11 ms·
Where does my computer get the time from?
- ryangs 3y agoInteresting breakdown. But this format is horrible for conveying information. An improvement would be removing the slides, crafting some coherent paragraphs and then reinserting some of the more crucial images for support.
- phantom784 3y agoWatching the actual talk is much better: https://ripe86.ripe.net/archives/video/1126/ https://ripe86.ripe.net/archives/video/1126/
- nayuki 3y agoThe linked PDF has clear page delineations, unlike the HTML page: https://ripe86.ripe.net/presentations/134-2023-04-whence-time.pdf https://ripe86.ripe.net/presentations/134-2023-04-whence-tim...
- m348e912 3y agoI have never seen this format before but it does mirror what going down a rabbit hole of a particular topic looks like for the average curious person. I liked it.
- FL410 3y agoI thought it was a very fun, stream-of-consciousness kind of read.
- johnnyanmac 3y agoI simply assume any "slides" format comes from porting over a live talk. Lazy, yes. Efficient, yes.
- hbn 3y agoI was mostly confused about the images being above the line of text you're supposed to read before looking at the image. "Here's a picture of an NTP packet" picture of a man sitting at a desk
- zoky 3y agoI mean, put a little gnome hat on him and I’d believe it…
- fanf2 3y agoWhen I gave the talk, I showed the slide before I talked about it. It’s normal to show the speaker notes below the slides in software like Keynote or Powerpoint.
- dclowd9901 3y agoI can tell the talk would have been really enjoyable but I agree this format is just lazy for conveying that information.
- OJFord 3y agoThat might be clearer if the header was just 'slides and notes from my talk', instead you actually claimed the opposite, that it's a 'blogified version', but it's not really - I tripped up on the same thing, and then got through several 'duplicate images', 'oh no very slightly different images', before it finally dawned on me that they were slides.
- fanf2 3y agoI’ve clarified the introductory paragraph and added lines between each slide. Should be a bit easier to read now.
- SilasX 3y agoAnd when I shift a work to a new medium, I also shift over the conventions used to match that new medium -- and audience. It's an empathy thing.
- chankstein38 3y agoEspecially because half of the text just repeats what's on the slides and ultimately I didn't see an easy way to make the slides bigger. Like the NTP packet format slide was mostly unreadable.
- deleted 3y ago[deleted]
- svat 3y agoAfter someone gives a talk in person, some of the things they can do online: 1. Mention that they gave a talk 2. Post a video recording online 3. Post the slides online, as-is (PDF or whatever) with no explanation 4. Lay out the slides on a HTML page, with accompanying text (what would have been said by the speaker), so that it's easier to read — while still being clear you're “reading” a talk. 5. Redo/rewrite the whole thing into text form, paragraphs and all. The author here has done 1 to 4, and you're complaining they've not also done 5, but that's a lot of work and I don't begrudge someone not doing that. I'll be grateful someone presented their talk in a readable form in the first place. [I do agree this page was hard to read, at least on mobile and at least in its initial version—it's much better now—but I've seen many others post these "annotated talks" online and the format itself is not necessarily bad: for instance see https://idlewords.com/talks/ https://idlewords.com/talks/ (example: https://idlewords.com/talks/superintelligence.htm https://idlewords.com/talks/superintelligence.htm) or https://noidea.dog/talks https://noidea.dog/talks (example: https://noidea.dog/impostor https://noidea.dog/impostor) or https://simonwillison.net/tags/annotatedtalks/ https://simonwillison.net/tags/annotatedtalks/ (example: https://simonwillison.net/2022/Nov/26/productivity/ https://simonwillison.net/2022/Nov/26/productivity/) — maybe just some minor tweaks to CSS like putting the text to the right of the images would make it easier to read.]
- user3939382 3y agoA hydrogen atom being looked at by the Navy right?
- caymanjim 3y agoCesium, NIST.
- aa-jv 3y agoAnd not just one, millions of them.
- gumby 3y agoWhat a waste of taxpayers’ money! They should just pick one and stare at it. Why should we be paying for millions of them???
- seanthemon 3y agoIf you don't use the budget you won't get the budget, sailor.
