https://xkcd.com/2867

Alt text:

It’s not just time zones and leap seconds. SI seconds on Earth are slower because of relativity, so there are time standards for space stuff (TCB, TGC) that use faster SI seconds than UTC/Unix time. T2 - T1 = [God doesn’t know and the Devil isn’t telling.]

  • chuckEnglish
    48·
    11 months ago

    Ah I’ve gotten to the point where I have to define what “frame” and epoch each time base is in before I’ll touch the representation of time( Unix,Gregorian, etc) .To be honest I’m probably just scratching the surface of time problem.

    Hell probably the reason we haven’t seen time travellers is we suck at tracking time and you probably need to accurately know your time and place to a very good precision to travel to a given point and we can’t say where and when that is with enough accuracy to facilitate where to land. And people don’t want to land in the earth’s surface or 10000 km away from a stable orbit. Maybe some writer can build that out for a time travel book or to discount it for some reason lol

    • kurwa@lemmy.worldEnglish
      191·
      11 months ago

      I recall a short story like that where someone died because they time traveled, but didn’t account for position.

    • niktemadur@lemmy.worldEnglish
      5·
      11 months ago

      Then there’s continental drift, which as Indiana Jones reminded us this past summer, Archimedes didn’t know about when he built his time machine.

      Pet peeve: brushing aside the time travel fantasy element, there is not a single shred of evidence of any type of connection between Archimedes and the Antikythera Mechanism.

      As if the only person clever enough in Ancient Greece was that one famous dude from Syracuse.
      Ionians: “Are we a joke to you?”

    • Omniraptor@lemm.eeEnglish
      1·
      11 months ago

      Could you eli5 what frame and epoch are? I don’t get why aren’t unix timestamps an adequate way to store time, they seem pretty easy and intuitive

      • chuckEnglish
        1·
        11 months ago

        Well in three dimensions you can have an cartiesian coordinate frame (x,y,z) with it’s length of measure you also have an origin (a (0,0,0)

        With time you can have an arbitrary length of time say a certain number of ticks of a cessium atom vibration, and you have a point where you start ticking from say a specific time where all the stars were one way. Let’s call that our inertial time base

        Now lets add a clock into the mix. The clock counts seconds in it’s own way from the time they power on so it has it’s own time frame (length of second) and epoch (zero time).

        Now if the clock second is the same as the inertial time frame you are golden t2-t1 + the offset in the zeros. If the clock is fast or slow (let’s assume linear for now)

        You need to juggle around the difference in slopes between time the clock and the inertial time frame while performing the subtraction and even the offset

        So you end up with stuff like clocktime_rel_J2000epoch_TAI = clocktimeclock*TAisloperelCLK+ CLKzerooffsetrelTAI in production code and other people remove it and wonder why you’d bother having a relative slope at all and later find out nothing works when the clock gets hot or cold and the slope drifts…