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Cosmic rays may have just unveiled a hidden chamber within Egypt’s most famous pyramid.

An international team led by at Nagoya University in Japan used muons, the high-energy particles generated when cosmic rays collide with our atmosphere, to explore inside Egypt’s Great Pyramid without moving a stone.

Muons can penetrate deep into rock, and get absorbed at different rates depending on the density of the rock they encounter. By placing muon detectors within and around the pyramid, the team could see how much material the particles passed through.

“If there is more mass, fewer muons get to that detector,” says at Los Alamos National Laboratory, who uses similar techniques to image the internal structure of nuclear reactors. “When there is less mass, more muons get to the detector.”

By looking at the number of muons that arrived at different locations within the pyramid and the angle at which they were travelling, Morishima and his team mapped out cavities within the ancient structure.

This type of exploration – muon radiography – is perfect for sensitive historical sites as it uses naturally occurring radiation and causes no damage to the structure.

Mysterious cavern

The team mapped the pyramid’s three known chambers – the subterranean chamber, the Queen’s chamber, and the King’s chamber – along with connecting corridors. They also detected a new large void above the Grand Gallery that connects the King and Queen’s chamber. This new void is approximately the same volume as the Grand Gallery. The team believes it’s another oversized tunnel similar in dimensions to the Grand Gallery that is at least 30 metres long.

The team used three different muon detectors, starting with nuclear emulsion film within the Queen’s chamber. Like photographic film is exposed to light to make a photo, the emulsion reacts to muons and makes a record of their paths.

Once their initial findings indicated a potential cavity, they confirmed it by placing an instrument that emits a flash of light when struck by muons within the pyramid. Outside the pyramid, they also used detectors that record muons indirectly when the high-energy particles ionise the gas inside. After several months in position to record muons, all three methods confirmed a void in the same location.

“It’s marvelous,” Morris says, noting that the long exposure times increase the robustness of the results. “What they’ve seen is fairly definitive,” he says, although it will take drilling and cameras to determine if the cavity is a structural chamber, or a void created by a long-forgotten collapse.

A team led by Luis Alvarez first tried using muon radiography to map pyramids in 1970, but they were unable to detect new voids. If confirmed, this would be the first newly rediscovered chamber within the Great Pyramid in more than a century.

“I’d love to be there when they first stick a camera through a drill hole,” Morris admitted. “It’s not every day we discover a chamber in a pyramid.”

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