Muography of the Great Pyramid
Cosmic-ray muons pass through tens of metres of stone. Counted by direction in 2017, they showed a void at least 30 m long inside Khufu’s pyramid.
Chapters · 14
- 01A Void Above the Grand Gallery
- 02Muons from the Sky
- 03Through Tens of Metres of Stone
- 04More Muons Than Expected
- 05The First Search with Muons
- 06The Pyramid in Section
- 07Nuclear Emulsion Films
- 08Scintillator Hodoscopes
- 09Gas Detectors Outside
- 10Behind the Chevron
- 11Volcanoes and Reactors
- 12What It Cannot Do
- 13A Hodoscope, Taken Apart
- 14Laboratory: Counting by Direction
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A Void Above the Grand Gallery
In November 2017, researchers from Egypt, Japan and France reported in Nature a void above the Grand Gallery of Khufu’s pyramid, at least 30 m long, with a cross-section similar to the gallery’s. The paper calls it the first major inner structure found in the pyramid since the nineteenth century.
No stone was moved. Three kinds of detector recorded muons passing through the pyramid: emulsion films and scintillator hodoscopes in the Queen’s chamber, gas detectors outside the north face. Three teams analysed their data separately, and all saw more muons than expected from the same place.
Its shape is not known: one structure or several side by side, horizontal or inclined. Of its purpose, the paper says there is no information. The red hatching on the section only marks where the extra muons point.
At least 30 m long · cross-section like the gallery’s · three kinds of detector
Muons from the Sky
Cosmic rays are mostly protons. In the upper atmosphere they hit the nuclei of air, and the pions and kaons they make decay quickly into muons. Most muons are made about 15 km up.
A muon carries one charge, has about 207 times the electron’s mass and lives 2.2 microseconds on average. In that time, even light goes only about 659 m; muons reach the ground because, seen from the ground, their time runs slow: a 4 GeV muon travels about 25 km on average before it decays.
At sea level, a flat detector receives about one muon per square centimetre per minute, at a mean energy of about 4 GeV. Most come from overhead, fewer the more slanted the direction, roughly as the square of the cosine of the zenith angle.
Made about 15 km up · about 1 per cm² per minute · mean about 4 GeV
Through Tens of Metres of Stone
In stone a muon keeps ionising atoms and losing energy; only those with enough energy get through. The thicker the stone, the more energy it takes and the fewer muons arrive.
The 2017 analysis took the pyramid’s limestone at 2.2 g per cubic centimetre. By the PDG’s range tables, crossing 50 m of such stone straight down takes a muon of at least about 24 GeV, 100 m about 51 GeV. Above the Queen’s chamber lie 65 to 115 m of stone, and the paper notes that only about 1% of muons reach the detectors.
How many muons arrive from a direction records how much stone lies along it in all. Where part of a direction is empty, there is less stone and more muons come through.
50 m: about 24 GeV · 100 m: about 51 GeV · about 1% arrive
More Muons Than Expected
The detectors record where each muon came from. The researchers first built a 3D model of the known pyramid, its shape, passages and chambers, worked out how many muons each direction should bring, and compared that with what they measured.
The Grand Gallery is in the model: it raises the count, but as expected. A direction with still more muons than expected, by far more than the statistical scatter, points at an empty space nobody knew of.
In 2017 the hodoscopes measured an excess of 5.2% to 8.9% and 8.9% to 11% at two places in the Queen’s chamber, mostly above 10 standard deviations. The figure at the top right is this page’s model, computed in the plane of the section alone.
Excess 5.2–8.9% (H1) · 8.9–11% (H2) · mostly above 10 standard deviations
The First Search with Muons
Muons were first used to gauge the rock overhead in 1955, in a tunnel in Australia’s Snowy Mountains. Using them to look for hidden chambers came in the 1960s.
Alvarez led Egyptian and American researchers who put detectors in the Belzoni Chamber, near the centre of the base of Khafre’s pyramid, the second pyramid at Giza: two spark chambers about 2 m square, with scintillation counters above and below. Recording began in early 1968, and more than a million muons were measured, each through about 100 m of limestone on average.
