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."
Yeah thats right. (Score:5, Funny)
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Doesn't Man = Nature? :P
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You obviously never had some of my professors.
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Strictly speaking, as there are elements in nature that are not elements in man, but no elements in man that are not elements in nature; man is a subset of nature. There is a symbol for the relationship, but slashdot's unicode-fu is weak and fails to render it.
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Remarkably, Slashdot translates it correctly from the raw Unicode character into the ampersand notation (⊂), but then strips it out going to HTML. It also fails to handle the named entity (⊂) and the hex version (⊂).
Re:Yeah thats right. (Score:4, Funny)
Doesn't Man = Nature? :P
It depends on how you dispose of your waste.
Leaving it wherever: Nature
Flush: Man
Flinging it: Funny
Burying it in gravel: Nature, but with an air of superiority
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> Doesn't Man = Nature?
According to the Church, no.
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Probably why I don't go to church haha.
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in dutch: hoogmoed komt voor de val.....
Religion is something man made, mostly based on something big that happened.... And at the moment they are mostly busy with child abuses, or blowing them selves up...
But saying that man made the best in the universe, without ever having left our solar system is a little bit naive...
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Yeah, yeah, where's their patent submission?
Uh-huh, that's what I thought. Freakin' alien anonymous posters. Go back to Alienastistan or wherever you're posting from.
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Ditto. I thought it was very egotistical of us to believe that in the entire universe, our way is best.
There are 9 × 10^21 (9,000,000,000,000,000,000,000) stars in the observable universe. Many of the stars themselves are unobservable, but we can see them because they are part of a galaxy that is obviously far away, and appears as a faint dot in our sky. That's only in the 46 billion light years from our lonely rock in the cosmos that we can observe.
The
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H.U.M.A.N! H.U.M.A.N!
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Why does this statement hurt my head so much? ;-)
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"Man-made" as in "artificial'.
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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."
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:Yeah thats right. (Score:5, Funny)
To which Religion retorts: "You can't disprove I didn't create you first, so therefore I did!"
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And then Religion says "All that shows is that you can put different faces on Religion, which is still Religion, therefore I win!"
Religion then goes off to have a pint at the local pub.
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To which particularly religious men reply: "We created you, Religion, out of absolutely nothing!"
Which has a nice ironic ring to it
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OTOH, atomic clocks make pretty lousy pulsars. Are you truly surprised that a large, chaotic body, interacting with it's environment, is less useful for marking time than a purpose-built device in a pre-defined environment?
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the most accurate rely on atoms in a very artificial man-made condition, being tossed upward in laser "atomic fountain".
I hate to be condecending... (Score:3, Interesting)
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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I'm nowhere near being an astrophysicist.
I'm not either, so ... honest question. How does gravity affect light? How much matter is in space? Or, more specifically, in the space between Earth and pulsars visible on Earth?
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How does gravity affect light?
For one thing it can bend light and create gravitational lenses [wikipedia.org].
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How does gravity affect light?
The same way it affects everything else - except since photons have essentially no mass, the attraction is very weak.
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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.
General Relativity Simplified (Score:5, Interesting)
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.
Re:I hate to be condecending... (Score:5, Funny)
How much matter is in space?
Strictly speaking, all of it.
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Or matter *is* space and vice versa, matter being just a bit twister.
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I prefer to be pedantic instead of condescending. hee hee :)
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My my, aren't we humans full of ourselves? Sure, our man-made clocks might be more precise. But extraterrestrial life across the universe doesn't have access to them, couldn't use them as a common reference, and they've only been around for the past ~60 Earth years.
Relativity... (Score:2)
Really, time accuracy depends on your frame of reference. 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.
As long as GPS, Cell phone networks, and TV channels are within a split second of each other, I'm fine.
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.
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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.
True that, and you have to account for General Relativity too. I didn't notice GPS among the list of applications along with cell phone and tv networks. However it should be noted that the atomic clocks on GPS satellites are good but not better clocks than pulsars.
