6 ms·

Physicists Unveil World's Most Precise Clock

43 points by Libertatea 13y ago

yread 13y ago
>These clocks are so sensitive that they can easily measure the gravitational redshift, in which clocks tick more slowly in more powerful gravitational fields. In other words they can sense changes in height....The new clock should be able to discern changes of around 1 cm at the Earth’s surface This seems like a pretty big deal! Perhaps not for measuring height, but measuring gravity field with such a precision can have more applications
- peterwaller 13y ago
  Some grad students at my university are studying the use of atom interferometers as a so-called "gravimeter" to look for nuclear contraband (uranium has high density, you may have heard) inside shipping containers. It was surprising to me to hear that this was in the realms of possibility. They can essentially do a 3D scan of the container showing the density within (With pretty poor resolution). With enough precise enough clocks, I imagine it might be possible to do the same by measuring timing differences. Funny thought, really.
  - ISL 13y ago
    Do they have any published results/webpage? (Also, the inverse problem for the Laplacian is hard. Hiding a dense object inside a sphere of lower density (in a background of uniform moderate density) is easy, and fully cloaks against external gravitational detection.)
- dcminter 13y ago
  I'm kind of curious as to how close we are to being able to use them for Gravitational-Wave astronomy giving LIGO[1] a run for its money. Anyone know if this is even possible? [1] http://en.wikipedia.org/wiki/LIGO http://en.wikipedia.org/wiki/LIGO
  - Zikes 13y ago
    This project is the first thing I thought of, but LIGO is attempting to detect changes at the subatomic level. [1] > Based on current models of astronomical events, and the predictions of the general theory of relativity, gravitational waves that originate tens of millions of light years from Earth are expected to distort the 4 kilometer mirror spacing by about 10−18 m, less than one-thousandth the charge diameter of a proton. [1] http://en.wikipedia.org/wiki/LIGO#Observations http://en.wikipedia.org/wiki/LIGO#Observations
  - ISL 13y ago
    Short answer - not anytime soon. Longer answer: there might be a clever way to use clocks to pick off gravitational waves, particularly at low frequency, but I doubt that they'll be competitive with pulsar timing/LISA. There are proposals to use atom interferometers for gravitational wave detection. The community is quite divided on the chances for success (I'm in the pessimistic camp at the moment). Barring any surprises, an atom interferometer is much more likely than a timing-based measurement to see any gravitational wave signal. On the LIGO front, so long as the source estimates for gravitational wave signals are correct and as long as Advanced LIGO hits its sensitivity goals, a LIGO GW detection is imminent. There's always room for cleverness.
    - jessriedel 13y ago
      Could you explain why you're pessimistic on GW atom interferometers, or point me to an argument elsewhere? I'm especially interested in the AGIS proposal by the group at Stanford ( http://arxiv.org/abs/0806.2125 http://arxiv.org/abs/0806.2125 ). Also, is it obvious how one could use an ultra precise clock to see evidence for GWs? Such clock can reveal spatial gradients in the rate of ticks (and so reveal things like local mass densities), but GWs should be spatially homogeneous, no? Thanks for any help!
      - ISL 13y ago
        There are some rebuttals by Peter Bender (his abstract for the 2013 April APS meeting may point in useful directions). For the space-based experiment, barring concerns about the technique itself, the right question may be, "Even if the atom interferometer might work, is it a better bet than the existing plans for LISA?" I haven't studied the atom interferometer GW stuff in great detail, but the measurements look challenging from a feasibility and systematic perspective. Any one objection can be addressed, but there are a lot of them, making it challenging in the aggregate. Continued work on the ground in the atom interferometer field over longer baselines will explore both. If that work can show that it works as proposed, then pessimism will turn to optimism; experiment is the arbiter of truth. As for the second point, regarding clocks, my initial response of "no" came from exactly your argument. I hesitated when considering a global array of clocks. For wavelengths comparable to the size of Earth and smaller, there's enough phase difference that perhaps a sufficiently precise clock, read out sufficiently fast, might pick off a signal. Additionally, if there are signals in the micro-to-nanohertz regimes, it might appear as an unexplained fit residual to an overall model of the gravitational potential at any one clock. My GR-fu is insufficient to make reliable estimates of the sizes of these effects (I bet they're small!).
- jessriedel 13y ago
  The "geology" applications briefly mentioned in the article include, I've been told, possibly lucrative techniques for identifying good sites for mining and drilling.
ctdonath 13y ago
