# At the third beep, the Atomic Clock will be 60 ... imprecisely

The atomic clock celebrates its 60th birthday this year. John Watkinson looks at the story of this enabling technology that lies behind GPS and DAB and discusses its roots in quantum mechanics and relativity. Readers are warned that they might need to lie down for a while after reading this article. The story probably begins …

1. "5893 Ångström Units. [...] In 1960 the metre would be re-defined as 1010 Ångström Units, the wavelength of Sodium yellow became 589.3 nanometres "

It's early Sunday morning but that statement seems inconsistent?

If a metre is 1010 Ångström Units - then Sodium yellow would only be 583.5 nanometres.

Possibly "1010" is a typo - and should be "1000" ?

1. 10^10 - I can't be bothered trying superscripts as the original article got the html wrong too. An Ångström unit is 0.1 nanometres.

1. "10^10"

Thanks. As I went back to sleep there was a niggle in my mind that I hadn't considered the magnitude.

2. Unicode has superscript digits. (The one and zero are particularly well supported in everyday fonts.) When the superscript is important to the meaning, rather than the presentation, it is best to use those characters rather than messing about with formatting.

2. #### A metre is 10 to the 10 angstroms

It looks like some of the formatting fell out - a metre is defined at 10**10 Angstroms, i.e. a tenth of a nanometre. So Sodium yellow is 5893 Angstroms, or 589.3 nanometres (actually it's two very close wavelengths about half a nanometre apart, and that's the average).

3. #### The third beep arrives 15s late

Precise atomic clocks accurate to the femtosecond. Connected to the 'Third Beep' machine, delivered by satellite radio about 15 seconds after the fact.

Stupid.

Of course I used other low latency time references. But it bothers me that they still broadcast the late beep.

1. #### Rubidium - how it works

I have one. A rubidium atomic 'clock' (oscillator). Doesn't everyone? Relax, they're about \$100+ on eBay. Not a big deal.

The block diagram and description of my rubidium brick says that the rubidium cell provides absorption of the GHz RF signal. The electronics probes the vaporized rubidium for an absorption response, and locks onto the correct frequency.

The rubidium cell does not itself emit a signal as implied in this article. Acts more like a filter really.

2. #### Re: The third beep arrives 15s late

Not entirely unheard of. That's like a principle from Muphry: "Measure with a micrometer. Mark with chalk. Cut with an axe."

Of course, if 15s delay happens to be precise, then it can be properly accounted for. But where's the fun in that.

4. This post has been deleted by its author

2. The caesium clocks flown around the world in 1971 were Hewlett-Packard ones, from the days when HP had a well-deserved reputation for innovation and quality. Sic transit gloria mundi.

1. The good bits became Agilent, which still has a good rep in test & lab eqipment, I think.

1. After the HP-Agilent split in 1999, the healthcare divisions were the first to be sold off -- to Phillips. Components spun off as Avago. Test and measurement (the original HP) shrunk a lot, I think, and recently split off as Keysight Technologies, leaving Life Sciences and Chemical Analysis as Agilent.

2. The atomic watchmaking part of Agilent was sold to Symmetricom shortly after the HP / Agilent split.

Agilent has just undergone another schism, this time with the Test & Measurement stuff going by the name "Keysight" and Agilent retaining some Life Sciences and Chemical Analysis businesses, possibly some others too...

2. #### A man with a van - Project Great 2005

http://leapsecond.com/great2005/

3. #### nice, as a primer...

But it could have been much more technical.

1. #### Re: nice, as a primer...

Look, the man talked about prodding atoms with pointed sticks: how much more technical do you need? I think it is time to "release the tiger".

Personally, I thought this article hit the mark nicely and, as other commentards have said, should be required reading at the sharp end of school Physics classes.

4. This post has been deleted by its author

1. #### Re: Two theories of relativity

No

http://en.wikipedia.org/wiki/Time_dilation#Velocity_and_gravitational_time_dilation_combined-effect_tests

http://www.einstein-online.info/spotlights/Twins

http://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System#Relativity

1. This post has been deleted by its author

5. Just got a new Nissan Leaf.

It doesn't come with DAB.

It comes with Bose, so DAB would have been a great match.

6. "Another problem was that the Earth’s rate of rotation is slowing down, largely due to tidal energy dissipation."

I've been warning people about tidal power generation for years, this is the first time I've seen it written somewhere to back me up that energy is lost in that system. The same goes for windmills - we simply don't have the data to know they aren't causing massive changes to the planet which we've yet to notice.

1. AC, I couldn't agree more! Especially with wind turbines; it's obvious that they slow down the wind. And what happens when the wind gets too slow? As every* pilot knows, when it gets too slow the earth will stall. And then we all die.

*Maybe not every pilot, but even Trans Asia is now making sure that their pilots know.

