Call me cynical / Call me thick ... but

Someone please explain how the length of a second can be measured more accurately than its definition

**LINK**

https://www.smithsonianmag.com/smart-news/new-atomic-clocks-hone-length-second-180977387/

I guess the answer lies in the semantics ... and that “Time” is not quite the same thing as our defined method of measuring the second.

MichaelG.

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Note: I haven’t yet read the published paper ... it may make more sense when I do

The space/time continuam is regularly distorted by Q.

Regards Ian.

Isn't it just saying how a second is defined? So the new definition of using the frequency of some alternative atom is found to be more consistent under different conditions.

Like a foot used to be the length of someone's foot but as they change a bit from person to person, a more universal definition has been chosen.

An inch might have been the width of a thumb but got redefined to make it be easier to map onto metric.

Temp scale has had a few changes, some quite recent.

+1 for Jacks view. The article seems to be saying "they" have found that several different atoms give slightly different results and in due course there may have to be a reconsideration of what is the most useful way to define the second. It's happened before, but it seems unlikely that any non-specialist will notice any difference.

Rod

It does not make any difference to me. Time is something I loose by not being in the workshop. As I get older it speeds up.

I believe mass is now defined by the number of atoms in some lump of metal (I bet it is not cheap mild steel).

JA

In my home workshop I can measure time to 20 picoseconds for one off events, much better for something that can be averaged. Thats 2x10^-11 or 0.00000000002 s. Thats good enough for most practical purposes. Light travels about 6mm in 20 ps.I can measure frequency to over to 25 GHz (2.5s10^10). I have 4 atomic frequency standards, but like most time nuts I mostly use GPS based clock. I have several of those with 3 different models running 24/7. You need three because if you only have two and they are different you don't know which is right
I built a precsion quartz oscillator at over the weekend. I can easily see the effect of gravity on this e.g. the frequency change when you turn it on its side, +1 G to 0 G

Robert G8RPI.

Time is like a toilet roll, the older it gets the faster it goes

If the selected atom outputs light at a given frequency then the higher the frequency then there are more subdivisions of time available and hence greater potential accuracy..

Ignore Roberts quip re difference in gravity and hence frequency if his oscillator is upright or on its side. However time does alter depending on gravity. A satellite born atomic clock will give a different time to one on the ground . This has to be taken into account for GPS location otherwise the system will give an incorrect result.

Andrew.

It was not a quip, the oscillator I was refering to is a quartze one (HP 10811D based) and it has a detectable change in frequency when turned on its side or inverted.

Robert G8RPI.

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I have no problem with that situation, jaCK ... but my question was a little more philosophical

If we currently have a definition of the Second ...

how can they claim to have measured it more accurately than that ?

MichaelG.

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[quote] Researchers used three atomic clocks to measure time accurately down to the quadrillionth of a percent [/quote]

Edited By Michael Gilligan on 06/04/2021 15:35:08

A man with one clock always knows what time it is. A man with two clocks is never quite sure.

The actual experiment was more about different means of time transfer, fibre optic vs direct ( free space) laser than the actual references themselves. The problem is that it takes time to transfer the time from one place to another. Even in the time of clockwork noon at Greenwich was signalled by both sound and visual signals as sound takes too long to travel. Thransferring time long distances relied on radio but even this has delays. When HP desigined the 5061A "transportable" cesium beam frequency standard in the early sixties the enabled "flying clocks and accurate time transfer around the world.
https://www.hpmemoryproject.org/news/flying_clock/celebration_01.htm

Robert G8RPI.

Take heed from one who found out the hard way! Accurate time is highly addictive, whether by clockwork or electronics. Sucks you in with promised delights, spends all your money, and nothing you do is quite right. Bit like marriage really...

Dave

Tell me about it. 6 GPSDOs, (one Rubidium), 4 other Rubidium oscillators, LF off-air standards, GPS receivers, crystal oscillators (some cost thousands of pounds when new) about 10 frequency counters including HP 5370B and Philips PM6654, the list goes on....

Robert G8RPI.

Robert, you have some very strange ideas on gravity. Turning an oscillator on its side does not change gravity from 0 G to 1 G

I have specialised in the study of relativity and gravity for the last 50 years and you are just plain wrong.

Andrew.

But it could easily make a wire move a micron or so - unless it has strain relief.

Michael - as I suspect you suspect, the author of the Smithsonian mag article is a bit woolly in his thinking and reporting. He somehow seems to suggest that 'the second' is an objective entity which can be measured, but he doesn't make a clear distinction between definition and measurement. His background is in is in biology/ecology, so perhaps that's not surprising.

The article in Nature on which his report is based is certainly interesting, - thanks for drawing attention to it.

Robin

By far the best discussion re the nature of time is given here :-

GS1

Enjoy.

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Nicely put, Robin ... We are ‘on the same page’

MichaelG.

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Fond memories

I’ve just sent that link to our son [currently out in Laos], to see if he can explain it to the locals.

MichaelG.