- fluoridation 3y agoI see no downside.
- vel0city 3y agoI get the confusion for the US Navy though, as the clock is at the US Naval Observatory. If you ever need the time, just call (719) 567-6742 "US Naval Observatory, Master Clock, at the tone, Mountain daylight time, nine hours, sixteen minutes, fifteen seconds...beep!"
- goblinux 3y agoJust called the number holy cow it’s real. I love obscure infrastructure stuff like that
- gentleman11 3y agoWhere does my car get the time from? It drifts and changes every time I start it up. Every 3 months I have to change it manually by 10ish minutes or more, but it’s inconsistent
- willis936 3y agoIt sounds like it gets the time from you.
- fuzzfactor 3y agoLaurens Hammond invented the synchronous electric motor once A/C domestic voltage had proliferated enough as an alternative to the original D/C electrification first established by Edison. This made it possible for the first time to build clocks based on the stable frequency of the incoming A/C supply voltage, much more reliably than those based on the incoming line voltage, which varies quite a bit whether it is A/C or D/C. This put him on the map as a manufacturer when he went forward to build Hammond clocks commercially. Years later his engineers encouraged him to consider developing an electric church organ, which would be possible to remain in tune regardless of variations in line voltage themselves. Hammond was not musically inclined but he did it anyway. Right up there with the Great Men in the most legendary way. http://thehammondorganstory.com/ http://thehammondorganstory.com/ By the time the 1960's came around, almost all new American vehicles were recognized as modern Space Age conveniences, and a factory clock (mechanical analog, naturally) had become almost a universal standard accessory beyond the most budget price points. There were a couple drawbacks to the factory clocks, they had to be connected to the car battery at all times to keep running, they didn't drain the battery very much at all but still would eventually deaden it if undriven, way worse than no clock. And they depended on the incoming voltage which determined the internal clock motor speed to begin with. Different automotive electrical systems and batteries themselves do vary perhaps 10 percent about a nominal design voltage of 12 VDC. There is no stable A/C in the car that a synchronous motor would need to run on[0]. These now-vintage clocks were self-correcting. You correct them yourself. Actually the same twisting of the knob to move the hands of the clock, which was familiar from earlier non-correcting clocks simply did the job. So they were somewhat backward-compatible. Only the Space Age units had smart enough mechanical ability to take into account how much and in which direction you moved the hands, and adjusted the previous running speed accordingly. If the clock was not very close to correct time when you adjusted it, it would take repeated adjustments over a number of days or weeks to get it to very realistic speed. All it really did was successive approximation. You had to supply your own natural intelligence. Even at the time lots of drivers never knew this, and there was widespread disappointment over the wildly inaccurate clocks "which were OK when new but went downhill 'through time'". They only added maybe a dollar to your car payment but that was very expensive compared to a highly reliable cheap household clock at the time. When you think about it, today lots of drivers are not quite up to par when it comes to engaging the amount of natural intelligence that would be needed in many other ways besides timekeeping. [0] The electrical "vibrator" which provided switch-mode 12VAC which could be stepped up by a transformer to supply much higher voltage to power vacuum tube radios still produced a variable A/C voltage & frequency, dependent on the underlying D/C supply voltage.
- tbm57 3y agoI think we need a community-maintained and democratized time-tracking standard so we're not so beholden to Big Time
- deleted 3y ago[deleted]
- callalex 3y agoPut it on the clockchain
- urbandw311er 3y agoPlease tell me you just coined this.
- runlaszlorun 3y agoThat’s hilarious.
- kristopolous 3y agoIt's probably possible to calibrate your clock using a clear night sky and a modern cell phone camera. I bet second accuracy isn't an absurd expectation. Now it'd probably take an unreasonable amount of time to calibrate...
- crote 3y agoThat's pretty much what we already have, isn't it? True Time™ is determined by essentially averaging dozens of atomic clocks from laboratories all over the world. It doesn't really get any more "community-maintained" and "democratized" than that!
- huehehue 3y agoThe article, and this comment, makes me wonder what impact a coordinated attack on the root time-keeping mechanisms might have. It seems like there's a fair bit of redundancy / consensus, but what systems would fail? On what timeline? How would they recover?
