Jetlagga: Clocks Around the World 1971
Relativity & Gravity arc, page 32 of 193. Back to The Pixelated Physics Universe
Who they are
Jetlagga flies with a caesium clock in her backpack. East or west, it comes home not quite agreeing with the ground.
Jetlagga is a character of the Relativity & Gravity arc: drawn in pixels, ruled by one piece of real physics, and never allowed to break it.
The physics
In October 1971 four caesium-beam atomic clocks were flown around the world on airliners, once eastward and once westward. Speed slows a clock; height speeds it up. Earth's spin means the eastbound plane moves faster than the ground and the westbound one slower, so the two trips differ. J. C. Hafele and R. E. Keating flew the clocks in October 1971 and published in Science in 1972.
$$ \begin{gathered} \text{Eastward: observed } -59 \pm 10\ \mathrm{ns}, \quad \text{predicted } -40 \pm 23\ \mathrm{ns} \\ \text{Westward: observed } +273 \pm 7\ \mathrm{ns}, \quad \text{predicted } +275 \pm 21\ \mathrm{ns} \end{gathered} $$
| Symbol | Meaning | SI unit |
|---|---|---|
| $\mathrm{ns}$ | nanosecond, 10⁻⁹ s: time gained (+) or lost (−) by the flown clocks relative to the ground clocks | s |
Sources
- Hafele & Keating (1972) Around-the-World Atomic Clocks: Predicted Relativistic Time Gains, Science 177, 166
- Hafele & Keating (1972) Around-the-World Atomic Clocks: Observed Relativistic Time Gains, Science 177, 168
Crossovers
Jetlagga meets Twinne & Twynne (Twin Paradox). Twinne and Twynne predict that the travelling clock records less proper time. Jetlagga carried real caesium clocks around the world in 1971 and measured differences, east versus west, that combine motion and gravity as relativity predicts.
Jetlagga meets The Accelerant (Unruh Effect). Jetlagga's clocks feel motion and gravity. The Accelerant feels something stranger: an observer with constant proper acceleration a sees the vacuum as a thermal bath at temperature ħa/(2πck_B). For everyday accelerations it is far too cold to measure.
Jetlagga meets Mossbra (Mössbauer Effect). Mossbra's recoil-free gamma rays are sharp enough to measure gravitational redshift over a tower about 22 m tall, as Pound and Rebka did. Jetlagga measured relativity with clocks instead.
Wear the lore
- Jetlagga – Clocks Around the World 1971 Physics T-Shirt
- Related infographic poster: Ives–Stilwell – Plate 027 Physics Poster
Concept keywords: Clocks Around the World 1971, Jetlagga, Relativity & Gravity, physics lore, Pixelated Physics