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Agnew DC. A global timekeeping problem postponed by global warming. Nature 2024; 628:333-336. [PMID: 38538793 DOI: 10.1038/s41586-024-07170-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Accepted: 02/06/2024] [Indexed: 04/01/2024]
Abstract
The historical association of time with the rotation of Earth has meant that Coordinated Universal Time (UTC) closely follows this rotation1. Because the rotation rate is not constant, UTC contains discontinuities (leap seconds), which complicates its use in computer networks2. Since 1972, all UTC discontinuities have required that a leap second be added3. Here we show that increased melting of ice in Greenland and Antarctica, measured by satellite gravity4,5, has decreased the angular velocity of Earth more rapidly than before. Removing this effect from the observed angular velocity shows that since 1972, the angular velocity of the liquid core of Earth has been decreasing at a constant rate that has steadily increased the angular velocity of the rest of the Earth. Extrapolating the trends for the core and other relevant phenomena to predict future Earth orientation shows that UTC as now defined will require a negative discontinuity by 2029. This will pose an unprecedented problem for computer network timing and may require changes in UTC to be made earlier than is planned. If polar ice melting had not recently accelerated, this problem would occur 3 years earlier: global warming is already affecting global timekeeping.
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Affiliation(s)
- Duncan Carr Agnew
- Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA.
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2
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Kaur N, Frank F, Pinto J, Tuckey P, Pottie PE. A 500-km Cascaded White Rabbit Link for High-Performance Frequency Dissemination. IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL 2022; 69:892-901. [PMID: 34878974 DOI: 10.1109/tuffc.2021.3134163] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
We perform experiments exploring the use of white rabbit precision time protocol (WR-PTP) for time and frequency dissemination over long-distance optical fiber links. We use unidirectional links, to ensure compatibility with active telecommunication networks, and White Rabbit equipment with modifications for improved performance. Using fiber spools, we realize a 500 km, four-span cascaded white rabbit link. We show short term fractional frequency stability of 2×10-12 , averaging down to 2×10-15 at one day of integration time, with no frequency shift within the statistical uncertainty. We demonstrate the impact of increasing the White Rabbit SoftPLL bandwidth and the PTP message rate. We show evidence of the effect of thermal fluctuations acting on the fiber, and finally discuss the limitations of the achieved performance. We show comparisons with experimental data acquired with commercial good quality global positioning system (GPS) receivers and show that the medium- and long- term stability and accuracy are more than one order of magnitude better with a WR-PTP link.
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Lombardi MA. Multi-Source Common-View Disciplined Clock: A Fail-Safe Clock for Critical Infrastructure Systems. JOURNAL OF RESEARCH OF THE NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY 2022; 126:126041. [PMID: 38469436 PMCID: PMC10112849 DOI: 10.6028/jres.126.041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Accepted: 12/05/2021] [Indexed: 03/13/2024]
Abstract
The multi-source common-view disciplined clock (MSCVDC) is a recent NIST invention designed to support critical infrastructure timing systems that require a verifiably accurate and fail-safe clock. This paper introduces the MSCVDC, provides a technical description of how it works, and discusses its reliability, redundancy, security, and performance. It also discusses the possibility of a commercially available MSCVDC product.
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Milner WR, Robinson JM, Kennedy CJ, Bothwell T, Kedar D, Matei DG, Legero T, Sterr U, Riehle F, Leopardi H, Fortier TM, Sherman JA, Levine J, Yao J, Ye J, Oelker E. Demonstration of a Timescale Based on a Stable Optical Carrier. PHYSICAL REVIEW LETTERS 2019; 123:173201. [PMID: 31702265 DOI: 10.1103/physrevlett.123.173201] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2019] [Indexed: 06/10/2023]
Abstract
We report on the first timescale based entirely on optical technology. Existing timescales, including those incorporating optical frequency standards, rely exclusively on microwave local oscillators owing to the lack of an optical oscillator with the required frequency predictability and stability for reliable steering. We combine a cryogenic silicon cavity exhibiting improved long-term stability and an accurate ^{87}Sr lattice clock to form a timescale that outperforms them all. Our timescale accumulates an estimated time error of only 48±94 ps over 34 days of operation. Our analysis indicates that this timescale is capable of reaching a stability below 1×10^{-17} after a few months of averaging, making timekeeping at the 10^{-18} level a realistic prospect.
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Affiliation(s)
- William R Milner
- JILA, NIST and University of Colorado, 440 UCB, Boulder, Colorado 80309, USA
| | - John M Robinson
- JILA, NIST and University of Colorado, 440 UCB, Boulder, Colorado 80309, USA
| | - Colin J Kennedy
- JILA, NIST and University of Colorado, 440 UCB, Boulder, Colorado 80309, USA
| | - Tobias Bothwell
- JILA, NIST and University of Colorado, 440 UCB, Boulder, Colorado 80309, USA
| | - Dhruv Kedar
- JILA, NIST and University of Colorado, 440 UCB, Boulder, Colorado 80309, USA
| | - Dan G Matei
- Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany
| | - Thomas Legero
- Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany
| | - Uwe Sterr
- Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany
| | - Fritz Riehle
- Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany
| | - Holly Leopardi
- National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
| | - Tara M Fortier
- National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
| | - Jeffrey A Sherman
- National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
| | - Judah Levine
- National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
| | - Jian Yao
- National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA
| | - Jun Ye
- JILA, NIST and University of Colorado, 440 UCB, Boulder, Colorado 80309, USA
| | - Eric Oelker
- JILA, NIST and University of Colorado, 440 UCB, Boulder, Colorado 80309, USA
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