- 3y ago
- dghughes 3y agoMy cat is crazy accurate for time down to the minute. I can be sitting reading, on the web, or watching a movie all of which are random and not repeated at any specific time. Yet at 9pm exactly any time of the year she sits by the stool and complains if I am not there to give her a treat at 9pm Atlantic time. Note she does get thrown off by seasonal time changes in the fall and spring but she only needs about a week to reset.
- diggan 3y agoSame with my dogs! One of them come and puts her paw on me at exactly 20:00 every day, down to the minute as well, to remind me that it's foodie time. Maybe I could use my dog instead of NTP and have her press a button that syncs my computers to exactly 20:00? Would work offline at least.
- deleted 3y ago[deleted]
- augusto-moura 3y agoIt gives me an idea of training my dog to hit a button to get food and eventually plot the data onto a graph. Would be funny to draw some patterns from it
- dghlsakjg 3y agoThat’s so interesting. My dog runs on a solar clock. He starts begging for his dentastick when it gets dark out, and stays in bed until the sun comes up in winter.
- hellotheretoday 3y agoWe started using an automated feeder with our dog. It broke one day and we were surprised to see that he was prompting us to feed him almost exactly at the programmed times. Like down to the minute. Not sure if he’s relying on other sensory information like certain smells or sounds. I don’t believe that’s the case; we didn’t replace the broken feeder for 3-4 months and he was able to keep time within a few minutes during that period. Our behavior is erratic and changes often; we work jobs with very inconsistent schedules (thus the automatic feeder) so it’s likely not that our behavior is prompting him as well. We can even observe him consistently going to his feeding area on the security camera at the correct time when no one is home. Interesting stuff!
- deleted 3y ago[deleted]
- fckgw 3y agoJust want to take a moment to appreciate the URL of "dot at, dot at, slash at"
- nayuki 3y agoDefinitely reminds me of H T T P colon slash slash slashdot dot org
- alch- 3y agoOooooh decades later I finally get the name Slashdot! Thank you!
- runlaszlorun 3y agoHa, same here.
- FireBeyond 3y agoIIRC there was an ISP or web host in Australia way back in the day called DotNet (obviously before the MSFT days)... Their website was http://www.dotnet.net.au http://www.dotnet.net.au (www dot dotnet dot net dot au).
- firatt 3y agoyou should see the email address of the author :)
- perihelions 3y ago/Meta: There's three different posts on the front page on the theme of "what is time, anyway", and I'm curious if there some reason for that? Did I miss some news event? Did some leap-second bug crash something?
- wwalexander 3y agoI’ll often see articles on the front page related to a popular thread from a day or two ago. I always assume that someone either went down a rabbit hole based on the original thread and wanted to share their findings, or already knew about that topic and felt inspired by the original thread to share something useful about it.
- pbhjpbhj 3y agoHypothesis: People gaming clicks using popularity of subjects from past years would want to drift (heh!) the time forward slightly, these topics probably normally arise around the time clocks change for Winter (29 October this year is the end of British Summer Time). So, I speculate that this is a drifted "clocks go back, but will your computer adjust itself?" topic area.
- adenner 3y agoThis reminds me of a talk I gave several years ago to my local linux users group (CIALUG) about time... I don't have the recording anymore but still have the slides https://www.slideshare.net/denner1/all-about-time-or-how-to-stop-from-going-back-to-the-future https://www.slideshare.net/denner1/all-about-time-or-how-to-...
- gandalfian 3y agoIt used to irritate me that my old dumb mobile must have known exactly the correct time in order to operate on the cell phone network. Yet it kept it secret from me. I had to manually set the clock by guesstimate
- callalex 3y agoIn the early days of mobile networks, it was my experience that the network time was not very good. Sometimes off by a minute or two, but most often filled with DST bugs.
- NovemberWhiskey 3y agoI think the poster is getting at the fact they had a CDMA phone - those require extremely tight clock synchronization in order to work. Like a phone needs a sub-chip level of synchronization to a base station (order of a few hundred ns) otherwise it won't be locked to the relevant codes. All this is down at the modem layer and was probably not externalized to the crappy CPU that ran the OS for the phone though. You can still use the CDMA networks to get a very precise time reference, suitable for a stratum-1 timeserver, but I think not for very much longer.
