jeff@heurikon.UUCP (02/16/84)
Einstein's Universe was on TV (again) last week. I pick
up a little bit more each time I watch it. But, I have a
question about atomic clocks and what the heck the correct
"time" means:
What if the NBS atomic clock went out? A power failure
perhaps, or a critical component goes berserk. They have
a backup clock, you say? Okay, make it a catastrophic
event like an earthquake. Anyway, *ALL* the NBS clocks stop.
(Also, assume that our sister atomic clocks in Europe also
go on the fritz or were down for maintenance. Let Murphy
loose: "Previously unneeded backup systems will all fail at
the same instant the primary unit looses power.")
How would they reset the NBS clock? And how would anyone know
if it was set correctly? What would be used as a standard?
And what problems would develop it it were wrong, anyway?
I know it's important to have syncronization between various
places or events, but what's so important about knowing what
time it is in *absolute* terms?
Post responses, please. Thanks.
--
/"""\ Jeffrey Mattox, Heurikon Corp, Madison, WI
|O.O| {harpo, hao, philabs}!seismo!uwvax!heurikon!jeff (news & mail)
\_=_/ ihnp4!heurikon!jeff (mail - fast)bill@utastro.UUCP (William H. Jefferys) (02/16/84)
This is an interesting question. My best suggestion is that
pulsar timings could be used to resynchronize the atomic
time standards. The newly discovered millisecond pulsars
do not seem to have the "glitches" that the slower pulsars
have, so they would probably be the best. My guess is that
you could probably get things going to within a few microseconds,
but I am not an expert in this area.
I discussed this with a colleague, and none of the other schemes
we came up with were anywhere near as accurate or straightforward.
As to the utility of doing this, there are many astronomical
observations that require *epoch* as well as *interval*; orbital
observations are an obvious example. Pulsar timings are another.
--
Bill Jefferys 8-%
Astronomy Dept, University of Texas, Austin TX 78712 (USnail)
{ihnp4,kpno,ctvax}!ut-sally!utastro!bill (uucp)
utastro!bill@ut-ngp (ARPANET)dap@ihopa.UUCP (afsd) (02/19/84)
I've got a question that is related to Jeffrey Mattox's question regarding atomic clocks. EVERY clock, even atomic ones, are not in perfect agreement with the sun so that sooner or later they are going to show the time as midnight when the sun is high in the sky. I realize that this is going to be next to forever before it happens, but assuming we don't all go up in World War III or some kind of solar conflagration, it is inevitable. My question is: What is going to happen? Is there some sort of committee to keep track of this drift and reset the atomic clock if necessary? If so, how do they recognize that a drift has taken place? It would require a more accurate clock that the atomic clock to detect it unless somebody just happens to notice that the sun is setting at 3AM on the equator. I think that this is just an academic question and the sun itself may noticeably slow down before this happens (more properly, at least from our solar system's viewpoint, the earth may slow down) but I'm wondering if anyone has any contingency plans for this future drift or if we're going to let night slowly drift into day. Darrell Plank ihnp4!ihopa!dap
darrelj@sdcrdcf.UUCP (Darrel VanBuer) (02/20/84)
Already, every few years, the timekeeppers find it necessary to insert a
leap-second every few years . This is needed even if the atomic clocks were
set perfectly once because the earth's rotation is both wobbly and slowing,
the former causes a little jitter, the latter permanent effects.
Errors of a few seconds can be spotted with a good observatory (such as the
Naval Observatory at Anapolis and the one at Greenwich, England).
Atomic clocks are already "more accurate" than the Earth's rotation and
revolution (in the sense of drift from an exactly constant second).
By the way, in many millions of years hence, a day will be substantially
longer than 86,400 seconds, so "we" will have to decide how to restructure
timekeeping. Do we inflate the second? the minute? use a 25 hour day? use
seconds since FOO and cumpute solar time?
--
Darrel J. Van Buer, PhD
System Development Corp.
2500 Colorado Ave
Santa Monica, CA 90406
(213)820-4111 x5449
...{allegra,burdvax,cbosgd,hplabs,ihnp4,sdccsu3,trw-unix}!sdcrdcf!darrelj
VANBUER@USC-ECL.ARPAstekas@hou2g.UUCP (J.STEKAS) (02/21/84)
Since there is no such thing as absolute time, no clock can be
constructed which is correct in an absolute sense. To wonder
when an atomic clock will get out of synch with the sun is missing
the point. The atomic clock has replaced astronomical standards
because the physical processes which govern the atomic clock are
better understood and can be better controlled. Atomic clocks also
have a great advantage in that they are transportable.
Dirac has suggested that the ratio of the gravitational force to the
electromagnetic force is changing with time. That means that if astro-
nomical standards of length and time are used, elecromagnetic forces would
be increasing with time. If atomic (E&M) standards are used, then gravity
would be weakening. Lunar laser ranging experiments were done to measure
the effect, and the last I heard the evidence favored Dirac.
Jim
decreasing with respect to the electromagnetic force.
When atomic and astronomical clocks disagree,