This is really the story of the cosmological constant, which Einstein introduced to make the
Universe static and unchanging. But since the Univese has no center, or perhaps the center
is everywhere, so there can't be a single spot of equlibriium becuae not all parts of the Universe
will agree on the same equilibrium spot. Either this equilibrium exists throughout the whole cosmos
or it doesn't exist at all.
Einstein and others assumed that gravity will eventually pull everything together in a "Big Crunch",
and to avoid this problem, Einstein tampered with his equations and added a new term called
the cosmological constant, whose purpose was to match the inward pull of gravity by an outward
force of exact same magnitude. This way the universe would neither pull inwards or expand outwards
because the cosmological constant would exactly balance gravity, hence the Static Universe.
It was Willem de Sitter, who used Einsteins own mathematics to show that a static universe is
impossible. The equations of general relativity shows that the Universe HAS to either contract or
expand, it can not be static. Later, Friedmann, Lemaitre and Gamow argued that a Universe starting
small and expanding outwards is a more logical way. But Einstein opposed this and defended
his Static Universe theory all the way until Hubble was able to find observational proof of the
expansion of the Universe.
Still people thought that some sort of equilibrium will occur, but even so, it can only be temporary, it
would only be a transition where gravity stops the expansion and becomes the dominant force,
but the Univserse will start to contract after that, becuase one has to win, either gravity or the
expansion. And for a long time almost everyone thought it would be gravity, despite the fact that
the expansioon of the Universe was known, gravity would still overcome it they thought.
Discovering the accelerated expansion changed everything though, then it became clear that the
expansion always win, and it appears it always will since the expansion will supposedly last
"forever". Gravity can still pull things together, but it's only at a local scale and totally insignificant
on the Universe as a whole. Chances are though, that the model is not entirely correct, even
though it's accelerating, we don't know if the acceleration is slowly slowing down and gravity could
in a very very distant future gain the upper hand again.
But the key lesson here is that either gravity or the expansion has to win. There cannot be a tie
between them. General Relativity says that such a solution is too unstable to last.