Introduction {\`a} l'oeuvre de S. Kichenassamy en Physique Th{\'e}orique

TL;DR

This paper reviews S. Kichenassamy's extensive work in theoretical physics, emphasizing his reinterpretation of the equivalence principle in General Relativity and its implications for measurements and observer theory.

Contribution

It introduces the C-equivalence principle as a new interpretative framework in General Relativity, expanding the understanding of observer measurements.

Findings

Replaces the strong equivalence principle with the C-equivalence principle

Provides a mathematical framework for observer-based measurements in relativity

Outlines applications of the new interpretation in physical measurements

Abstract

The work of S. Kichenassamy (1926-2015) in Theoretical and Mathematical Physics covers the spectrum of Relativistic Physics: from the clarification of the postulational basis of the two theories of Relativity, to applications to the measurement of proper time, image formation, collision theory, kinetic theory and radiative transfer, or pulsar electrodynamics, to name a few. After brief biographic remarks,we show, by following an argument first formulated in 1963, and developed in a series of papers, that the physical interpretation of General Relativity requires the replacement of the strong equivalence principle by the C-equivalence principle. By giving a mathematical status to the observer, his insight yields new results regarding measurements actual observers can make, both in Special and in General Relativity. Applications are outlined. His contributions to Indology will be discussed elsewhere.