The new clock should be able to discern changes of around 1 cm at the Earth’s surface Another reminder the amount of information hitting us every moment is absolutely astounding. That we're building devices which can collect & present that information is equally astounding.
pkfrank 13y ago
Can anyone provide more background to this point? >And physicists rely on clocks to test the fundamental laws of the universe to ever deeper levels. What will this instrument allow us to further discover, confirm, or understand? This project also reminds me of the 10,000 Year Clock-- http://longnow.org/clock/ http://longnow.org/clock/
- breadbox 13y ago
  Presumably a more accurate clock will make it much easier to detect small relativistic effects. This could be useful for e.g. measuring gravity waves. Or it may just make it possible to do various kinds of experiments on a smaller scale. An early direct test of relativity involved putting an atomic clock on a jet to measure time dilation due to relative motion. A more precise clock might allow the same test to be done with an automobile. In the end, the real answer to your question might well be something that we currently know nothing about. In other words: "If we already knew the answer to that question, we wouldn't need the clock."
peeters 13y ago
It's the combination of accuracy and precision that makes this remarkable. It's either the world's most accurate clock with a certain precision, or the world's most precise clock with a certain accuracy. I'm not sure which they actually claim. >They say their new clocks can keep time with an unprecedented precision of one part in 10^18. That seems to a measure of accuracy, not precision. I can make a clock that gives the time in trillions of years since the Big Bang, and it will be perfectly accurate for the distant future as long as it always returns "0". But that's not a great precision. I can also make a clock that gives the time in one 10^256th of a second, but it won't be accurate.
- ISL 13y ago
  This measurement states that it's possible to build two clocks that differ by less than two parts in 10^18. Accuracy: getting as close to the target as you can. Precision: hitting the same spot repeatedly. The paper is correct - these measurements hit the same spot repeatedly. Accuracy in this context is a tricky thing. The SI second is defined by the Cesium standard, but the best Cesium clocks are >100 times less precise. These two clocks are hitting the same tiny spot over and over again somewhere within the fuzzy bullseye that is the Cesium target. The SI standard is not defined as well as the new generation of clocks can measure. Once the world settles in on an optimal optical clock design (the previous leader has been an Aluminum clock, this one uses Ytterbium), the SI standard will move to the new technology. The impressive success of these clocks as a measure of gravitational redshift is also an Achilles heel. I'm not sure that anyone really knows how to do reliable time transfer with them yet, as one's depth in Earth's gravitational potential relative to another clock must be known at the centimeter scale. Another factor of 10-100 in precision will require that such metrology will improve by the same factor. It's a challenge.
  - peeters 13y ago
    You're right. I was thinking that precision in a clock would be its claimed resolution. Similar to how the precision of a measuring tape would be the finest line markings on it, regardless of whether they were actually correct.
  - 13y ago
niels_olson 13y ago
The NIST Time and Frequency Division is one of the unsung heros of physics. Their senior guy, Wineland, got the 2012 Nobel Prize. I remember when the current Primary Standard, NIST-F1, was meeting the press in the late 90s. I was in undergrad and one of their junior guys came through interviewing for a faculty job. His lecture remains one of the most memorable hours of my life. Probably helped by the fact that I had just heard about the F1 in Scientific American a few weeks prior. It is unclear that this particular clock will take over as the Primary Standard, whose data is compared to a competing project in France and coordinated with the astronomical measurements at the US Naval Observatory to construct the Universal Coordinated Time standard. That is then what the USNO transmits to coordinate the GPS satellites, radio services, etc. http://www.nist.gov/pml/div688/ http://www.nist.gov/pml/div688/
- breadbox 13y ago
  "one of the unsung heros of physics ... got the 2012 Nobel Prize." I can't say that I would complain about being forgotten like that.
  - adestefan 13y ago
    When one thinks of "power house" national labs NIST is the first thing that springs into people's mind.
- adestefan 13y ago
  William Phillips won the 1997 prize in physics while at NIST. I had the honor of having lunch with him when he came back to his undergraduate alma mater for a visit a few years later. It was probably the most interesting lunch discussions I've ever been a part of. All four of the NIST Nobel luareates won for the work they've done in laser cooling for the atomic clocks.
tenpoundhammer 13y ago
It's about time.
guimarin 13y ago
awesome. when can I buy one to put in my HFT datacenter...

