A mystery hollow sits within Egypt’s Great Pyramid of Giza, its vacuum unseen by any living human and its surface undisturbed by contemporary hands. Fortunately, scientists are no longer constrained by human perception.
Scientists tracked the pathways of small subatomic particles called muons to map out the features of the pyramid’s unknown core. Those particles, which were born high in the Earth’s atmosphere, sped toward the surface and burrowed their way through the pyramid. Some of the particles left traces of what they came across on sensitive detectors in and around the pyramid. The pathways of the particles indicated the unexpected presence of the secret chamber, which was reported in 2017 (SN: 11/25/17, p. 6).
That astounding discovery prompted scientists’ ideas to employ muons to investigate additional ancient buildings. Some researchers are also utilizing the technique, known as muography, to map the infrastructure of volcanoes. “You can truly see within the volcano,” says geophysicist Giovanni Leone of Chile’s Universidad de Atacama in Copiapó. This interior perspective might provide scientists with greater knowledge about how and when a volcano will erupt.
Muons may be found all over the Earth’s surface. They’re formed when high-energy particles from space, known as cosmic rays, fall into Earth’s atmosphere. Muons constantly shower down through the sky at varying angles. When the particles reach the Earth’s surface, they tickle the insides of big buildings like pyramids. They also penetrate tiny objects: A muon pierces your thumbnail around once per minute. Measuring how many particles are absorbed as they travel through a structure might disclose an object’s density and any concealed holes therein.
According to Mariaelena D’Errico, a particle physicist at the National Institute for Nuclear Physics in Naples, Italy, who analyzes Mount Vesuvius using muons, the approach is evocative of obtaining a massive X-ray photograph. But “instead of X-rays, we employ … a natural source of particles,” the Earth’s very own, never-ending supply of muons.
Physicists have traditionally researched cosmic rays in order to better comprehend the cosmos from whence they originated. However, muography flips this trend by employing cosmic particles to discover more about previously unknown aspects of our planet. “Particles arriving from the universe have not been applied to our normal life,” explains particle physicist Hiroyuki Tanaka of the University of Tokyo. Tanaka and his colleagues are working to alter that.
Muography was shown in a pyramid. In the 1960s, physicist Luis Alvarez and colleagues used the approach to search for secret chambers in Khafre’s pyramid in Giza, a little smaller neighbor of the Great Pyramid. Detectors detected no evidence of unanticipated rooms, yet the strategy worked.
Nonetheless, the concept took some time to catch on since muon detectors at the time were heavy and performed best in well-controlled laboratory circumstances. Alvarez’s team employed detectors known as spark chambers to detect muons. Under high voltage, spark chambers are filled with gas and metal plates, and charged particles pass through from spark trails.
Spark chambers have been substantially supplanted as a result of developments in particle physics technology. “We can construct extremely tiny, very durable detectors,” says nuclear physicist Edmundo Garcia-Solis of Chicago State University. These detectors can be built to function outside of a tightly controlled laboratory environment.
In 2017, a new but extremely low-maintenance type of detector known as a nuclear emulsion film was critical in revealing the Great Pyramid’s concealed emptiness. Nuclear emulsions use a unique form of photographic film to record particle tracks. The detectors are left in place for a period of time, then transported back to a lab for the study of the tracks imprinted in them.
Through his work on an international effort called ScanPyramids, particle physicist Kunihiro Morishima of Nagoya University in Japan assisted in the discovery of the secret room. “Nuclear emulsions are lightweight, small, and do not require electricity,” he says. That meant that many detectors could be placed in good viewing places in one of the pyramid’s rooms, the Queen’s Chamber, and a tiny nook adjacent to it.
The detectors’ readings were complemented with plastic scintillator detectors inside the Queen’s Chamber, and gas-based detectors outside the pyramid.
Scientists expect that such research may disclose new chambers or features that are not evident with conventional methods of peeking within things. According to Bross, ultrasound, ground-penetrating radar, and X-rays, for example, can only penetrate a limited distance from the surface. Muons, on the other hand, provide a detailed image. “Muons truly are great” for studying pyramids, according to Bross.
Reference: Emily Conover@sciencenews.org
