12 ms·
A clock that can detect tiny shifts in the flow of time itself
- FlailFast 12y agoArmchair astrophysicist here: any way that these clocks could be used to detect evidence of gravitational waves? Seems like it would be a good use case for increasingly sensitive clocks.
- jessaustin 12y ago"At this level, maintaining absolute time scale on earth is in fact turning into nightmare," Ye says. This clock they've built doesn't just look chaotic. It is turning our sense of time into chaos. This seems a bit sensationalist. The new clocks will be more accurate than any we have now, for existing applications. Those who develop new applications that actually use the increased precision will just need to be more careful about which frames of reference they use. Those who built GPS already solved some version of these problems.
- sp332 12y agoIf you can't synchronize the clock with any other clock in the world, timekeeping gets a bit meaningless.
- droopybuns 12y agoIf we designed houses around planck lengths as the unit of measurement, we'd get nothing done. It's not that timekeeping gets meaningless- it just means that there is a threshold where the variability of unsynchronized clocks disrupts certain highly precise problems.
- treve 12y agoI was looking for someone to make a comment like this. I also felt that it simply meant that the last few digits were less meaningful for applications such as sync, but it definitely doesn't mean that that's the case for all the digits.
- GauntletWizard 12y agoBut you can predict and account for relativity; We already have good protocols for dealing with expected drift. NTP already takes into account that your PC is not keeping time as accurately as the upstream servers, and keeps a driftfile that guesses at the time differential needed. The NTP daemon silently adjusts the time every second to deal with this. If two clocks are at different heights, they can compute the differential in their rates and agree on a time unit. Sure, it might be 1 quadrillion ticks in on one clock and 1 quadrillion and 1 ticks on the other, but it's still a 'second' so long as both sides see it as simultaneous.
- sp332 12y agoThat doesn't help if one clock is drifting because it's being moved by tectonic activity, or being vibrated slightly by gravitational waves.
- jessaustin 12y agoIf you have a protocol and enough fancy clocks, you don't have to know what's causing the perturbations or how big they are. At some level, there isn't actually a "real" time at all (partially, for the reasons you state). Rather, there is a time that we can agree upon. If some precise operation requires better time coordination than we can obtain via a particular configuration of these fancy new clocks, then we just need a different configuration, probably with more of them.
- amosgewirtz 12y agoA "world in which your watch starts to tick faster, because you're working on the floor above me." and "your 3:30 happens earlier than mine, and we miss our appointment," seems ridiculous but it's not a totally foreign idea. For example, if your apartment is above the 150th floor of Burj Khalifa (the tallest building on earth), you must wait an additional 3 minutes to break the fast during the month of Ramadan, while if you live between the 80th floor and the 150th floor you only need to wait an additional 2 minutes. This mismatch in time happens for a different reason, but the result is the same and people seem to manage alright. Saying that this new clock might "End Time As We Know It" is pretty sensationalist.
- EGreg 12y agoActually software developers have long been aware that different clocks can run at different speeds and tryto compare apples to apples. Does anyone remember the name of that article that describes various clock synchronization techniques? I think it went something like "more than you ever wanted to know about computer time" and was based on an earlier similar title about another subject.
- deleted 12y ago[deleted]
- furyofantares 12y agoPerhaps "what every programmer should know about time" and "what every programmer should know about memory" ?
- EGreg 12y agoYep! THANK YOU
- guelo 12y agoThe Ramadan fast ends at sunset. The sunset ends later for people at higher elevation because you can see over the horizon a little bit more. Not because of the time dilation of gravity.
- taylorbuley 12y agoThe bit about why humanity collectively seeks to measure time so accurately -- perhaps, because, in fact we don't really understand it at all -- is an interesting and salient morsel for us technologists to chew on. What do we do when we don't understand something? Measure it!
- gokhan 12y agoA comment of the article by Joey N correctly notes that: Right now, on the top of Mount Everest, time is passing just a little bit faster than it is in Death Valley. That's because speed at which time passes depends on the strength of gravity. Einstein himself discovered this dependence as part of his theory of relativity, and it is a very real effect. "Just to be clear, the clock in Death Valley appears to run slowly from the point of view of the eagle-eyed observer standing on top of Everest. To a person in Death Valley, the clock appears to tick at precisely the rate it would appear to tick if both person and clock were on top of Everest."
