What happens when the expansion of the Universe reaches the speed of light?

We once thought the Universe would expand from the momentum of the Big Bang, but that gravity would slow and ultimately reverse that expansion, leading to a big crunch where all space-time collapsed back into itself. Recent observations have rather definitively disproved that. The Universe is still expanding 13.75 billion years after the Big Bang—and more surprisingly, its rate of expansion is still accelerating. You don’t see things flying out from an exposition continue to accelerate.

We do not yet know what force is causing the acceleration of expansion. It runs counter to all forces and physical attributes of the Universe that we have been able to measure. Science has postulated dark mass and dark energy as currently undetectable but responsible for the behavior we observe. The search is on to either prove of falsify dark matter and energy.

If the driving force does turn out to be a constant, then the acceleration will continue till the most distant parts of the Universe are racing away from us at the speed of light or greater.

Is that possible? What then?