I came across a paper recently which seems to be getting a lot of popular press, and a student also emailed me to ask about it: --
Farnes, "A Unifying Theory of Dark Energy and Dark Matter: Negative Masses and Matter Creation within a Modified ΛCDM Framework," https://arxiv.org/abs/1712.07962
After replying to her with some vague impressions, I thought I would edit my email and recycle it as a question here. After spending some time looking at the paper, I wasn't really able to tell much about whether it was any good -- I'm only kind of a dilettante at general relativity. It seemed pretty similar to the steady state model, or to some of the more recent kookish attempts to revive the steady state. But the surface similarity to disproven or kookish models doesn't necessarily mean it's not good work. It wasn't clear to me whether it suffered from the same problems as the steady state model: inconsistency with the CMB (he gets an oscillating universe), and breaking of Lorentz invariance (which is probably the most extensively and precisely tested scientific theory in history).
Is this idea any good? Consistent with observation? Does it solve a problem that actually is a problem?