William Thomson (Lord Kelvin), born in Belfast (Northern Ireland) and trained in Glasgow and Cambridge, proposes in 1848 an absolute temperature scale based on thermodynamic principles, independent of any substance's properties. He defines absolute zero (0 K = −273.15 °C) as the point of minimum possible thermal energy. The Kelvin scale is today the SI base unit of temperature. Thomson built his entire career at the University of Glasgow, where he was a professor for 53 years. His Northern Irish origin rarely appears in the canonical narrative of British physics.