12 ms·
New atomic clock loses only one second every 300B years
- jer0me 5y agoCurrent atomic clocks are 1 second every few hundred million years.
- silisili 5y agoThat means it could be off by as much as 20 to 30 seconds when the sun finally burns out. Obviously unacceptable accuracy.
- foota 5y agoWhich in fairness is 1 microsecond every couple years, an easily measurable amount by a computer.
- sambroner 5y agoItd be hard for your computer to have the accuracy to detect it!
- notum 5y agoIt doesn't have to have the accuracy, if both computers had their own atomic clocks they would end up out of sync every couple of years, just like GPS satellites do.
- SamBam 5y agoWhat would your computer be comparing it to?
- CheezeIt 5y agoAnother atomic clock.
- p1esk 5y agoHow do we know which clock is the accurate one?
- kingkawn 5y agoThe one we arbitrarily choose
- CheezeIt 5y agoBoth are, up to the level of drift between them.
- CamperBob2 5y agoAnother atomic clock. (No, really: with three uncorrelated clocks you can separate their variances.)
- puzzledobserver 5y agoI'm speculating here, but I think the idea is to ascribe accuracy to processes, not to specific clocks. So you make two clocks on the same principle, say pendulum oscillations, and measure how quickly they start to disagree. Then you make two clocks based on a new principle, say quartz oscillations, and measure their rate of disagreement. You'll notice that the two quartz clocks agree with each other better than the two pendulum clocks do. So quartz clocks keep time better than pendulum clocks. Then you build a new type of clock, say of the atomic kind, and compare two atomic clocks to each other and to quartz clocks. As you repeat this process, I suppose the clock frequencies have to get progressively higher (Cesium clocks are measuring radiation at about 9 GHz), but this allows you to measure finer and finer discrepancies between them.
- credit_guy 5y agoDo you mean one microsecond every couple hundred years? Which would be a few nanoseconds per year?
- Psychlist 5y agoI love claims like this headline that rely entirely on our inability to observe the clock after the stated interval. We can be pretty sure that the clock will not be working at all, let alone accurate, but we can't be certain. At least until we get claims in the trillion year range, at which point the heat death effect will make the claim even more unlikely.
- teaearlgraycold 5y agoIt's just a matter of poor wording. I would hope that everyone's pedantry would be at bay should the title be "New atomic clock loses only one 300 billionth of a second every year".
- deepspace 5y agoI think it is more than pedantry. The clock will not last even a billionth of "300B years", and losing a whole second would be disastrous to its purpose. The kind of people who are interested in atomic clocks can surely understand "loses only 3 picoseconds per year".
- fsh 5y agoA car can measure its speed in kilometers per hour without having to travel for an hour. The choice of units is completely arbitrary and is ultimately a matter of taste. Most people know what a second is, and that a billion years is a really long time. They probably have no idea what a picosecond is. Clock experts generally use fractional frequency errors which have no unit at all.
- jquery 5y agoAt this level of accuracy, I wonder if there are effects even the researchers aren't aware of that could cause drift. Or maybe it's best to say they're that accurate under certain assumptions. I would expect a cosmic ray or a lightning strike or an earthquake to violate the umpteenth nines of accuracy they're claiming.
- btilly 5y agoPrevious optical clocks were able to measure gravitational time dilation from under a meter of altitude. I'll bet that this one measures it to the order of a centimeter. And it isn't just height that is going to have an impact. Any major mass shift affects it. For example in Scandinavia, melting ice in Greenland and rising land will combine to make ultra-precise clocks there run measurably faster over time relative to where they started.
- wbl 5y agoSo this accuracy claim is not saying that they engineered a clock that will only lose 1 second in several trillion years. For one thing that clock would have to survive the sun going nova. Rather it's a statement about the width of the frequency they are measuring and their ability to divide that down to a second. They are saying that they have two clocks measuring the same frequency and have analyzed their dispersion against each other over a period of time and gotten this result. Long-term aging effects aren't going to change the frequency of the atoms (except new physics, but we can rule that out via observations of the Lamb shift in distant hydrogen), but things like gas infiltration, lamp aging, changes in laser characteristics can all cause atomic clocks to drift. This is pretty significant for rubidium which is why the lamps need recalibration periodically.
- vosper 5y ago> For one thing that clock would have to survive the sun going nova. Off-topic, but our sun won’t go nova. https://www.space.com/14732-sun-burns-star-death.html https://www.space.com/14732-sun-burns-star-death.html
- 5y ago
- JaggerFoo 5y agoThat's nothing. I hear they're inventing a blockchain that can lose $300 billion in one second.
- zapdrive 5y agoYou spelled "fb stock" wrong.
