[Dylan16807]

Delays do not affect ordering.

Relativity means that observers with different velocities view timings differently.

Mere distances do not matter.

Pick a reference frame for your protocol, and relativity stops being a problem. (Hint: If all endpoints are on Earth you probably won't have enough precision to even need to compensate for relativistic effects.)

[robotresearcher]

Delays alone do affect the ordering perceived by receivers at different locations.

[Dylan16807]

Only for a very misleading definition of ordering. Delays affect the order in which receivers see events, but the receivers can compensate for transmission factors and calculate the exact same times for all events.

Except when relativity kicks in from the observers moving at different speeds. Now events that are outside each other's light cones have no objective order.

[robotresearcher]

That definition of ordering is of course the standard, everyday definition. And to guarantee correct compensation for transmission factors in the same frame, do we not require perfectly synchronized local clocks: impossible in general?

[Dylan16807]

>That definition of ordering is of course the standard, everyday definition.

I would disagree and say the standard definition is the order things happen in, not when you feel the effects. There's rarely a different in practice, though, because people usually experience things via sight at a distance of miles at most. And in one of the few places where it differs, astronomy, people talk all the time about how events 'actually' happened a massive amount of time in the past.

But that doesn't matter. We're talking about relativity. Order, when talking about relativity, clearly means the timing of the events themselves, not the reception of the events.

You need such a definition before you can understand the ways even that can vary per observer. And importantly, the specific ways it can't vary per observer.

>And to guarantee correct compensation for transmission factors in the same frame, do we not require perfectly synchronized local clocks

Not at all. We do need to agree on a same reference frame (because different reference frames give different rates of time and different distances). Thankfully everyone on earth is in the same reference frame to a very very precise degree. And if that's not good enough you can do a few calculations to get nearly perfect compensation for different altitudes and latitudes and such.

Our clocks don't have to be in the same century to say that light A went on before light B. You just take the point in time you saw each fiber light up and subtract the distance of the fiber times propagation speed. And then you could set both clocks to be in sync by using A or B as a reference point, if you wanted.