Laid out in 3° × 3° bins of direction, the data showed the pyramid’s four edges clearly. Within a cone of half-angle 35° above the chamber, 19% of the pyramid’s volume, there was no space as large as the known chambers. The result appeared in Science in 1970.
Spark chambers · more than a million muons · 19% of the volume searched
The Pyramid in Section
The section is the north–south vertical plane of the passages, about 7.3 m east of the pyramid’s centre line. The descending passage slopes down from 17 m up the north face at about 26.5°; the ascending passage branches off it and climbs to the Grand Gallery.
The gallery is 46.7 m long and 8.6 m high. From its foot a level passage runs to the Queen’s chamber, whose floor is about 21 m above the base; from its top an antechamber leads to the King’s chamber, lined with granite, its floor 43 m up, five low spaces stacked above it.
The pyramid was built 230.35 m along each side and about 146.7 m high (Petrie’s survey of 1883). Today about 9 m of the top is missing and the outer casing is almost all gone, leaving the steps of the courses.
Base 230.35 m · originally about 146.7 m high · gallery 46.7 × 8.6 m
Nuclear Emulsion Films
Nagoya University used nuclear emulsion films: a plastic base 175 microns thick, coated on both sides with 70 microns of emulsion, in which crystals of silver bromide are dispersed. A charged particle leaves a latent image; developed, it becomes a line of silver grains.
The films need no power. They lay in the south-west corner of the Queen’s chamber and in a narrow “Niche” on its east side, were changed every two months on average, developed in a darkroom of the Grand Egyptian Museum Conservation Center and scanned by microscope, to about 1 micron.
Exposed for 98 and 140 days at the two places, they recorded about 10.6 million tracks. The excess was seen first on the films.
One film 30 × 25 cm · about 1 micron · no power
Scintillator Hodoscopes
KEK’s detector has four layers of plastic scintillator bars, 120 to a layer, each 1 × 1 cm across and 1.2 m long. One layer across and one along make a unit; two units sit one above the other, 1.5 m apart.
A muon crossing a bar makes a faint flash; a wavelength-shifting fibre through the bar’s middle carries it to a photosensor at the end. Each unit gives one point, and the two points give the direction, to about 7 mrad.
It gives data in real time and needs power, about 300 W. Set up in the south-east corner of the Queen’s chamber in August 2016, it recorded 4.8 million events in five months; in January 2017 it moved to the south-west corner, the units 1 m apart.
1.2 × 1.2 m · 480 scintillator bars · 7–10 mrad
Gas Detectors Outside
CEA’s “telescopes” are stacks of four Micromegas gas detectors, each 50 × 50 cm. A muon ionises the gas, the electrons multiply in a strong field and are picked up by readout strips, to about 0.4 mm.
Two telescopes stood in front of the Chevron on the north face, 17 and 23 m from it, looking in from outside towards the Grand Gallery. From May to July 2017 they reconstructed about 12.9 million good tracks between them; each drew only 35 W.
They saw the Grand Gallery at 8.4 standard deviations and the excess above it at 5.8. The paper calls it the first time an instrument detected a deep void from outside a pyramid.
4 layers of 50 × 50 cm · 0.8–4 mrad · 35 W
Behind the Chevron
Above the original entrance on the north face stand two pairs of large limestone beams set like a gable, the Chevron. In 2016 the emulsion films saw extra muons behind it. In 2019–2020 films and gas telescopes went into the descending passage and measured for months more.
The two teams analysed separately and reported in Nature Communications in 2023: a level corridor about 9.1 m long, about 2 m wide and about 2 m high, running south from 0.84 m behind the Chevron, its floor about 20 m above the ground.
Its place was fixed to a few centimetres. In early 2023 the researchers passed an endoscope through a gap beneath the Chevron’s blocks and saw inside the corridor for the first time.
9.06 m long · 2.02 m wide · 2.18 m high (Nagoya)
Volcanoes and Reactors
The same method has looked into other things. At Mount Asama in Japan, emulsion films about 1 km from the crater showed dense and light zones 100 to 200 m below the crater floor.
