4 ms·

Can anyone explain why leap seconds exist vs. a gradual skewing of atomic time to match the earth's rotation. Like say, "from date X to Y, civil time will be at

Can anyone explain why leap seconds exist vs. a gradual skewing of atomic time to match the earth's rotation. Like say, "from date X to Y, civil time will be atomic time slowed by Z parts-per-billion". It just seems like such a better solution than this discontinuity that occurs once every few years and _surely_ everyone would have prepared and tested for. Civil time just doesn't require the accuracy where it actually matters, and if it does matter to you, use a continuous timescale like TAI or compute the current skew offset using a simple formula. Really, I love leap seconds as geeky trivia, but they seem so impractical.

drzaiusapelord 12y ago
Whose algorithm do we use? How much time has deviated is arguable and ties in with things like rotation, earthquakes, inertia, tidal forces, etc. Would your proposal be yet another buggy and heavily patched update we need to worry about constantly being updated on the world's IT infrastructure? Incorporating a simple leap second via fiat seems to be a simple and sane solution. Then what of high accuracy computing? If my clock randomly adds or substracts 2ms a day, that could fuck up my calculations. Better to have things work in a classical sense and to just tack on or remove a second once in a while and be prepared for it in advance. 25 leap seconds have been added since 1972, according to wikipedia. Why make this harder than it needs to be? Atomic clocks are right and human calendering is arbitrary/wrong. Trying to merge the two automatically can only cause more problems as our arbitrary political and cultural nature could spill over into our scientific nature. See trying to legislate the value of pi in Indiana for an example. The current method works the other way. We push science into our calendering. We keep them nice and separate.
- mrgriscom 12y ago
  You would continue to use the IERS as the authority on what the true solar time is. They would continue to declare when leap seconds are, but instead of inserting them as a discontinuity, you would simply amortize them slowly over a long period. Like I said, if you demand high accuracy, use a timescale like TAI where seconds are really SI seconds. But very few people need that kind of accuracy. My computer clock probably already drifts more than 2ms a day. Anyone tracking time for civil purposes is just syncing from a more authoritative source anyway. My computer talks to upstream ntp servers. They could/should hide the fact that leap seconds exist from me entirely. Some of Google's ntp servers already do this.
acomjean 12y ago
Calculating the time delta between two events becomes very difficult when your standard unit (seconds) is shifting in size. >that occurs once every few years and _surely_ everyone would have prepared and tested for. yeah... like y2k, ipv6 and the US conversion to the metric system!
- mrgriscom 12y ago
  But don't we already have this problem? If, for example, I wanted to calculate exactly how many seconds old I am, I would probably do it the naive way, adding up the years, months, days, hours, etc. But to get the truly exact answer, I'd also have to look up how many leap seconds occurred during my life, making the calculation roughly just as complex. Or I could not bother and just report the result in "civil" seconds, which are slightly and variably longer than "atomic" seconds. If I cared enough about the difference, I probably would be using a true atomic timescale (without leap seconds) anyway.
  - klodolph 12y ago
    If you were born before 1972, it's impossible because that's when UTC became reality. And really, do you think you know the time of your birth to within, say, 35 seconds (which is the number of leap seconds you have to add)? Do you think the clock at the hospital was accurate to within 35 seconds?
    - mrgriscom 12y ago
      That was kind of my point -- that second-perfect accuracy over such long time spans is rarely needed or even possible.
lmm 12y ago
The second is the physical unit of time; if you tried to skew seconds to be longer or shorter you would break physics (physical constants would change in value, it would be impossible to compare current experiments with previous experiments...). Would it be smart for civil time to be based on another unit, decoupled from the physical second? Yes, but no-one thought of that earlier, in the same way that no-one bothers to use LVM on the first server they set up. This sort of thing wasn't thought of when governments were first setting up time laws back in 18xx, and many countries' laws included reasonable-sounding provisions like "The average difference between 12:00pm and solar noon shall be zero". There's a proposal to abolish leap seconds, but it's been pushed back to 2015 to give national governments more time to amend such laws. I suspect and hope that we'll get rid of them sooner or later, but changing one nation's laws is a slow process; changing 190-odd much more so.
- mrgriscom 12y ago
  That's why I made a distinction between civil time and atomic time. If you're doing stuff with enough precision that differences of parts-per-billion matter, then use SI seconds, which aren't changing. But civil time is for stuff like "what is the current time right now?", a question whose answer hardly ever needs more than 3-4 digits of precision. Getting rid of leap seconds entirely just seems lazy, kicking the can 600 years down the road with some nebulous "leap hour" concept. Especially so when there is already a timescale without leap seconds: TAI. I'm not surprised this proposal came from the US... "let the next generation deal with it" seems to be our solution to most problems.
MichaelGG 12y ago
Leap seconds should be replaced with a leap hour or day or something. Then we could just ignore this forever and hopefully people eons in the future will realise having time sync'd with the sun is ... rather useless.
- gpvos 12y ago
  Au contraire, it is why civil time exists: to be able to talk about when something happens during the day, and everyone will be confused if 9 AM is not somewhere near the beginning of the work day. Leap hours or days are a cop-out, it's just shifting the problem and making it worse.
klodolph 12y ago
What you are describing already exists, it is called UT1. However, most hardware does not support subtle changes in clock speed.

