There is a symmetry between length space and duration space (time). As one can transform an observation by rectilinear motion (translation), or by rotation, or by a time line change, so one can transform 3D length into an equivalent 3D duration. This is not a continuous change so don’t expect a simple equation. There are four things that must be done to transform 3D length into 3D duration, that is, 3+1 spacetime into 1+3 timespace:

(1) The ordering of events should be switched between a time line (1D time order) and a baseline (1D space order). So a measurement of time, such as the duration from a reference event, should be switched with a measurement of place, such as the distance from a reference event.

(2) Scalars should be inverted: speed = 1/pace, mass = 1/vass, (space) energy ∝ 1/time energy, work = 1/effort, etc.

(3) Vectors that are ratios of base units or products of base units should switch their numerators and denominators such that (a) the denominator becomes a magnitude of the former numerator and (b) the numerator becomes the vector with units of the former denominator: velocity ⇒ lenticity, momentum ⇒ levamentum, etc. This is similar to an inversion since s/t ⇒ t/s = (1/s)/(1/t).

(4) Other units should be derived from these, with new rates relative to the time line for 3D space and the baseline for 3D duration: acceleration ⇒ relentation, force ⇒ release, power ⇒ placidity, etc.

There should be no duration vectors in 3D length and no length vectors in 3D duration. The distance from a reference place and duration from a reference event should be the same for both, apart from a change of reference points. The laws of physics should be the same for observation or transportation in each frame.

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