There is No Now – Problems with simultaneity in distributed systems(queue.acm.org)
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There is No Now – Problems with simultaneity in distributed systems
https://queue.acm.org/detail.cfm?id=2745385
2 comments
Thanks for the thoughtful comment!
I think there’s a small misunderstanding, though: while systems like GPS do account for relativistic effects at the clock level (and even with extremely precise atomic clocks and practical synchronization via NTP), this doesn’t mean we have a universal or perfectly shared notion of “the same time” across distributed nodes — especially once you consider network delays, clock drift, and faulty or unreachable nodes
In physics there is no absolute global time for spatially separated events, and in distributed systems this shows up as unavoidable uncertainty in synchronization.
Also, the FLP result isn’t about relativity or physical clocks at all — it’s a theoretical result about the impossibility of guaranteed consensus in fully asynchronous systems with failures.
So even with very accurate clocks and practical time bounds, distributed algorithms still have to explicitly deal with uncertainty and partial synchrony rather than assuming perfect global time.
I think there’s a small misunderstanding, though: while systems like GPS do account for relativistic effects at the clock level (and even with extremely precise atomic clocks and practical synchronization via NTP), this doesn’t mean we have a universal or perfectly shared notion of “the same time” across distributed nodes — especially once you consider network delays, clock drift, and faulty or unreachable nodes
In physics there is no absolute global time for spatially separated events, and in distributed systems this shows up as unavoidable uncertainty in synchronization.
Also, the FLP result isn’t about relativity or physical clocks at all — it’s a theoretical result about the impossibility of guaranteed consensus in fully asynchronous systems with failures.
So even with very accurate clocks and practical time bounds, distributed algorithms still have to explicitly deal with uncertainty and partial synchrony rather than assuming perfect global time.
GPS clocks take special and general relativity into account. I'm no expert, just something I thought I'd read.
I'd never heard of the FLP result before and it seems mostly a theoretical concern with distributed systems which do have time bounds etc so it doesn't apply (unlike CAP which always does).
Edit: I like the details that are presented, but not the way it's done. If organized as reference material could be more useful for this volume of info. As long as we're digging in the weeds, I'd like to hear about how there is no absolute/universal "same time" for spatially separated events.