10 ms·
UTC might be redefined without Leap Seconds
- lisper 11y agoAt root, this is all just a quibble over terminology. The fundamental problem is that there are two reasonable time standards for different applications: mean solar seconds for ordinary day-to-day timekeeping, and cesium seconds for applications that require a precision of more than a second per year. These two standards drift, so you have two choices: 1. Let them drift 2. Introduce a computational complication (leap seconds) to synchronize them But the dispute is not over which of these is "right", the dispute is over which of these two options gets to go by the label "UTC". This could be easily resolved by simply defining two UTCs, one with leap seconds, and the other without. You could call them UTC-L and UTC-N (or UTC-S and UTC-N if you wanted to mollify the French ;-).
- Zikes 11y agoI should imagine it would be easier to use the cesium seconds for UTC and just bundle everything else into the time zone offsets, which everyone is already using to turn scientific timekeeping into something "meaningful" for human consumption.
- SEMW 11y ago"Like UTC but without adding leap seconds" already exists; it's called TAI (http://en.wikipedia.org/wiki/International_Atomic_Time http://en.wikipedia.org/wiki/International_Atomic_Time)
- lisper 11y agoThen what is really at issue here? Is it really a dispute about whether WWV broadcasts (what is currently known as) UTC or TAI?
- gpvos 11y agoBasically, yes. (Not only WWV, but also DCF77 et al., of course.) Several countries have enshrined UTC in law, so it's a pretty big thing.
- gpvos 11y ago...and just to add that this enshrining in law was most likely done with the general expectation that UTC would keep a close relationship with solar time.
- imh 11y agoWe already have these. UTC keeps the the time lined up with an earth day, while GPS and TAI are absolute times.
- brownbat 11y agoThe rotation of the Earth is a terrible timekeeper. We used to have 6 hour days. Now it wobbles. Major earthquakes throw it off. On the other hand, ignoring this leads to weird results. In Rome, the priests used to control the Calendar, and they had to decide how many leap days to put into the cycle. Senators served through the end of the year, and they had influence over the priests. By the time Julius Caesar implemented a new calendar, this sort of political drift in the calendar had January in the middle of summer. I guess people don't like mid-summer January because it makes historical comparisons more difficult. Not impossible, just awkward. It's a horrible messy dilemma. Leap seconds don't seem as dramatic as the Roman intercalary days, but there's the same battle between synchronicity and simplicity (where simplicity = something short of insane perturbations). Maybe none of this matters for radio broadcast time signals. Maybe you just want a fixed counter everyone's synchronizing to, and people should convert to the Earth's messy system at the last possible moment. Fun story about the awesome 13 month Calendar that we could have adopted (except for Hitler): http://99percentinvisible.org/episode/the-calendar/ http://99percentinvisible.org/episode/the-calendar/ http://www.livescience.com/38083-earth-core-day-length-pattern.html http://www.livescience.com/38083-earth-core-day-length-patte... http://www.scientificamerican.com/article/earth-rotation-summer-solstice/ http://www.scientificamerican.com/article/earth-rotation-sum... http://news.nationalgeographic.com/news/2011/03/110316-japan-earthquake-shortened-days-earth-axis-spin-nasa-science/ http://news.nationalgeographic.com/news/2011/03/110316-japan... https://www.uwgb.edu/dutchs/PLATETEC/RotationQk2004.HTM https://www.uwgb.edu/dutchs/PLATETEC/RotationQk2004.HTM https://en.wikipedia.org/wiki/Julian_calendar#Motivation https://en.wikipedia.org/wiki/Julian_calendar#Motivation
- alienasa 11y agoThat Wikipedia article on the Julian calendar is both fascinating and a great example of Wikipedia at its best in terms of attention to detail.
- matt_kantor 11y agoKeep in mind that leap days serve a different purpose than leap seconds. Leap days exist because the number of rotations of the earth per one revolution around the sun is not a whole number. Leap seconds exist because the duration of one rotation is not constant.
- gpvos 11y agoI see that the solution the author proposes on the "right+gps" subpage is basically the same as what Dan Bernstein has proposed for many years now, except using GPS time rather than TAI (which only differs in the seconds offset). Sounds like the sanest approach to me.
- sla29970 11y agoDan Bernstein proposed it and Bradley White wrote the code in the time zone package used by Unix-like systems. The point of "right+gps" is that all of the pieces needed to implement such a scheme are already deployed and tested and with appropriate caveats anyone can decide to use that to avoid leap second issues.
- kozak 11y agoWhy don't they just use TAI time in places where leap seconds are not practical?
- regularfry 11y agoBecause that's everywhere. Whether everywhere should "just use TAI" is exactly the question (only they're not talking about TAI as far as I can see, but a new standard which would I think map 1:1 to it).
- sp332 11y agoRight, so why make a new standard that looks just like this old one?
