There are certain things about which we can be certain. For example, we can be reasonably certain that our predictions made about the effects of force and gravity can be extremely accurate, even at vast astronomical distance.
What we can't be certain of, in fact what we do not actually understand is, how those forces actually work.
We live in a mulitdimensional universe, as many as 10 some theorize, but we are only capable of perceiving and experiencing three of those. Which means our ability to observe the universe is strictly curtailed. We can observe and accurately measure electromagnetic radiation, but we cannot perceive or measure what we refer to as "dark energy". We can only theorize its existence based on how it perturbs what we can perceive.
While it may seem paradoxical, the only thing we can truly know, is that we don't know everything.