This image denotes a ball that is moving even though there are no visible forces acting upon it in a vacuum (and if the image seems weird it’s because the ball is only around 1/10th of a millimetre).
This small example explains why the Universe is still expanding, and faster then it ever has been expanding before. The theory goes that at the beginning of the Universe things expanded slower because gravity was strong enough, with everything still relatively close together, to counteract the effects of this dark energy.
As the Universe expanded further and everything moved further away from each other the force of gravity grew weaker, and therefore the speed caused by the dark energy increased.
This tiny ball provides evidence that the universe will expand forever. Measuring slightly over one tenth of a millimeter, the ball moves toward a smooth plate in response to energy fluctuations in the vacuum of empty space.
The attraction is known as the Casimir Effect, named for its discoverer, who, 55 years ago, was trying to understand why fluids like mayonnaise move so slowly. Today, evidence indicates that most of the energy density in the universe is in an unknown form dubbed dark energy.
The form and genesis of dark energy is almost completely unknown, but postulated as related to vacuum fluctuations similar to the Casimir Effect but generated somehow by space itself. This vast and mysterious dark energy appears to gravitationally repel all matter and hence will likely cause the universe to expand forever.
Understanding vacuum energy is on the forefront of research not only to better understand our universe but also for stopping micro-mechanical machine parts from sticking together.