- EGreg 12y agoI always wondered what happens to quantum entanglement when time dilation is involved. For example if one of the particles falls into a black hole, can we get info out?
- pavel_lishin 12y agoAs I understand it, you can't actually use this to transmit information. If you entangle two particles, and then send one away, and attempt to measure the appropriate property (I think it's spin), hurray: you know that the other particle's spin is the opposite. But that's not communication. It's like slicing a coin down the middle without looking at it, hiding each half in a box, and giving one of the boxes to someone going to the moon. A week later, you both open your box, and you know exactly which side of the coin the other person has - but that's not communication. (Someone smarter than me, please correct whatever mistakes I've made, and explain this in a better way.)
- beachwood23 12y agoWouldn't changing the spin be the way to communicate? Is spin not a changeable property?
- Igglyboo 12y agoNope, the spin isn't changeable and you cannot communicate via entaglement. If the spin was changeable however we'd have a long distance bit (0 or 1).
- darkhorn 12y agoDegauss a quarts watch and time will seed up!
- darkhorn 12y agoEdit: I mean clock! Not real time.
- pbz 12y agoI thought the reason time flows differently on top of Mount Everest is because the top of the mountain travels faster through space-time than the base (because of the rotation of the earth), not because of gravity...
- deleted 12y ago[deleted]
- DennisP 12y agoIt's gravity. The mountaintop doesn't travel faster through space-time. There's no such thing as absolute speed, there's only the velocity compared to something else. Special relativity covers time dilation due to relative velocity, general relativity covers time dilation due to gravity.
- haberman 12y agoEven in relative terms, the top of Mt. Everest is traveling faster than objects at sea level, no? Wikipedia says: "Time dilation is caused by differences in either gravity or relative velocity. Both factors are at play in the case of ISS astronauts (and are actually opposing one another)." Why wouldn't the same apply to the top of Mt Everest. Sure, unlike the ISS, Everest is actually attached to the Earth, but still it is traveling a longer distance than the oceans over the same period, and therefore would be moving faster in relative terms AFAICS.
- tedunangst 12y agoIs the top of Mt. Everest traveling faster? The distance between here and there is a constant, no? From my frame of reference it's not moving at all.
- haberman 12y agoMt. Everest is higher. Because of the Earth's rotation, every point on earth traces 360 degrees every day. However the radius of these arcs depends on elevation. Ergo the top of Mt. Everest travels farther every day due to rotation that any other place on earth. That is the same as saying it is moving faster. EDIT: I guess compared to a rotating reference frame this isn't true? Clearly this isn't my area of expertise.
- DanielBMarkham 12y agoSeems to me they haven't built a clock: they've built a tricorder. Put an array of these in a box. Then computationally map the changes in gravity from each clock. Bingo presto, you've just created a 3-D model of the mass in the local area.
- pavel_lishin 12y agohttp://en.wikipedia.org/wiki/Robert_L._Forward#Forward_Mass_Detector http://en.wikipedia.org/wiki/Robert_L._Forward#Forward_Mass_...
- trhway 12y agoit would take some time to develop "gravitationally stealth" F-22 :)
- pavel_lishin 12y agoCan't wait to invade a country to secure America's source of cavorite.
- jofer 12y agoFor what it's worth, just directly measuring changes in gravitational acceleration is much easier and much more sensitive to changes in mass distribution. We've been able to measure gravitational acceleration very precisely for over a century now. An 80-year-old LaCoste & Romberg gravimeter will do the job quite nicely, though it's slow to use and you need to know the elevation you're taking the measurement at very precisely. (Interestingly, the ones made before ~1950 are more precise than the ones made in the 60's to 90's. It's basically a very well made and well calibrated spring. When they switched to mass-producing them, the quality fell.) Now you have a second problem, though... Regardless of whether you've measured things through gravitation acceleration or time dilation, going from the measured effect back to an actual mass distribution is a non-unique inverse problem. There are an infinite number of equally correct solutions (and a larger infinite number of incorrect ones). You can make a pretty good guess at what the mass distribution by applying reasonable a-priori constraints, but there's no single unique way to get the mass distribution from the gravitational effect of the mass.