43 points by Libertatea 13y ago

yread 13y ago

>These clocks are so sensitive that they can easily measure the gravitational redshift, in which clocks tick more slowly in more powerful gravitational fields. In other words they can sense changes in height....The new clock should be able to discern changes of around 1 cm at the Earth’s surface This seems like a pretty big deal! Perhaps not for measuring height, but measuring gravity field with such a precision can have more applications

peterwaller 13y ago
Some grad students at my university are studying the use of atom interferometers as a so-called "gravimeter" to look for nuclear contraband (uranium has high density, you may have heard) inside shipping containers. It was surprising to me to hear that this was in the realms of possibility. They can essentially do a 3D scan of the container showing the density within (With pretty poor resolution). With enough precise enough clocks, I imagine it might be possible to do the same by measuring timing differences. Funny thought, really.
- ISL 13y ago
  Do they have any published results/webpage? (Also, the inverse problem for the Laplacian is hard. Hiding a dense object inside a sphere of lower density (in a background of uniform moderate density) is easy, and fully cloaks against external gravitational detection.)
dcminter 13y ago
I'm kind of curious as to how close we are to being able to use them for Gravitational-Wave astronomy giving LIGO[1] a run for its money. Anyone know if this is even possible? [1] http://en.wikipedia.org/wiki/LIGO http://en.wikipedia.org/wiki/LIGO
- Zikes 13y ago
  This project is the first thing I thought of, but LIGO is attempting to detect changes at the subatomic level. [1] > Based on current models of astronomical events, and the predictions of the general theory of relativity, gravitational waves that originate tens of millions of light years from Earth are expected to distort the 4 kilometer mirror spacing by about 10−18 m, less than one-thousandth the charge diameter of a proton. [1] http://en.wikipedia.org/wiki/LIGO#Observations http://en.wikipedia.org/wiki/LIGO#Observations
- ISL 13y ago
  Short answer - not anytime soon. Longer answer: there might be a clever way to use clocks to pick off gravitational waves, particularly at low frequency, but I doubt that they'll be competitive with pulsar timing/LISA. There are proposals to use atom interferometers for gravitational wave detection. The community is quite divided on the chances for success (I'm in the pessimistic camp at the moment). Barring any surprises, an atom interferometer is much more likely than a timing-based measurement to see any gravitational wave signal. On the LIGO front, so long as the source estimates for gravitational wave signals are correct and as long as Advanced LIGO hits its sensitivity goals, a LIGO GW detection is imminent. There's always room for cleverness.
  - jessriedel 13y ago
    Could you explain why you're pessimistic on GW atom interferometers, or point me to an argument elsewhere? I'm especially interested in the AGIS proposal by the group at Stanford ( http://arxiv.org/abs/0806.2125 http://arxiv.org/abs/0806.2125 ). Also, is it obvious how one could use an ultra precise clock to see evidence for GWs? Such clock can reveal spatial gradients in the rate of ticks (and so reveal things like local mass densities), but GWs should be spatially homogeneous, no? Thanks for any help!
    - ISL 13y ago
      There are some rebuttals by Peter Bender (his abstract for the 2013 April APS meeting may point in useful directions). For the space-based experiment, barring concerns about the technique itself, the right question may be, "Even if the atom interferometer might work, is it a better bet than the existing plans for LISA?" I haven't studied the atom interferometer GW stuff in great detail, but the measurements look challenging from a feasibility and systematic perspective. Any one objection can be addressed, but there are a lot of them, making it challenging in the aggregate. Continued work on the ground in the atom interferometer field over longer baselines will explore both. If that work can show that it works as proposed, then pessimism will turn to optimism; experiment is the arbiter of truth. As for the second point, regarding clocks, my initial response of "no" came from exactly your argument. I hesitated when considering a global array of clocks. For wavelengths comparable to the size of Earth and smaller, there's enough phase difference that perhaps a sufficiently precise clock, read out sufficiently fast, might pick off a signal. Additionally, if there are signals in the micro-to-nanohertz regimes, it might appear as an unexplained fit residual to an overall model of the gravitational potential at any one clock. My GR-fu is insufficient to make reliable estimates of the sizes of these effects (I bet they're small!).
jessriedel 13y ago
The "geology" applications briefly mentioned in the article include, I've been told, possibly lucrative techniques for identifying good sites for mining and drilling.

