Man-Made Atomic Clocks the Best In the Universe 267
An anonymous reader writes "The widespread belief by astrophysicists that pulsars and white dwarfs are the best clocks in the universe is wrong, say two Australian physicists. John Hartnett and Andre Luiten from the University of Western Australia have recently shown that man-made terrestrial atomic clocks take the crown, contrary to numerous claims in astrophysical literature that the natural timing provided by pulsars and white dwarfs is the most precise. The preprint of their paper, available on the arXiv, shows that terrestrial clocks exceed the accuracy and stability of the astrophysical 'clocks' by all sensible measures, in some cases by several orders of magnitude."
Too much noise in pulsars (Score:3, Informative)
Re:Relativity... (Score:4, Informative)
You need to trust something as the "absolute truth" before you can start saying that something is off-the-standard, because its off THAT standard that you chose already.
Aside from there being no privileged reference frame to say has the "absolute true time", this has nothing to do really with saying that it's exactly 4:20pm exactly when it should be 4:20pm.
The measure they're talking about is how much variance there is in the frequency of the pulses over time, and you can measure that without any 'standard' to compare to -- you're actually comparing the signal to itself.
As long as GPS, Cell phone networks, and TV channels are within a split second of each other, I'm fine.
They could all claim exactly the same time as each other, but if the method they use to track time is "x many events in a second", then if the event in question does not have a stable period then you'll eventually have to add/subtract a second from the GPS, cell phone, etc time.
But yeah, for the majority of practical purposes you don't need timing precision equal to that of a pulsar, much less better.
Re:I hate to be condecending... (Score:3, Informative)
How does gravity affect light?
For one thing it can bend light and create gravitational lenses [wikipedia.org].
Re:I hate to be condecending... (Score:3, Informative)
How does gravity affect light?
The same way it affects everything else - except since photons have essentially no mass, the attraction is very weak.
Re:Definition is the Key (Score:4, Informative)
Not really. What we're looking at here is the suitability of something for BEING the measuring stick. You can say that 300 pulsar pulses is a second, or you can say that the time it takes for 2000 cesium atoms to decay is a second if you like (both numbers pulled completely out of thin air, as for the purposes of this discussion actual measurements are irrelevant), and that technically can define a second, but the suitability of that measuring stick is in how consistent those events are. If the cesium atoms are decaying at a far more consistently measurable rate than the pulsar is pulsing, then that is a better measuring stick.
It'd be like saying that a mile is officially defined as how far a certain runner can run in 10 minutes. The fact that it's the official definition doesn't change that it's a poor measurement method, because of the inherent variability involved.
Re:Yeah thats right. (Score:5, Informative)
Man > Nature... Take that religion!
LOL... I think religion would answer, "when you've created something from nothing, rather than simply measure something accurately, give us a call."
To which man replies: "We created you, Religion, out of absolutely nothing!"
Re:I hate to be condecending... (Score:3, Informative)
It is more accurate to say that mass affects space by bending it. Light though it is traveling in a straight line follows the curves in space. A good starter example would be taking a thin rubber surface, like a baloon and drawing graphing paper like lines on it. If you stretch it out and place a heavy metal ball in the middle it will sag and the once straight lines will now appear to curve around the ball.
Though incomplete this example explains gravity pretty well.
Re:Too much noise in pulsars (Score:3, Informative)
I looked at the article too, because I wanted to find out how pulsars are supposed to be so stable. Other discussions about pulsars often point out that as they get older, they lose rotational momentum due to magnetic fields and/or gravity waves, and they slow down. In fact, they slow down drastically from their initial rate over the first billion years or so. (I've also seen articles about "starquakes", where there's a sudden shift in frequency as the neutron star's crust snaps to a new configuration as the spin forces change.) That doesn't sound like a good clock to me.
The article didn't directly address the issue, other than the term "period drift" (which they didn't seem to define) which I assume could be such a slowdown, and they can somehow factor it out. However, I wouldn't assume that the loss of energy would be particularly linear or predictable. So I'm still as confused as ever on these "stable pulsar" claims.
Re:Relativity... (Score:3, Informative)
Re:Duh. (Score:3, Informative)
From the paper, it appears at least some of these claims highlight the accuracy of some of these natural oscillators while not taking into account the increased random noise from a stellar source, or the long-term decay of the natural system. It appears that other claims are simply due to the claimants not keeping up with the rapid pace of advancement in atomic clock design, such that whatever super-accurate pulsar or white dwarf an astrophysicist finds is really only as good as the best atomic clocks used to be.
This makes obvious sense to me (Score:2, Informative)
My guess is that pulsar timing is similar in concept to what happened when John Harrison when he tried making an accurate clock for determining longitude.
http://en.wikipedia.org/wiki/John_Harrison [wikipedia.org]
His early clocks just kept getting larger and more complex, but they were never able to achieve the needed accuracy on a moving, rocking ship for weeks on end.
His solution? He made an very SMALL clock, what amounts to a pocket watch, and was able to achieve accuracy in a variable environment.
Atoms are always going to be more consistent than a celestial object, because electrons can be less susceptible to external forces like aerodynamic drag, object imperfections and inconsistencies, impact bombardment, proximity of other similar objects, and the myriad other things that can affect rotation of an object larger than, say, a cat.
Sure, our "man-made" clocks are more accurate, but that is only because nature has better oscillators that we are capable of observing.