- haberman 12y agoIt amazes me that our master clocks can be so accurate and yet our devices, which ostensibly get their time from the master clocks through networks, can be so off. My Android phone is very frequently 30 seconds or more off from my friends' iOS phones. I don't even...
- brianpan 12y agoWell, it's off by 30 seconds now. But eventually....
- haberman 12y ago"My own personal opinion is that time is a human construct" What is this supposed to mean? We can measure time with non-human instruments and time is at the core of physics. How can it be a human construct? Sure, hours, minutes, days, etc. are human constructs based on movements of the earth, but time itself?
- beachwood23 12y agoI think his point is that time is so inherently relative to the location / inertia of the observer that it is in practice a human construct.
- physonaught 12y agoThe physicists definition of time is "What clocks measure". It sounds like he was just saying the party line.
- kbart 12y agoTime only defines the state of the extremely complex system known as universe. It's an idea to make things more simple for us humans, not a physics phenomena. Stop all the particles and waves in the universe and time has no meaning. At least that's how I understand what he meant by this.
- VLM 12y agoIf you enjoy the article, you'd enjoy these guys: http://www.leapsecond.com/time-nuts.htm http://www.leapsecond.com/time-nuts.htm I hang out more with the volt nuts. (how bout that LTZ1000A voltage ref, eh? got three in my basement, because two aren't very useful LOL). I do not remember who begat who but there is probably commentary in the archives of both, if you go back far enough.
- pit 12y ago> "But it can tick for billions of years without loosing a second." Is it loosing or losing? Are both correct?
- leoc 12y agoMaybe time really is running out. ;)
- pit 12y agoIt's not running out, it's unwinding.
- egamble 12y agoIt's losing. For some reason, I see the "loosing" misspelling more often now than a few years ago. It seems to be a sort of orthographical meme that's spreading.
- 205guy 12y agoMy brain always stumbles on the loose-lose pair. I don't usually substitute them for each other, but I always have to think about which one to write. I believe it is because of the odd spelling and pronunciation of the pair. The extra o does not change the vowel sound, instead it changes the sound made by the s (and neither sound like "close"). Typically, the hard and soft s sound depends on the one or two s's [1]: desert and dessert. Or it could just be the auto-correct (now in desktop apps as well, not just mobile). [1] I hate 's for plurals, but how else would you write "esses".
- Retr0spectrum 12y ago'But this new clock is so sensitive, little changes in height throw it way off. Lift it just a couple of centimeters, Ye says, "and you will start to see that difference." ' How do they do these differences? Surely they would need a second, equally accurate clock to compare it with?
- sp332 12y agoIf it's repeatable, you can just raise and lower the clock a few times and see the difference. If the clock didn't keep good time, you'd just get a bunch of noise. But if it's good enough, you should see similar drift each time.
- Animats 12y agoBoth special and general relativity effects are well known to affect clocks. This is a major headache for GPS satellites, which have atomic clocks that gain about 38 microseconds a day vs earth-based clocks from the combination of speed and gravity difference. 38us/day slip is huge. That's 6 miles of GPS positional error. So GPS was designed with an correction and adjustment scheme to deal with this. So it's been a practical problem for decades.
- ithkuil 12y agoAs far as I know there is no headache, and although the theory is non intuitive, it just works as expected. The physics behind it can get complicated at the fundamental level, but computing a time dilation for an orbit is hardly rocket science. You don't even have to compute it, you can actually measure it right? Do you know about any specific painful effect that was revealed only after general relativity was tried to be applied to GPS satellites in particular?
- dendory 12y agoI'm glad to hear an actual scientist in this field also think what I've thought for a long time, which is that time is a human invention. I can't really explain it, but I've always felt like the universe doesn't really have a concept of time, that everything is just right now, hence why I don't believe in time travel either. Time is just a way for us to say 'something was' or 'will be', but in reality what was isn't anymore, it's not that it's in the past, but that the object was changed into what it now is.
