Reversal in time order of interactive events: Collision of inclined rods

TL;DR

This paper investigates how the time order of collisions between inclined rods appears reversed in different inertial frames, illustrating the relativity of simultaneity and extended present concepts in special relativity.

Contribution

It extends previous studies by analyzing collision events of inclined rods and demonstrating time order reversal due to relativity of simultaneity.

Findings

Collision events are observed in reversed order in different frames.

Time order reversal is explained by the extended present concept.

Relativity of simultaneity affects collision event perception.

Abstract

In the rod and hole paradox as described by Rindler (1961 Am. J. Phys. 29 365-6), a rigid rod moves at high speed over a table towards a hole of the same size. Observations from the inertial frames of the rod and slot are widely different. Rindler explains these differences by the concept of differing perceptions in rigidity. Gron and Johannesen (1993 Eur. J. Phys. 14 97-100) confirmed this aspect by computer simulation where the shapes of the rods are different as observed from the co-moving frames of the rod and slot. Lintel and Gruber (2005 Eur. J. Phys. 26 19-23) presented an approach based on retardation due to speed of stress propagation. In this paper we consider the situation when two parallel rods collide while approaching each other along a line at an inclination with their axis. The collisions of the top and bottom ends are reversed in time order as observed from the two co-moving frames. This result is explained by the concept of extended present derived from the principle of relativity of simultaneity.