Covariant is dual to contravariant -- vectors, functors or a dual basis in Riemann geometry. Stationary is dual to moving -- inertial reference frames are dual as the laws of physics do not change! The laws of physics are independent of the observer's inertial reference frame -- Tensors. Space is dual to time -- Einstein. "Always two there are" -- Yoda.
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Covariant is dual to contravariant -- vectors, functors or a dual basis in Riemann geometry.
Stationary is dual to moving -- inertial reference frames are dual as the laws of physics do not change!
The laws of physics are independent of the observer's inertial reference frame -- Tensors.
Space is dual to time -- Einstein.
"Always two there are" -- Yoda.