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If one wants to summarize our knowledge of physics in the briefest possible terms, there are four really fundamental observations: | If one wants to summarize our knowledge of physics in the briefest possible terms, there are four really fundamental observations: | ||
1. Space-time is a pseudo-Riemannian manifold `M`, endowed with a metric tensor and governed | 1. Space-time is a pseudo-Riemannian manifold `M`, endowed with a metric tensor and governed by geometrical laws | ||
2. Over `M` is a principal bundle `P_{G}` with a nonabelian structure group `G`. | 2. Over `M` is a principal bundle `P_{G}` with a nonabelian structure group `G`. |