I have to disagree with you about dark matter and dark energy seeming contrived. First it's hard to call dark energy "contrived" when it hasn't really been con

I have to disagree with you about dark matter and dark energy seeming contrived. First it's hard to call dark energy "contrived" when it hasn't really been contrived, conceived, or created at all. That is, no one has really made any strong, convincing claims as to what it actually is. The term is really just a placeholder for the fact that something is providing a long-scale repulsive force (and so probably has negative energy density). Although it can be "explained" by a cosmological constant, that just punts the question to what the cosmological constant physically is. As for dark matter, it is the simplest, most elegant way to explain the variety of observations that point to its existence. These observations include small-scale dynamics of dwarf spheroidal galaxies, the rotation curves of galaxies, gravitational lensing due to galaxy clusters, and more. All of them can be explained if there exists some unknown particle which interacts only weakly with other particles. While it's true that the standard model predicts no such particle, it's also true that it's known that the standard model is an incomplete theory. You might argue that it could just as well be that our theory of gravity is wrong. (Certainly at the quantum level we know for sure that that is the case.) But inaccuracies in our theory of gravity at large scales have difficulty explaining the dark matter problem in an elegant matter. Consider dwarf spheroidals. These are the smallest of galaxies; in terms of luminous mass, they are only slightly more massive than globular clusters. Yet globular clusters are 1000s of times smaller than dwarf spheroidals. How can they possibly remain gravitationally bound on the scale of 1000s of light-years when globular clusters are only bound on scales of a few light-years? Dark matter can explain this by simply saying that dwarf spheroidals have relatively massive dark matter halos, whereas globular clusters have almost no dark matter. (Which one would expect in standard galaxy formation scenarios.) But modified gravity theories have difficulty explaining why two systems with similar masses interact so differently. We can similarly see that galaxies of all sizes exhibit a range of dark matter fractions. If the problem was merely with our theory of gravity one would expect all galaxies of a given luminous mass to have the same dark matter fraction. Any modified theory of gravity which explained these observations would not be aesthetic. The aesthetic explanation would be some hitherto unknown weakly interacting massive particle.