After the Fukushima Daiichi accident, no one could enter the reactors. In 2015, muons measured outside Unit 1 showed no fuel left where the core had been, no lump larger than 1 m; in 2016, Unit 2 showed a large amount of heavy material at the bottom of the pressure vessel.
These detectors sit beside buildings and mountains and look along nearly horizontal directions, where muons are few and energetic: in the Fukushima set-up, muons below about 7–8° of elevation could not be measured well.
Asama: 100–200 m below the crater floor · Fukushima Unit 1 (2015) · Unit 2 (2016)
What It Cannot Do
A muon count tells how much stone lies along a direction, not a shape. Where an empty space’s edges are, whether it is one or several, level or inclined: counting alone cannot say, and for the Big Void these questions are still open.
Only about 1% of the muons get through, and they must be split by direction, so it takes months; the nearer a direction is to horizontal, the fewer muons and the slower. The corridor could be fixed to centimetres because it is close to the detectors and was measured from several places.
Nor can muons say what a space was for. The paper offers no guess at the Big Void’s purpose.
Total stone, not shape · months · no purpose
A Hodoscope, Taken Apart
The enlarged one is the scintillator hodoscope from the Queen’s chamber, drawn at 1 : 12.5. The upper and lower units each have a layer of X bars and a layer of Y bars; along one edge of each layer, a readout board holds a row of photosensors facing the fibres’ ends.
Each bar is wrapped in a black light-tight skin; the cut ends show the clear plastic and the hole for the fibre in the middle. The units sit in aluminium frames on four posts.
The frames, posts and readout electronics are this page’s drawing; the paper gives the layers, bars, sizes and spacing.
Upper X / Y · lower X / Y · upper frame · readout electronics
Laboratory: Counting by Direction
The lever aims the detector in the Queen’s chamber at a direction in the plane of the section: 0° is straight up, positive towards the north. The slider sets the days of exposure. Each press of “Count” counts again from zero.
The figure at the top right shows, for each direction, the count against what the known rooms alone predict, with the statistical error as a bar. Most directions sit around 1; those through the void sit above it. More days, smaller errors, a clearer excess.
This is a model: one plane only, the void drawn with the gallery’s cross-section, statistics only. Real measurements also deal with directions in 3D, detector efficiency and the uncertainty of the model itself, which is why they took months.
Readings: counted / expected · excess in standard deviations
Try thisTurn the detector from straight up towards the north: from which angle do the counts exceed what the known rooms alone predict? How many days until the excess passes 5 standard deviations?
What the model leaves out
The pyramid follows Petrie’s survey of 1883: the shape, the passages, the Grand Gallery and the three chambers are at their measured places and sizes; the relieving chambers, the Big Void’s extent and the Chevron’s place are read off the papers’ figures. The courses are drawn 0.68 m high, all alike; the real ones vary. The niche around the Chevron is drawn a little larger so the blocks show. The descending passage goes on down into the rock to an underground chamber; the model stops it at the ground. The Big Void is a hatched band because its shape is not known. The hodoscope is drawn twice: in the Queen’s chamber at the pyramid’s scale of 1 : 384, and enlarged, at 1 : 12.5, where the cut-away half was. Muon tracks are drawn; real muons are invisible and move at nearly the speed of light.
Some easy misreadings
Muography is not a photograph: it counts particles that get through and gives the total stone along each direction. The muons do not come from the detector; they come from the sky, and the detector only receives them. A “void” only says there is less stone than expected there; it does not say whether it is a room, a corridor or several small spaces, or whether anything is inside. The North Face Corridor and the Big Void do not appear to connect. These muons come from natural cosmic rays; they pass through everything on the ground all the time, ourselves included.
Common questions · 5
- What did muons find inside Khufu’s pyramid?
In November 2017, researchers from Egypt, Japan and France reported in Nature a void above the Grand Gallery of Khufu’s pyramid, at least 30 m long, with a cross-section similar to the gallery’s.
01A Void Above the Grand Gallery ↑- How many muons get through the pyramid to the Queen’s chamber?
Above the Queen’s chamber lie 65 to 115 m of stone, and the paper notes that only about 1% of muons reach the detectors.
