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Big Void in pyramid
A cutaway view of the Pyramid of Khufu shows the location of the “Big Void” as well as a corridor close to the pyramid’s north face. Click on the image for a larger view. (ScanPyramids Illustration)

An international team of researchers has detected a mysterious, previously unknown void deep inside Egypt’s Great Pyramid that may be as large as an art gallery space.

The anomalous space, known as the ScanPyramids Big Void, showed up on imagery produced by tracking concentrations of subatomic particles called muons as they zoomed through the pyramid’s stones.

“We don’t know if this Big Void is made by one structure, or several successive structures,” said Mehdi Tayoubi, president of the Heritage Innovation Preservation Institute and co-founder of the ScanPyramids campaign. “What we are sure about is that this Big Void is there, that it is impressive [and] that it was not expected, as far as I know, by any kind of theory.”

Tayoubi and his colleagues report the discovery in a paper published online today by the journal Nature.

The find raises far more questions than answers: Assuming the void is really there, what purpose might it have served? Are there any methods that could show more detail about the structure? And it is at all possible to get an archaeologist or a robot inside?

It will take years of further study and engineering work to answer those questions. But that’d be just a moment in the millennia-old history of the Great Pyramid.

The 455-foot-tall pyramid was built on the Giza Plateau, on the outskirts of present-day Cairo, during the reign of the Pharaoh Khufu (Cheops), roughly 4,500 years ago. It sits alongside two smaller, younger pyramids erected by Khufu’s successors.

Since the 19th century, archaeologists have known about three major chambers within the Great Pyramid: the King’s Chamber, the Queen’s Chamber and the Subterranean Chamber. Those chambers are connected by several corridors, including a high-ceilinged passageway called the Grand Gallery.

The ScanPyramids campaign represents the latest effort to look into whether more hidden chambers remain to be discovered within Egypt’s pyramids. Over the past couple of years, research teams have used muon detectors as well as thermal imagers to look for anomalies.

Muon detection apparatus
Researchers from Japan’s KEK particle physics lab set up a muon radiography imaging system in the Queen’s Chamber, inside the Great Pyramid of Khufu. (ScanPyramids Photo)

Muons are subatomic particles that are created when cosmic rays hit atoms in the upper atmosphere. The particles zip through earthly materials at predictable concentrations, and by tracking their position and direction, scientists can build up a low-resolution picture of a solid object’s interior.

The technique, known as muography, has been used to chart the composition of Teotihuacan’s Pyramid of the Sun in Mexico and study underground cavities at ancient sites in Italy.

ScanPyramids’ team includes groups of researchers from Japan’s Nagoya University and KEK particle physics lab, as well as from the CEA, France’s atomic energy commission. The three groups use different methods to detect muons, in order to verify each other’s results.

Last October, the muographers reported the detection of a void that looked like a short corridor. That void was blocked off from the pyramid’s north face by as little as a few feet of rock.

They picked up an even bigger signature from what is now known as the Big Void, located above the Grand Gallery. Muon signals suggested that the void was at least 100 feet (30 meters) long, with a cross section comparable to that of the 153-foot-long Grand Gallery (which is roughly 7 feet wide and 28 feet high, or 2.1 meters wide and 8.6 meters high).

Augmented-reality view of pyramid
ScanPyramids team members use Microsoft HoloLens headsets to work with an augmented-reality model of the Pyramid of Khufu. (ScanPyramids Photo)

Experts don’t know whether the Big Void and the north face corridor were ever connected, and they can’t say whether the Big Void is a purpose-built interior structure or merely a dead space that was left open during the construction process, perhaps for structural reasons. (For what it’s worth, the purpose of the Grand Gallery is still unknown as well, although some suspect it was used as an astronomical observatory while the pyramid was being built.)

Tayoubi said longer-exposure muography may reveal additional details about the Big Void’s structure.

Study co-author Hany Helal of Cairo University cautioned that further experiments would have to progress carefully, in a step-by-step fashion. “It’s important for public opinion to know what is in the pyramid,” he told reporters. “But it’s also important for the development of science and technology, and new techniques in technology.”

Another co-author, French robotics researcher Jean-Baptiste Mouret, is working on the design for a flying robot that could enter an interior space through a 1.5-inch-wide (3-centimeter-wide) hole drilled into the rock. “For the moment, we are just in the thinking and designing process,” he said.

Tayoubi speculated that such a robot could be sent into the short corridor that’s close to the pyramid’s surface. “If an exploration has to be imagined, maybe it has to be imagined from this place,” Tayoubi said.

The researchers emphasized that the current ScanPyramids expedition received the necessary go-ahead from Egyptian authorities on the condition that it would be non-destructive and non-invasive. Any attempt to get inside the hidden voids would face additional scrutiny from those authorities.

“It’s too early now to say that we will use this technique to go in, or that technique,” Helal said.

Tayoubi, Helal and Mouret are among 34 authors of the Nature paper, titled “Discovery of a Big Void in Khufu’s Pyramid by Observation of Cosmic-Ray Muons.”

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