Discovery of a big void in Khufu’s Pyramid by observation of cosmic-ray muons

Abstract

The Great Pyramid, or Khufu’s Pyramid, was built on the Giza plateau in Egypt during the fourth dynasty by the pharaoh Khufu (Cheops)1, who reigned from 2509 bc to 2483 bc. Despite being one of the oldest and largest monuments on Earth, there is no consensus about how it was built2,3. To understand its internal structure better, we imaged the pyramid using muons, which are by-products of cosmic rays that are only partially absorbed by stone4,5,6. The resulting cosmic-ray muon radiography allows us to visualize the known and any unknown voids in the pyramid in a non-invasive way. Here we report the discovery of a large void (with a cross-section similar to that of the Grand Gallery and a minimum length of 30 metres) situated above the Grand Gallery. This constitutes the first major inner structure found in the Great Pyramid since the nineteenth century1. The void, named ScanPyramids’ Big Void, was first observed with nuclear emulsion films7,8,9 installed in the Queen’s chamber, then confirmed with scintillator hodoscopes10,11 set up in the same chamber and finally re-confirmed with gas detectors12 outside the pyramid. This large void has therefore been detected with high confidence by three different muon detection technologies and three independent analyses. These results constitute a breakthrough for the understanding of the internal structure of Khufu’s Pyramid. Although there is currently no information about the intended purpose of this void, these findings show how modern particle physics can shed new light on the world’s archaeological heritage.

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Figure 1: Muon detectors installed for Khufu’s Pyramid.
Figure 2: Results of the analysis of the nuclear emulsion films.
Figure 3: Results of the analysis of the scintillation hodoscopes.
Figure 4: Results of the analysis of the gas detectors.

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Acknowledgements

This experiment is part of the ScanPyramids project, which is supported by NHK, La Fondation Dassault Systèmes, Suez, IceWatch, le Groupe Dassault, Batscop, Itekube, Parrot, ILP, Kurtzdev, Gen-G and Schneider Electric. Measurement with nuclear emulsions was supported by the JST-SENTAN Program from the Japan Science and Technology Agency and JSPS KAKENHI (grant JP15H04241). The CEA telescopes were funded partly by the Région Ile-de-France and the P2IO LabEx (grant ANR-10-LABX-0038) in the framework ‘Investissements d’Avenir’ (grant ANR-11-IDEX-0003-01) managed by the Agence Nationale de la Recherche (France). The detectors were built by the ELVIA company and the CERN Micro-Pattern Gaseous Detector workshop. We thank the members and benefactors of the ScanPyramids project, and in particular: T. Hisaizumi, the members of Cairo University, the members of the F-laboratory in Nagoya University, Y. Doki, the Aïn El Shams University 3D scanning team, the members of the Egyptian Ministry of Antiquities, K. El Enany, M. El Damaty, T. Tawfik, S. Mourad, S. Tageldin, E. Badawy, M. Moussa, T. Yabuki, D. Takama, T. Shibasaki, K. Tsutsumida, K. Mikami, J. Nakao, H. Kurihara, S. Wada, H. Anwar, T. de Tersant, P. Forestier, L. Barthès, M.-P. Aulas, P. Daloz, S. Moignet, V. Raoult-Desprez, S. Sellam, P. Johnson, J.-M. Boursier, T. Alexandre, V. Ferret, T. Collet, H. Andorre, C. Oger-Chevalier, V. Picou, B. Duplat, K. Guilbert, J. Ulrich, D. Ulrich, C. Thouvenin, L. Jamet, A. Kiner, M.-H. Habert, B. Habert, L. Gaudé, F. Schuiten, F. Barati, P. Bourseiller, R. Theet, J.-P. Lutgen, R. Chok, N. Duteil, F. Tran, J.-P. Houdin, L. Kaltenbach, M. Léveillé-Nizerolle, R. Breitner, R. Fontaine, H. Pomeranc, F. Ruffier, G. Bourge, R. Pantanacce, M. Jany, L. Walker, L. Chapus, E. Galal, H. A. Mohalhal, S. M. Elhindawi, J. Lefaucheux, J.-M. Conan, E. M. Elwilly, A. Y. Saad, H. Barrada, E. Priou, S.Parrault, J.-C. Barré, X. Maldague, C. Ibarra Castenado, M. Klein, F. Khodayar, G. Amsellem, M. Sassen, C. Béhar, M. Ezzeldin, E. Van Laere, D. Leglu, B. Biard, N. Godin, P. der Manuelian, L. Gabriel, P. Attar, A. De Sousa, F. Morfoisse, R. Cotentin, C. Delache and G. Perrin.

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Authors

Contributions

K.M., M.K., A.N., N.K., Y.M. and M.M. performed the experiments and analysed the results for the nuclear emulsion films; F.T., H.F., K.S., H.K., K.H. and S.O. performed the experiments and analysed the results for the scintillator hodoscopes. S.P., D.A., S.B., D.C., C.F., P.M., I.M. and M.R. performed the experiment and analysed the results from the gas detector telescopes. B.M., P.G., E.G., N.S., Y.D. and M.S. created the 3D models used for the muography simulations and the RTMS. B.M. designed and implemented the RTMS and contributed to the analyses. Y.E., T.E., M.E. and V.S. coordinated the different experimental operations in the field (muography, 3D scans).The paper was mainly written by K.M., S.P., F.T., M.T., B.M. and J.-B.M., with contributions from all the other authors. H.H., M.T., B.C., B.M. and Y.E. designed and coordinated the project (ScanPyramids).

