General relativity predicts that clocks run more slowly near massive objects. The effect is small—a clock at sea level lags behind one 1000 m above sea level by only 9.4 ns/day. Here, we demonstrate that a measurement of this effect can be done by undergraduate students. Our paper describes an experiment conducted by undergraduate researchers at Colorado College and the United States Air Force Academy to measure gravitational time dilation. The measurement was done by comparing the signals generated by a GPS frequency standard (sea-level time) to a Cs-beam frequency standard at seven different altitudes above sea level. We found that our measurements are consistent with the predictions of general relativity.
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The HP 5071A frequency standards were obtained at no cost as surplus from another laboratory. New 5071A standards are available from Microsemi Corporation for approximately $65,000. As these frequency standards have a long useful life (ours were manufactured in 1999 and 2000), many used units are available over a wide range of prices. We found some used units online for about $2000.
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The Trimble Thunderbolt Lab Kit included a GPS receiver, antenna, and associated power adapter and cables. The kit cost $1,195 at the time of purchase.
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A new two-channel frequency counter similar to the ones we used currently costs $2600 from Keysight Technologies (formerly Agilent). Many older frequency counters would also be capable of performing the time interval measurements required in this experiment.
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2017
American Association of Physics Teachers
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