Particle physics reveals there is more to wonder about one of the Seven Wonders of the World
High-energy particles from outer space have helped uncover an enigmatic void deep inside the Great Pyramid of Giza.
Using high-tech devices typically reserved for particle physics experiments, researchers peered through the thick stone of the largest pyramid in Egypt for traces of cosmic rays and spotted a previously unknown empty space. The mysterious cavity is the first major structure discovered inside the roughly 4,500-year-old Great Pyramid since the 19th century, researchers report online November 2 in Nature.
“It’s a significant discovery,” says Peter Der Manuelian, an Egyptologist at Harvard University not involved in the work, “although precisely what it means is unclear.”
The open space may comprise one or more rooms or corridors, but the particle-detector images reveal only the rough size of the void, not the details of its design. Eventually, though, this detail of the Great Pyramid’s architecture could offer new insights into one of the world’s largest, oldest and most famous monuments. The only one of the ancient Seven Wonders of the World that’s still standing, the Great Pyramid was built as a burial tomb for Pharaoh Khufu.
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“Imagine you’re an archaeologist and you walk into this room no one has walked in for [over] 4,000 years,” says Nural Akchurin, a physicist at Texas Tech University in Lubbock who wasn’t involved in the study. “That’s huge. It’s incredible.”
Researchers probed the Great Pyramid’s interior with devices that sense muons — by-products of spacefaring subatomic particles called cosmic rays striking atoms in the atmosphere. Muons continuously rain on Earth at nearly the speed of light. But while the subatomic particles easily streak through open air, rock can absorb or deflect them. By placing detectors near the base and areas deep inside of the Great Pyramid and measuring the number of muons that reach the detectors from different directions, scientists could spot empty spaces inside the ancient edifice.
For instance, if a detector inside the pyramid picked up slightly more muons from the north than the south, that would indicate there was slightly less rock on the north side to intercept incoming muons. That relative abundance of muons could indicate the presence of a chamber in that direction.
Muon imaging an enormous, dense construction like the Great Pyramid “is not an easy game,” Akchurin says. The monument obstructs 99 percent of incoming muons before the particles can reach detectors, so collecting enough data to spot its hollow spaces takes several months.
These images from the special films laid out in the Queen’s chamber show excess muons incoming from the direction of the King’s chamber, the Grand Gallery and the newly discovered void.
The newly identified void was first seen with a type of muon detector called nuclear emulsion film, which the researchers laid out in a space called the Queen’s chamber and the adjacent corridor inside the pyramid. When muons zip through these films, the particles’ chemical interactions with the material leave silver trails that reveal which direction the particles came from, explains Elena Guardincerri, a physicist at Los Alamos National Laboratory in New Mexico not involved in the work.
Upon developing these films, the researchers saw a surprising excess of muons coming through a region above the Grand Gallery, a sloping corridor that runs north-south through the center of the pyramid. The cavity appears to be at least 30 meters across — about the size of the Grand Gallery itself. “Our first reaction was a lot of excitement,” says study coauthor Mehdi Tayoubi, cofounder of the Heritage Innovation Preservation Institute in Paris. “We said, ‘Wow, we got something big!’”
Tayoubi and colleagues confirmed their discovery with observations from two other types of muon detectors, which generate electrical signals when muons pass through them, placed inside the Queen’s chamber and outside at the base of the pyramid.
Akchurin hopes this finding will pave the way for muon imaging of other ancient monuments around the world — particularly at archaeological sites where traditional excavation may be difficult, like deep in the jungle or on mountainsides.
Editor's note: This story was updated November 3, 2017, to correct the name of the muon detector used to initially see the void.
K. Morishima et al. Discovery of a big void in Khufu’s Pyramid by observation of cosmic-ray muons. Nature. Published online November 2, 2017. doi: 10.1038/nature24647.