[ntp:questions] A Suggestion For Abolishing the Leap Second

Danny Mayer mayer at ntp.isc.org
Wed Jun 6 03:28:16 UTC 2007

jlevine wrote:
> Dave,
>> Picking a small nit: WWVB and other Time and Frequency Stations happily
>> transmit a variety of frequencies for carrier and modulation. That's how
>> I calibrate my radios.
>    Sure. The audio tone bursts transmitted by WWV (and WWVH) could be
> set
> to anything. However, it would not be so easy to untangle the carrier
> frequency
> from the time code on WWVB. The time code generators for WWVB (and for
> the GPS system, for that matter), assume that the frequency of the
> carrier
> and the chipping rate of the time code are locked together in some
> fixed
> relationship. This fixed relationship is buried pretty deeply into the
> design,
> and I would guess that it would be quite difficult to change the
> length of the
> transmitted second without changing the frequency of the carrier and
> the
> chip clock.
>> Last we talked you said the goal of Ultimate Timekeepers of the World
>> was to the nanosecond using Two-Way Satellite Transfer. The NIST method
>> used to wrangle an unruly herd of cesium clocks is described in my book.
>> The method provides nominal time and frequency offsets between all
>> clocks in the herd and establish a nominal laboratory timescale. I call
>> this NTP distributed mode and have threatened to implement it.

We have developers standing by to implement this! :)

>    Absolutely. The frequencies of our internal ensemble of clocks can
> differ
> by as much as  1e-11 from the frequency of TAI or UTC. However, if I
> allowed
> an offset this large to escape from the clock room I would be sent to
> bed without
> dinner for a month. Our serious customers expect (and pay for)
> fractional frequency
> stabilities on the order of 1e-14 or 5e-15. These frequencies
> correspond
> to time dispersions on the order of nanoseconds per day.

How do they get it from your clock room to their target without the
error budget overwhelming these dispersions?

>>  If I could reinvent the world, I would run the master clocks in barycentric
>>  time and distribute offsets via the web. This is TAI at the mass center
>>  of the solar system where the gravitational potential is zero.
>    Yes, this idea was proposed some time ago, and it is currently
> being
> pushed pretty hard by the folks who need to plan for going to Mars.
> Some
> version of this idea will probably be adopted if/when space travel
> becomes
> more common. However, the idea that the rotating geoid (which is the
> basis for the current SI defintion) is the center of the universe will
> not
> be easy to overcome.

Particularly for us cosmologists who don't believe that there is a
center of the universe. From a relativistic point of view it makes no
sense. Otherwise we might as well go back to Galileo.


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