Corresponding authors

Correspondence to Kunihiro Morishima or Mehdi Tayoubi.

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Reviewer Information Nature thanks G. Saracino, L. Thompson and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Figure 1 Overview of the nuclear emulsion films (Nagoya University).

a, A cross-sectional schematic view of a nuclear emulsion. b, Enlarged schematic view of the emulsion layer. Silver bromide crystals are dispersed in gelatin. The red dashed arrow shows the trajectory of the charged particle. c, After the photographic development process, silver grains are aligned along the trajectory (track) of the charged particle. d, An optical microscopic photograph of the track of a minimum ionizing particle recorded in a nuclear emulsion. e, A nuclear emulsion after development. f, A vacuum-packed nuclear emulsion. g, Schematic view of the detector configuration: six packed nuclear emulsion films with a detection area of 30 cm × 25 cm each (yellow) are fixed between aluminium supporting plates (honeycomb plate, in grey). Two films stacked on top of each other are pressed with a rubber sheet (black) by four short screws. Three additional long screws are used as legs to correct the inclination of the detector. h, Cross-sectional schematic view of the nuclear emulsion detector as shown in g. Two packed films are stacked between two honeycomb plates and rubber sheet.

Extended Data Figure 2 Slices of the data for the nuclear emulsion plates.

Each panel shows slices for tanθy every 0.25 units (in tangent) and separated into four ranges at 0 ≤ tanθy < 1 (see Fig. 2a–d). The top part of each panel shows muon flux distribution and the bottom part of each panel shows the difference of muon flux. In the top part of each panel, the red line shows the data, the black solid line shows the simulation with the internal structures, and the grey dashed line shows the simulation without any internal structure. In the bottom part of each panel, the red line shows the subtraction between the data and the simulation with the internal structures, and the black line shows subtraction between the simulation with and without the internal structures, so that the Grand Gallery appears as a muon excess. Error bars indicate statistical error of 1σ (standard deviation). The comparison between the excess that corresponds to the Grand Gallery and the one that corresponds to the new void shows that the two structures are of a similar scale. For each projection of difference of muon flux, we performed a Gaussian fitting to estimate the direction of anomalies. The fitting zone was 0 ≤ tanθx ≤ 0.2 for position NE1 and −0.2 ≤ tanθx ≤ 0 for position NE2. These fitted centres were used for the triangulation.

Extended Data Figure 3 Overview of the scintillator hodoscopes (KEK).

a, Vertical view of the detector, consisting of two units of orthogonal double scintillator layers. A blue arrow indicates a muon track passing through the whole instrument. b, Cross-section of a scintillator element, showing the central hole for the optical fibre. c, Grid made of double layers, detecting the position of incident muons. d, Plane view of the detector, with an active area of 1.2 m × 1.2 m.

Extended Data Figure 4 Slices of the data for the scintillator hodoscopes.

Left, relative yield of the measurement to the simulation (including known structures) at position H1 for four slices (the width of each bin is 24 Δy). Right, relative yield at position H2 for five slices (the width of each bin is 16 Δy). Error bars show statistical errors of 1σ (standard deviation).

Extended Data Figure 5 Overview of the gas detectors (CEA).

a, Design of a telescope (without its cover) showing the four detectors, the electronics box, the battery and the gas bottles. b, Design of the multiplexed Micromegas detector. c, Principle of a Micromegas detector, showing the ionization and amplification of the signal initiated from a charged particle (dotted array). d, Layout of the detector with the micromesh in red, the resistive strip film in blue, and the Y and X copper readout strips in yellow. HV, high voltage; ADC, analogue digital converter. eg, Amplitude variation of a detector in the Alhazen telescope as a function of time for two previous campaigns (ScanPyramids missions 1 and 2) and the one reported here (g), showing the effect of the patented feedback. Large variations (as observed in e and f) can lead to inefficiency or degraded resolution, and are totally absent from the data of this paper. The only step observed in g corresponds to a manual change of the target amplitude. h, Typical signal recorded in a detector, where each line corresponds to an electronic channel.

Extended Data Figure 6 tanϕ, horizontal slices on the Alhazen muography.

The slices are 0.10 (in tangent) thick, and each slice is shifted by 0.02 with respect to the previous one, which means they overlap. Distributions are generally smooth, with two large muon excesses on histograms 5, 6 and 15 (see Methods). Error bars show statistical error of 1σ (standard deviation).

Extended Data Figure 7 RTMS and 3D models.

a, RTMS output, showing the CEA position G2 (Alhazen) sensor with a 6-view layout. Interactive view with display of sensor field of view and cone projections. Real-time simulation with internal structure overlaid in wireframe. Result with sensor point-of-view superposition. b, Zoom on chevron area (shaded wireframe). c, Enlarged view of optimized 3D model (shaded wireframe). d, Detail of optimized 3D model.

Extended Data Table 1 Comparison of the three muon detection technologies

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Morishima, K., Kuno, M., Nishio, A. et al. Discovery of a big void in Khufu’s Pyramid by observation of cosmic-ray muons. Nature 552, 386–390 (2017). https://doi.org/10.1038/nature24647

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