the PNAS article published now is the "forthcoming article". But at any case they seem to be discussing the same thing.