Void lifeforms could neither be seen nor touched. The dark matter that composed them participated in neither electromagnetic force nor the strong and weak nuclear forces.
It was known to participate only in gravity and a "dark nuclear force" that could be subdivided into countless phenomena.
Dark matter was bound together by dark nuclear force, possessed dark electromagnetic fields, and could release dark energy.
Dark energy undoubtedly had many effects, but the only one that creatures of the bright matter world could observe was its effect on spacetime, which caused the universe to expand.
Just as dark matter did not participate in the interactions of bright matter, bright matter did not participate in the various interactions between dark matter.
The two seemed like separate physical worlds occupying the same spacetime, each with its own set of fundamental forces, connected only by their distortion of spacetime.
Yet these two vastly different sets of fundamental forces were also unified. Inertia and the laws of interaction still existed, and gravity was their shared bridge.
In theory, scientists could combine both sets of fundamental forces into a single "grand unified force."
Even the Unified Force Civilizations of the Milky Way had yet to accomplish that, however. They had only unified the fundamental forces of the bright matter world.
Research down this path was extremely difficult, because without tools capable of receiving "dark radiation" or otherwise detecting dark nuclear force or dark electromagnetic fields, it was practically impossible.
Simply put, there were no instruments to detect them!
How could a blind person study the mixing of pigments? Likewise, the various civilizations knew what dark matter did, but not why. They could make some use of it, but much of that came down to blind luck. Every model had been cobbled together through trial and error