One-Way Speed of Light Experiment (Quantum Entanglement Approach)


  • Dhruv Agarwal The International School Bangalore
  • Kristine Rezai Harvard University



Detectors, Entanglement, quantum non-demolition, one-way speed of light, synchronization


Since Einstein stated the constancy of the speed of light to be a mere “stipulation … to arrive at a definition of simultaneity”, theorists argued that it could be possible for the speed of light to differ in different directions since there are many anisotropies like the amount of matter vs antimatter. However, this assumption has not been confirmed yet. No experiment has been proposed that measures the one-way speed of light; all experiments to date measure the round-trip speed of light. The experiment proposed in this paper seeks to measure the one-way speed of light by using an entanglement-controlled stopwatch while remaining blind (during the experiment) on whether the speed of light is isotropic or anisotropic, thereby answering the century-long question.


Download data is not yet available.

Author Biography

Kristine Rezai, Harvard University


References or Bibliography

Einstein, A. (2005). Zur Elektrodynamik bewegter Körper [AdP 17, 891 (1905)]. Annalen Der Physik, 14(S1), 194–224.

Heighway, J. (n.d.). Toward a Deeper Understanding of General Relativity.

Rédei, L. B. (1967). Validity of Special Relativity at Small Distances and the Velocity Dependence of the Muon Lifetime. Physical Review, 162(5), 1299–1301.

Greaves, E. D., Rodríguez, A. M., & Ruiz-Camacho, J. (2009). A one-way speed of light experiment. American Journal of Physics, 77(10), 894–896.

Aoki, K., & Mitsui, T. (2008). A tabletop experiment for the direct measurement of the speed of light. American Journal of Physics, 76(9), 812–815.

Greaves, E. D., Rodríguez, A. M., & Ruiz-Camacho, J. (2010). Erratum: “A one-way speed of light experiment” [Am. J. Phys. 77 (10), 894–896 (2009)]. American Journal of Physics, 78(8), 878–878.

Salmon. (n.d.). The philosophy of Hans Reichenbach. Synthese, 34(1), 5–88.

Lin, Y., et al. “Dissipative Production of a Maximally Entangled Steady State of Two Quantum Bits.” Nature, vol. 504, no. 7480, Nov. 2013, pp. 415–18,

Kraus, B., et al. “Preparation of Entangled States by Quantum Markov Processes.” Physical Review A, vol. 78, no. 4, Oct. 2008,

Krauter, Hanna, et al. “Entanglement Generated by Dissipation and Steady State Entanglement of Two Macroscopic Objects.” Physical Review Letters, vol. 107, no. 8, Aug. 2011,

Yin, J., Cao, Y., Li, Y.-H., Liao, S.-K., Zhang, L., Ren, J.-G., Cai, W.-Q., Liu, W.-Y., Li, B., Dai, H., Li, G.-B., Lu, Q.-M., Gong, Y.-H., Xu, Y., Li, S.-L., Li, F.-Z., Yin, Y.-Y., Jiang, Z.-Q., Li, M., & Jia, J.-J. (2017). Satellite-Based Entanglement Distribution Over 1200 kilometers.

Wu, T.-Y., Kumar, A., Giraldo, F., & Weiss, D. S. (2019). Stern–Gerlach detection of neutral-atom qubits in a state-dependent optical lattice. Nature Physics, 15(6), 538–542.

Grangier, P., Levenson, J. A., & Poizat, J.-P. (1998). Quantum non-demolition measurements in optics. Nature, 396(6711), 537–542.

Brehme, R. W. (1988). On the physical reality of the isotropic speed of light. American Journal of Physics, 56(9), 811–813.

Lewis, G. F., & Barnes, L. A. (2021). The one-way speed of light and the Milne universe. Publications of the Astronomical Society of Australia, 38.

Drągowski, M., & Włodarczyk, M. (2020). The Doppler Effect and the Anisotropy of the Speed of Light. Foundations of Physics, 50(5), 429–440.

Nissim‐Sabat, C. (1982). Can one measure the one‐way velocity of light? American Journal of Physics, 50(6), 533–536.

Will, C. M. (1992). Clock synchronization and isotropy of the one-way speed of light. Physical Review D, 45(2), 403–411.

Spavieri, G. On measuring the one-way speed of light. Eur. Phys. J. D 66, 76 (2012).

Krisher, T. P., Maleki, L., Lutes, G. F., Primas, L. E., Logan, R. T., Anderson, J. D., & Will, C. M. (1990). Test of the isotropy of the one-way speed of light using hydrogen-maser frequency standards. Physical Review D, 42(2), 731–734.

Yoneda, J., Takeda, K., Noiri, A., Nakajima, T., Li, S., Kamioka, J., Kodera, T., & Tarucha, S. (2020). Quantum non-demolition readout of an electron spin in silicon. Nature Communications, 11(1).



How to Cite

Agarwal, D., & Rezai, K. . (2022). One-Way Speed of Light Experiment (Quantum Entanglement Approach). Journal of Student Research, 11(2).



HS Research Projects