Physicists argue that black holes from the Big Bang could be the dark matter

A technical explanation of the expansion involves the inflaton field.

(There's also energy density of the gravitational field.)

"Bugorski understood the severity of what had happened, but continued working on the malfunctioning equipment, and initially opted not to tell anyone what had happened."

"The left half of Bugorski's face swelled up beyond recognition and, over the next several days, the skin started to peel, revealing the path that the proton beam (moving near the speed of light) had burned through parts of his face, his bone and the brain tissue underneath.[3] As it was believed that he had received far in excess of a fatal dose of radiation, Bugorski was taken to a clinic in Moscow where the doctors could observe his expected demise. However, Bugorski survived, completed his PhD, and continued working as a particle physicist.[4] There was virtually no damage to his intellectual capacity, but the fatigue of mental work increased markedly.[2] Bugorski completely lost hearing in the left ear, replaced by a form of tinnitus.[5] The left half of his face was paralyzed due to the destruction of nerves.[1] He was able to function well, excepting occasional complex partial seizures and rare tonic-clonic seizures."

It's a good schema to get all the baggage of Earth out of the novel.

He just says, whoops, earth got eaten, don't worry about Yosemite anymore, now here are some space monks that live in huge bubbled space trees.

Much more fun than having to explain things minutely.

Of course General Relativity is not the final answer, we know that. But that does not mean we know nothing about gravity, or that we somehow can't use our current theory to make predictions.

Dark matter as a concept assumes General Relativity is good enough, and takes it as-is. Without modifying gravity we need some other way to explain the discrepancies like galactic rotation curves, and so for dark matter we add in some new, so-far unseen, particles. We also know they have to interact very weakly with normal matter besides gravity, otherwise we'd would already have noticed them in existing observations and experiments. Based on this we can make predictions.

What would happen if we have some matter that only interacts gravitationally buzzing around?

Well as mentioned in my previous post such matter can't cool down and clump like normal matter, so instead it would be spread out in diffuse blobs around galaxies. And when we model galaxies with such dark matter halos we find that indeed, that might explain galaxy rotation curves. It also makes other predictions which also seem to match other observations. So overall dark matter looks like a pretty good candidate.

The alternative of course is to assume there aren't dark matter particles, but rather that GR has to be replaced or modified in some non-trivial way. There are many people working on that.

However they're so far struggling, because it turns out to be very difficult to change or replace GR without failing to match existing observations. So that seems to indicate that GR is a pretty darn good theory of gravity.