Could Dark Energy be a "Cosmic Gravity Background" Could dark energy (the accelerating expansion of the universe) be the result of gravity from the dense past universe "pulling" outward from all directions? The universe theoretically started out extremely dense and hot, and we can see the light reaching us as the cosmic microwave background. I wonder if that same region and denser portions beyond are exerting a gravitational effect that is stretching out everything within toward it, effectively being a cosmic gravity background. If so, is this the explanation for dark energy?
There is in fact a cosmic gravitational wave background. These waves are expected to be stochastic, having originated in the early universe (much earlier than the cosmic microwave background). Random fluctuations were subsequently stretched during inflation, making them observable over many wavelengths. A good and reasonably up-to-date introduction I read is Lasky et al. (2016), which gives some of the most recent constraints on the parameters of the frequency spectrum $\Omega_{\text{GW}}(f)$. The great thing about the wide spectrum is that a number of different tools (pulsar timing arrays, interferometers like LIGO, etc.) can be used to constrain different parts of it, both directly and indirectly.

That said, dark energy is almost certainly not a result of the gravitational wave background. First, there's no theoretical mechanism to explain how such an effect would arise. Second, the background is probably not strong enough to have an influence on the current expansion of the universe (see the graph here to see how weak it is). Finally, dark energy is a relatively recent phenomenon, arising several billion years ago. The background was around long before then, and yet had no effects.