The other day we went to a very thought-provoking talk by Jocelyn Bell Burnell (the discoverer of pulsars) at the Bath Science Café at The Raven.
There was talk of dark matter and dark energy, which are basically 'dark' in the sense that no-one knows what they are. We do know that dark matter is probably non-baryonic, unlike most matter in the universe. (Baryonic matter is matter with protons and neutrons in the nucleus.)
So, she said, there will be a paradigm shift when the nature of dark matter and dark energy is discovered.
There was a similar paradigm shift when it was finally realised that phlogiston didn't exist. Natural philosophers studying burning materials assumed that, since they gained weight after burning, they must be emitting a substance that had negative mass; they called this substance phlogiston. Joseph Priestley almost had it right when he produced "phlogisticated air" (air that, he believed, was rich in phlogiston), but it was Antoine Lavoisier who realised that phlogiston didn't exist, and that rather than losing a substance with negative mass, the burning material was actually fixing oxygen out of the air. The theory of phlogiston may seem daft now, but it made sense at a time when it was assumed that air was all one substance, not several different gases mixed together. (I remember watching a video about this in O-level Chemistry.)
Another paradigm shift that Professor Bell Burnell told us about occurred in astronomy when looking at planetary orbits; it was assumed they were circular, but then people observed anomalies in them and called them epicycles, and it all got very untidy until Johannes Kepler pointed out that the orbits were elliptical.
And of course the most famous paradigm shift of all was the one when Copernicus pointed out that we live in a heliocentric solar system, not a geocentric one.
At least nowadays you are not likely to get burnt at the stake or kept under house arrest for suggesting a radical new scientific idea. The worst thing that could happen to you is loss of tenure.
The point of all this is to say that, although there is speculation as to what dark matter and dark energy might be, it may be that something else is wrong, such as the basic assumptions which led to the need to theorise their existence, in which case whatever is causing the need to insert them into the theoretical models turns out to be something completely different. In a hundred years' time, people could be laughing at those early 21st century scientists who believed in 'dark matter' and 'dark energy', in the same way that we find phlogiston, flat earth theory and geocentric cosmology amusing nowadays. Such is the weirdness when we're sitting on the brink of a paradigm shift. Maybe a bit like sitting at the event horizon of a black hole - nothing will ever be the same again once you have passed the threshold.