03Through Tens of Metres of Stone ↑- How is a void found from muon counts?
The researchers first built a 3D model of the known pyramid, its shape, passages and chambers, worked out how many muons each direction should bring, and compared that with what they measured.
04More Muons Than Expected ↑- How large is the corridor behind the Chevron?
The two teams analysed separately and reported in Nature Communications in 2023: a level corridor about 9.1 m long, about 2 m wide and about 2 m high, running south from 0.84 m behind the Chevron, its floor about 20 m above the ground.
10Behind the Chevron ↑- What was the Big Void for?
The paper offers no guess at the Big Void’s purpose.
12What It Cannot Do ↑
Sources
- Morishima et al. (2017): Discovery of a big void in Khufu’s Pyramid by observation of cosmic-ray muons, Nature 552, 386–390 (preprint arXiv:1711.01576)
- Procureur et al. (2023): Precise characterization of a corridor-shaped structure in Khufu’s Pyramid by observation of cosmic-ray muons, Nature Communications 14, 1144
- Alvarez et al. (1970): Search for Hidden Chambers in the Pyramids, Science 167, 832–839
- Petrie (1883): The Pyramids and Temples of Gizeh, London
- Beatty, Matthews, Wakely: Cosmic Rays, Particle Data Group, Review of Particle Physics (2022)
- Particle Data Group: Atomic and nuclear properties of materials (muon tables)
- Reyna (2006): A simple parameterization of the cosmic-ray muon momentum spectra at the surface as a function of zenith angle, arXiv:hep-ph/0604145
Data
The pyramid is built from W. M. Flinders Petrie’s survey (The Pyramids and Temples of Gizeh, 1883): the base, the slope, the passages, the Grand Gallery and the chambers at his measured sizes and positions. The relieving chambers, the Big Void’s band and the Chevron’s place are read off the figures of Morishima et al., Nature 552, 386 (2017) and Procureur et al., Nature Communications 14, 1144 (2023); the North Face Corridor is the 2023 paper’s fit (9.06 × 2.02 × 2.18 m). The courses are drawn 0.68 m high and the niche around the Chevron is sized for the model. The detectors are drawn from the papers’ descriptions: emulsion film units of 30 × 25 cm, a hodoscope of four layers of 120 scintillator bars (1 × 1 × 120 cm) in two units 1.5 m apart, gas telescopes of four 50 × 50 cm Micromegas planes. Frames, stands and electronics are the model’s. The laboratory and the stone curve are this page’s model: the sea-level muon spectrum of Reyna (2006), the PDG’s muon range in calcium carbonate, the pyramid as drawn, limestone at 2.2 g/cm³, statistics only. Material presets, parts and the softbox studio of the site’s model kit are ported from AirsupHQ/machine-skill (MIT, © 2026 Air Supply Technologies Inc.).
The text, pictures and models on this page are licensed CC BY-NC 4.0: free to use and adapt for teaching and other non-commercial purposes, with credit to world.lapla.si. Third-party material listed above keeps its own licence.
Cite this plate
Laplace’s Mini World, Plate F57, “Muography of the Great Pyramid”, https://world.lapla.si/en/muography/, CC BY-NC 4.0, updated 2026-10-28.
Follow the question
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Plate F30Neutrinos in Water and IceNeutrinos hardly touch matter. Super-Kamiokande fills a tank with 50,000 tonnes of pure water under a kilometre of rock; IceCube hangs 5,160 optical modules in the Antarctic ice. Both wait for the rare neutrino that hits a nucleus and leaves a ring of light.
Plate M22Life from a Table of NumbersA few kinds of beads, and one number between every two kinds: pull or push. Make the table lopsided and Newton’s third law fails; the tank never settles again.
Plate F28ATLAS and the Higgs BosonThe Large Hadron Collider smashes protons head-on, and the energy of the collision becomes new particles. A Higgs boson decays as soon as it is made; ATLAS records the photons and leptons it leaves and works its mass back out.
Plate F48Hunting Dark MatterA tank of liquid xenon about 1.5 km underground, waiting for a dark-matter particle to strike a xenon nucleus: the LZ detector in South Dakota.