- MR4D 5y agoI think this is poor design. If he clock had used ZFS, I don’t think it would lose any seconds. I blame it on poor error correction or possibly non-ECC memory. /j
- dmix 5y ago> which separated strontium atoms into a line in a single vacuum chamber I’ve always wondered how stuff like this works in practice. Even with particular accelerators, how did they figure out how to control the particles to line them up and synchronized it to be blasted at high speeds? I always assumed it was something less sophisticated like bombarding it and just letting whatever gets sent across get measured. But this is taking about lining them up in a vacuum. This type of physics is like black magic to an outsider.
- ISL 5y agoThis answer sounds flippant, but it is not: Practice. A lot of clever people have worked very hard for a long time. At the end of the day, though, colliders get two beams as focused as they can in space and time, point them at each other, and hope for the best. Then they look at the results, make an adjustment, and try again.
- Xpol 5y agoA simple way of thinking it is consider laser as waves, they act like harmonic potentials (like sine curves) with crests and troughs. Atoms that are inside the potentials are trapped, like a ball in a deep well. Atoms trapped in optical lattices have a lifetime with a time constant which the population of trapped atoms keeps decreasing, but the timescale is like tens of seconds, so the atom loss is not significant when the clock interrogation is in milliseconds. In this paper the lattice is a 1D vertical lattice, so you can think of atoms being trapped in a huge stack of pancakes.
- dmix 5y agoThanks for the explanation. Do you know how they get the strontium atoms in place to be hit by the lasers? That’s the part that throws me given the scale.
- Xpol 5y agoAfter strontium atoms coming from an oven (usually at 400-ish degrees) reaches the main chamber, they're trapped via both optically (via lasers) and magnetically (there's coils surrounding the chamber), which we called magneto-optical trap, or MOT. For strontium, there're two stages of MOT, one is a blue (461nm) MOT which cools and traps hotter atoms into temperature of ~mK, and the second stage is the red (689nm) MOT that further cools the atoms into ~uK range. A MOT typically consists of 3 laser beams at different directions, and retroreflected on the other side after hitting the atoms (so 6 beams effectively). Some MOT can be done with less lasers. All 3 pairs of lasers (and 2 MOT, so 6 pairs) have to align perfectly so that they all hit the same point of intersection within the chamber. To align these lasers, one method is to shine another 461nm pulse to the chamber and check for fluorescence signal via a photodiode or camera located on the other side of the chamber. Since the beams are generally much larger than the atomic cloud itself, as long as you hit something, it is easy to optimize the signal. For a blue MOT with very high atom number, you can even see a small blue bulb suspending in the mid-air inside the chamber, which could serve as a rough reference to start with. So now atoms are trapped into the red MOT, you then turn off the red lasers while having the lattice laser (at 813nm) on, so the atoms are loaded into the optical lattice. Using the same method, you take a fluorescence image at the end of the experimental sequence to check if there's any signal. Note that the position of the red MOT depends on both the laser alignment and magnetic fields, so one can either (1) align the lattice beam, in this case, a vertical beam from top to bottom and retroreflected or (2) adjust the magnetic fields to fine-tune the red MOT position. It's an iteration of fine adjustments and looking at images. Another way to align the lattice to the atoms is instead of shining lattice beams to the atoms, you first send red light through the same fiber. When they hit the atoms in the red MOT, the red light will excite the atoms so you won't see anything now with the fluorescence imaging (as they no longer in the ground state that responds to the blue transition). We call this "the killing beam" as the name suggest. Once you know the rough alignment, switch it back to lattice laser and do the optimizations until you see atoms loaded into the lattice (the distribution and spread of the atom ensemble are different when viewed with camera for atoms that are still in red MOT vs loaded into lattice).
- tombert 5y agoHonest noob question: when we get to this level of precision with time, do we have to start worrying about Heisenburgian effects? As in, having such precision in our timing measurements influences the outcome of our results? I know nothing about physics but I find this fascinating.
- klodolph 5y agoThe Heisenberg uncertainty principle applies here… you cannot make a measurement which is both precise in frequency and compact in time. This should be, in some sense, natural to people who understand how a Fourier transform works… basically, when you apply a “window” function to measure a signal over a limited period of time, you end up with the signal smeared in the frequency domain.
- pyuser583 5y agoBut I’m this case, it’s not compact in time. It’s talking about billions of years. So can it be precise in frequency? Am I misunderstanding?
