5 ms·
To keep things in perspective, a vertical shift of a few centimeters could be measured if two of these clocks were placed next to each other, just by the lesser
by mikewarot 1y ago
To keep things in perspective, a vertical shift of a few centimeters could be measured if two of these clocks were placed next to each other, just by the lesser gravity/time dilation at the increased "altitude".
It's an amazing time to be alive. While not this precise, you can have atomic cesium beam clocks of your own for a few thousand dollars each, and some elbow grease.
- nuker 1y ago> ... vertical shift of a few centimeters could be measured In what amount of time? Not instantly, right?
- hcknwscommenter 1y agoInstantly more or less. Time instantly moves differently at altitude because you are in a weaker gravitational field. The time dilation effect would be noticeable after 1 (or at most a few) ticks of the clocks.
- mitthrowaway2 1y agoI'm very skeptical of this claim. While the physical effect of time dilation acts immediately, I expect it would take many many ticks of both clocks before the rate difference between them became resolvable.
- Plutoberth 1y agoI don't understand. Wouldn't it only be possible to find out by comparing two identical clocks that were at different altitudes for some larger number of ticks, allowing you to then compare the elapsed ticks? How would you conduct such an experiment? My mental model is that I have a black box that outputs an electrical signal every tick, and then maybe we could just figure out which clock ticked first with a simple circuit. But that seems like we would need to sync them, and that it's fundamentally wrong due to the fact that the information of the tick is also subject to the speed of light. I don't know much beyond high school physics, fwiw.
- rcxdude 1y agoMy comment here might give some intuition for it: https://news.ycombinator.com/item?id=44576004 https://news.ycombinator.com/item?id=44576004 . You do need to measure for some time, because the measurement of the clocks with respect to each other is noisy, but you don't need to wait for there to be a whole 'tick' of extra time between them.
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- GolDDranks 1y agoAccording to ChatGPT, the speedup factor for getting 10 cm higher is 1 + 1.09e−17. (With ΔT = gh /(c^2) The math seems to check out, but not sure if the formula itself is correct.) Surely, if the clock ticks at rate 1e-19 in a second, i.e. one tick is hundred times smaller than the dilation difference in a second, the clock would still need at least a hundreth of a second to accumulate enough ticks for the count of ticks to differ even by one tick because of the dilation.
- GolDDranks 1y agoTo make this even clearer: Let's imagine that there is a huge amount of time dilation (we live on the surface of a neuron star or something). By climbing a bit, we experience 1.1 seconds instead of 1.0 seconds experienced by someone who left down. We have a clock that can measure milliseconds as the smallest tick. But climbing up, back down, and comparing the amount of ticks won't let us conclude anything after a single millisecond. If anything, we must spend at least 11 milliseconds up to have a noticeable 11 to 10 millisecond difference. Now, if the dilation was 1.01 seconds vs 1.00, we would need to spend at least 101 milliseconds up, to get a minimal comparison between 101 and 100 milliseconds.
- josephcsible 1y ago> Let's imagine that there is a huge amount of time dilation (we live on the surface of a neuron star or something). That idea is the premise of https://en.wikipedia.org/wiki/Incandescence_(novel) https://en.wikipedia.org/wiki/Incandescence_(novel)
- rcxdude 1y agoThinking in terms of 'ticks' over-discretises it. You can in practice measure frequency to much more precision than any discrete cycle time in the system you're using, because you can usually measure phase, i.e. you're not just seeing some on-off flash, you're seeing a gradual pulse or wave, and it's how accurately you can measure that pulse (in terms of SNR) which sets your integration time for a given precision, not how rapidly you're measuring it.
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- CamperBob2 1y agoYes, and no. The time-dilation effect will happen instantly, but the more quickly you want to observe it, the better your measurement's S/N ratio will have to be... and that, in turn, requires narrow measurement bandwidths that imply longer observation times. So then the question has to be asked, does the effect really happen instantly? Or do the same mechanisms that impose an inverse relationship between bandwidth and SNR mean that, in fact, it doesn't happen instantly at all?