- auspiv 3y agoIf you have a Raspberry Pi laying around and want to run your own Stratum 1 NTP server - https://austinsnerdythings.com/2021/04/19/microsecond-accurate-ntp-with-a-raspberry-pi-and-pps-gps/ https://austinsnerdythings.com/2021/04/19/microsecond-accura...
- fanf2 3y agoNote that for NTP it’s better to use a Raspberry Pi 4 than older boards. The old ones have their ethernet port on the wrong side of a USB hub, so their network suffers from millisecond-level packet timing jitter. You will not be able to get microsecond-level NTP accuracy. For added fun, you can turn the Raspberry Pi into an oven compensated crystal oscillator (ocxo) by putting it in an insulated box and running a CPU burner to keep it toasty. https://blog.ntpsec.org/2017/03/21/More_Heat.html https://blog.ntpsec.org/2017/03/21/More_Heat.html (infohazard warning: ntpsec contains traces of ESR)
- ianburrell 3y agoThat's a Stratum 0 server since it gets its time from GPS. Stratum 1 server is one that gets its time from Stratum 0 servers.
- fanf2 3y agoStratum 0 is the reference clock itself; stratum 1 is an NTP server attached to one or more reference clocks. https://www.ntp.org/ntpfaq/ntp-s-algo/#5111-what-is-a-reference-clock https://www.ntp.org/ntpfaq/ntp-s-algo/#5111-what-is-a-refere...
- TacticalCoder 3y agoWhat's amazing is that if your computer is not set to automatically sync its time, you can see how fast it's drifting. My main desktop is 1.7 seconds ahead at the moment. Probably haven't updated the clock in a few weeks: which isn't that much. Other systems shall drift much more. As to "why" it's not setting the time using NTP automatically: maybe I like to see how quickly it drifts, maybe I want as little services running as possible, maybe I've got an ethernet switch right in front of me which better not blink too much, maybe I like to be reminded of what "breaks" once the clocks drifts too much, maybe I want to actually reflect at the marvel of atomic drift when I "manually" update it, etc. Basically the "why" is answered by: "because I want it that way". Anyway: many computer's internal clock/crystal/whatever-thinggamagic are not precise at all.
- harikb 3y agoFrom wikipedia > Typical crystal RTC accuracy specifications are from ±100 to ±20 parts per million (8.6 to 1.7 seconds per day), but temperature-compensated RTC ICs are available accurate to less than 5 parts per million.[12][13] In practical terms, this is good enough to perform celestial navigation, the classic task of a chronometer. In 2011, chip-scale atomic clocks became available. Although vastly more expensive and power-hungry (120 mW vs. <1 μW), they keep time within 50 parts per trillion.
- peteey 3y agoCrystal errors tend to be around 20 ppm (parts per million) After a week, 20 ppm would drift 12 * 10^-6 * 7 * 24 * 60 *60 = 12 seconds. Your motherboard probably has a cr2032 keeping it powered when unplugged. Crystals: https://www.digikey.com/en/products/filter/crystals/171?s=N4IgjCBcoExgrABiqAxlAZgQwDYGcBTAGhAHsoBtEAZhgDoB2ANgA4ACAawAkAvEAXRIAHAC5QQAVQB2ASxEB5DAFkCWPAFcATgRABffUA https://www.digikey.com/en/products/filter/crystals/171?s=N4...
- crote 3y agoIt kinda makes you wonder why desktop computers don't use the AC frequency as a stable-ish time source. Short-term accuracy is pretty poor, but it can definitely do better than 12 seconds over a week!