- klodolph 5y ago"One second per 300 billion years" is really a statement about the bandwidth of the signal that the clock generates, translated for lay readers. We don't know what the actual bandwidth of the signal is, since it's not stated in the article. Bandwidth is measured in Hz. In order to measure the bandwidth of the signal (and how accurate the clock is), you have to measure the clock over a period of time. The shorter that period of time, the worse your measurement will be. The smaller the bandwidth, the more time you need to measure it. Note that a signal with 5 Hz bandwidth and 5 Hz center frequency would make a very terrible clock, while a signal with 5 Hz bandwidth and 5 GHz center frequency would make a very nice clock. The bandwidth is the same in both cases, and the amount of time required to measure bandwidth is the same, but they make very different clocks.
- oshiar53-0 5y ago
- wly_cdgr 5y agoYeah but, which second?
- wly_cdgr 5y agoWouldn't it be simpler to just build everything so that a missing second even every hour or two isn't an issue? No? Why not?
- bagels 5y agoIt's a scientific instrument. Some things need the precision.
- alar44 5y agomicroscope invented Wly_cdgr: Why don't we just make things bigger?
- hobs 5y agoEvery additional unit of precision gives you an entire world of stuff you can do. To a computer a second is forever.
- magicalhippo 5y agoThese "clocks" are used more like stopwatches. They're useful for doing incredibly precise science experiments. The added timing precision translates into better precision of other measurements like distance if you're doing time-of-flight experiments like OPERA did[1]. [1]: https://en.wikipedia.org/wiki/OPERA_experiment https://en.wikipedia.org/wiki/OPERA_experiment
- NovemberWhiskey 5y agoWell, we wouldn't be able to have any useful kind of radio communications, for example.
- analog31 5y agoFor the most part we do. For instance, communications protocols -- both wired and wireless -- allow for a certain amount of error, typically defined in the specs for the protocol. If there's a small amount of frequency drift in the sending device, the receiver can detect the actual timing of bit transitions and adjust. Prior to the computer age, radios and TV's had oscillators that locked themselves to the timings of the transmitting signal. That way, the receiver didn't need to have a precise timer at all. Timing requirements tend to get more precise when you're trying to cram more data into a particular channel. On a more gross scale, bus and train systems can afford timing errors of seconds or even minutes. But precision science needs precision instruments, when the interesting effects are very small.
- Andrew_nenakhov 5y agoSince it is obvious it wouldn't last 300B years, how do they plan to synchronise time on a replacement clock? And if they can't do that with equal precision, what good is having it at all?
- bagels 5y agoThat'd only matter if you're trying to make measurements across the time where you switch from one clock to another. If you use it for 10 years to study gravitation waves, it'd be fit for that purpose since you'd be comparing intervals from the same clock.
- edf13 5y agoBut at which point does the loss of time kick in for such experiments? So you lose a second over a vast timescale but the micro incremental losses still count right?
- MattPalmer1086 5y agoI think the point is that it provides very precise measurements for each independent experiment. I don't think anyone is trying to track the absolute time elapsed over long periods with this clock since it started.
- fsh 5y agoThese experimental clocks are generally not used for time keeping. They are room-filling atomic physics experiments, which are not reliable enough for permanent operation. It is better to think of them as frequency standards. This means that the clock laser will have the same frequency in a month as it does today (to a very high level of precision). If you have multiple such frequency standards, you can put them in different locations and compare their frequencies via optical fiber links. The frequencies are affected by gravitational time dilation, so this can be used for mapping the earth's gravitational potential. In the future, it might also allow detecting gravitational waves.
- hughrr 5y ago
- terafo 5y agoI, for one, hope that more research would be put into lowering the cost of atomic clocks, not into precision, so it is possible to put atomic clock into everyday devices.
- Xpol 5y agoThey are not mutually exclusive. There're groups that are developing portable atomic clocks, and then we have this group that are pushing the frontiers. While not in everyday devices, cesium/ rubidium clocks which are less accurate but there're already commercial products that are used in observatories around the world. The standard time of your country might already be referenced to one of these.
- terafo 5y agoActually, I think spending research time on lowering cost is much more beneficial to accuracy in the long run. It is possible to spend much more on research in case when there are tens of millions of devices produced each year, than in the case when these things cost a couple of grand per PCIe card, which is reasonable cost for servers, but not for consumer devices.
- fsh 5y agoIt is usually much simpler to put a GPS receiver in the device and to make use of the dozens of atomic clocks flying over our heads. Or to use NTP over the internet.
- gorgoiler 5y agoWhat’s the most precise clock I can buy, as an overpaid computer programmer? I suppose anything that shows a human time representation is out of the question. It wouldn’t be able to incorporate legal changes to time such as let’s insert a leap second! or days are now divided into 32 hourlets!. I would settle for an output that shows elapsed seconds from an agreed upon datum. I guess having a human readable time would be fine but the science part is more interesting. With a clock of such precision, how could I synchronise it? Or rather: is there something better than NTP that Serious Clock Owners(tm) use? Perhaps what I want is a clock with reasonable-ish accuracy but incredible longevity. Having a long running independent mechanical source of time is appealing, and kind of orthogonal to having an ultra accurate but electrical one.
