[yingw787]

I know that system clock drift can be bounded to milliseconds using an atomic clock or GPS receiver, but I didn't know whether we could overcome synchronization difficulties when speed-of-light differences are significant. I thought we could package some coordinate reference system, directional travel metadata (I'm traveling 0.000002c this way), and current system clock time, and synchronize that way.

Fantasy use case: Asteroid mining and traffic control. If you want to boost prepared asteroids to an orbit closer to Mars and you had a space station / spaceships to watch out for, different mining companies might want a clock protocol, a request buffer, and a map instead of synchronously planning, timing, and verifying each and every asteroid orbit change in a central location ("What do you mean you were using Earth time and not correcting for relativity??").

[etaoins]

There is Barycentric Coordinate Time which is the time from a hypothetical clock at rest at the centre of mass of the Solar System. This is easier to calculate across spacecraft than an Earth-centric time would be. However, because it's outside of Earth's gravity well it ticks slightly faster than Earth time.

[tim333]

If it was at rest at the centre of mass of the Solar System wouldn't it be in the sun's gravity well?

Edit - I looked it up - it's "a clock that performs exactly the same movements as the Solar system but is outside the system's gravity well."

[Retric]

While true it’s still trivial to do such calculations and then output in GMT or whatever. In theory such calculations can get really messy, but atomic clocks are still not accurate enough to make a huge range of minor issues important.

For example we are not just in the sun’s and earth’s gravity field but also the other planets as well. So, with enough precision you would need to account for their locations.

[ramses0]

If you ever get the chance go to the Royal Observatory in Greenwich, which has a great explanation of the difficulties (and values) associated with timekeeping:

https://en.wikipedia.org/wiki/Royal_Observatory,_Greenwich#O...