Time Runs Faster At Your Head Than At Your Feet

Time does not pass at the same rate everywhere. It runs faster higher up and slower lower down, and the difference has been measured across a height of thirty three centimetres, which is small enough to fit inside a human body. Tonight we follow that measurement all the way down. From the navigation satellites that carry clocks deliberately built to run at the wrong frequency, gaining thirty eight microseconds a day on every clock below them, to a lift shaft at Harvard where two physicists moved a radioactive source more slowly than a fingernail grows in order to catch a shift one five hundredth the width of their own measuring line. From four caesium clocks that bought seats on commercial airliners and came home disagreeing, to a single aluminium ion in Colorado, raised a third of a metre on a workshop jack, ticking faster for it. By the end, the picture of time as a single current carrying everyone along will not hold. Time has contours. It runs quickly on high ground and slowly in valleys, with a measurable slope through the height of a single room, and across the length of a sleeping body. A calm, cinematic documentary for falling asleep to. No sudden volume changes. Just the quiet physics of the ground you are lying on. SOURCES Einstein, A. (1907). Ueber das Relativitaetsprinzip und die aus demselben gezogenen Folgerungen. Jahrbuch der Radioaktivitaet und Elektronik, 4, 411. Pre-DOI publication, no DOI exists. Einstein, A. (1915). Die Feldgleichungen der Gravitation. Sitzungsberichte der Koeniglich Preussischen Akademie der Wissenschaften, 844 to 847. Pre-DOI publication, no DOI exists. Pound, R. V., and Rebka, G. A. Jr. (1960). Apparent Weight of Photons. Physical Review Letters, 4, 337 to 341. DOI 10.1103/PhysRevLett.4.337 Hafele, J. C., and Keating, R. E. (1972). Around the World Atomic Clocks. Science, 177, 166 to 170. DOI 10.1126/science.177.4044.166 Ashby, N. (2003). Relativity in the Global Positioning System. Living Reviews in Relativity, 6, 1. DOI 10.12942/lrr-2003-1 Chou, C. W., Hume, D. B., Rosenband, T., and Wineland, D. J. (2010). Optical Clocks and Relativity. Science, 329, 1630 to 1633. DOI 10.1126/science.1192720