[HN Gopher] MIT physicists improve the precision of atomic clocks
___________________________________________________________________
MIT physicists improve the precision of atomic clocks
Author : pykello
Score : 48 points
Date : 2025-10-11 20:21 UTC (6 days ago)
(HTM) web link (news.mit.edu)
(TXT) w3m dump (news.mit.edu)
| ram_rar wrote:
| 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.
| IAmBroom wrote:
| Since their precision is essential to measuring relativistic
| effects, I'm not sure we're near that limit.
|
| For your precise question, it may already be there.
| halestock wrote:
| I know that Google's Spanner[0] uses atomic clocks to help with
| consistency.
|
| [0] https://en.wikipedia.org/wiki/Spanner_(database)
| gaze wrote:
| It hit diminishing returns for most things long, long ago, but
| this physics is directly related to stuff in quantum computing
| and studying gravity.
| KeplerBoy wrote:
| I guess very few systems have better absolute time than a few
| microseconds. Those systems are probably exclusively found in
| HFT and experimental physics.
|
| This past week I tried synchronizing the time of an embedded
| Linux board with a GPS PPS signal via GPIO. Turns out the
| kernel interrupt handler already delays the edge by 20 us
| compared to busy polling the state of the pin. Stuff then gets
| hard to measure at sub microsecond scales.
| westurner wrote:
| From https://news.ycombinator.com/item?id=44054783 :
|
| > _" Re: ntpd-rs and higher-resolution network time protocols
| {WhiteRabbit (CERN), SPTP (Meta)} and NTP NTS :
| https://news.ycombinator.com/item?id=40785484 :_
|
| >> _" RFC 8915: Network Time Security for the Network Time
| Protocol" (2020)_
| KeplerBoy wrote:
| Yes, I'm aware of some of these developments. Impressive
| stuff, just not the level of precision on achieves
| tinkering for a few days with a basic gnss receiver.
| toast0 wrote:
| 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)
| TrueDuality wrote:
| 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.
| pyuser583 wrote:
| 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.
| nomel wrote:
| 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.
|
| [1] https://en.wikipedia.org/wiki/Precision_Time_Protocol
|
| [2]
| https://www.arista.com/assets/data/pdf/Whitepapers/Absolute-...
| xchip wrote:
| "Improve" means nothing unless you give a number.
| zokier wrote:
| straight from the abstract:
|
| > we can demonstrate quantum-amplified time-reversal
| spectroscopy on an optical clock transition that achieves
| directly measured 2.4(7) dB metrological gain and 4.0(8) dB
| improvement in laser noise sensitivity beyond the standard
| quantum limit.
| programjames wrote:
| That isn't a comparison to the state of the art, just a naive
| quantum clock.
| at-fates-hands wrote:
| 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.
| svl7 wrote:
| This topic of time being a western construct, it's impact on
| society and life is one of the subjects in the excellent book
| "Borderliners" [1] by Peter Hoeg. A favorite of mine, though I
| never read the English translation. It's a fascinating topic,
| and impacts our live more than we might be aware of or care to
| admit. I started thinking about it in a different way after
| reading this book.
|
| [1] https://en.wikipedia.org/wiki/Borderliners
| o11c wrote:
| > time was a Western construct
|
| 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.)
| technothrasher wrote:
| > how time was a Western construct
|
| 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.
| westurner wrote:
| Is this (the OT [1]) with ytterbium a more or less efficient way
| to count clock ticks with high precision than is described in
| [2]?
|
| [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...
| crispyambulance wrote:
| 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.
___________________________________________________________________
(page generated 2025-10-17 23:00 UTC)