[time-nuts] Einstein Special on PBS
Tom Van Baak
tvb at LeapSecond.com
Fri Nov 27 12:16:08 EST 2015
That's a good summary. I'm glad you got to visit the mountain. Did you happen to check the elevation? Are there lodges along the road on the way up?
I ask because at 2726 feet a clock will run 9.0e-14 fast (compared with sea level), which is 7.8 ns/day, or 31 ns over 4 days. But they measured 20 ns. So either they didn't stay close to 4 days, or they didn't stay close to the summit or maybe their clock rate was off or they didn't use a high-perf 5071A, or something.
I'll make just a one word correction to your summary. The clocks run a bit faster not because of "the spinning earth" but because of "the earth". In other words, the clocks are experiencing a gravitational effect not a velocity effect. Gravity is a tiny bit less as you rise in elevation and this is what the clocks experience. Presumably the experiment would work fine even if the earth did not spin at all, or spun backwards.
What's confusing is that in articles about relativity and shows like this, they talk about speed and trains and light and stuff (SR, special relativity) and so people are pre-disposed to be thinking in those terms. Worse yet, we know outer points of spinning objects have greater tangential speed than inner points so again people think of speed. There's mention of satellites, also high speed.
But the main thing that is affecting the clocks at home vs. mountain is simply gravity. With a stationary clock at home and a stationary clock on the mountain, there's no velocity to talk about. The situation with airplanes and rockets and satellites is different; in these cases there is a large and combined gravitational and velocity effect.
> In the special it looks like they used two HP5071A standards, an
> SRS620 counter, and a scope. They first made sure the stds were
> in sync then took one to the building at the top of the ski lift
> on New Hampshire's Mount Sunapee at 2726' elevation for 4 days
> where it would be running a little faster because it would be
> slightly further from the center of the spinning earth. After
> bringing the 5071A back from the top of the mountain they checked
> the difference in the start of square waves displayed on the scope
> and detected the 5071A at altitude was now 20ns ahead of the
> 5071A kept at sea level, as predicted, if I understood everything
> correctly. They explained that the clocks in the GPS satellites
> traveling at a much higher speed had to correct for the speed
> difference which also verified Einstein's theory.
> My wife and I were on the top of Mt. Sunapee this summer where we
> enjoyed the views but didn't run any experiments. ;-)
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