ctdonath 13y ago

The new clock should be able to discern changes of around 1 cm at the Earth’s surface Another reminder the amount of information hitting us every moment is absolutely astounding. That we're building devices which can collect & present that information is equally astounding.

pkfrank 13y ago

Can anyone provide more background to this point? >And physicists rely on clocks to test the fundamental laws of the universe to ever deeper levels. What will this instrument allow us to further discover, confirm, or understand? This project also reminds me of the 10,000 Year Clock-- http://longnow.org/clock/ http://longnow.org/clock/

breadbox 13y ago
Presumably a more accurate clock will make it much easier to detect small relativistic effects. This could be useful for e.g. measuring gravity waves. Or it may just make it possible to do various kinds of experiments on a smaller scale. An early direct test of relativity involved putting an atomic clock on a jet to measure time dilation due to relative motion. A more precise clock might allow the same test to be done with an automobile. In the end, the real answer to your question might well be something that we currently know nothing about. In other words: "If we already knew the answer to that question, we wouldn't need the clock."

peeters 13y ago

It's the combination of accuracy and precision that makes this remarkable. It's either the world's most accurate clock with a certain precision, or the world's most precise clock with a certain accuracy. I'm not sure which they actually claim. >They say their new clocks can keep time with an unprecedented precision of one part in 10^18. That seems to a measure of accuracy, not precision. I can make a clock that gives the time in trillions of years since the Big Bang, and it will be perfectly accurate for the distant future as long as it always returns "0". But that's not a great precision. I can also make a clock that gives the time in one 10^256th of a second, but it won't be accurate.

ISL 13y ago
This measurement states that it's possible to build two clocks that differ by less than two parts in 10^18. Accuracy: getting as close to the target as you can. Precision: hitting the same spot repeatedly. The paper is correct - these measurements hit the same spot repeatedly. Accuracy in this context is a tricky thing. The SI second is defined by the Cesium standard, but the best Cesium clocks are >100 times less precise. These two clocks are hitting the same tiny spot over and over again somewhere within the fuzzy bullseye that is the Cesium target. The SI standard is not defined as well as the new generation of clocks can measure. Once the world settles in on an optimal optical clock design (the previous leader has been an Aluminum clock, this one uses Ytterbium), the SI standard will move to the new technology. The impressive success of these clocks as a measure of gravitational redshift is also an Achilles heel. I'm not sure that anyone really knows how to do reliable time transfer with them yet, as one's depth in Earth's gravitational potential relative to another clock must be known at the centimeter scale. Another factor of 10-100 in precision will require that such metrology will improve by the same factor. It's a challenge.
- peeters 13y ago
  You're right. I was thinking that precision in a clock would be its claimed resolution. Similar to how the precision of a measuring tape would be the finest line markings on it, regardless of whether they were actually correct.
- 13y ago

niels_olson 13y ago

The NIST Time and Frequency Division is one of the unsung heros of physics. Their senior guy, Wineland, got the 2012 Nobel Prize. I remember when the current Primary Standard, NIST-F1, was meeting the press in the late 90s. I was in undergrad and one of their junior guys came through interviewing for a faculty job. His lecture remains one of the most memorable hours of my life. Probably helped by the fact that I had just heard about the F1 in Scientific American a few weeks prior. It is unclear that this particular clock will take over as the Primary Standard, whose data is compared to a competing project in France and coordinated with the astronomical measurements at the US Naval Observatory to construct the Universal Coordinated Time standard. That is then what the USNO transmits to coordinate the GPS satellites, radio services, etc. http://www.nist.gov/pml/div688/ http://www.nist.gov/pml/div688/

breadbox 13y ago
"one of the unsung heros of physics ... got the 2012 Nobel Prize." I can't say that I would complain about being forgotten like that.
- adestefan 13y ago
  When one thinks of "power house" national labs NIST is the first thing that springs into people's mind.
adestefan 13y ago
William Phillips won the 1997 prize in physics while at NIST. I had the honor of having lunch with him when he came back to his undergraduate alma mater for a visit a few years later. It was probably the most interesting lunch discussions I've ever been a part of. All four of the NIST Nobel luareates won for the work they've done in laser cooling for the atomic clocks.

tenpoundhammer 13y ago

It's about time.

guimarin 13y ago

awesome. when can I buy one to put in my HFT datacenter...