Tatyana Afanasyeva

Her father was Alexander Afanassjev, a chief engineer on the Imperial Railways, who would bring Tatyana on his travels around the Russian Empire.

Since Tatyana was a Russian Orthodox and Ehrenfest was Jewish, they both decided to officially renounce their religions in order to remain married.

[4] The Conceptual Foundations of the Statistical Approach in Mechanics, by Paul and Tatyana Ehrenfest was originally published in 1911 as an article for the German Encyklopädie der mathematischen Wissenschaften (Encyclopedia of Mathematical Sciences), and has since been translated and republished.

[7][8] Albert Einstein was a frequent guest in the 1920s to her home at Witte Rozenstraat 57 in Leiden [nl], as evidenced by the many signatures on the wall.

She wanted to give thermodynamics a rigorous mathematical foundation which was lacking and describe pressure, temperature and entropy in changing systems.