- vilhelm_s 11y agoTAI currently differs from UTC by 35 seconds, so if you literally switched to it, every clock in the world would jump 35 seconds. If leap seconds are abolished, UTC and TAI will remain 35 seconds apart forever.
- kozak 11y agoAnd then that time will be neither UTC not TAI. Either we'll have to call it something different (like GPS time: always offset from TAI by certain number of seconds), or a different name will have to be made for what used to be called UTC (time tied to earth rotations, from which zoned wall time is to be delivered). Great. That's exactly what https://xkcd.com/927/ https://xkcd.com/927/ is about.
- vilhelm_s 11y agoI don't know if that's true. We already have a name for the time that is tied to Earth rotation, "UT1". Users who care about positions of astronomical objects can refer to that. UTC was always a bit of a compromise, which partly tracked UT1, but only up to the nearest second. On the other hand, I think the idea of abolishing leap seconds is to no longer derive wall time from earth rotation, and to derive it from atomic time instead. So "UTC" would still refer to "the source of wall time". As I understand it, this is the point of changing the derivation of UTC: there are lots of laws in different countries that say that wall clock time is tied to UTC, so if we want to switch from earth rotation to atomic time, it is easier to change the definition of UTC than to change the laws in all those countries.
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- IvyMike 11y agoWhenever I read about leap seconds, somewhere in my mind I wonder if wouldn't just be easier to blow up a bunch of "booster" nukes every few years. ;)
- pavel_lishin 11y agoWould that actually alter the spin of the Earth? I assumed that you'd be more likely to have more success by making a few passes past the planet with a sizable asteroid.
- chc 11y agoIvyMike's plan is silly, but it sounds a lot more feasible than this one.
- pavel_lishin 11y agoI don't know enough about any of this to judge which one is more feasible. Detonating nukes on the surface is "easy", but would it be effective? How much energy and money would it take to divert some asteroids? I haven't done the research, and almost certainly won't :P
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- jarin 11y agoIt would take a hell of a lot of nukes to create enough energy to alter Earth's spin in any significant way. http://www.livescience.com/32120-can-a-nuclear-blast-alter-earths-rotation.html http://www.livescience.com/32120-can-a-nuclear-blast-alter-e...
- Zancarius 11y agoConsidering your username, this suggestion somehow doesn't surprise me. ;) (I'm assuming that particular test served as your inspiration.)
- acqq 11y agoEven if UTC were redefined the number of the time-related bugs wouldn't decrease.
- politician 11y agoOT: Does anyone know what sort of calendar Martian rovers use? Is there a NASA calendar for solar system operations?
- termain 11y agoI can't speak for the rovers, but in my experience you start with the UTC time and the convert to a UT1 for space launches. We have to correct for the difference, which is called DUT1: https://en.wikipedia.org/wiki/DUT1 https://en.wikipedia.org/wiki/DUT1
- Hyperborian 11y agoIf I'm reading the linked projections correctly, even the worst predicitions put us at less then three minutes off from the earths rotation by the year 2100, and it will take somewhere in the area a thousand years to be off by an hour. I'll be frank: if we haven't progressed to the point that those offsets generally don't matter by those points in time, we've probably already failed as a species. I say we drop leap seconds.
- ajross 11y agoOffsets "generally don't matter" now, which is why this is an obscure bit of minutiae you're reading about on HN instead of NYT. But they matter to some applications, and those people have arguments trying to decide which to use. But yes: the ultimate solution if the world were to move to atomic/absolute clock synchronization instead of referencing the Earth's rotation is that every few hundred years we would need to adjust all the time zones by an hour to keep "noon" in the middle of the day. Given that we do this every decade or two anyway chasing DST vogues, I think this would be acceptable.
- Trombone12 11y agoIt is the heavens that set the time for humanity, all else must either imitate or pick another name. Abandoning the leap seconds means breaking the connection between utc and what the people consider time to mean. It is not so much that the actual times drift apart very fast, it is that the clock tries to corrupt the meaning of the word "day". If leap seconds cause problems for your application, you probably should find another source of synchronisation signal.
- yellowapple 11y agoYeah, another source like... seconds. Plenty of applications need to know a precise number of seconds (or milliseconds or nanoseconds) between the present and a past or future date/time. Leap seconds throw a wrench in that. Whether UTC should serve the role of an unaltered time source is indeed a matter of debate (and for good reason), but it's pretty clear that we do need an unaltered stream of seconds (upon which UTC - or an intermediate between UTC and various timezones should UTC fill this role as advocated - would base itself, as would any other applications that require said unaltered stream of seconds). This isn't even mentioning more far-fetched things like space travel (at which point the non-constant rotational parameters of an arbitrary planetary body are neither relevant nor appropriate for system-wide/galaxy-wide/universal/multiversal timekeeping).