- hnarn 5y agoThere’s nothing wrong with NTP and anything beyond the accuracy of a normal Casio watch is a fools errand in my mind: unless you get a watch that actually NTP syncs itself (like a smart watch), but the battle for an “on-wrist” super accurate watch was won by the digital wrist watch decades ago, there are no serious mechanical competitors.
- kijin 5y agoThere are differences even among quartz watches, due to the quality of the crystal and the circuitry surrounding it. A normal sub-$50 Casio watch will gain or lose a few seconds every month, accumulating to more than 1 minute of error per year. A particularly bad one I've had gained a minute a month, worse than some of my mechanical watches! Meanwhile, Seiko sells quartz movements that are accurate to within 10 seconds per year. Citizen's top line is accurate to within 1 second per year, uses GPS signals to correct even that little error, and charges itself from any available light source. It's going to be accurate to within a few milliseconds for the next 20 years with no maintenance, all at a price that a typical overpaid programmer can easily afford.
- hnarn 5y agoThere's two parts to the original question: - What kind of high precision clocks are there - How do I synchronize them (implying NTP is not for serious use) Since any "smart" device including your "simple" smartphone, smart watch or even your laptop will synchronize itself via NTP, their time keeping abilities are likely already better or at least equal than that of any high tech mechanical watch, because the first question ties into the other: there is no point in perfect accuracy if you can have constant error-correction. While my inability to understand why anyone would care about a 10 second per year loss for personal use -- especially since the time and effort required to recalibrate even a manual clock is tiny if it does matter -- is completely subjective, I don't think the comparison between NTP-enabled devices and "ultra-correct" time keeping devices is. I just don't see a convincing argument for buying something like an atomic watch, or a high-end wristwatch, unless in the first case you yourself plan on hosting an NTP service for example (and you would, of course, even then at least verify it via: NTP!) -- or in the second case if you knew you would for an extended time be without access to any other trustworthy time-keeping device, via the Internet or otherwise. Everyone obviously has their own interests and anyone is free to spend any amount they want on expensive time keeping devices, I just think one should be aware of what the level of normality already is these days for many devices we use, which in my mind is pretty high.
- KingOfCoders 5y agoTimeline of the far future (including 350B years from now) https://en.m.wikipedia.org/wiki/Timeline_of_the_far_future https://en.m.wikipedia.org/wiki/Timeline_of_the_far_future
- rigrassm 5y agoThank you for posting this! A fun (if not slightly sad towards the end) list to go through. Just trying to wrap your brain around some of the timescales in there (not that you really can but it is fun to ponder it) is crazy
- Eddy_Viscosity2 5y agoI've read somewhere someone having a clock so precise that it was affected by the relativistic effects of small changes in Earth's gravity caused by the natural movements of tectonic plates. Don't these sorts of things also limit the practical accuracy of clocks -- if they can only accurately measure the time passing at their specific spot in the ever changing curvature of space-time which is different from every other spot?
- weberer 5y agoYes, which is why the International Atomic Time standard is based on the averaged value of readings from over 400 clocks around the world. https://iag.dgfi.tum.de/fileadmin/IAG-docs/Travaux2013/08_BIPM.pdf https://iag.dgfi.tum.de/fileadmin/IAG-docs/Travaux2013/08_BI...
- Eddy_Viscosity2 5y agoThanks, I did not know this. But then comes the follow up question. For every increase in accuracy of an individual clock, how many extra of these improved clocks scattered around the world do you need to improve the overall accuracy of the system time?
- LegionMammal978 5y agoAs a general rule, sampling a normal distribution N times decreases the uncertainty by a multiple of 1/sqrt(N). For instance, to know the mean of an unknown distribution to within N digits, the number of observations must be on the order of 2N digits long. I learned this the hard way when attempting some statistical experiments; it may answer your question here.
- amelius 5y agoHow does that work for the median (as opposed to the mean)? Asking because median rejects outliers better than the mean.
- amznbyebyebye 5y agoIf you know how much time it loses, can’t you correct for it and in theory make a “perfect” clock that doesn’t lose any time?
- i5heu 5y agoBut you don’t know if you have to add a second or subtract a second. You only know that your error is between -1s and +1s.
- kevincox 5y agoThis is my understanding but the term "loses" implies to laypeople like me that it is slow. Maybe better phrasing could avoid implying if it gained or lost time in the long term.
- raymondh 5y ago300B years is impressive. I wonder how they overcame the problem of our sun turning into a red giant 5 billion years from now ;-)