Einstein's Clocks and Langevin's Twins

TL;DR

The paper clarifies the historical and conceptual differences between Einstein's original clock paradox and Langevin's twin paradox, emphasizing Einstein's focus on measurement rather than biological or aging aspects of observers.

Contribution

It distinguishes Einstein's original focus on measurement procedures from Langevin's extension involving biological aging, clarifying misconceptions about the twin paradox.

Findings

Einstein did not explicitly present the twin paradox.

Einstein's work focused on measurement, not biological aging.

Langevin's twin paradox involves biological aging of observers.

Abstract

In 1905 Einstein presented the Clock Paradox and in 1911 Paul Langevin expanded Einstein's result to human observers, the "Twin Paradox." I will explain the crucial difference between Einstein and Langevin. Einstein did not present the so-called "Twin Paradox." Later Einstein continued to speak about the clock paradox. Einstein might not have been interested in the question: what happens to the observers themselves. The reason for this could be the following; Einstein dealt with measurement procedures, clocks and measuring rods. Einstein's observers were measuring time with these clocks and measuring rods. Einstein might not have been interested in so-called biology of the observers, whether these observers were getting older, younger, or whether they have gone any other changes; these changes appeared to be out of the scope of his "Principle of relativity" or kinematics. The processes and changes occurring within observers seemed to be good for philosophical discussions. Later writers criticized Einstein's clock paradox. Einstein quickly replied with witty, smart and clever retorts.