- myrmidon 1y agoTime dilation from general relativity is approximately gh/c^2 (1e-18 -ish), which is an order of magnitude bigger than the uncertainty on your clock frequency (1e-19 -ish). But you would need a more precise characterization of the clock to answer this. There might be significant noise on individual measurements, meaning that you need to take multiples to get precise enough (see https://en.wikipedia.org/wiki/Allan_variance https://en.wikipedia.org/wiki/Allan_variance). Edit: If you just have clock output in ticks, you also need enought time to elapse to get a deviation of at least one tick between both bot clocks you are comparing. This is a big limitation, because at a clock rate of 1GHz you are still waiting for like 30 years (!!). (In practice you could probably cheat a bit to get around this limit)
- rcxdude 1y ago>Edit: If you just have clock output in ticks, you also need enought time to elapse to get a deviation of at least one tick between both bot clocks you are comparing. This is a big limitation, because at a clock rate of 1GHz you are still waiting for like 30 years (!!). (In practice you could probably cheat a bit to get around this limit) In practice with this level of precision you are usually measuring the relative phase of the two clocks, which allows substantially greater resolution than just looking at whole cycles, which is 'cheating' to some degree, I guess. (The limit is usually how noisy your phase measurement is) (To give some intuition, imaging comparing two pendulum clocks. I think you can probably see how if you take a series of pictures of the pendulums next to each other you could gauge whether one of them is running fast relative to the other, and by how much, without one completing one full swing more than the other)
- fsh 1y agoThese are optical clocks, so their rates are in the hundreds of THz to PHz range (1.121 PHz in the case of the Al+ clock). A 1e-18 shift corresponds to a ~mHz frequency deviation which a decent frequency counter can resolve in around 1s. However, no optical clock is actually that stable at short time scales, and the averaging is required to get rid of these fluctuations.
- MengerSponge 1y agohttps://en.wikipedia.org/wiki/Allan_variance https://en.wikipedia.org/wiki/Allan_variance It takes a longer measurement to be more confident.
- perihelions 1y agoIn a 2010 experiment based on an older version of this clock[0], NIST succeeding in measuring the gravitational time dilation across a 33 cm vertical separation—a frequency difference of 4.1×10^{-17}—with 140,000 seconds of integration time (<2 days). I don't really understand how that worked. [0] https://sci-hub.se/https://doi.org/10.1126/science.1192720 https://sci-hub.se/https://doi.org/10.1126/science.1192720 ("Optical Clocks and Relativity" (2010))
- dlcarrier 1y agoFrom the article: This improves the clock’s stability, reducing the time required to measure down to the 19th decimal place from three weeks to a day and a half. So no, not instantly.
- ortusdux 1y agoThis is compared to the ~1 mile vertical shift resolution of cesium clocks. The fun part of cesium clocks is that you throw three in the back of a minivan and take them camping! http://leapsecond.com/great2005/ http://leapsecond.com/great2005/
- jahnu 1y agoCould we realistically get so accurate that we can measure time changes due to (human scale) mass movements near a clock?
- accrual 1y agoThat would be an amazing proximity sensor. "Looks like time slowed down again, there must be someone close by."
- gooseus 1y agoI'm curious if any sci-fi authors were knowledgable and prescient enough to write this into their world building? If not, it'd make for a pretty cool plot device if done well.
- globalise83 1y agoSubmarine detection would be interesting with a few such precise clocks.
- Avamander 1y ago> It's an amazing time to be alive. While not this precise, you can have atomic cesium beam clocks of your own for a few thousand dollars each, and some elbow grease. How hard or expensive would it be for a reasonably equipped lab to build their own optical clock though? I see there are optical clocks the size of few rack units on the market for a rather hefty price, are the materials needed that expensive or is it just the expertise?
- wbl 1y agoExpertise
- CamperBob2 1y agoWhat keeps your average home experimenter from building an optical clock is the fact that femtosecond combs are still way too expensive and exotic. Some progress has been made -- you can get them from ThorLabs, for instance ( https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=11422 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=11... ) -- but they are still in the "Call for pricing and lead time" category. Once optical comb sources are commoditized to the extent that solid-state lasers are now, a lot of fun stuff will become possible.
- pumphaus 1y agoHeh, I would not ever have expected to see my company mentioned on HN. I'm the software tech lead at Menlo Systems, we're building those frequency combs that Thorlabs sells. Re the commoditization: Part of the problem is that customers, especially the scientific ones, don't want "commodity" frequency combs. Nearly every comb we sell is tailored to the specific customer in one way or another. Industrial customers start to be interested in frequency combs more and more. I guess this will be the clientele that values off-the-shelf products more, eventually paving the way for commoditization.
