Dark matter has never been detected, yet it is a key part of the dominant theory of cosmology. An alternative theory, MOND, is empirically equivalent and more successful at making predictions. But the fact that it has no place for the existence of dark matter is a problem for scientific realists who see science as building on past theories. MOND would signal a break with our current cosmological model, making a mockery of the idea of scientific progress as gradually getting closer to a true account of reality, argues David Merritt.
The universe is vast, and the longer we observe it, the more we learn about its composition and structure. But historians of science tell us that periods of steady growth in science tend to last only so long: they are interrupted by revolutions during which the old assumptions are thrown out and a radically new set are brought in. The initial decades of the twentieth century witnessed a number of such episodes. Classical mechanics and electromagnetism were replaced by quantum electrodynamics, Newton’s theory of gravity and motion was replaced by Einstein’s. The changes in these theories were so radical that even basic concepts like mass and time acquired fundamentally new meanings.
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