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Optical clock comparison for Lorentz symmetry testing

Nature volume 567, pages 204–208 (2019)Cite this article

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Abstract

Questioning basic assumptions about the structure of space and time has greatly enhanced our understanding of nature. State-of-the-art atomic clocks1,2,3 make it possible to precisely test fundamental symmetry properties of spacetime and search for physics beyond the standard model at low energies of just a few electronvolts4. Modern tests of Einstein’s theory of relativity try to measure so-far-undetected violations of Lorentz symmetry5; accurately comparing the frequencies of optical clocks is a promising route to further improving such tests6. Here we experimentally demonstrate agreement between two single-ion optical clocks at the 10−18 level, directly validating their uncertainty budgets, over a six-month comparison period. The ytterbium ions of the two clocks are confined in separate ion traps with quantization axes aligned along non-parallel directions. Hypothetical Lorentz symmetry violations5,6,7 would lead to periodic modulations of the frequency offset as the Earth rotates and orbits the Sun. From the absence of such modulations at the 10−19 level we deduce stringent limits of the order of 10−21 on Lorentz symmetry violation parameters for electrons, improving previous limits8,9,10 by two orders of magnitude. Such levels of precision will be essential for low-energy tests of future quantum gravity theories describing dynamics at the Planck scale4, which are expected to predict the magnitude of residual symmetry violations.

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Fig. 1: Testing Lorentz symmetry with two earthbound optical Yb+ clocks.
Fig. 2: Six-month-long frequency comparison between two ytterbium single-ion clocks operating on the 642-THz electric octupole transition.

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Data availability

All data obtained in the study are available from the corresponding author on reasonable request.

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Acknowledgements

We thank B. Altschul, A. Goban, R. Hutson, A. Kostelecký, T. Mehlstäubler, M. Mewes, A. Vargas-Silva and J. Zhang for discussions and B. Lipphardt for experimental assistance. This research received funding from the European Metrology Programme for Innovation and Research (EMPIR project OC18), co-financed by the Participating States and the European Union’s Horizon 2020 research and innovation programme, and from DFG through CRC 1227 (DQ-mat). This work was also supported in part by the Office of Naval Research, USA, under award number N00014-17-1-2252, by NSF through grant PHY-1620687 (USA) and by the Russian Foundation for Basic Research under grant number 17-02-00216. C.S. thanks the Humboldt Foundation for support.

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  1. Christian Sanner

    Present address: JILA, Boulder, CO, USA

Authors and Affiliations

  1. Physikalisch-Technische Bundesanstalt, Braunschweig, Germany

    Christian Sanner, Nils Huntemann, Richard Lange, Christian Tamm & Ekkehard Peik

  2. Department of Physics and Astronomy, University of Delaware, Newark, DE, USA

    Marianna S. Safronova & Sergey G. Porsev

  3. Joint Quantum Institute, National Institute of Standards and Technology and the University of Maryland, College Park, MD, USA

    Marianna S. Safronova

  4. Petersburg Nuclear Physics Institute of NRC (Kurchatov Institute), Gatchina, Russia

    Sergey G. Porsev

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Contributions

C.S., N.H. and E.P. conceived the experiment and developed the methods. C.S., N.H., R.L. and C.T. designed and constructed the experimental apparatus. C.S., N.H., R.L., M.S.S. and S.G.P. acquired and analysed the data. All authors were involved in the preparation and discussion of the manuscript.

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Correspondence to Christian Sanner.

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Supplementary Information

This file contains details about the transformation between lab frame and celestial frame and derives explicit formulas for the matrix elements of the T0(2) operator.

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Sanner, C., Huntemann, N., Lange, R. et al. Optical clock comparison for Lorentz symmetry testing. Nature 567, 204–208 (2019). https://doi.org/10.1038/s41586-019-0972-2

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Comments

Commenting on this article is now closed.

  1. Xinhang Shen

    Dear Christian Sanner, Nils Huntemann, Richard Lange, Christian Tamm, Ekkehard Peik, Marianna S. Safronova & Sergey G. Porsev,

    It has been more than three years during which I have posted numerous comments here to show that Einstein's relativity is wrong and there is no such thing called spacetime in nature because time is absolute and independent of the three dimensional space. If you have found errors in my reasoning, please refute them. Otherwise, you should accept the discovery. I think it would be inappropriate to ignore this discovery and continue wasting taxpayers' money on wrong researches.

