Length and duration space are inverse perspectives on motion. Length is measured by a rigid rod at rest, whereas duration is measured by a clock that is always in motion. Duration is measured by a clock at rest relative to the time frame, whereas length is measured by a rigid rod in motion that counteracts time as it were.

This is illustrated by deriving the Lorentz factor for time dilation and length contraction from light clocks. The first derivation is *in length space* with scalar time and the second is *in duration space* with scalar stance.

The first figure above shows a light clock in length space as a beam of light reflected back and forth between two mirrored surfaces. Call the height between the surfaces that the light beam travels *h*. Let one time cycle Δ*t* = 2*h*/*c* = 2*h¢* or *h* = *c*Δ*t*/2 = Δ*t*/(2*¢*), with mean speed of light *c* and mean pace of light *¢*.

The second figure shows the light clock as observed by someone moving with velocity *v* and pace *u* relative to the light clock. Call the path length of each half-cycle *d*; and call the length of the base of one half-cycle *b*.

From the moving observer’s perspective, the clock travels *b* = *v*Δ*t*´ = Δ*t*´/*u*, with time interval Δ*t*´. The light beam travels 2*d* = *c*Δ*t*´ = Δ*t*´/*¢* each cycle. If we normalize *v* with *c* and *u* with *¢*, then *v*/*c* = *¢*/*u* = *β*, *c* = *¢* = 1, *b* = *β*Δ*t*´, 2*d* = Δ*t*´, and *h* = Δ*t*/2.

From the Euclidean metric, (*d*)² = (*b*/2)² + (*h*)². Substitution gives

(Δ*t*´/2)² = (*β*Δ*t*´/2)² + (Δ*t*/2)².

Multiply both sides by 2². Gather the Δ*t*´ coefficients to get

Δ*t*´² (1 − *β*²) = Δ*t*².

This leads to

Δ*t*´² = Δ*t*² / (1 − *β*²),

so that

Δ*t*´ = Δ*t* √(1/(1 − *β*²)) = *γ*Δ*t*,

which is the time dilation with the Lorentz factor *γ*.

Now consider the light clock *in time* with scalar space or stance.

In this case the observation in the first figure is of a light clock in time, i.e., a series of cycles. As before, it is a beam of light reflected back and forth between two mirrored surfaces. Call the half-cycle duration of the light beam between the surfaces *k*. Call one half-cycle Δ*r*´ = 2*k* or *k* = Δ*r*´/2, with the speed of light set to unity as above.

The second figure shows a light clock at rest as observed by someone moving with lenticity *u* relative to it. Let the round-trip duration of each cycle be *e*, and let the duration of the base of one triangle-shaped cycle be *a*.

The moving observer travels *a* = *β*Δ*r*, with stance interval Δ*r*. The light beam travels 2*e* = Δ*r* each cycle.

From the Euclidean metric, (*e*)² = (*a*/2)² + (*k*)². Substitution gives

(Δ*r*/2)² = (*β*Δ*r*/2)² + (Δ*r*´/2)².

Multiply both sides by 2². Gather the Δ*r* coefficients to get

Δ*r*²(1 − *β*²) = Δ*r*´².

This leads to

Δ*r*´ = Δ*r* √(1 − *β*²) = Δ*r* / *γ*,

which is the length contraction with the Lorentz factor *γ*.