Clive D.W. Feather writes:
WG14 is willing in principle to make changes to time_t, up to and including completely replacing it by something else. *BUT* it needs a complete and consistent proposal and, preferably, experience with it.
This is at the heart of my distaste for the so-called leap hour proposal. There is no coherent proposal, no implementation plan, no discussion of adverse effects, no budget, no collection of pertinent use cases, no exploration of requirements - no technical design discussion at all. Meanwhile, the astronomical community (like other prudent communities, presumably) has instituted long range planning efforts like the U.S. Decadal Surveys. Major (and minor) telescope and instrumentation projects involve multi-year design commitments with significant budgets of their own simply to develop coherent and complete proposals to submit to the funding agencies. The U.S. national centers have recently been subject to an NSF Senior Review process that is likely to have a major affect on all our operating budgets to free up funding for new initiatives. No pain, no gain. On the other hand, we have a "proposal" to change the fundamental underpinnings of world-wide civil timekeeping. A (publicly unavailable) proposal that can't even be bothered to suggest how DUT1 will be conveyed in a future in which this quantity would assume vastly greater importance. It's an embarrassment.
Any proposal has got to deal with a whole load of issues, many of which haven't been properly documented. For example, it should be possible to add and subtract times and intervals (e.g. "what time is 14 months and 87 days from now?").
Poul-Henning Kamp wrote:
... which is exactly the kind of thing you can not do with any {origin+offset} format, due to leap seconds.
Leap seconds are an effect, not a cause. The intrinsic difficulty is with mapping interval time to Earth orientation (mean solar time). Whatever mechanism is used to synchronize civil time to the sun - including embargoing leap seconds as leap hours - there will always be this complication. Consider an ISO 8601 compliant date/time representation, e.g.: % date -u +"%FT%TZ" 2006-12-27T16:47:27Z The first part is the (Gregorian) calendar date - the second clearly represents a fraction of a day. From my point of view, this is the beginning and end of the argument establishing an identity between civil time and mean solar time. Others are willing to permit a slow secular drift - in the calendar, too, of course, not just in the clock. Mucking with leap seconds is equivalent to redefining the concept of a "day". The point is that over a long enough period, a broad enough temporal horizon, we all agree that civil time must be synchronized to solar time. The emergence of the absurd leap hour proposal from among folks who loathe leaps of any sort demonstrates that. They weren't eager to center their notional position around leap hours - rather, they felt obligated. In short, there is no escaping the need to grapple with the fundamental distinction between Earth orientation and "atomic" interval counts. Just as, as one enlarges ones spatial horizon one cannot fail to run into relativistic effects. Timekeeping is a subtle business. Others on this list surely understand that better than I. Rob Seaman NOAO