- fuzzfactor 3y agoIt's an interesting situation when instruments or measurements become more precise, stable, or reliable than the reference material. And when someone (usually an individual) finally discovers that it has happened, or in some cases makes it so. >the ephemeris second is based on an astronomical ephemeris, which is a mathematical model of the solar system >the standard ephemeris was produced by Simon Newcomb in the late 1800s >he collected a vast amount of historical astronomical data to create his mathematical model >it remained the standard until the mid 1980s >in 1952 the international astronomical union changed the definition of time so that instead of being based on the rotation of the earth about its axis, it was based on the orbit of the earth around the sun >in the 1930s they had discovered that the earth’s rotation is not perfectly even: it slows down and speeds up slightly >clocks were now more precise than the rotation of the earth, so the ephemeris second was a new more precise standard of time
- darkwater 3y ago>in 1952 the international astronomical union changed the definition of time so that instead of being based on the rotation of the earth about its axis, it was based on the orbit of the earth around the sun >in the 1930s they had discovered that the earth’s rotation is not perfectly even: it slows down and speeds up slightly Yeah, I remember studying that back in high school but I wonder... what previous actual duration of a second they used? And also, being based on the rotation of Earth, what kind of data was the "vast amount of historical astronomical data" Newcomb collected? How can you reliably capture and store the length of time if you can only base it on the Earth rotation speed which varies over time? I would guess the data compared it to other natural phenomena?
- fanf2 3y agoWhen time was based on earth rotation, astronomers used “transit instruments” to observe when certain “clock stars” passed directly overhead. The clock stars had accurately known positions, so if you routinely record the time they pass overhead according to your observatory’s clock, then you can work out how accurate your clock is. Newcomb’s data would have been accurately timed observations, as many as he could get hold of, going back about two and a half centuries.
- The_suffocated 3y agoMost of those slides concern about the physics part of time measurement (GPS and atomic clock, etc.). While this is interesting in its own right, in order to understand how MY computer obtains the current time, a more relevant question is “how does a home computer measure the latency of a packet sent from a remote time server”? Does it measure the durations of several roundtrips and take the average duration as latency? What if congestion suddenly occurs during some roundtrip? I always think that these questions are more mysterious than the physical ones.
- tux3 3y agoHere's how that works: https://en.wikipedia.org/wiki/Network_Time_Protocol#Clock_synchronization_algorithm https://en.wikipedia.org/wiki/Network_Time_Protocol#Clock_sy...
- tiffanyh 3y agoTL;DR; The flow of how modern day time is sourced & relayed to your computer: 1. Based on quantum / atom movement -> units -> time 2. Atomic clock based on #1 3. Time from #2, relayed to US Naval Observatory Alternate Master Clock 4. Time from #3, relayed to Space Force Base 5. Time from #4, relayed to GPS 6. Time from #5, relayed to NTP 7. Time from #6, relayed to your home computer
- freedude 3y agoJust be careful which time source you use. One of our servers was configured to use tick.usno.navy.mil and tock.usno.navy.mil back 10-15 years ago or so. The Navy had an "issue" with the time they were sending out. The overnight result was several licensing servers wouldn't authenticate and we were locked out of those systems(SSH needs accurate time, within minutes I believe). We discovered the discrepancy by logging in locally (we were in the same building but a different office) and changed the time servers and then the sync method to resolve the issue.
- bityard 3y ago> SSH needs accurate time, within minutes I believe You may be mis-remembering a few details, SSH does not care about the time at all unless you are using _very_ short-lived SSH certificates.
- lazide 3y agoTime based OTP is pretty sensitive though. Probably that is what broke?
- crote 3y agoThe irony is that the TOTP spec explicitly takes this into account. By default tokens are valid for 30 seconds, with a token from the previous 30-second window also being accepted. Being off by more than that is pretty rare for NTP-connected systems. The specs also provide ways to deal with a dedicated hardware token slowly going out of sync by keeping track of the last-known clock drift, but that's pretty useless these days and can even do more harm than good.
- lazide 3y agoThe poster was referring to minutes, which has also been my experience. Something goes wrong, and suddenly you’re an hour off. Blam, now you can’t login. :s
- fanf2 3y ago
- karol 3y agoWe just create labels, which are rooted in Earths' rotation around the Sun at regular intervals measured by radiation and call it time.
- cmurf 3y agoAre smartphones using GPS for time, or NTP?
