My friend and scientific collaborator Kostya Trachenko, who has died aged 54 of cancer, was a theoretical physicist. He helped to reshape our understanding of liquids and revealed surprising connections between fundamental physical constants and the properties of everyday materials.
Kostya’s research findings, often in cooperation with his longtime collaboratorVadim Brazhkin, brought new clarity to the elusive behaviour of liquids. He developed a mathematical framework explaining how, under certain conditions, liquids behave like solids – such as when falling into water from a height. This insight led to a deeper understanding of how transverse sound waves propagate through liquids, and how these behaviours change with temperature. His work also explained the longstanding mystery of why the heat capacity of liquids often decreases with temperature, unlike in solids.
In addition Kostya showed how ultra-thin liquid films behave more like solids when confined to surfaces, offering explanations for phenomena observed in nanotechnology and material science.
In a separate line of inquiry, he made the striking discovery that fundamental constants – such as Planck’s constant and the proton radius – govern limits in everyday materials, such as the lowest possible viscosity of fluids or the upper bound for the speed of sound in solids.
Kostya was born in Ukraine to Oksana Trachencko, an English teacher, and her husband, Oleksiy Eigenson, an astronomer, later taking on his mother’s surname. After attending high school in Lviv he studied physics at Lviv University, and on graduation he moved, in 1996, to the UK to study for a PhD at theUniversity of Cambridge, completing it in 2001.
He remained at Cambridge for postdoctoral work, contributing to the theory of inorganic crystals and materials for nuclear energy, before moving to Queen Mary University of London in 2010, where he became professor of physics. He led the PhD programme in the physical sciences there, reshaping it into something that was intellectually vibrant and modern.
We met at a conference in Poland in 2017, and worked together trying to solve various conundrums connected with the rigidity of thin liquid layers under confinement and its scaling with film thickness.
Kostya was published widely and wrote the monograph Theory of Liquids (2023), which he completed while already ill. He was an inspiring teacher and a spirited, generous friend, known for his loyalty, warmth and curiosity. He rarely stopped talking about physics.
He is survived by his wife, Carmen, whom he married in 2013, their two children and his mother.