[LEAPSECS] Reliability

[Rob Seaman]

Tony Finch wrote:


> I find it odd that you are arguing that the mathematical model of  

> the earth's orbit and rotation is more real than the observations  

> from which the model is derived.


Clearly I failed again to make my point.

There are two different uses to which one might put statistics.   
(Well, many more than this, but two that are being confused here.)   
The first is your interpretation.  That multiple independent  
observations are combined to build a theory of some unknown process.

That is not the case we have, and haven't had since Newton explained  
Kepler's laws that were derived from Tycho's data.

Rather, we can now assume that Newtonian mechanics governs the solar  
system.  For investigations with more precise requirements, Einstein  
steps in.  To the level of precision needed to define civil  
timekeeping, we know the Earth follows an elliptical orbit around the  
Sun, and that the Earth spins at a constant rate on a tilted axis.   
There are also various wobbles and perturbations from the other  
objects in the solar system.  Laplace is handy to explain those.  We  
don't often need to model new theory in classical or relativistic  
mechanics at the modest velocities found in the solar system.

So yes, I think the angular momentum of the Earth is more real than  
the observations that might be compiled to generate an estimate for  
its value.  In freshman physics lab, I recall compiling a big grid of  
current measurements resulting from voltages applied to a wide range  
of resistances.  Unsurprisingly, Ohm's law was confirmed.  The solar  
system is not a mystery.

In any event, this isn't some big philosophical point.  I'm just  
looking for another way to emphasize that civil timekeeping has a  
diurnal cadence.  How's this:

1) The ITU says an hour excursion from mean solar time is acceptable.   
(They appear to assume that some procedure for handling the inevitable  
intercalary correction will self-organize before we reach that hour.)

2) The notion is that an hour's intercalary correction might first  
occur about 600 years out (when the excursion ought to be around a  
half hour).

3) The accumulation of a one-hour error term in 600 years is one-hour  
in 220,000 days is one-hour in 5.3 million hours.  That's equivalent  
to a clock that keeps mean solar time to better than 1 second in 60  
days.

4) Which is to say that the ITU position - a very extreme position -  
depends on staying aligned to mean solar time to better than one part  
in several million.

Civil time is solar time.  The rate is the issue, not local offsets.   
Let's move past the fantasy that the ITU can redefine timescales willy- 
nilly to serve the requirements of a civilization of mole people, and  
rather address the actual requirements of our own civilization.

The best way to build a consensus is to focus on the logistics of the  
approximation needed to align interval timekeepers with Earth  
orientation timekeepers.

Rob