On a related note, I'm wondering how distributed systems that rely on atomic clocks (e.g. Google Spanner) would work in the space era, given that relativity says that there's no such thing as a global clock.
They can still work, with a few changes and worse performance.
The clock is not used to say that the time is exactly the same on all nodes, it is used to guarantee that if two events have timestamps whose difference is larger than some threshold they can be ordered reliably. You don't need an atomic clock to do it, for instance CockroachDB only requires NTP, but of course, the smaller the error margin, the faster the system is.
That being said, given that speed will be limited by the distance traveled by information and the speed of light, I suppose those systems won't have much edge over purely causality-based ones. In other words, CRDTs will rule Space :)
Not an expert by any means but I would imagine you simply prefix your time with a specific „large-sclae time zone“ that you are moving in, e.g., it could be earth, another planet or your spacecraft. Wouldn‘t solve it completly but seems to be a pragmatic solution that could work alright for most cases.
However, a total ordering of events seems plausible only from the relative perspective of an observer and we would need to figure out, how to think about how things like transfer duration affect each oberservers understanding of ordering.
Not a physicist but isn't it the case that any two observers can still compute at what time the other person perceived any given event, if they know each other's history of travel and the history of travel of the event?
So you would just have to agree that one observer's clock is the "master clock", and then everyone translates their local clock time into the corresponding master clock time (and all timestamps are written with respect to the 'time zone' of the master clock).
I suppose those continue working fine in very local systems (contained in a ball of a few light-seconds radius) whose components move at speeds where relativistic effects can be discarded. Drop those constraints and you also need to drop even system-local globality because of relativity.
You _could_ introduce the One True Lamport Clock, and as long as you're in its light cone you can get global syncronization, but that comes at the cost of having to learn a lot about patience.