- ThinkingGuy 3y agoYes :)
- adrianmonk 3y agoI'm pretty sure the cell network itself can provide time. Not sure if smartphones use it. I think older cell phones that didn't have GPS or a data plan (voice only) did use it. ~15 years ago, I had an old flip phone that had an option to set the time manually or automatically, and T-Mobile "helpfully" provide a time source that was like 5 minutes slow.
- fanf2 3y agoThe time reference inside a cell tower is usually PTP
- Shakahs 3y agoGPS seems like a better choice for a cell tower.
- PeterisP 3y agoCell tower time. Modern cell communications use time-slot multiplexing with transmission slots in the scale of a millisecond and need the beginning/end of transmission to have microsecond-scale accuracy so that you don't miss stuff and don't step on the toes of the previous or next transmission, they need to adjust for light speed propagation, etc. So as a byproduct of needing to continuously sync time with the cell tower in order to function properly, your phone has quite accurate time; your computer might easily be half a second off of 'true' time, but your phone (at least on the broadband chip level - the main OS can not care) can't be even a millisecond off.
- NelsonMinar 3y agoShout out also to the NTP Pool, a volunteer group of NTP servers that is the common choice for a lot of devices. Particularly open source stuff. Microsoft, Apple, and Google all run their own time servers but the NTP Pool is a great resource for almost everything else. https://www.ntppool.org/en/ https://www.ntppool.org/en/
- diggan 3y agoReminds me of that time when the NTP pool was basically ddos'ed by a buggy Snapchat release to iOS devices. https://community.ntppool.org/t/recent-ntp-pool-traffic-increase https://community.ntppool.org/t/recent-ntp-pool-traffic-incr...
- lxgr 3y agoOr when Netgear flooded the University of Wisconsin by hardcoding their NTP server's IP address into some of their home routers: https://pages.cs.wisc.edu/~plonka/netgear-sntp/ https://pages.cs.wisc.edu/~plonka/netgear-sntp/
- ggm 3y agoI was in the pool for a while using a RIPE NCC gps synced pci card. It was fun, but machineroom dynamics made keeping a dome antenna attached was hard: they hate special cables, and roof access is a security and water nightmare. A rubidium clock is pretty cheap these days anyway. Now, I'm on Bert Huberts gps drift and availability thing with a raspberry pi measuring visibility and availability out my home office window. Much more fun.
- rantee 3y agoGreat overview, thanks for sharing. Maybe this was unintentional, but I got a good laugh out of, "In 1952, the International Astronomical Union changed the definition of time"!
- b8 3y agoIs there a way to get time to be 99% or 100% accurate? time.gov shows that my Win11 and Android Pixel are off by almost a second. It'd be cool if it could grab it from the atomic clock.
- LeoPanthera 3y agoI think this is a quirk of Windows and Android machines, which do not aim for perfect precision. macOS is generally accurate to less than a tenth of a second (assuming desktops - laptops maybe less so, as they sleep a lot), and Linux will be just as accurate as long as it is running ntpd and not systemd-timesyncd.
- BenjiWiebe 3y agoI think chronyd is the one you want running on your Linux computer. IIRC it uses NTP to adjust your system clock over time for more accuracy besides just setting the time with NTP. And has more options for more time-nutty things.
- zokier 3y ago99% accurate is pretty vague, but in terms of timekeeping 1% of 24 hours is still almost 15 minutes so being off by a second is couple of orders of magnitude better. Just to give some perspective. NTP definitely should be able to keep the clock correct to sub-second level, but for more accurate local clock something like Open Time Card would do the trick, it has local atomic clock together with GPS receiver to get pretty much reference quality time.
- crote 3y agoInstall a GPS module in your computer. Your Android phone is already capable of receiving GPS, so that's probably the most readily-available accurate time source. Getting your Android phone to sync to GPS time instead of just displaying it in an app might be a bit tricky, though...
- binbag 3y ago"the BIPM collects time measurements from national timing laboratories around the world" I'm really interested in how this is done with multiple clocks over a distance. Can anyone explain? It feels like it would be very difficult since asking "what time is it there?" at the timescale of atomic clocks is kind of a bit meaningless? And that's before considering the absolute local nature of time and the impossibility of a general universal time per relativity.
