[time-nuts] Absolute time accuracy pre-Cesium?

Tue Mar 26 20:52:17 UTC 2019

Hi

TIme is “just a number”, it has no inherent granularity. If you need to measure at the 10^-?? level, 
the units will not be the problem. Coming up with a device that provides 10^-15 or 10^-18 sort of 
stability (let alone accuracy …. yikes ….) would take a pretty big limit on your charge card. Bumping
the number an order of magnitude is the sort of thing that keeps an entire generation of staff at some 
pretty big national labs employed. 

That said, there have been some papers over the years about “what will you run into and when
will you run into it?”. At some point gravity noise from “stuff” moving around gets into the picture and 
you need to move your clock into deep space ….. there *is* a number and for how much you walking
across the room changes the gravity on your clock …. Needless to say, there are a lot of other things
to worry about before that is the limit you worry about. 

Bob

> On Mar 26, 2019, at 11:46 AM, Bob Albert via time-nuts <time-nuts at lists.febo.com> wrote: 
> 
> I have been pondering something somewhat related to all of this.
> We know that the smallest unit of a substance is a molecule.  The smallest unit of charge is maybe an electron.  So what could one imagine the smallest unit of time to be?  Is time digital in the nanoscale, or is it always an analog measurement?  Or, more fundamentally, is is just a concept rather than a reality?
> Bob
>    On Tuesday, March 26, 2019, 7:00:45 AM PDT, Kevin Birth <Kevin.Birth at qc.cuny.edu> wrote:  
> 
> It all depends on how far back you want to go.  With mechanical
> timepieces, even before the pendulum there was Jost Burgi¹s astronomical
> clock which achieved a precision of a second, and is reported to have been
> accurate to that level based on astronomical measurements.  Tycho Brahe
> tried to achieve accuracy through using multiple clocks.  This technique
> actually seems to have been developed before Brahe with potentates like
> Charles V having large numbers of clocks that he tried to synchronize.
> There is at least one case of a Holy Roman Emperor with a bundle of clocks
> getting angry at a clockmaker for having sold him a poor performing
> clock‹that was Rudolf II.
> 
> Before that you have some of the great Islamic observatories that measured
> time with very large instruments.  Here is a link, even without a
> knowledge of Arabic, one can get a sense from the pictures how these
> Muslim astronomers used scale to achieve great accuracy and precision.
> What limited them were their materials‹at a certain scale their
> instruments started to warp under their own weight.  Many of the
> principles in these instruments were based on Ptolemy¹s ALMAGEST, which
> takes things back to the 3rd century AD or so.
> 
> Here¹s the link: 
> https://gallica.bnf.fr/ark:/12148/btv1b8414999t.r=taqi%20al-din%20instrumen
> ts?rk=21459;2
> 
> Before that the most detailed account of time measurement equipment is in
> Vitruvius¹ work on architecture, but Vitruvius¹ descriptions are often
> garbled, so there is no good way to judge their accuracy in relationship
> to their claims of precision.
> 
> Less well documented are Persian and South Asian methods in which the
> smallest unit translates to something like the duration of a blink of an
> eye.  I do not know enough about those traditions to know what
> observational methods or instruments they used to measure such a unit
> (other than blinking a lot).
> 
> Best,
> 
> Kevin
> 
> 
> -- 
> Kevin K. Birth, Professor
> Department of Anthropology
> Queens College, City University of New York
> 65-30 Kissena Boulevard
> Flushing, NY 11367
> telephone: 718/997-5518
> 
> "Tempus est mundi instabilis motus, rerumque labentium cursus." --Hrabanus
> Maurus
> 
> "We may live longer but we may be subject to peculiar contagion and
> spiritual torpor or illiteracies of the imagination" --Wilson Harris
> 
> 
> 
> 
> On 3/26/19, 7:30 AM, "time-nuts on behalf of John Ackermann.  N8UR"
> <time-nuts-bounces at lists.febo.com on behalf of jra at febo.com> wrote:
> 
>> EXTERNAL EMAIL: please report suspicious content to the ITS Help Desk.
>> 
>> 
>> All -- thanks much for all the great references!  I am giving the preso
>> this afternoon (to a bunch of university space science students) so this
>> will be a big help.  And it looks like there's a lot of great reading for
>> when I have time to breathe.
>> 
>> Thanks again.
>> John
>> 
>> On Mar 25, 2019, 10:03 PM, at 10:03 PM, Ben Bradley
>> <ben.pi.bradley at gmail.com> wrote:
>>> For independent standards (not quite what you asked) I recall from
>>> "The Science of Clocks and Watches" (a book with much technical info
>>> if you're interested in these mechanical devices) that the most
>>> accurate mechanical/pendulum clock was the Shortt Clock that used a
>>> pendulum in a vacuum chamber for its standard. Mechanical clocks were
>>> replaced by more stable electronic quartz crystal oscillators, and
>>> then finally by atomic clocks.
>>> 
>>> Perhaps closer to your question: I recall in my readings about
>>> clockmaker John Harrison (likely either in "The Quest for Longitude"
>>> or Dava Sobel's "Longitude") that he would look from the edge of his
>>> window at a particular star each night and note (while counting the
>>> ticks he heard from his clock) the exact moment it would disappear
>>> behind a nearby chimney, and knowing the Earth's rotation takes four
>>> minutes and some (I forget) seconds off from a day, he used this to
>>> calibrate and test the precision and accuracy of his long clocks. It
>>> was suggested he could get within less than second with this method.
>>> This was around age 21, so the year would be about 1714. Looking
>>> online for PZT (photographic zenith tube), I didn't find much about
>>> it, but it was surely first made a couple centuries after this.
>>> 
>>> The Sobel book (all about how Harrison won the Longitude prize) is
>>> more a popular book and less technical, but "Quest" has many
>>> mostly-technical articles, mostly about Harrison, as well as beautiful
>>> photos of his clocks. One or two of the articles is by the man who
>>> made (or made the parts for it, the story is complicated) the
>>> one-second-in-100-days "Clock B" pendulum clock, built from Harrison's
>>> writings and claims of just that accuracy in the book he wrote shortly
>>> before his death.
>>> 
>>> On Mon, Mar 25, 2019 at 7:00 PM John Ackermann N8UR <jra at febo.com>
>>> wrote:
>>>> 
>>>> Does anyone have a pointer to information about the absolute time
>>>> accuracy (not stability) that was available via PZT or other
>>> techniques
>>>> prior to the Cesium definition?  I'm doing a presentation and want to
>>>> show the evolution of accuracy.  My Google-fu has failed me in
>>> finding
>>>> anything pre-Atomic.
>>>> 
>>>> Thanks!
>>>> John
>>>> 
>>>> 
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