4 ms·

> reconsider either the length of the second This one is done - the definition of the second is not based on astronomical observations. "Since 1967, the secon

by glurgh 13y ago

> reconsider either the length of the second This one is done - the definition of the second is not based on astronomical observations. "Since 1967, the second has been defined to be: the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom" The accuracy of this kind of measurement is so high it's also used (along with the speed of light) as the basis for defining the meter. Earth-time is a complicated and messy business but the base unit, the second, is pretty much nailed down and independent.

btilly 13y ago
I was stating logical possibilities, not feasible ones. You are right in how we define the second. It was chosen so that on average the number of seconds from midnight to midnight is 606024 = 86,400. At this point a ton of stuff depends on it - the only change that I think likely is to something that we can measure even more precisely than the current standard. But we have set up UTC such that the first second of every year starts close to midnight for the Royal Observatory at Greenwich, London. This sometimes requires having minutes with 59 or 61 seconds (usually 61). These weird minutes have real costs. For instance the June 30, 2012 leap second crashed Linux machines around the world, taking down quite a few websites. And the costs are only projected to increase as we have more programs that make assumptions about UTC, and the slowing day requires more leap seconds to be added. Therefore logically we have 3 choices. Change the meaning of a second (not feasible), continue putting up with leap seconds (costly, and serves no purpose unless you're an astronomer), or give up the UTC peg to an astronomical fact. Unfortunately astronomers control UTC right now, don't want to give it up, and don't care how much their leap seconds cost everyone else. But this can't last forever. Given the way that things work, I don't think that it will change until there is some disaster that is too big to ignore. For instance a leap second bug causes some critical control software to fail, leading to a industrial accident, which brings the attention of politicians and the general public to this ridiculous situations. (Or crashes critical aviation software. Or something else on that scale.) If the current situation maintains, it is just a question of time until something on that scale happens. But until that happens, I don't think that astronomers will understand the costs that they are imposing on the rest of the world. My thinking is that since it is obvious that we'll lose the astronomical peg eventually, we should lose it now. Before someone dies.
- glurgh 13y ago
  This is a genuine question - do you really believe the (to me, seemingly obvious and much greater and potentially more dangerous) costs of switching away from astronomical time for measuring something inherently astronomical like the length of a year are smaller than the costs of removing the occasional time-handling bug in software? Even in your example, Linux machines didn't actually crash - some processes spinlocked. And it wasn't even all Linux machines, if you were running a mildly old kernel (say, the one that came with debian etch and derivatives) nothing happened whatsoever. Beyond that, there is no shortage of time standards that are both based on SI seconds and free of leap seconds - Terrestrial Time, International Atomic Time, GPS Time come to mind - http://en.wikipedia.org/wiki/Terrestrial_Time http://en.wikipedia.org/wiki/Terrestrial_Time http://en.wikipedia.org/wiki/GPS_time#Timekeeping http://en.wikipedia.org/wiki/GPS_time#Timekeeping http://en.wikipedia.org/wiki/International_Atomic_Time http://en.wikipedia.org/wiki/International_Atomic_Time Google's solution is 'leap smear' and they, similarly, did not run into the problem http://googleblog.blogspot.com/2011/09/time-technology-and-leaping-seconds.html http://googleblog.blogspot.com/2011/09/time-technology-and-l...
  - lmm 13y ago
    Equally genuine counter: what costs do you see associated with redefining a year as e.g. a fixed number of seconds? To me none are obvious, surely they'd be small compared to what we've already lost from these software bugs. Leap smear is a good solution, as is TA1; sadly the posix/unix standards do not permit it (which makes it difficult to use on e.g. government projects).
    - glurgh 13y ago
      Well, for one thing a non-constant second seems like it would break just about all of physics in deeply unpleasant ways. I think 'btilly is right - it's an unpleasantly difficult problem. I suppose my point is 'it just happens to be unpleasantly hard problem' - given that a great number of specialists have put serious time in thinking about it trying to solve it, I have a very difficult time imagining that the solution (or satisfactory answer) is as simple as 'just blame astronomers'. Having _two_ or more slightly different units that measure the base unit of time (which would be the case if we defined seconds in terms of (siderial? some other?)) year seems like a far greater potential source of cock-ups than just having a well-defined unit that might not quite, but more often than not, matches astronomical detail.