- fanf2 3y agoThe term of art you want for searchengineering is “time transfer”. There are a variety of mechanisms: * fibre links when the labs are close enough * two-way satellite time transfer, when they are further apart * in the past, literally carrying an atomic clock from A to B (they had to ask the pilot for precise details of the flight so that they could integrate relativistic effects of the speed and height) * there’s an example in the talk, of how Essen and Markowitz compared their measurements by using a shared reference, the WWV time signal.
- crote 3y agoI believe an important aspect is that the actual time offset between the clocks doesn't matter all that much - it is the drift between them you care about. True UTC is essentially an arbitrary value. Syncing up with multiple clocks is done to account for a single clock being a bit slow or fast. It doesn't matter if the clock you are syncing with is 1.34ms behind, as long as it is always 1.34ms behind. If it's suddenly 1.35ms behind, there's 0.01ms of drift between them and you have to correct for that. And if that 1.34ms-going-to-1.35ms is actually 1.47ms-going-to-1.48ms, the outcome will be exactly the same. This means you could sync up using a simple long-range radio signal. As long as the time between transmission and reception for each clock stays constant, it is pretty trivial to determine clock drift. Something like the DCF77 and WWVB transmitters seems like a reasonable choice - provided you are able to deal with occasional bounces off the ionosphere. Of course these days you'd probably just have all the individual clocks somehow reference GPS. It's globally available, after all.
- fanf2 3y ago
- waterheater 3y agoRelated to timekeeping is the NIST Randomness Beacon: https://csrc.nist.gov/projects/interoperable-randomness-beacons/beacon-20 https://csrc.nist.gov/projects/interoperable-randomness-beac... "This prototype implementation generates full-entropy bit-strings and posts them in blocks of 512 bits every 60 seconds. Each such value is sequence-numbered, time-stamped and signed, and includes the hash of the previous value to chain the sequence of values together and prevent even the source to retroactively change an output package without being detected." People here were joking about putting time on the blockchain, and, well, NIST is already doing it.
- sandpaper26 3y agoCan someone give an example use case of this? I'm not sure I understand why a very public long string of random characters on a block chain is useful, except as a way to prove an event didn't happen prior to a certain time
- nonameiguess 3y agoThe draft of the version upgrade explains the possible uses of this: https://nvlpubs.nist.gov/nistpubs/ir/2019/NIST.IR.8213-draft.pdf https://nvlpubs.nist.gov/nistpubs/ir/2019/NIST.IR.8213-draft... Mostly, it's so the public can verify events that were supposed to be random really were random. The executive summary gives plenty of examples, but think of a pro sports draft lottery. Fans always think those are rigged. They could simply use these outputs and a hashing function that maps a 512-bit block to some set with cardinality equal to the number of slots and pre-assign slots to participating teams based on their draft weight. Then fans could verify using this public API that the draw the league claims came up randomly really did come up randomly. People always think polls are rigged. This could be used to publicly produce random population samples for polling. This was also used to prove a Bell inequality experiment worked with no loopholes.
- codetrotter 3y agoIf they want to believe the polls are rigged, won’t they just assume that the NIST random data is “rigged” as well.
- qbxk 3y agomore importantly, where does my computer let the time go?
- iamnotsure 3y agohttps://girard.perso.math.cnrs.fr/mustard/article.html https://girard.perso.math.cnrs.fr/mustard/article.html
- thakoppno 3y agoThis was a real talk? I would have lost my mind attending this. I am adding the Naval Observatory to my travel destination wish list.
- urbandw311er 3y agoIt’s hard to tell if you “losing your mind” in this context means you would have enjoyed the talk or the opposite.
- distract8901 3y agoDoes anyone have a good explainer for how the NTP protocol works? I can't quite wrap my head around how you could possibly synchronize two machines in time over a network with unknown and unpredictable latency.
- mhh__ 3y agoIt's not quick but "Computer Network Time Synchronization" by Mills
- LVB 3y agoSpecifically on the latency question, have a look at https://stackoverflow.com/a/18779822 https://stackoverflow.com/a/18779822 for a basic explanation. tldr, once you allow for two-way communication you can start to factor out the network delay.
