Egyptologists have scores of theories about how the pyramid was built, but there are no reliable accounts of its construction. Herodotus wrote of stones being drawn from quarries near and far, with some being shipped down the Nile on boats. The mammoth construction project occupied the lives of a hundred thousand men, fuelled in part by radishes, onions and leeks, he noted.
To pinpoint the cavity, scientists from Nagoya University in Japan, and KEK, the countrys high energy physics lab, installed muon-detecting photographic plates and electronic muon detectors around the Queens chamber. At the same time, researchers from CEA, Frances energy research organisation, trained muon telescopes on the pyramid from the outside. All three techniques can tell from which direction incoming muons arrive.
When the teams compared their results, all had found a muon hotspot in the same place, indicating the presence of a large cavity in the pyramid. While most of the monument is made of stone that absorbs muons, chambers and cavities let the particles pass through.
Muon analysis allows scientists to look deep inside ancient monuments without drilling holes or causing other damage to the precious structures. But the technique produces low resolution images, making it impossible for the researchers to tell if the newly-found void runs horizontally or parallel to the grand gallery. Nor can they be sure it is a single enclosure rather than a series of smaller cavities close together, they report in Nature.
What we are sure about is that this big void is there, that it is impressive, and was not expected by any kind of theory, said Tayoubi. To shed more light on the purpose of the cavity, Tayoubi called on specialists in ancient Egyptian architecture to come forward with ideas of what it may be so they can be modelled and checked against the teams data. The cavity may have relieved weight on the roof of the underlying grand gallery, or be a hitherto unknown corridor in the pyramid. The team has no plans to drill into the cavity to explore inside, but they are developing a tiny flying robot that might one day be sent in, if the Egyptian authorities approve.
Its a tribute to humankind, said Tayoubi of the pyramid. It asks a question about what is our future. If they have been able to do this with the means they had 4,000 or 5,000 years ago and they left this heritage today, what will our own society leave for future generations?
Peter Der Manuelian, professor of Egyptology and director of the Harvard Semitic Museum, said the discovery was potentially a major contribution to our knowledge about the Great Pyramid.
Im sure there are imperfections and perhaps small voids or cavities in several locations in the pyramid. What makes this one so interesting is the size, seeming to rival the grand gallery itself in scale, he said.
The muons cant tell us about chambers, form, size, or any possible objects, so its far too early to speculate. I know most people want to know about hidden chambers, grave goods, and the missing mummy of King Khufu. None of that is on the table at this point. But the fact that this void is so large warrants further non-invasive exploration, he added.
In 2011, Rob Richardson, a researcher at the University of Leeds, sent a small snake-like robot into one of the tunnels of the Great Pyramid and took pictures of hieroglyphs that had not been seen for 4,500 years. I think people assume that all these mysteries of whats in our world are known but there are still places like the pyramids where we simply dont know, he said. The pyramids have been there for thousands of years and we still dont know exactly why they are there, what they were used for, or how they were built.