Amalkumar Raychaudhuri. "Relativistic Cosmology. I" in Physical Review, May 15, 1955, volume 98 number 4, pp 1123-1126. Original wrappers. Near-fine copy. $250
Absrtact (From APS): "The paper presents some general relations obtaining in relativistic cosmology. It appears from these that a simple change over to anisotropy without the introduction of spin does not solve any of the outstanding difficulties of isotropic cosmological models."
From the AIP site celebrating the 100th anniversary of General Relativity:
"Looking at the Whole of Spacetime Two theoretical breakthroughs paved the way for global analyses of spacetime structures without the need for specific solutions of Einstein’s equation. In 1955 Amal Kumar Raychaudhuri introduced evolution equations for curves describing the flow of nearby point particles without making assumptions about the homogeneity, or isotropy of the background spacetime. A few years later Roger Penrose proposed an extremely powerful diagrammatic technique for capturing the global causal structure of any spacetime. These techniques allow the global properties of spacetimes to be gleaned. For example, Penrose was able to show that, rather than being artifacts of specific solutions, spacetime singularities are a generic outcome of gravitational collapse."
And according to Wiki on the r-equation this is where it was first published.
Obituary and appreciation: https://arxiv.org/pdf/physics/0604186.pdf
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