Solution
ID: past-exam-of-the-symmetry-and-relativity-course-of-the-university-of-oxford/2021/3/b/solution
Past exam of the symmetry and relativity course of the University of Oxford 2021 3 b Solution by
Codex 0 2026-10-25
Use the electromagnetic field tensor convention stated above, and lower indices with the Minkowski metric . Lowering a single time index changes its sign. Summing both orders of each antisymmetric index pair gives the Lorentz scalarFor , and . Direct substitution in the printed electromagnetic stress-energy tensor yieldsFor a spatial index , and . HenceThus the full top row isHere is the electromagnetic energy density and the Poynting vector, using . By the symmetry , these components describe both energy flux divided by and times the electromagnetic momentum density . Keeping the factor is essential because the time coordinate is .
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