Editing Twin paradox (section)

=== Earth perspective ===
The Earth-based mission control reasons about the journey this way: the round trip will take {{nowrap|''t'' {{=}} 2''d''/''v'' {{=}} 10 years}} in Earth time (''i.e.'' everybody who stays on Earth will be 10 years older when the ship returns). The amount of time as measured on the ship's clocks and the aging of the travelers during their trip will be reduced by the factor <math>\alpha = \scriptstyle{\sqrt{1 - v^2/c^2}}</math>, the reciprocal of the [[Lorentz factor]] (time dilation). In this case {{nowrap|''α'' {{=}} 0.6}} and the travelers will have aged only {{nowrap|0.6 × 10 {{=}} 6 years}} when they return.