I’ve spent a decent chunk of my career wrestling with time sync — NTP/PTP, GPS, timezones, all that fun stuff. For real world network time infrastructure, where do we actually hit diminishing returns with clock precision? Like, at what point does making clocks more precise stop helping in practice?
Asking partly out of curiosity, I have been toying with a future pet project ideas around portable atomic clocks, just to skip some of the headaches of distributed time sync altogether. Curious how folks who’ve worked on GPS or timing networks think about this.
For most applications, clock precision of synchronization isn't really necessary. Timestamps may be used to order events, but what is important is that there is a deterministic order of events, not that the timestamps represent the actual order that the events happened.
In such systems, ntp is inexpensive and sufficient. On networks where ntpd's assumptions hold (symetric and consistent delays), sync within a millisecond is acheivable without much work.
If you need better, PTP can get much better results. A local ntpserver following GPS with a PPS signal can get slightly better results (but without PPS it might well be worse)
Another commenter mentioned that this is needed for consistently ordering events, to which I'd add:
The consistent ordering of events is important when you're working with more than one system. An un-synchronized clock can handle this fine with a single system, it only matters when you're trying to reconcile events with another system.
This is also a scale problem, when you receive one event per-second a granularity of 1 second may very well be sufficient. If you need to deterministically order 10^9 events across systems consistently you'll want better than nanosecond level precision if you're relying on timestamps for that ordering.
My understanding is that precise measurement of time is the basis of all other measurements: space, mass, etc. They are all defined by some unit of time. So increasing time precision increases potential precision in other measurements.
Including of course information - often defined by the presence or absence of some alterable within a specific time.
We invent new uses for things once we have them.
A fun thought experiment would be what the world would look like if all clocks were perfectly in sync. I think I'll spend the rest of the day coming with imaginary applications.
For network stuff, high security and test/measurement networked systems use precision time protocol [1], which adds hardware timestamps as the packets exit the interface. This can resolve down to a couple nanoseconds for 10G [2], but can get down to picosecond. The "Grandmaster" clock uses GPS/atomic clocks.
For test and measurement, it's used for more boring synchronization of processes/whatever. For high security, with minimal length/tight cable runs, you can detect changes in cable length and latency added by MITM equipment, and synch all the security stuffs in your network.
I use fairly precise time but that's because I control high speed machinery remotely. The synchronization is the important part (the actual time doesn't matter). At 1200 inches per minute, being a millisecond off will put a noticeable notch in a piece.
Ptp and careful hardware configuration keeps things synced to within nanoseconds
When I was in anthropology, many of the cultures I studied had very vague concepts of time (sunrise/sunset, passage of stars and constellations, different seasons). One of my professors spent two weeks about how time was a Western construct and how people want to go to such great lengths to have such precise measurement of it.
The very lengthy discussion around the concept was fascinating to me as a 23 year old college student who only knew it from one perspective.
That really doesn't seem to make sense as written. Even if for "Western" you count all the way to the Middle East (where much of our chronometry originates), there's still a lot found in China and the New World. (From what I can tell, India does not seem to have a strong independent record here? Though they certainly borrowed from the inventors, just like Europe did.)
Japan had a whole fancy temporal hour system before Western contact. It was more complicated than our modern framework, as it was based on the time between sunrise and sunset and so the length of the hours had to be adjusted about every two weeks. But they certainly thought quite a bit about it, so I'm not sure how it could be claimed to not be a concept there at the time.
It wasn't even a daily utilized concept in the West until trains were chugging their way to various stations. Farmers didn't need to know the exact minute the cows came home.
Your professor was just wrong if they claimed time was a Western construct. Calendars, sundials, and other time keeping devices were created independently around the world.
All you need to create a clock is realize that your oil lamp consumes its fuel in a somewhat consistent interval, or a similar observation for the time it takes drips of water to fill a cup. People figured it out.
I don't think its fair to say that atomic clocks represent a western cultural value. After all, they are extremely niche. Physicists care but the average "westerner" does not.
And paper money is a Chinese invention. Doesn't mean it's worthwhile to spend two weeks in an anthropology class talking about how much awesomer they are.
They mention a "quantum noise limit", that must be the ultimate precision that is physically possible, right?
What is this ultimate precision? I imagine that at some point, even the most modest relative motion at ordinary velocities would introduce measurable time dilation at fine enough clock precision.
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[ 2.4 ms ] story [ 48.4 ms ] threadAsking partly out of curiosity, I have been toying with a future pet project ideas around portable atomic clocks, just to skip some of the headaches of distributed time sync altogether. Curious how folks who’ve worked on GPS or timing networks think about this.
In such systems, ntp is inexpensive and sufficient. On networks where ntpd's assumptions hold (symetric and consistent delays), sync within a millisecond is acheivable without much work.
If you need better, PTP can get much better results. A local ntpserver following GPS with a PPS signal can get slightly better results (but without PPS it might well be worse)
The consistent ordering of events is important when you're working with more than one system. An un-synchronized clock can handle this fine with a single system, it only matters when you're trying to reconcile events with another system.
This is also a scale problem, when you receive one event per-second a granularity of 1 second may very well be sufficient. If you need to deterministically order 10^9 events across systems consistently you'll want better than nanosecond level precision if you're relying on timestamps for that ordering.
Including of course information - often defined by the presence or absence of some alterable within a specific time.
We invent new uses for things once we have them.
A fun thought experiment would be what the world would look like if all clocks were perfectly in sync. I think I'll spend the rest of the day coming with imaginary applications.
For test and measurement, it's used for more boring synchronization of processes/whatever. For high security, with minimal length/tight cable runs, you can detect changes in cable length and latency added by MITM equipment, and synch all the security stuffs in your network.
[1] https://en.wikipedia.org/wiki/Precision_Time_Protocol
[2] https://www.arista.com/assets/data/pdf/Whitepapers/Absolute-...
Ptp and careful hardware configuration keeps things synced to within nanoseconds
ah yes - that would be Planck's second which can be derived from Planck's constant and the speed of light
The very lengthy discussion around the concept was fascinating to me as a 23 year old college student who only knew it from one perspective.
That really doesn't seem to make sense as written. Even if for "Western" you count all the way to the Middle East (where much of our chronometry originates), there's still a lot found in China and the New World. (From what I can tell, India does not seem to have a strong independent record here? Though they certainly borrowed from the inventors, just like Europe did.)
Japan had a whole fancy temporal hour system before Western contact. It was more complicated than our modern framework, as it was based on the time between sunrise and sunset and so the length of the hours had to be adjusted about every two weeks. But they certainly thought quite a bit about it, so I'm not sure how it could be claimed to not be a concept there at the time.
All you need to create a clock is realize that your oil lamp consumes its fuel in a somewhat consistent interval, or a similar observation for the time it takes drips of water to fill a cup. People figured it out.
[1] "Quantum-amplified global-phase spectroscopy on an optical clock transition" (2025) https://www.nature.com/articles/s41586-025-09578-8
[2] "Quantum watch and its intrinsic proof of accuracy" (2022) https://journals.aps.org/prresearch/abstract/10.1103/PhysRev...
What is this ultimate precision? I imagine that at some point, even the most modest relative motion at ordinary velocities would introduce measurable time dilation at fine enough clock precision.