by glurgh 13y ago

btilly 13y ago

I was stating logical possibilities, not feasible ones. You are right in how we define the second. It was chosen so that on average the number of seconds from midnight to midnight is 606024 = 86,400. At this point a ton of stuff depends on it - the only change that I think likely is to something that we can measure even more precisely than the current standard. But we have set up UTC such that the first second of every year starts close to midnight for the Royal Observatory at Greenwich, London. This sometimes requires having minutes with 59 or 61 seconds (usually 61). These weird minutes have real costs. For instance the June 30, 2012 leap second crashed Linux machines around the world, taking down quite a few websites. And the costs are only projected to increase as we have more programs that make assumptions about UTC, and the slowing day requires more leap seconds to be added. Therefore logically we have 3 choices. Change the meaning of a second (not feasible), continue putting up with leap seconds (costly, and serves no purpose unless you're an astronomer), or give up the UTC peg to an astronomical fact. Unfortunately astronomers control UTC right now, don't want to give it up, and don't care how much their leap seconds cost everyone else. But this can't last forever. Given the way that things work, I don't think that it will change until there is some disaster that is too big to ignore. For instance a leap second bug causes some critical control software to fail, leading to a industrial accident, which brings the attention of politicians and the general public to this ridiculous situations. (Or crashes critical aviation software. Or something else on that scale.) If the current situation maintains, it is just a question of time until something on that scale happens. But until that happens, I don't think that astronomers will understand the costs that they are imposing on the rest of the world. My thinking is that since it is obvious that we'll lose the astronomical peg eventually, we should lose it now. Before someone dies.

glurgh 13y ago
This is a genuine question - do you really believe the (to me, seemingly obvious and much greater and potentially more dangerous) costs of switching away from astronomical time for measuring something inherently astronomical like the length of a year are smaller than the costs of removing the occasional time-handling bug in software? Even in your example, Linux machines didn't actually crash - some processes spinlocked. And it wasn't even all Linux machines, if you were running a mildly old kernel (say, the one that came with debian etch and derivatives) nothing happened whatsoever. Beyond that, there is no shortage of time standards that are both based on SI seconds and free of leap seconds - Terrestrial Time, International Atomic Time, GPS Time come to mind - http://en.wikipedia.org/wiki/Terrestrial_Time http://en.wikipedia.org/wiki/Terrestrial_Time http://en.wikipedia.org/wiki/GPS_time#Timekeeping http://en.wikipedia.org/wiki/GPS_time#Timekeeping http://en.wikipedia.org/wiki/International_Atomic_Time http://en.wikipedia.org/wiki/International_Atomic_Time Google's solution is 'leap smear' and they, similarly, did not run into the problem http://googleblog.blogspot.com/2011/09/time-technology-and-leaping-seconds.html http://googleblog.blogspot.com/2011/09/time-technology-and-l...
- lmm 13y ago
  Equally genuine counter: what costs do you see associated with redefining a year as e.g. a fixed number of seconds? To me none are obvious, surely they'd be small compared to what we've already lost from these software bugs. Leap smear is a good solution, as is TA1; sadly the posix/unix standards do not permit it (which makes it difficult to use on e.g. government projects).
  - glurgh 13y ago
    Well, for one thing a non-constant second seems like it would break just about all of physics in deeply unpleasant ways. I think 'btilly is right - it's an unpleasantly difficult problem. I suppose my point is 'it just happens to be unpleasantly hard problem' - given that a great number of specialists have put serious time in thinking about it trying to solve it, I have a very difficult time imagining that the solution (or satisfactory answer) is as simple as 'just blame astronomers'. Having _two_ or more slightly different units that measure the base unit of time (which would be the case if we defined seconds in terms of (siderial? some other?)) year seems like a far greater potential source of cock-ups than just having a well-defined unit that might not quite, but more often than not, matches astronomical detail.