- fastaguy88 12y agoThis may make sense to a physical scientist, but biological phenomena do have a concept of time, because many biological molecules have an evolutionary history. It's not only that something was, but also that something is that embodies the trace of what was.
- jhallenworld 12y agoAtomic clocks are cool.. if one wanted to transmit a sporting event in the era before time base correctors, one had to bring a video sync generator timed by an atomic clock from the TV station to the event. This gets you the same frame rate as the TV station (phase still needs to be adjusted to account for speed of light delay). With all the signals in sync you can switch to a commercial without messing up everyone's TV. Time base correctors are also cool: the first generation ones were rack sized and used core-memory. I think they were an enabling technology for on-location news. You can buy your own: rubidium standards sell for less than $300 on ebay.
- nullc 12y agoCrappy article. Sure, the more precise your oscillator is the more you need to worry about other effects. Basic cesium beam clocks are precise enough the altitude based corrections for relativity are required to achieve full accuracy. Each km of altitude is about 10ns/day of slew, ... I can measure this myself with equipment I have at home (I have an unusual home). So sure, when you start making optical clocks with accuracy in the 1e-18 land then external effects may well be much harder to correct for, e.g. tides have an effect at the 1e-17 level ... but such a device could still keep time better than prior techniques. The "They just may not be able to tell us the time" is rubbish hyperbole that just serves to confuse readers who don't already know the subject well.
- wuliwong 12y agoThe comment where the man makes a comparison to measuring electric current but tries to make it seem like we understand time better than electric current annoyed me. As if we have a greater fundamental understanding of what an electric charge "is" vs. time.
- jacquesm 12y agoI love this page on that subject: http://amasci.com/elect/charge1.html http://amasci.com/elect/charge1.html It's not exactly 100% current (pun intended) but it makes the point nicely.
- healsjnr1 12y agoThis is the worst kind of comment and what is wrong with Hacker News. No one cares about your intellectual superiority, or the fact this might be a special interest for you. This article wasn't written for you, you already know and understand its content. There is literally nothing you could have got from it. I on the other hand enjoyed the article. This isn't a field I'm familiar, so in general my knowledge was increased. That some concepts are misrepresented and dumbed down is obvious, but this is far out weighed by the general knowledge that was imparted. Writing is all about picking an audience and conveying it effectively to the audience. It's fine to point out inaccuracy or build on the finer points, but don't be aggressive about it and don't insult the article because it offended your superior intellect.
- kazinator 12y agoTime as "we" know it can only be coming to an end if by "we" mean those who are completely ignorant of early 20th century discoveries in physics, and who haven't even been exposed to enough science fiction (let alone nonfiction) to know about phenomena like the twin paradox. But for time as they know it to be coming to an end, there has to be some expectation that they will suddenly be enlightened. The existence of this new clock will certainly not the catalyst of that enlightenment. We have already had clocks for decades whose perturbation by relativistic effects matters. Every GPS receiver (commonly found in now inexpensive technology in use by millions of consumers) makes relativistic corrections to the time base received from satellite signals, without which the positioning would be hopelessly inaccurate. Why would this clock "end time as we know it", when millions of users of GPS navigation still have a naive view of time.
- mikeash 12y agoA nitpick that doesn't detract from your main point: the relativistic corrections for GPS are applied on the satellites with a slight change in how fast their clocks run, so that they appear to run at the correct rate when seen from the ground. The receivers don't have to know about it.
- iandanforth 12y agoI'm a little sad this article doesn't make the connection to acceleration. The idea that sitting at different points of a gravity well is exactly equivalent to different points along an acceleration curve (from the perspective of time) is a delightful one and I wish it had been mentioned.
