Explanations for/of the metric expansion of space

[Kharakov]

I'm pretty sure it's just that Tom left the water running upstairs, but I'll list a couple of the explanations that I've seen.


1) Dark energy: causes space itself to grow. <- this is a primary one, created by some scientists who couldn't resist a dark side of the force pun, and figured whatever the explanation is, we'll call the mathematical variable associated with it "Dark ENERGY" and say "yeah, that's what we were talking about all along, see, we're right!"

2) tired light: light looses energy as it travels through space, not too popular among the non-crystal wearing, mantra chanting crowd, afaI read

3) consequence of GR: Energy higher in a gravity well contributes more to the stress-energy tensor of the universe, because more time passes for it.... or something like that. There is more than one "consequence of GR" theory (Dark Energy is technically one of them, associated with the cosmological constant, but....), and some of them are sort of out there.


I'm just looking for some nice rewordings to stimulate the old noggin. Maybe someone can put up craziness for us to attack. Or I can later.

 

[none]

http://www.cbc.ca/news/technology/universe-missing-baryons-1.4206311

Physicists have calculated how much matter exists in the universe, but there's a big chunk they haven't been able to find. Recently, two separate groups of researchers say they've managed to spot some of the "missing" matter.

Astrophysicists from the University of British Columbia and the University of Edinburgh independently reported that they found the missing baryonic matter in filaments of gas stretching between galaxies using data from the European Space Agency's Planck telescope
...