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Man-Made Atomic Clocks the Best In the Universe
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."
Man > Nature... Take that religion!
But .. duh? I mean, there is a lot of stuff between these pulsars and us. Any change in the local matter density, nearby gravitational disturbances, and there is no reliable time out of a pulsar. We can't honestly think that there is no undetectable gravitational effects between us and every pulsar in the universe, do we?
Then again, I'm nowhere near being an astrophysicist.
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The authors say that basically there's too much noise in the pulsars. I just skimmed the article, but I didn't see anything that said why the pulsars are noisy, nor did they answer the question if that noise can be fixed, i.e. using a space based telescope (light or radio), or does the noise come from interstellar sources.
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Isn't the best clock going to be one in your frame of reference?
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Considering that we're using atomic clocks to detect the rate of _spin_ _down_ of several neutron stars (and of course, starquakes and glitches), claiming that neutron stars are somehow superior is just stupid.
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.
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The summary seems to use precision and accuracy interchangeably, they are in fact quite different.
Well, maybe your atom clock is more accurate, but my pulsar timepiece has way brighter display.
Well now I know why astronomers have such huge error bars - they've been using pulsars to tell time!
How do you determine which is the best clock in the universe? Don't you need a better one to run a comparison against?
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Maybe aliens do (i'm half joking)
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.
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How does gravity affect light?
Strictly speaking it does not - it bends space-time and light travels on a straight line which looks bent. Think of it this way - you took off and flew in a straight line from Edmonton, Alberta to London, UK someone in orbit would see that you had actually flown a curved path on the surface of the Earth. Light is the same - it thinks it is following a straight line but when looked at from a different frame it appears as a curve.
The irregularity of pulsars has been known for decades now. Most of them are better than your watch, but I've got a textbook on pulsars that's twenty years old and mentions the drifts in their frequency in the first few pages.
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GPS would not work without atomic clocks. Multiplying even a small error by the speed of light means a big error.
Most of them are better than your watch, but I've got a textbook on pulsars that's twenty years old and mentions the drifts in their frequency in the first few pages.
Uh yes it's been known that pulsars do in fact have period drift for many years. However for quite some time after their discovery, their drift was vastly smaller than any man-made clock. This is what lead to the common belief that pulsars are the best (known) clocks in the universe, because for at least several decades they were. Man-made clocks have made tremendous improvements however, and now are better than pulsars. Those super-awesome clocks still experience frequency instability, though. It's just on the order of 1 in 10^17 instead of 10^15 like the best pulsars.
Which based on the statement that our clocks have improved "more than an order of magnitude, on average, in each decade", while we have not found pulsars significantly better than those previously known, means that it's possible that when your textbook was written man-made clocks were only just surpassing pulsars or possibly even still behind.
So yeah this probably is not NEW news, but it's probably going to be news to a lot of people who had the (previously correct) idea that pulsars were better than the best man-made clocks. And no you shouldn't have assumed man-made clocks were better based simply on the existence of frequency instability in pulsars.
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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
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.