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But what if like, time itself is changing speed, man? How do you know there's "variance" in the frequency of pulses unless you have a non-varying pulse to compare it to? Dude, maybe the pulsar is even keeping perfect time and our clocks are varying wildly!
Personally my clock says it's exactly 4:20pm.
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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.
Pulse variance... is measured... in terms of time? And how are you measuring time? With a cesium atomic transition clock? Well, then, oddly enough, a cesium clock is clearly more accurate!
This has always bothered me about metrology. You have to establish a standard for any measurement. How c
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My stove and microwave clocks are off.
Too much noise in pulsars (Score:3, Informative)
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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 th
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I didn't see anything that said why the pulsars are noisy
They're hot, and hot things are electrically noisy. Once they cool to say 20K they'll be quiet, but too cool to detect. They do not transmit a perfect carrier wave with zero phase noise. Heck that's pretty hard for us on the earth to do a "good enough" job much less make a signal cleaner than can be measured.
They're electromagnetically active, and theres junk surrounding them that messes with them. aka "unknown localized source"
There's a lot of "stuff" in space between us and them moving at different dir
Relatively speaking... (Score:5, Funny)
Isn't the best clock going to be one in your frame of reference?
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Either that, or time itself is an illusion...
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Lunch time doubly so.
(couldn't resist)
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Whoa there! Look at the science you're talking about before you start throwing "crackpot" around.
The measurements which claimed to show that the speed of light was changing were *based* on looking at slight changes in pulsar frequencies. Measurements using atomic clocks have failed to reproduce this effect despite being many orders of magnitude more precise.
You really can't claim that pulsar frequencies change, meaning that the speed of light is changing, meaning you expect pulsar frequencies to change!
Cheap inferior intergalactic imports ... (Score:2)
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."
... are obviously not a quality substitute for stuff Made on Earth, despite what Wal-Mart may claim.
Are you sure that the star child workers billions of light years away from our planet are not putting poisonous lead into the atomic clocks made for *your* childeren . . . ?
Buy Made on Earth!
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Buy Made on Earth!
...in China!
Duh. (Score:4, Insightful)
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.
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there is a strong ideological motivation for the claim that pulsars do it best.
consider that humans can do something new in the universe that the universe can not otherwise do
so this has implications on the nature of the universe and mans relationship to the universe
many of the resulting treatments crap on dominate assumptions that many people think are true
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Well, since the man-made clocks still rely on natural phenomena (just different phenomena than a pulsar) I don't understand why a knowledgeable person would have that motivation. Perhaps I just answered my own question.
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so let us suppose you are knowledgable. then let us frame this as similar to an ideological motivation, really deeper, but we are not really dealing very often with an actually conscious bias. so since you are knowledgeable, I do not have to bring up unfortunate examples in science of ideological influence. even with good data, the ones that immeadiately come to mind take 50-80 years to deal with. and a little more broadly, it is useful to think of creationism as an ideology. and still more broadly yo
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The universe can't count in prime numbers. Thinking we can't keep time (a relative concept to begin with) better for than the universe can is somewhat silly.
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I can not speak exactly for why there is a claim that astrophysics guys seem to like to claim pulsars are the best time keepers. elsewhere I talked about ideology. keeping it simple, if you think physics is finite, you could easily not like the idea of truly new man made configurations of matter exhibiting phenomena that could be considered new in the universe.
on prime numbers, I recall reading sort of a jesuit journal on math around the golden mean and so on, and while I am easily correctable, I seem t
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> consider that humans can do something new in the universe that the universe can not otherwise do
Like, say, grow a beard, drive a car, eat popcorn, watch TV, or post on /.
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come on, grow a beard, this is pretty much a genome thing and lots of non-human entities have facial hair, usually a lot of hair all over. you would hardly bother to classify this phenomena as generated by individual intelligence, individual brains, or individual creativity. are you actually trying for a honest meaniful remark or are you just playing ideology games.
you might see my remark on physics as finite
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How?
The speed of spindown is far less than the rate of typical pulsar. You just won't get enough precision to detect spin down and glitches.