drzaiusapelord 12y ago

Whose algorithm do we use? How much time has deviated is arguable and ties in with things like rotation, earthquakes, inertia, tidal forces, etc. Would your proposal be yet another buggy and heavily patched update we need to worry about constantly being updated on the world's IT infrastructure? Incorporating a simple leap second via fiat seems to be a simple and sane solution. Then what of high accuracy computing? If my clock randomly adds or substracts 2ms a day, that could fuck up my calculations. Better to have things work in a classical sense and to just tack on or remove a second once in a while and be prepared for it in advance. 25 leap seconds have been added since 1972, according to wikipedia. Why make this harder than it needs to be? Atomic clocks are right and human calendering is arbitrary/wrong. Trying to merge the two automatically can only cause more problems as our arbitrary political and cultural nature could spill over into our scientific nature. See trying to legislate the value of pi in Indiana for an example. The current method works the other way. We push science into our calendering. We keep them nice and separate.

mrgriscom 12y ago
You would continue to use the IERS as the authority on what the true solar time is. They would continue to declare when leap seconds are, but instead of inserting them as a discontinuity, you would simply amortize them slowly over a long period. Like I said, if you demand high accuracy, use a timescale like TAI where seconds are really SI seconds. But very few people need that kind of accuracy. My computer clock probably already drifts more than 2ms a day. Anyone tracking time for civil purposes is just syncing from a more authoritative source anyway. My computer talks to upstream ntp servers. They could/should hide the fact that leap seconds exist from me entirely. Some of Google's ntp servers already do this.

acomjean 12y ago

Calculating the time delta between two events becomes very difficult when your standard unit (seconds) is shifting in size. >that occurs once every few years and _surely_ everyone would have prepared and tested for. yeah... like y2k, ipv6 and the US conversion to the metric system!

mrgriscom 12y ago
But don't we already have this problem? If, for example, I wanted to calculate exactly how many seconds old I am, I would probably do it the naive way, adding up the years, months, days, hours, etc. But to get the truly exact answer, I'd also have to look up how many leap seconds occurred during my life, making the calculation roughly just as complex. Or I could not bother and just report the result in "civil" seconds, which are slightly and variably longer than "atomic" seconds. If I cared enough about the difference, I probably would be using a true atomic timescale (without leap seconds) anyway.
- klodolph 12y ago
  If you were born before 1972, it's impossible because that's when UTC became reality. And really, do you think you know the time of your birth to within, say, 35 seconds (which is the number of leap seconds you have to add)? Do you think the clock at the hospital was accurate to within 35 seconds?
  - mrgriscom 12y ago
    That was kind of my point -- that second-perfect accuracy over such long time spans is rarely needed or even possible.

lmm 12y ago

The second is the physical unit of time; if you tried to skew seconds to be longer or shorter you would break physics (physical constants would change in value, it would be impossible to compare current experiments with previous experiments...). Would it be smart for civil time to be based on another unit, decoupled from the physical second? Yes, but no-one thought of that earlier, in the same way that no-one bothers to use LVM on the first server they set up. This sort of thing wasn't thought of when governments were first setting up time laws back in 18xx, and many countries' laws included reasonable-sounding provisions like "The average difference between 12:00pm and solar noon shall be zero". There's a proposal to abolish leap seconds, but it's been pushed back to 2015 to give national governments more time to amend such laws. I suspect and hope that we'll get rid of them sooner or later, but changing one nation's laws is a slow process; changing 190-odd much more so.

mrgriscom 12y ago
That's why I made a distinction between civil time and atomic time. If you're doing stuff with enough precision that differences of parts-per-billion matter, then use SI seconds, which aren't changing. But civil time is for stuff like "what is the current time right now?", a question whose answer hardly ever needs more than 3-4 digits of precision. Getting rid of leap seconds entirely just seems lazy, kicking the can 600 years down the road with some nebulous "leap hour" concept. Especially so when there is already a timescale without leap seconds: TAI. I'm not surprised this proposal came from the US... "let the next generation deal with it" seems to be our solution to most problems.

MichaelGG 12y ago

Leap seconds should be replaced with a leap hour or day or something. Then we could just ignore this forever and hopefully people eons in the future will realise having time sync'd with the sun is ... rather useless.

gpvos 12y ago
Au contraire, it is why civil time exists: to be able to talk about when something happens during the day, and everyone will be confused if 9 AM is not somewhere near the beginning of the work day. Leap hours or days are a cop-out, it's just shifting the problem and making it worse.

klodolph 12y ago

What you are describing already exists, it is called UT1. However, most hardware does not support subtle changes in clock speed.