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Equation 114 · Part 3 · The Atlas That Refuses to Close

Symbol Sigma

Xμ(u,Σ)X^\mu(u,\Sigma)
Σ\Sigma

What this part means

Sigma is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.

Its job in the formula

Sigma is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.

The passage around this formula

Collect the pieces. Three charts, the Newtonian centroid RN\mathbf R_N , the observer-dependent stress-energy centroid Xμ(u,Σ)X^\mu(u,\Sigma) , and the canonical Newton–Wigner operator XNW\mathbf X_{\mathrm{NW}} , form a genuine, well-behaved sub-atlas. Define, for any two of them evaluated on the same hypersurface Σ\Sigma ,

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A variable is a named place for a value. Its letter is a local label: x can mean position in one formula and a data point in another.

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