You can't separate A from B in the above. For instance dark matter and relativity. Dark matter was invented (or at least expanded) precisely because certain rot

You can't separate A from B in the above. For instance dark matter and relativity. Dark matter was invented (or at least expanded) precisely because certain rotational characteristics of distant galaxies seem to contradict what we'd expect based on relativity and gravity. But we believe these theories are correct, so there 'must' just be a bunch of matter there we can't see or measure. And it must be invisible to the point that it only interacts with itself and gravity -- dark matter by another name. However, another recent discovery now indicates that galactic rotational curves are fully explained by visible matter alone, which poses a direct contradiction to the dark matter model that can't be so easily massaged into it. [1] The point of this is that 'something' is very wrong, and nobody really knows what it is. And this something could be something incredibly fundamental. If it turns out dark matter simply does not exist then we'll 'set physics back' (it would be progress, but the effect would be the same) many decades, but also open the door to an explosion of new knowledge and exploration. Then there are question like why is the universe accelerating? As you mention the bandaid here is dark energy, but again A cannot be separated from B. There are even open questions about things such as the big bang. Why are things like the cosmic microwave background radiation near homogeneous, even in areas of space that should not be causally connected (light has not had time to go from A to B since the birth of the universe)? One explanation for this is cosmic inflation which in turn created it's own dark matter analog - the 'inflaton' that's even more bizarre than dark matter, but once again it's just a bandaid to try to explain something that goes against everything we'd otherwise expect. There's an immense amount of room for progress in physics by removing these bandaids - either by testable physical explanations, or by providing better bandaids. And this is also just scratching the surface. There's so much we have no clue about. Even basic observations remain inexplicable, fast radio bursts, the rapid dimming of stars such as KIC8462852, and so on. I would speculate that there are probably more 'known unknowns' in physics today than ever before. Of course all of the questions seem incredibly difficult to answer, but this is what it always looks like when you're at any given state in science. We only see the answers as obvious or easy once we already know what they are. And then the next questions are the ones that suddenly take the place of seeming incredibly difficult to answer, only for this pattern to repeat to seemingly no end. [1] - https://phys.org/news/2016-09-spiral-irregular-galaxies-current-dark.html https://phys.org/news/2016-09-spiral-irregular-galaxies-curr...