[time-nuts] Hafele-Keating, 50 years ago today

[Tom Van Baak]

The Hafele-Keating experiment was performed 50 years ago. Starting 
October 4th, 1971, Joe Hafele and Dick Keating took 4 hp cesium clocks 
on an airplane trip, a very long trip, all the way around the world, 
twice. The purpose of the trip was to see if they could detect predicted 
relativistic effects using "flying clocks".

At that point in history portable hp cesium clocks were just 
accurate/stable enough to try this bold experiment. Subsequent work 
during the 70's confirmed and refined their results. For a brief 
description of the experiment:

https://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment

Here's the detailed technical paper Hafele presented at PTTI in 1971:

"Performance and Results of Portable Clocks in Aircraft"
https://apps.dtic.mil/sti/pdfs/ADA489971.pdf

Links to their two scientific journal articles in 1972:

"Around-the-World Atomic Clocks: Predicted Relativistic Time Gains"
https://www.science.org/doi/10.1126/science.177.4044.166

"Around-the-World Atomic Clocks: Observed Relativistic Time Gains"
https://www.science.org/doi/10.1126/science.177.4044.168

For a collection of PDF and photos see my 50th anniversary 
Hafele-Keating page:

http://leapsecond.com/museum/HK50/

I've also attached a photo of their clock setup in the back of my car. 
Two vintage 5061A cesium clocks, each with 1PPS and Patek Philippe clock 
option. Between them a K02-5060A NiCad battery pack. Combined it's about 
200 lbs of equipment. Two of these racks were used for a total of 4 
clocks. In addition they had a hp 5360A computing counter with time 
interval plugin to make 4-way clock consistency comparisons periodically 
during the experiment. Nearly 500 lbs of "carry-on". You won't be able 
to do that today...

For those who want a time nut introduction to cesium clocks and 
relativity here's a talk at Stanford a few years ago:

http://web.stanford.edu/group/scpnt/pnt/PNT18/presentation_files/I08-VanBaak-GPS_Flying_Clocks_and_Relativity.pdf

/tvb

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