- nativeit 1y agoThe presence of individuals such as yourself is what makes the HN comments such a frequently meaningful place to find insightful discussions. Thanks for the context!!
- FredPret 1y agoThis is a great way to compare ultra-precise clocks! Also, I'm looking forward to Einsteinian altimeters everywhere.
- jl6 1y agoI fear this altimeter idea may be scuppered by local variations in the Earth’s density (it’s not an exactly uniform sphere of rock). Or maybe that just means the clocks could be great density-mappers!
- bravoetch 1y agoAre you saying they would be relatively inaccurate?
- ianburrell 1y agoIt is easier to measure density with gravimeter than measure gravitational force directly. Satellite, ACES, was launched recently that uses atomic clocks to accurately measure Earth's gravity field.
- FredPret 1y agoI had the same thought, but I still want one! On second thought, you need a base station on the ground to tell you its time for comparison anyway, so if that base station is nearby the density thing should mostly work itself out
- naikrovek 1y agoIsn’t the second defined as a specific number of cesium transitions? How can anything … you know what? Never mind. No matter what answer anyone provides, I won’t understand.
- nhecker 1y agoI don't think this changes the way the second is defined. Rather, that definition describes some theoretical ideal where the cesium transitions are all perfectly equally spaced over the course of the second. I think this new clock is simply able to generate more precisely spaced ticks than those of a traditional Cs clock. Less jitter and variation in the timing of those ticks. Similar to how a one-hour water clock or sand timer's runtime will vary between "transitions", but a one-hour quartz stopwatch timer is much more regular. I could keep going, but I'm already out on a limb so I'll stop before my own uncertainty rises too much. (Edit: I read the article. I don't think my words above are correct.)
- maxnoe 1y agoThe idea here is to have a clock that actually ticks faster and to redefine the second in terms of that new, faster ticking speed.
- shric 1y ago> Isn’t the second defined as a specific number of cesium transitions? Yes > How can anything … So your cesium counting device will fauthfully provide such a count and depending on their altitude it will be at different rates. Both clocks are each experiencing time at the usual one second per second but gravity dilates spacetime. Locally, a second is always a second, but from everywhere there is no such asbsolute, just as there is no universal "now".
- bilsbie 1y agoCould you detect gravity waves with accurate enough clocks?
- dtgriscom 1y agoThey would have to be extremely low-frequency. Plus, you'd need something to compare them to that wasn't affected by the wave, which is hard. (You'd need as accurate a clock, placed at a distance greater than the gravitational wavelength.) I think.
- tombert 1y agoI have had to talk myself out of the buying one of those atomic clocks on a chip. I'm kind of a watch geek, and I find the entire history of timekeeping to be endlessly fascinating, and I think it would be so cool to have atomic clock level of precision just running in my house. I've just never been able to justify actually buying one; outside of looking at a console and saying "how cool it that!?!", I don't know what I'd do with it. I'm not above buying a toy to look at logs and geek out over it, but I can't justifying spending several grand for it.
- reader9274 1y agoI was in the same boat some time ago, ended up settling for a Casio radio controlled "atomic" clock for multiple orders of magnitude cheaper
- tombert 1y agoYeah I have one of those, and of course my smartwatch syncs with my phone and gets very accurate time from the towers (which in turn probably gets very accurate time from NIST or something). They are very cool and realistically more than accurate enough for anything I am likely to ever need. Just something very cool about the idea of a hyper-accurate clock living in my house. I don’t know what I would do with it, just that it would be neat. If I ever become a billionaire or something, I will absolutely buy one. Sadly I don’t think that’s likely to happen any time soon.
- coldspoon95 1y agoWondering if we could spatially place a bunch of these to make a time based gravitational wave detectors. A single location could infer magnitude, and direction of a gravitational wave. I propose calling it TIGO(Time Interferometer Gravitational-Wave Observatory) ;-)
- pdmccormick 1y agoI wonder how many more orders of magnitude of precision will be realistically possible. I wonder if we'd ever be able to use gravity to "see" things at non-cosmological scales, like if you could resolve the gravitational waves and interference patterns caused by a person walking by.