The atomic clock on a jetliner experiment

[jaydnul]

Something I don't understand about that experiment, or about relativity in general. Why the clock on the jet flying around the world is the slower one. I mean isn't the stationary clock moving the same speed away from the jetliner clock relative to the jetliner clock?

 

[bcrowell]

Consider the standard twin paradox. Alice stays on Earth while Bob flies off in a relativistic rocket ship and then returns. There's no symmetry between Bob and Alice. Bob knows he traveled because he experienced accelerations. Alice knows she didn't because she never experienced any accelerations.

The Hafele-Keating experiment is basically the same thing. For simplicity, suppose Alice flies west at such a speed that she exactly cancels out the Earth's rotation, while Bob flies east at the same speed relative to the ground. It's not a matter of opinion who did what. Bob experienced a centrifugal force that Alice never experienced.

 

[Dale]

I mean isn't the stationary clock moving the same speed away from the jetliner clock relative to the jetliner clock?

In addition to what bcrowell mentioned the experiment that you are talking about also was significantly affected by gravitational effects. The centrifugal acceleration breaks the symmetry wrt motion, and the altitude breaks the symmetry wrt gravitation.

 

[tiny-tim]

hi lundyjb!

… isn't the stationary clock moving the same speed away from the jetliner clock relative to the jetliner clock?

let's put the stationary clock at the north pole, and the moving clock in polar orbit

the stationary clock has zero acceleration

the moving clock has centripetal acceleration

so the stationary clock is stationary in an inertial frame, and the moving clock isn't

an observer stationary in an inertial frame regards all other clocks as slow ​

 

[Agerhell]

Something I don't understand about that experiment, or about relativity in general. Why the clock on the jet flying around the world is the slower one. I mean isn't the stationary clock moving the same speed away from the jetliner clock relative to the jetliner clock?

Experience tells us that on or near earth, given two clocks at the same gravitational potential (altitude) the relevant velocity to use in the formulas for time-dilation is the velocity relative to a non-spinning Earth (eg. relative to the centre of the Earth or the north pole).

This is consistent with all experiments. Notice that there are also a form of time-dilation due to gravity which makes clocks high up in the atmosphere tick faster than clocks on the surface of the earth.

The clock on the jet flying eastwards is thus the slowest, the clock on the jet flying westwards the fastest, and the clock attached to the surface of the Earth comes in between.