- polemic 12y agoAll that this means is it's high time we abandoned our datetime's in favour of spacetime's. from spacetime import spacetime, spacetimedelta then_and_there = spacetime.here_and_now() + spacetimedelta(years=1, x=5, y=3, z=-2) Now all we need a detailed time-dependant gravity model of the universe to account for relativistic effects, and some what to throw in quantum scale stuff and we've solved.... everything. (edit: formatting is hard)
- wuliwong 12y agoIf one part of this clock is accurate to 10^-16 but noise/error contributed by some other aspect of it is larger than that, then it is misleading to claim these clocks have an accuracy of 10^-16. This is the same type of stuff they are dealing with in the gravitational wave experiments like LIGO and VIRGO. They have amazing sensitivity but it is still lost in the noise. They don't claim to be able to make measurements to accuracy which is lower than the noise levels. And I don't see why these clock people should either.
- aqme28 12y agoI may be wrong but this sounds like a confusion of accuracy vs. precision (http://en.wikipedia.org/wiki/Accuracy_and_precision http://en.wikipedia.org/wiki/Accuracy_and_precision) edit: By which I mean that this clock could be precise to 10^-16 but be off by 10^-14 due to a mis-calibration.
- danbruc 12y agoCould we (easily) build a clock that accurately measures space time intervals? If you place two of them next to each other and synchronize them, you should be able to separate them and they should still be synchronized whenever you bring them back together no matter what happened in between.
- imaginenore 12y ago> It's one of the most accurate clocks on the planet: an atomic clock that uses oscillations in the element cesium to count out 0.0000000000000001 second at a time For comparison, Planck time = 5.39106×10^-44 sec We're pretty far from measuring time precisely.
- snarfy 12y ago> Time itself is flowing more quickly on the wall than on the floor Velocity is a function of distance and time. How can time have a velocity? Couldn't you also say the distances in the clock stretched or shrunk by the lorentz factor?
- adventured 12y agoI don't understand what's so confusing about time. "but what time really is, is a question that I can't answer for you." O'Brian almost correctly answers that right off the bat: "My own personal opinion is that time is a human construct" Time is a measurement, nothing more. It's not magic, it's not difficult to understand, it's not separate from reality. It'd be like calculating how long it takes you to walk around your coffee table, and then being confused by what it means or what that measurement consists of.
- callesgg 12y agohttp://en.m.wikipedia.org/wiki/International_Atomic_Time http://en.m.wikipedia.org/wiki/International_Atomic_Time The time we use it based on an average of many clocks. The fact that time passes at different rates at different locations is already account for.
- stevewilhelm 12y ago> This new clock can keep perfect time for 5 billion years. In theory. In practice, I'll bet it stops keeping time before I do. Check out the Long Now's 10,000 year clock project. http://longnow.org/clock/ http://longnow.org/clock/
- ck2 12y agoA network of clocks in space might be used to detect gravitational waves from black holes and exploding stars. We need to fund this!
- whattime 12y agoHey I've been pondering this article for a little while now and my friends and I have come up with a question. Say we have two people, Bob and Jane. Bob and Jane blink at similar rates when they are standing next to one another. Both Bob and Jane have the accurate watches described in this article. Bob then takes a trip to space traveling near the speed of light. Right when he takes off a laser initiates both stopwatches (one on bob's wrist and one on jane's). At some time (...), from an equidistant point to both Bob and Jane a light originates and then stops both Bob's and Jane's wrist watches. Btw, both Bob and Jane have been blinking the whole time their watches have been running. The questions: Upon stopping the watches: 1. Do Bob and Jane see a different amount of time passed on their stopwatches? (most of us are not in contention about this one) 2. Have Bob and Jane blinked the same number of times?
- whattime 12y agoHey I've been pondering this article for a little while now and my friends and I have come up with a question. Say we have two people, Bob and Jane. Bob and Jane blink at similar rates when they are standing next to one another. Both Bob and Jane have the accurate watches described in this article. Bob then takes a trip to space traveling near the speed of light. Right when he takes off a laser initiates both stopwatches (one on bob's wrist and one on jane's). At some time (...), from an equidistant point to both Bob and Jane a light originates and then stops both Bob's and Jane's wrist watches. Btw, both Bob and Jane have been blinking the whole time their watches have been running. The questions: Upon stopping the watches: 1. Do Bob and Jane see a different amount of time passed on their stopwatches? (most of us are not in contention about this one) 2. Have Bob and Jane blinked the same number of times?