A set of "tensor" equations Einstein devised to describe how mass warps spacetime. The set of equations may be written as \(G = 8 π T\), where both \(G\) and \(T\) each represent a set of ten quantities. The \(G\) quantities represent the warping of spacetime, while the \(T\) quantities — the "Stress-Energy tensor" represent the mass.
Come, you lost Atoms, to your Centre draw,
And be the Eternal Mirror that you saw:
Rays that have wander'd into Darkness wide,
Return and back into your Sun subside.
From Farid al-Din Attar's
The Conference of the Birds