The unsolved problems of the physical world now seem even more formidable than those solved in the twentieth century. Though in application it works splendidly, we do not even understand the physical meaning of quantum mechanics, much less how it might be united with general relativity.We don't know why the dimensionless constants (ratios of masses of elementary particles, ratios of strength of gravitational to electric forces, fine structure constant, etc.) have the values they do, unless we appeal to the implausible anthropic principle, which seems like a regression to Aristotelian teleology.
Gerald Holton, Physics, the Human Adventure: From Copernicus to Einstein and Beyond
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