[lxgr]

> Doesn't 4G include a time synchronization service for receivers with no GPS

Yes, but I believe accuracy is on the order of minutes.

> is the SI second unit (which is currently defined in terms of the cesium decay) const hardcoded in the new system?

Are you saying that a moon second should be defined to be slightly longer/shorter than an earth second to compensate for the relativistic difference? That wouldn't help, since relativity affects all physical processes; if you do that, all your other measures would be off too, including e.g. length (defined as the distance light travels in a given unit of time).

[vel0city]

4G and 5G need devices to be synchronized to each other by like 1.5 microseconds or they'll start getting a lot of errors. They do a lot of time division duplexing, so if things are not well synchronized people start talking all over each other.

Now, that's just synchronized with each other, so if the Moon is off by whatever difference in time that's not a problem. It is not like that 4/5G cell is also participating in the same RF environment as cells on Earth.

[lxgr]

Yeah, that’s what I mean: They don’t need an absolute time reference; they can just respond with whatever delay/frequency offset compensates for the one observed as they communicate.

S-CDMA did have close timing requirements between cells, as far as I know, but the GSM/3GPP family of standards never did.

[g_p]

TDD networks (where the same frequency is used for downlink and uplink, but with timeslots for each) do need tight timing between cells though, but it doesn't have to be absolute - just in sync with each other so one cell doesn't blast out a full power downlink while adjacent and nearby cells are quietly trying to listen for the (much quieter) uplink transmissions of their user devices.

[westurner]

"Matrix Theory: Relativity Without Relative Space or Time" https://youtube.com/watch?v=B94o-P93ExU&

Does the time difference due to time dilation due to relativity change suddenly upon orbiting or landing on another planet spherical reference frame?

[lxgr]

Not suddenly, but gradually as you enter/leave the gravitational well.

The dominating relativistic factor is the gravitational potential (ie general relativity), not the orbital velocity (special relativity), as far as I understand.

GPS compensates for both by offsetting the frequency standard of the satellites’ atomic clocks accordingly.