4 ms·

A negative leap-second will be crazy interesting given how the first few leap seconds in computing caused a little havoc.

• BitwiseFool 6y ago
  Woudln't it be easier to just "let it ride" and the next time a leap second is due, just not add it?
  • throwaway894345 6y ago
    It's interesting to think about the ramifications of decoupling our measurement of time from the earth's position in the solar system. For example, when we read that something happened around 11 AM, we know that it's probably daylight time, but if we allow for drift, then we can't make that assumption anymore for certain timescales. If the error is small, we can probably deal with it the same way most people understand that dollars in 1950 don't have the same value as dollars today.
    • Archelaos 6y ago
      GPS time is like this. See: https://en.wikipedia.org/wiki/Global_Positioning_System#Timekeeping https://en.wikipedia.org/wiki/Global_Positioning_System#Time...
    • wcoenen 6y ago
      Note that we don't sync to the Earth's position in the solar system (sidereal year), but to the seasons (tropical year).
    • myself248 6y ago
      Unless you're within a few feet of the longitude of the center of the timezone, this is already the case. That ship sailed, back in the railroad era when we decided to standardize time away from mean solar time. If we assume that the Gregorian calendar remains in use for as long as it's already been in use, the total accumulated error would likely be on the order of minutes. We could use a monotonic time scale like TAI for literally centuries and nobody would notice except astronomers, and arguably it would simplify astronomical corrections too because the underlying scale would be monotonic, which it isn't presently.
      • klodolph 6y ago
        > That ship sailed, back in the railroad era when we decided to standardize time away from mean solar time. I’ll make the case here that we still use mean solar time, we just quantize it and push it around for political reasons. In any case, using time zones just means that your clock is off by maybe a half hour or 45 minutes in the lower US, and given the natural variation for sunrise and sunset, that doesn’t seem like an outrageous amount of error for temperate latitudes. Granted, there are a few places in the world with larger differences, like Spain or western China, or Argentina for some reason. Changes in the period of the Earth’s rotation have been estimated based on records of eclipses from as far back as the 8th century, which show that the Earth’s rotational speed is slowing down. Trying to extrapolate from fifty years of atomic time is going to give you the “on the order of minutes” estimate which is likely wrong. If you are trying to work out the error over five centuries, you should probably be using the best available data, which is records of eclipses and ephemerides.
        • kevin_thibedeau 6y ago
          It's more than 45 minutes on the western extremes in the EST, CST, and MST zones.
          • klodolph 6y ago
            I chose the wording “maybe a half hour or 45 minutes” to make it crystal-clear that the exact number was not relevant to the argument, in a vain effort to avoid responses like this one. Perhaps I should be more explicitly vague in the future. HN is tiring.
            • danaliv 6y ago
              No, you’re absolutely right. As someone who uses UTC professionally in aerospace ops, trust me when I say your clock is still definitely tied to solar time even if it’s “off” by whatever. Try using UTC exclusively—I don’t just mean on your servers, I mean in every single aspect of your life—and you’ll see what I mean.
          • deleted 6y ago
    • zokier 6y ago
      You are assuming that timezones wouldn't change if the difference would be great enough to notice, something that I don't see any reason to assume.
  • anigbrowl 6y ago
    Suppose for argument's sake that this year produces shorter days, and the trend continues.
• tantalor 6y ago
  A negative leap second would suppress second 23:59:59 of the last day of a chosen month so that second 23:59:58 of that date would be followed immediately by second 00:00:00 of the following date. Since the introduction of leap seconds, the mean solar day has outpaced atomic time only for very brief periods and has not triggered a negative leap second. https://en.wikipedia.org/wiki/Leap_second#Process https://en.wikipedia.org/wiki/Leap_second#Process
  • layer8 6y ago
    Just a quick reminder that this is in UTC. The missing second will be at varying times of day depending on time zone.
• Avamander 6y ago
  Sounds worth it to me honestly, sets a precedent that it's possible and it's harder to ignore the possibility in future software.
• Ericson2314 6y ago
  I don't think positive or negative makes much difference. Whether we speed up or slow down we can still "make it monotonic".
• toast0 6y ago
  A removed leap-second is gobs easier to handle. I can't say if it will or won't be handled properly, because I never tested it, but roughly you have three options: a) software ignores it, and your clock is a second behind as of the discontinuity, and adjusts eventually b) software handles it properly and jumps ahead c) software handles it by explicitly dithering the difference over a day d) c, but it also jumps ahead at the discontinuity e) your network has a mix of b, c, and d, resulting in wonky clocks throughout the day, but generally still +/- 1 second of real time. This could be problematic for forensics, or for distributed software that uses time as measured on nodes to determine order of operations, but using time as measured on nodes requires constant vigilence to ensure clocks are in sync enough. An added leap second is a lot trickier because at least Linux and FreeBSD simply repeat the last second of the minute at the discontinuity if you don't take special action to dither it. That brings two new problems: a) real time is no longer monotonic b) a logic error can result in repeating that second forever