Any experiment for relative simultaneity?

Question

Any introduction of relative simultaneity usually is like this : Alice on a train car shines two beams of light towards both ends where two clock are. She sees both clocks see the light at the same time.
Bob on the station looks at the same event and says the trailing clock was hit before the leading clock.

I have no doubt about what Bob is measuring, but if speed of the light stays independent of the source, then it should not matter if the frame of reference is moving with the targets -i.e clocks- or not , both Alice and Bob should see clocks are being hit non-simultaneously .

Is there any actual experiment that proves Alice is seeing simultaneous clock hit ? I mean has anyone placed clocks on very fast moving objects to prove light hits both leading and trailing sides at the same time ? Or do radio signals arrive at different times to equidistant Eastern and Western stations due to rotation of the Earth?

Answer 1

Yes, many. Michelson and Morley did it first and hence most famously in 1887, looking for (and failing to find) evidence of luminiferous ether.

Answer 2

As of recently there are fleets of (commercial) satellites in operation that have satellite-to-satellite communication.

At present the Starlink fleet, launched and operated by SpaceX has over 4000 Starlink satellites in active service.

It seems likely that for the satellites of a fleet like that there is no technical obstacle to performing the experiment that you suggest.

That said, in actual operation the way that the satellites of the fleet are kept synchronized is not Einstein synchronization procedure.

That has to do with the fact that the fleet of satellites wraps around the world.

For the entire Earth there is for scientific use and engineering use a single Coordinated Universal time (UTC) Most countries have a dedicated center for time keeping, so there are a lot of centers for time keeping, spread around the globe. All of those centers combined form an assembly that wraps around the world. That makes it possible to organize a single international time.

The satellites of the GPS system are synchronized to the UTC, and no doubt any satellite constellation will be designed to operate synchronized to the UTC. Any other decision would be subpar engineering.

(From the wikipedia article about UTC: There is International Atomic Time (TAI), and UTC is TAI plus leap seconds that over the years have been inserted. From time to time a leap second is inserted to keep UTC in sync with the Mean Solar Day. The GPS constellation follows TAI, not UTC.)

Einstein synchronization procedure is particularly applicable when an assembly of clocks is arranged in a straight line.

As pointed out in the answer by contributor 'g s', the Michelson-Morley experiment can be seen as an instance of Einstein synchronization.

Answer 3

Simultaneous events in one inertial frame are not simultaneous in a different inertial frame. Simultaneity is a property in and of the frame of reference.

Symmetry is how we all know Alice 'sees' light hit the clocks at the same time. When you boil it down that's how she synchronised them in the first place.

All inertial frames behave in the same way as referenced in earlier answers, which is why a particular simultaneity is only ever seen in one inertial frame.

Your question about the radio signal travelling East or West is more interesting. You cannot synchronise clocks around a roundabout, but if you adjust their rate you can synchronise each one with a clock at the centre, and as a result they agree with all the stationary clocks they pass.

If you do that, everybody agrees the trailing (West) clock sees the radio signal at an earlier time than the leading (East) one. The East and West clocks do not see the same time on one another, but since they are not in the same inertial frame - or arguably in any inertial frame - they don't have to.