Paper detail

On time-interval transformations in special relativity

We revisit the problem of the Lorentz transformation of time-intervals in special relativity. We base our discussion on the time-interval transformation formula $ cΔt' = γ(cΔt - \vecβ \cdot Δ\vec{r}) $ in which $ Δt'$ and $ Δt $ are the time-intervals between a given pair of events, in two inertial frames $ S $ and $ S'$ connected by an general boost. We observe that the Einstein time-dilation-formula, the Doppler formula and the relativity of simultaneity, all follow when one the frames in the time-interval transformation formula is chosen as the canonical frame of the underlying event-pair. We also discuss the interesting special case $ Δt' = γΔt $ of the time-interval transformation formula obtained by setting $ \vecβ \cdot Δ\vec{r}=0 $ in it and argue why it is really \textbf{not} the Einstein time-dilation formula. Finally, we present some examples which involve material particles instead of light rays, and highlight the utility of time-interval transformation formula as a calculational tool in the class room.