144 — Discovery of a big void in Khufu’s Pyramid by observation of cosmic-ray muons
The Khufu Pyramid — the Great Pyramid — has been explored by foot, with excavation and exploration starting thousands of years ago (though modern archaeological exporation really began in the 1800s). But the design of the pyramids, in addition to their age, makes it very difficult to conduct a full architectural scan of every room and every space.
If the pyramid were puppy-sized, we could put it in an X-ray scanner and scan the full volume to reconstruct a model of the spaces of this building. But the pyramid is not puppy-sized. And so we cannot.
Instead, more complex particle physics approaches are applicable: Muons are one type of particle produced in cosmic rays which fall on earth in a relatively reliable distribution. By measuring variances in this distribution over space, it is possible to look for differences in material density or structure in a process known as muon transmission imaging.
This technique was used first in the 1960s to look for spaces in the Pyramid of Chephren. Though none were found, this paper describes a reuse of this technology on the larger pyramid, the Pyramid of Khufu.
Using MTI, the authors were able to establish the thickness of the pyramid stone along each axis in each area of the pyramid. This means that they could combine the known information about the outside of the pyramid with the unknown information about the inside structure of the pyramid in order to determine where there were secret recesses inside.
They found one particular, previously unknown area in the Pyramid higher than previously explored regions, that is now the target of further study. Without MT imaging, we likely would not have found this space for many more years.