- LeoPanthera 3y agoNTP uses the "intersection algorithm": https://en.wikipedia.org/wiki/Intersection_algorithm https://en.wikipedia.org/wiki/Intersection_algorithm
- martin1975 3y agoIf you're interested in precise time keeping, this is Time-Nuts is a great place to start (http://www.leapsecond.com/time-nuts.htm http://www.leapsecond.com/time-nuts.htm).
- mindcrime 3y agoSee also: the Metrology forum at eevblog.com. Lots of time-nuts (and volt-nuts, etc) hang out there.
- kilbuz 3y agoevery NTP story needs a link to the Netgear/UW-Madison fiasco: https://pages.cs.wisc.edu/~plonka/netgear-sntp/ https://pages.cs.wisc.edu/~plonka/netgear-sntp/
- fanf2 3y agoAnd PHK / D-Link https://en.m.wikipedia.org/wiki/Poul-Henning_Kamp#Dispute_with_D-Link https://en.m.wikipedia.org/wiki/Poul-Henning_Kamp#Dispute_wi...
- donalhunt 3y agoDARPA are funding the Robust Optical Clock Network (ROCkN) program, which aims to create optical atomic clocks with low size, weight, and power (SWaP) that yield timing accuracy and holdover better than GPS atomic clocks and can be used outside a laboratory. Most of the big cloud providers have deployed the equivalent of the opencompute time card which sources its time from GPS sources but can maintain accurate time in cases of GPS unavailability. https://www.darpa.mil/news-events/2022-01-20 https://www.darpa.mil/news-events/2022-01-20
- hansoolo 3y agoAll of this beautiful discussion here tells me: time is a man made thing!
- gloryless 3y agoGreat question and great article. This is an "old Internet" vibe for me
- archsurface 3y agoHaving just finished watching Idiocracy I have no choice but to point out that it comes from the time masheen.
- readyplayernull 3y agoAnd Caesium gets the time from spacetime dilation.
- gorgoiler 3y agoA very enjoyable read! If I wanted to be super nerdy about time and have the most precise time source possible, at home, what are my options?
- fanf2 3y agosee https://news.ycombinator.com/item?id=37780788 https://news.ycombinator.com/item?id=37780788 and https://news.ycombinator.com/item?id=37782982 https://news.ycombinator.com/item?id=37782982
- jen729w 3y agoDo I remember the dotat.at domain for having some funny naming thing way back in the day? Was it the email dot@dotat.at? Yeah that’ll be it. It might have inspired me to register `signaslongasitendswith.com` so that I could tell people that my email address was “put whatever you like before the ‘at’ sign as long as it ends with ‘dot.com’”. Felt clever in 2003. I never got any mail.
- phanimahesh 3y agoThat was very clever.
- JoeDaDude 3y agoGreat talk! I'd like to see explained a separate branch tree explaining how WWV, WWVB, and WWVH, the shortwave stations that continuously broadcast time, get their time from (I presume) the USNO.
- fanf2 3y agoThey are civilian not military, so they get their time from NIST https://news.ycombinator.com/item?id=37779909 https://news.ycombinator.com/item?id=37779909
- hcfman 3y agoSoon hopefully from my raspyberry pi stratum 1 time server project :) https://github.com/hcfman/sbts-aru https://github.com/hcfman/sbts-aru
- jackninja1 3y agoGreat post! Also, Rotterdam is definitely worth a visit.
- HocusLocus 3y agoOne of my forays into maybe-fiction, "The Time Rift of 2100: How We lost the Future --- and Gained the Past." is possibly the only sci-fi story ever written about NTP protocol. ( https://tech.slashdot.org/comments.pl?sid=7132077&cid=49308245 https://tech.slashdot.org/comments.pl?sid=7132077&cid=493082... ) For antique computer aficionados it also contains a shout out to Windows NT.
- myrandomcomment 3y agoThis is a great write up. Easy to follow for those that are non-technical. I sent this to my kid that is pre-med in college and the feedback was "wow, I wish my Chemistry professors wrote up concepts like this."
- Pooge 3y agoThis has to be the worst way of explaining something I've seen in here.