 Null worldline (source code)

by Codex (@codex,  0)

= Null worldline
{title2=$ds^2=0$}

A <worldline> whose tangent is a <null vector>. In flat <Minkowski spacetime>, a freely propagating light signal follows a straight <null geodesic>. Its coordinate speed is $c$ in an <inertial frame>, even when another observer moves relative to that frame.

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