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Really? Let's assume that pulsars are accurate to 10^-1
Cesium clocks got down to 1 part in 10^9 accuracy by 1954. By 1960 the cesium standard was ratified (1 second = 9 192 631 770 hyperfine transitions of Cs-133 atom between ground states) which had 10 significant digits.
By 1967 commercial atomic clocks of that precision were on the market and laboratories were developing the rubidium standard (which can give you 1 in 10^15 parts precision).
Pulsars were first discovered in 1967. And since the rate of pulsa
Precision is not the same as Accuracy (Score:5, Insightful)
The summary seems to use precision and accuracy interchangeably, they are in fact quite different.
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Well, no, they said "precision", and then they said "accuracy and stability", two things that combine to imply precision.
And they're talking about precision as a feature of the natural phenomenon being measured, not numerical precision as a mathematical construct used to record the measurements.
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I am not an expert on these things, but I'll give an explanation of my best understanding of what they are talking about. Someone please correct me if I am wrong. I am basing a lot of this comment off this page (http://www.febo.com/pages/stability/).
The article is talking about "frequency stability", which is related to both accuracy and precision. When you are talking about keeping time, frequency stability effectively provides a ceiling on both accuracy and the precision you should use. In other words, if
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And here the correct one is precision. Accuracy implies the existence of an absolute standard of time to compare them to, which doesn't exist. If something is precise, it's not necessarily being accurate ("correct"), but it's being consistent.
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At the time of my posting this, the comment immediately above yours is asking whether the best clock is simply the one in your frame of reference.
As a physicist, I find the combination of these two posts very entertaining.
When it comes to time, precision and accuracy are the same thing in the "normal" 3D world we live in due to relativity. That is, accuracy is a function of a set of measurements different from your measurement of time.
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The funny thing is you may be both right (and both wrong ;) The importance of accuracy vs precision for a clock really depends on how you want to use it.
Do you want to make sure you are on time for your meeting? Then it's better to be accurate. Do you want to build a good DAC? Then you better have a precise clock.
In the first case, you want to minimize drift from some accepted "true reference value" over time, but the precision of each pulse/tick probably won't matter. In the second, you want to minimi
Better than all natural clocks, perhaps. (Score:2)
But best in the universe? Unlikely.
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Do you have a better one?
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Overstate much? (Score:2)
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Known universe is implied you pedantic dolt.
If more data comes in, then they can reevaluate the claim. We can not base a claim on what data might happen in the future.
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The universe is 13.75 +/- .17 billion years old.. (Score:4, Funny)
Well now I know why astronomers have such huge error bars - they've been using pulsars to tell time!
How do they know? (Score:4, Interesting)
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If you had just one atomic clock and one pulsar, and you tried to measure the period of one against the period of the other, you wouldn't know which was introducing more noise.
But,
You can run your atomic clocks against each other to determine relative accuracy of atomic clocks.
And you can run pulsars against each other to determine relative accuracy of pulsars.
So then you can run pulsars against atomic clocks to determine relative accuracy between them.
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So pulsars as a group are not perfect timepieces, but there may still exist a specific pulsar that is superior?
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Only if it were manufactured to very exacting specifications.
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And when they're not the same, how do you know which one is better?
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You evaluate them against the "one-mississippi, two-mississippi" method, which as everyone knows is the gold standard for counting seconds.
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You compare two clocks built the same way. Since they are basically identical, it's a fair assumption that they also have the same precision.
If you have a clock with known precision (measured the way described above), you can measure a different clock with it. If the measured precision is worse than the known precision of the known clock, you know the other clock is worse. If the measured precision is equal to the precision of the known clock, the other clock is at least as precise. In order to learn more a
This is news? (Score:4, Interesting)
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.
It's one in 10^15 (Score:4, Interesting)
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.
Re:science journal DUH! (Score:5, Funny)
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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.
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The problem is when you cross correlate 100 or 1000 pulsars or atomic clocks to see how well these "measuring sticks" match each other.
Turns out pocket watches are pretty cruddy, pulsars are OK although they assumed they'd be the best (oops), various atomic standards are best although some are better than others.
Look at how NTP works and select clocks.
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Legal or illegal aliens?