Apparently a new clock, using an aluminum atom, has been perfected. It is said it will lose/gain no more than one second in 3.7 billion years.
How the fuck do they determine that? The amount of gain/loss in any given lifetime would be virtually unmeasureable.
Well, technically, the second is currently defined in terms of subatomic physical properties of a cesium atom, so literally nothing else can be more accurate. But if you come up with a better way to measure electron vibration and/or use an atom that vibrates faster you can get better granularity and change the definition to be more precise.
They tune a microwave generator to hit a Cesium atom at 9,192,631,770 cycles per second. When the Cesium atom of the right energy state pops out they know they have the microwave generator at that frequency. There is your accuracy measurement.
Dunno how that aluminum one works but how they know the accuracy would be something like this.
For those interested I looked up this aluminum clock. Pretty cool…called a Quantum Logic clock and it is a huge leap in accuracy over the current Cesium clocks.
Nothing else can be more accurate than what? More accurate than a cesium clock? Certainly clocks could be made more accurate than today’s cesium clock. Defining the second with cesium atoms gives a value people should be able to reproduce, more or less, but clocks that can keep time and agree with one another to much better than the precision of the cesium clock, and whos frequency does not appear to drift with respect to large cesium clock ensembles and does appear to drift less than individual clocks within the ensembles, are more accurate than cesium clocks.
I believe the OP means how do they know that it will lose/gain no more than one second in 3.7 billion years. As in how can they measure this estimate… or is it just that, an estimate.
Based on my reading of Whack a mole’s link, it sounds like this clock has significant jitter. That is the quantum detector tells them if the laser needs tweaking upward, or downward, but doesn’t really lock in. If that is the case then measuring the average accuracy becomes even more difficult. It could have the accuracy stated in the OP while still varying up and down by milliseconds per day.Aslong as those average out, then yes, it is accurate on average, but may not be all that over the short term. So you’ve to measure over a VERY long time to be sure you have the average.
Then it seems that a the second is not actually defined by the cesium atom. It is defined by the most consistent time measurement we can find, which just happens to be a property of a cesium atom.
By coincidence my daughter was asking me this morning about super accurate clocks. She asked why we didn’t get ourselves one of these fancy atomic clocks. I said we couldn’t afford one, so she asked how much one would be.
That stumped me. I have absolutely no idea. Assuming someone were to make one for commercial release, is there any way of getting a ballpark figure on how much it would cost?
It is defined by the cesium atom. If we produce a technology that’s significantly better than the cesium atom, then it’s likely that we will change the definition at that time, but that isn’t a given, and it hasn’t happened yet, so for now, yes, that’s the definition.
You measure it by making more than one such clock and studying the statistics of the deviations between those clocks. You have to be careful not to be fooled by two clocks that are drifting at the same rate. You also want to compare it to the previous best clocks. When they deviate you are left with the question of which clock(s) are responsible for the deviations, this is why you need multiple clocks and good physical models for the sources of error.
Also it is important to distinguish between accuracy (how close the measurement is to the absolute standard) and precision (how precisely can you measure).
Finally, there is not just one number that specifies the accuracy, you need to know the spectrum of fluctuations as a function of frequency (commonly expressed as the phase noise spectrum).
No really…well sorta really.
It is not an atomic clock itself (obviously) but it receives a time signal from NIST which is run by their atomic clock. So, essentially this clock gives you the time that the actual atomic clock outputs. Your daughter would probably get a kick out of it.
(Note there are many other makers of clocks like that one…this is just an example)
Why by the clock when you can get the slave or repeater for free. I have to admit that it was cool to see that both my cell phone and crackberry were exactlly calibrated with the atomic clock when I toured the Naval Observatory. It was expected of course, but still cool.
For the real answer the best I could find was $35,000 for a Cesium tube (cite). I assume there is a lot of other stuff that needs to go into it though (the microwave generator, computers and all that stuff).
From the same cite they say you can get a rubidium tube which is very accurate (but not as accurate) for $50. I presume again there is more to it than that tube though.
You can buy a rubidium clock for under $1000.
An atomic clock is really easier to consider as a frequency standard. Many have a main output that is a 10 MHz sine or square wave. You usually need to add a counting and display device, though they can be built in. It depends on how you want to use it.
leapsecond.com shows you all sorts of fun timekeeping stuff, like home atomic clock ensembles, and a camping trip with the kids up to a mountaintop for long enough for two synchronized atomic clocks to deviate by a relativistic amount.
You can also buy GPS devices with a “pps” output line, for example the Garmin devices that look like a blob on the end of a mast, no display, no batteries, with NMEA output. These are sometimes mounted on boats to feed a chartplotter. The pps line is a wire in the cable that pulses for a fraction of a second every second. The thing is, the leading edge of the second happens right on the coordinated universal time and GPS time second, within about 1e-6 seconds. These things cost around $150.
That’s for a NIST-grade tube. This complete setup (here and here) was around $5K at surplus. That’s a complete Cesium primary reference source (pdf), dual Rubidium backup, and GPS tertiary. The price on these fell through the floor because common maintenance parts are no longer available (pdf), and the tubes are coming to the end of their expected service life.
Well, the second can be defined by the cesium atom and still measured more accurately by another kind of clock.
For one thing, the world maintains a bunch of cesium clocks that are usually running, and those that are running participate in regular intercomparisons. There is a version of the time they keep that is only announced some time later - weeks, I think. That is, there are broadcast ticks, and analysis over a longer time period of how those broadcast ticks appear to be drifting fast and slow. You can test your clock by comparing its ticks to the broadcast ticks, and analyzing everything later when the world ensemble has been studied and the now historic broadcast ticks are better characterized.
For another thing, there are different kinds of clocks that are better over different time periods. I think cesium clocks, especially the fountain clocks that throw cesium atoms upward in a vacuum and get to sample resonance in undisturbed atoms for the entire time they are aloft, are the long term favorites. But hydrogen maser clocks are better for accuracy in a shorter time period - maybe a few hours or a few days. And, for second-to-second accuracy, I think TCXO’s, or temperature controlled crystal oscillators, are better than either of these. In fact, cesium and rubidium and hydrogen atomic clocks are all actually quartz crystal clocks that can be steered (or tweaked), combined with some kind of tube or chamber or device that has a strong peak in its frequency response spectrum. These are used to steer the quartz crystal.
And you can also get the time to reasonable short-term accuracy and astounding long-term accuracy on your computer by synchronizing to an atomic clock via a network time protocol server, like time.nist.gov or time.windows.com. My clock is updated hourly and is always within a few milliseconds of the correct time, even though my computer’s built-in clock is quite innacurate.
Wasn’t there some proof of the accuracy of atomic clocks and/or time dilation by flying one in one direction around the earth and the other in the opposite direction, and comparing those to each other and to the stable click time on Earth?
