Physics can tell us about space-time and the movement of particles, but what can it tell us about people and past cultures? The archaeological record tells us a great deal about past peoples that inhabited the earth. That is, once archaeological objects can be effectively excavated and observed. The most limiting factor when searching for historical information is our ability to know whether or not something is actually there. Naturally, we would want to look for tools that could help us determine where to look to find these objects and learn about past cultures. Surprisingly enough, particle physics provides just the type of technology to do so.

The ability to not damage the structures or disturb the locations where they are excavating... is another plus for using Muon technology

Physicists have long considered Muons, a type of particle created by cosmic rays from space, great tools for detecting and “seeing” into where humans cannot physically go. These cosmic rays are influxes of particles, made up of almost 90% protons. When the protons from the rays hit the elements of the Earth’s atmosphere, they generate the Muon particle. In our standard model of elementary particles, a Muon is characterized in the same group as an electron. Though it shares some characteristics with an electron, like it’s negative elementary charge, it is 200 times as massive.

It is this relatively large mass of the Muon that makes it a fairly good tool for underground imaging. It can penetrate fairly dense material, like rock and other materials used in excavation which usually are in archaeologists’ way. For especially dense materials, like uranium, that Muons cannot get through, they reflect which allows us to generate a rough image of what is buried beyond our reach.

Most recently, archeologists using cosmic ray muons, have detected an unexpected void in the Pyramid of Giza in Cairo. The archaeologists working at the Pyramid sought a non-invasive way to peer inside of the pyramid and found this cavity. The discovery points out another important feature of the Muon technology that cannot be achieved by humans through brute-force excavation. The ability to not damage the structures or disturb the locations where they are excavating, which is important when trying to form as close to an accurate and complete archaeological record as possible, is another plus for using Muon technology.

 

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By measuring the deflection patterns of cosmic ray muons (depicted here as streaks of light), scientists were able to determine that the Great Pyramid of Giza contained a previously-undiscovered large void above the interior Grand Gallery. They speculate the cavity is structural in nature, though it may represent a hidden chamber.

Photo by: PBS - Secrets of the Dead

If Muons are both non-invasive to archeological excavation and also provide a 3D image of what lies within the ground or ancient structures, why is it the technology not being used more frequently? Though the research done so far allows for a very rough image of 3D objects, the images are not yet up to the grade at which they will be of much use to archeologists besides knowing if something is there or if nothing is there (as in the cavity discovery in the Pyramid of Giza). This calls into question whether or not Muons are the route to take for this type of excavation or whether researchers should be focused on new solutions.

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Ayanna Matthews