GMT Date Format Anomaly

[Dr John Stockton]

Re: GMT Date Format Anomaly

JRS: In article <crbrsq$lii$1$8 30fa79d@news.de mon.co.uk>, dated Mon, 3
Jan 2005 16:31:02, seen in news:comp.lang. javascript, Mark Preston
<usenet@nosourc e.co.uk> posted :[color=blue]
>Dr John Stockton wrote:[color=green]
>> JRS: In article <cr3g6r$h39$1$8 302bc10@news.de mon.co.uk>, dated Fri, 31
>> Dec 2004 12:22:24, seen in news:comp.lang. javascript, Mark Preston
>> <usenet@nosourc e.co.uk> posted :
>>[color=darkred]
>>>Dr John Stockton wrote:
>>>
>>>>The wise programmer will allow for getting either UTC or GMT (and know
>>>>that the two are not synonymous, and in principle neither is correct).
>>>>AFAIK, however, one need not expect utc or gmt.
>>>>
>>>
>>>The wise reader will also know that GMT and UTC are the same thing.
>>>Unfortunatel y, as we all know, wise readers are as rare as rocking-horse
>>>droppings. .. :)[/color]
>>
>> No, GMT and UTC are not the same thing, even apart from what I was
>> referring to, which is that a coder must allow for the possibility of
>> getting either string from a Date Object method.
>>[/color]
>Technically, you are correct. GMT is a standard-period time recording
>(that is, it counts how long the Earth takes to revolve) and is
>consequently "inaccurate " since nothing in this life is as simple as a
>spinning planet is assumed to be.[/color]

Approximately correct.
[color=blue]
>UTC, on the other hand, is a derived
>probabilisti c decay-rate measurement.[/color]

Total rubbish. It has nothing at all to do with decay rates. UTC is
based on the SI second, which is based on a precise transition of Cs-133
(see footnote [+] to my previous article), plus adjustments to make it
agree with one of the GMT-class time scales to within 0.9 seconds.

See my WWW site, and confirm by means of the links it contains; do not
trust amateur sources.
[color=blue]
>But, be honest, who really cares about the odd leap-second or so?[/color]

Quite a number of people care quite a lot - granted, only a minority
know, but many more could be affected if a mistake were made.


The important things for this group remain that (a) one can never be
really safe in assuming that a string generated by the javascript
processor will not include GMT where UTC might be expected, or /vice
versa/, (b) javascript knows nothing of leap seconds, and behaves
arithmetically as GMT does.

--
© John Stockton, Surrey, UK. *@merlyn.demon. co.uk / ??.Stockton@phy sics.org ©
Web <URL:http://www.merlyn.demo n.co.uk/> - FAQish topics, acronyms, & links.
Correct <= 4-line sig. separator as above, a line precisely "-- " (SoRFC1036)
Do not Mail News to me. Before a reply, quote with ">" or "> " (SoRFC1036)

[Mark Preston]

Re: GMT Date Format Anomaly

Dr John Stockton wrote:[color=blue]
> JRS: In article <crbrsq$lii$1$8 30fa79d@news.de mon.co.uk>, dated Mon, 3
> Jan 2005 16:31:02, seen in news:comp.lang. javascript, Mark Preston
> <usenet@nosourc e.co.uk> posted :
>[color=green]
>>UTC, on the other hand, is a derived
>>probabilist ic decay-rate measurement.[/color]
>
> Total rubbish. It has nothing at all to do with decay rates. UTC is
> based on the SI second, which is based on a precise transition of Cs-133
> (see footnote [+] to my previous article), plus adjustments to make it
> agree with one of the GMT-class time scales to within 0.9 seconds.
>
> See my WWW site, and confirm by means of the links it contains; do not
> trust amateur sources.
>[/color]
Umm - yes, it is. But as I just pointed out in one sentance exactly the
same thing I don't see your problem.

In case you are not sure why they are the same then I suggest you look
again at your description which nicely summarises that UTC is based on
decay transitions of Caesium 133 and ordered to a standardised average
(which is what the SI units are all about). Why average? Well, because
decay rates at the atomic level are all probabilities (not certainties)
and so have a pretty wide spread of actual values... hence the infamous
Schroedinger's Cat experiment.

[Dr John Stockton]

Re: GMT Date Format Anomaly

JRS: In article <crejio$ec8$1$8 300dec7@news.de mon.co.uk>, dated Tue, 4
Jan 2005 17:27:34, seen in news:comp.lang. javascript, Mark Preston
<usenet@nosourc e.co.uk> posted :[color=blue]
>Dr John Stockton wrote:[color=green]
>> JRS: In article <crbrsq$lii$1$8 30fa79d@news.de mon.co.uk>, dated Mon, 3
>> Jan 2005 16:31:02, seen in news:comp.lang. javascript, Mark Preston
>> <usenet@nosourc e.co.uk> posted :
>>[color=darkred]
>>>UTC, on the other hand, is a derived
>>>probabilisti c decay-rate measurement.[/color]
>>
>> Total rubbish. It has nothing at all to do with decay rates. UTC is
>> based on the SI second, which is based on a precise transition of Cs-133
>> (see footnote [+] to my previous article), plus adjustments to make it
>> agree with one of the GMT-class time scales to within 0.9 seconds.
>>
>> See my WWW site, and confirm by means of the links it contains; do not
>> trust amateur sources.
>>[/color]
>Umm - yes, it is. But as I just pointed out in one sentance exactly the
>same thing I don't see your problem.
>
>In case you are not sure why they are the same then I suggest you look
>again at your description which nicely summarises that UTC is based on
>decay transitions of Caesium 133 and ordered to a standardised average
>(which is what the SI units are all about). Why average? Well, because
>decay rates at the atomic level are all probabilities (not certainties)
>and so have a pretty wide spread of actual values... hence the infamous
>Schroedinger 's Cat experiment.[/color]

Obviously you have stuck in your mind a total misapprehension about the
physics of a Caesium Clock. The operation is utterly different from the
possibly so-called Atomic Clock used in archaeological carbon dating,
which is based on radioactive decay of the C14 nucleus; it is a matter
of transitions between electronic energy levels, and "decay" is not an
appropriate term.

Don't argue physics with an experienced physicist when you are not one
yourself; and, if you must do so, be careful to choose a topic which is
not so closely adjacent to his own. By adjacent, I don't just mean
similar, but literally along-the-corridor.

For further information on the physics of the Caesium Clock, consult the
NPL, NIST, and BIPM Web sites - it should be on all of them (NIST, at
least, is liable to call it Cesium). It will also be in books in the
larger public libraries.

--
© John Stockton, Surrey, UK. *@merlyn.demon. co.uk / ??.Stockton@phy sics.org ©
Web <URL:http://www.merlyn.demo n.co.uk/> - FAQish topics, acronyms, & links.
Correct <= 4-line sig. separator as above, a line precisely "-- " (SoRFC1036)
Do not Mail News to me. Before a reply, quote with ">" or "> " (SoRFC1036)