Climbing with Atomic Clocks


A century ago Einstein predicted that clocks run slower the faster their speed. Another prediction from his general theory of relativity is that clocks run slower the stronger the gravity.

It follows then that clocks run a tiny bit faster the higher they are above the earth (as gravity weakens). You could prove this relativistic time dilation effect for yourself by taking a sufficiently accurate clock to a high altitude for a long duration and precisely measuring to see if it gains a tiny bit of time. Don't laugh; it's been done and the theory works.

Now there are several ways to take an atomic clock to high altitude: airplane, rocket, satellite, and mountain. Over the decades scientists have performed wonderful relativity experiments using each of these methods. Planes are rather expensive and a rocket or satellite is out of the question. So that leaves me with the mountain. Fortunately, there are many high mountains near Seattle.

I can think of two ways to carry an atomic clock up a mountain: climb or drive. After trying for a few minutes, I'd say climbing is out of the question. But I had to be sure. Time for plan B.

Tom checks if climbing with an atomic clock is possible:

Yes, but is that a grin or a grimace?

Hewlett Packard model 5071A:

Rear and side views (cesium beam tube visible inside):

Two more shots while we're at it:

Oh, and for long trips remember to carry external power; lots of power:

For the rest of the story, read about Project GREAT. Hint: we drove instead ;-)

See also:


Return to LeapSecond.com home page.
Comments/questions to tvb.