    Here is a summary of the reasoning to disprove special relativity for your convenience:

    Let's look at the twin paradox which is designed to demonstrate that relative speed would generate time dilation as predicted by special relativity which claims that when the speed of a clock relative to an observer was close to the speed of light, the observer would see the clock slow down close to stop. But, as shown on Wikipedia, the final conclusion of the twin paradox becomes that, after a high speed space travel, it is the acceleration of the traveling twin (not his speed relative to his brother) that made him younger than his twin brother staying on the earth because both twins had experienced exactly the same speed relative to each other during the entire trip. Is it funny that the original argument that relative speed generates time dilation is completely lost, although relativists still think that the paradox has been solved? In fact, this paradox has simply confirmed that relative speed can never generate time dilation and special relativity is wrong.

    Actually Einstein's relativity has already been disproved both theoretically and experimentally for more than three years. The fatal mistake of Einstein’s relativity is that it uses Lorentz Transformation to redefine time and space and the newly defined time is no longer the physical time we measure with physical clocks. We know the physical time shown on any physical clock is T = tf/k where t is the theoretical time, f is the frequency of the clock and k is a reference frame independent calibration constant.

    In Newton’s mechanics, f is a reference frame independent constant too. Therefore, we can set k = f to make the clock show the theoretical time i.e. the absolute Galilean time t: T = tf/k = tf/f = t.

    But in special relativity, frequency f is a reference frame dependent variable and can’t be eliminated by setting k = f. Thus, T can never be relativistic time t: T = tf/k != t. Therefore, relativistic time t is never the clock time i.e. the physical time which we are using to observe all physical phenomena. On the other hand, when a clock is observed in another inertial reference frame, we have t’ = rt and f’ = f/r and T’ = t’f’/k = rt(f/r)/k = tf/k = T, where r = 1/sqrt(1 - v^2/c^2), which means that the physical time T won’t change with the change of the inertial reference frame, and is Lorentz invariant and absolute. That is, a clock still measures the absolute time in special relativity.

    This absoluteness of the physical time can be more clearly illustrated by the following thought experiment:

    There are a series of vertically standing candles with the same burning rate and moving at different constant horizontal velocities in an inertial reference frame of (x, y, z, t) where x, y, z, t are relativistic space coordinates and time. At any moment t of relativistic time, all candles have the same height H in the reference frame of (x, y, z, t) and the height has been calibrated as the physical time. Therefore, we have the simultaneous events measured in both relativistic time t and physical time H in the frame of (x, y, z, t): (Candle1, x1, y1, H, t), (candle2, x2, y2, H, t), ... (CandleN, xn, yn, H, t). When these events are observed in anther horizontally moving inertial reference frame (x', y', z', t'), according to special relativity, these events can be obtained through Lorentz Transformation: (Candle1, x'1, y'1, H, t'1), (Candle2, x'2, y'2, H, t'2), ... (CandleN, x'n, y'n, H, t'n) where t'1, t'2, ... and t'n are relativistic times of the events observed in the frame of (x', y', z', t'). It is seen these events have different relativistic times after Lorentz Transformation in the frame of (x', y', z', t'), i.e., they are no longer simultaneous measured with relativistic time in the frame of (x', y', z', t'), but the heights of the candles remain the same because the vertical heights here do not experience any Lorentz contraction. Since the heights of the candles are the measures of the physical time, we can see these events still have the same physical time, i.e., they are still simultaneous measured with the physical time. Therefore, the physical time is invariant of inertial reference frames and absolute, which is completely different from relativistic time.

    As relativistic time is not the physical time we measure with physical clocks, all what special relativity describes is irrelevant to real physics.

    That the physical time (i.e. clock time) is absolute has been clearly confirmed by the physical fact that all the atomic clocks on the GPS satellites are synchronized not only relative to the ground clocks but also relative to each other to show the same absolute physical time, which directly denies the claim of special relativity that clocks can never be synchronized relative to more than one inertial reference frame no matter how you correct them because "time is relative".

    You will find the mathematical proofs that in special relativity, the real speed of light still follows Newton's velocity addition law, and both time dilation and length contraction are simply illusions in my peer-reviewed publications which are available free of charge at: https://www.researchgate.ne... and https://www.researchgate.ne...

    If you don't agree, your refutation will be welcome and greatly appreciated.

    Sincerely,

    Xinhang Shen

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