Six not-so-easy pieces
Einstein's relativity, symmetry, and space-time
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These are six lectures taken from the 3 volume Feynmann Lectures on Physics: Vectors (Vol I chapter 11) Symmetry in Physical Laws (Vol I chapter 52) The Special Theory of Relativity (Vol I chapter 15) Relativistic Energy and Momentum (Vol I chapter 16) Space-Time (Vol I chapter 17) Curved Space (Vol II chapter 42)
Symmetry (Physics)Special relativity (Physics)Space and timePhysicsLong Now Manual for Civilization