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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!
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?
If I can be modded down for being a troll, can I be modded up for being an orc, or a balrog?
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.
"People who think they know everything are very annoying to those of us who do."-Mark Twain
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.
How much matter is in space?
Strictly speaking, all of it.
Ignorance is the root of all evil.
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.
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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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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