1. The problem with wind turbines is more that they disrupt the interconnected whirly weather patterns of the planet, surely? If we stop the whirl over Britain, it may disrupt the arctic whirl which could lead to warm wind directly finding it's way to the ice, which is apparently so precious we have to stop burning things. The problem with hippies is that if something doesn't look damaging they ignore it. Oil spills, deforestation and burning stuff they flock to and protest, but anything which looks clean like Prius' or windmills and they won't even consider that there may be a downside for the planet.

1. #### The problem with hippies

"The problem with hippies is that if something doesn't look damaging they ignore it."

Like all the smoke and CO2 from them camp fires they gather round, all the chemicals they use to process their drugs, the mess they leave behind at campsites etc etc

bloody tree huggers

2. #### Re: The problem with wind turbines:

It's not a problem. There will always be enough wind to go around as long as that butterfly in China flaps its wings at just the right time.

2. Yes, you are correct in thinking that a tidal energy plant will have some effect on the the Earth-Moon relationship, but the impact it will have is almost infinitesimal.

How much do you think the tide is affected by one tidal energy plant, as opposed to the entire coastline of the UK?

The tidal effects mentioned in the article that are causing the earth's rotation to slow are mainly the effects of the moon's gravity on the Earth itself, not the effect on the seas.

tl/dr Yes the Earth's rotation is slowing, but at such a slow rate that you should really be worried about the lifetime of the Sun

1. @phuzz how do you know this, have you tested? You seem to be making just as much assumption that it won't cause issues which was surely the point of the OP?

3. "I've been warning people about tidal power generation for years, this is the first time I've seen it written somewhere to back me up that energy is lost in that system."

The energy is lost in the tidal system regardless of whether we tap it or not. It's lost in the form of heat via friction with the shore/sea-bed.

The only thing tidal power generation is doing is preventing the rocks eroding a little bit. And we're talking an infinitesimal amount.

Now, you should direct your ire at all those NASA space missions, using the earth and other planets to get a gravitational assist and slowing down their orbits by a small amount...

7. #### Another DAB "put-down" !!

The writer said "The multiple transmitters in DAB networks are synchronized by GPS. All that technology and still it sounds awful."

This is perhaps only true where specific circumstances are met: (1) The people in charge make limited bandwidth available for DAB (due to not encouraging multiple ensembles to exist. (2) the commercial cost of carrying a DAB signal is higher than it needs to be and given the case in (1) so it forces broadcasters to limit their bandwidth (in order to save money) and hence lower the quality heard by listeners :(

Issue (1) can be resolved if Ofcom (or whatever their name is now) licensed all 37 ensembles (instead of the 2 national and upto 4 regional MUX's currently) that could be used on the DAB network. This then provides far greater bandwidth and broadcasters could then transmit at 256kb, even 384kb and then DAB would sound much better and hence it would stifle any further criticisms.

Even at 192kb, BBC Radio 3 can sound exceptionally good. So please stop tarnishing DAB with the "same old, same old" argument and lets push Ofcom to release new ensembles and get Arqiva to reduce their rates.

PS: The 2nd commercial national multiplex is likely to be on air by 2016, and one of the applicants, Listen2Digital is proposing to broadcast 4 DAB+ stations. http://www.wohnort.org/DAB/uknat.html

1. #### Re: Another DAB "put-down" !!

My DAB radio sounds like a potato. Underwater. And needs a dedicated landfill site for the batteries it eats. And has a mass of at least 500g.

Until it doesn't, DAB is dead to me.

Whereas my long wave portable Roberts radio can achieve similar potato-like sound quality for a whole winter cricket test match series, all on a single pair of AAAs.

1. #### @bfd:Re: Another DAB "put-down" !!

Rechargeables work well in my portable battery consumption device/DAB radio.

Cheers,

Jay

2. #### Re: Another DAB "put-down" !!

I'm going with the analogy of DAB is to digital radio what NTSC was to colour TV. NTSC was a great idea and an improvement over black and white, but then PAL came along and had more accurate colours, but the US was stuck with NTSC because it had too much capital invested in it to change. DAB was a great idea and has the potential to be better than FM, but then improved digital radio technologies came along and left the UK behind because it was too invested in DAB.

(off topic 1: can you get a DAB receiver that can be switched on from the mains socket switch (without having to turn on at the unit as well)? You could do that with a cheap FM receiver! Meant you could keep the radio out of the way (e.g. top of a cupboard) and switch on and off at the mains without having to switch on at the unit, which can be fiddly for smaller units, often requiring two (clean) hands)

(off topic 2: yeah, yeah, some of DAB's problem is over-compression, much like Freeview/YouView, where SD broadcasts look awful, where they used to be nice and now HD barely looks better than analog)

8. #### All that technology and [DAB] it sounds awful.

There are other stations besides Magic.

9. #### Thank You

Thanks for this article Mr. Watkinson and to all the commentards. Absolutly enlightining. Should be a read at schools.

R.A.

## POST COMMENT House rules

Not a member of The Register? Create a new account here.