It sounds like it is saying that dark energy is not necessary to explain the expansion of the universe not necessarily that it doesn’t exist. On the other hand, the expansion of the universe would be the only reason to think that it does exist.
It’s apparently necessary to explain inflation, though I read an alternative a few years back that had to do with meta-geometry, i.e. geometry of a greater “space” that our spacetime’s geometry is contained in.
Don’t ask how that worked; about all I remember is the term “metastable” and the idea of (the universe as) a ball rolling off the edge of a bowl shape that sloped both inward and outwards.
My mind keeps going back to the Bullet Cluster.
A collision between two galaxy clusters resulted in four regions of mass. First, you have the two areas of luminous matter (red) that interacted and slowed down during the collision. You then have areas (blue) where there is non-luminous matter, as illustrated by the gravitational distortion of the stars/galaxies behind those regions. I don’t see how modified versions of gravitation can explain this. Rather, this is just what we would expect from non-interacting non-luminous matter.
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