Little Story of Infinity: When the Universe deciphers History

Who has never dreamed of unlocking the secret of the pyramids and discovering a sacred tomb that has never been explored? This perspective also led Tintin to follow Sophocles Sarcophagus in his quest, the trigger for the album Cigars of the Pharaoh.
© Hergé / Tintinimaginatio
You will no doubt be surprised to learn that, here too, the infinitely small coming from the infinitely big provides the solution! Indeed, using elementary particles, researchers from France and Japan discovered a few years ago an empty chamber in the Great Pyramid of Giza in Egypt, highlighting evidence of a new structure inside this pyramid for the first time since the 19th century! The missing Egyptologists that Sophocles Sarcophagus mentions might have been able to escape their grim fate through this method….

Principle of muography

Seeing inside our body is something that (almost) all of us have already experienced! Using X-rays, radiography makes it possible to visualize the denser parts of our body, such as the bones for example, and to check if one of them is damaged. Since our bones are denser than the tissues that surround them, they stop X-rays more and therefore stand out from our organs, muscles or tendons on the photographic plate.
Muography is based on the same principle: denser parts of a monument, a pyramid for example, will absorb more particles, and conversely, empty spaces will allow these particles to pass unhindered. You might have guessed it by the name of the technique, the particles we are talking about here are muons. A muon is an elementary particle, similar to an electron but heavier. Those used in muography are produced in our atmosphere following the collision of cosmic rays, emitted by the very energetic phenomena populating our universe, and our atmosphere. Particle showers are then created as illustrated in Figure 1, where muons are among the most abundant particles at ground level and are therefore perfect candidates for non-invasively exploring the interior of the pyramids.
Figure 1: Artist illustration of a cosmic ray shower. Credits: A. Chantelauze / S. Staffi / L. Bret, Pierre Auger Observatory
The principle of muography is illustrated in figure 2: depending on the number of muons seen by the telescope, researchers can find the opacity, how much the muons are stopped, of the object and then derive its density. By using several telescopes or by moving them around the object to be studied, it is therefore possible to "see" denser areas (or conversely empty ones!) without having to damage the site.
The technique was originally proposed by Luis Alvarez and his team, who were searching for a void in pyramids as early as 1970! Unluckily, their study focused on the second pyramid of Giza and did not reveal any unknown structure.
© Hergé / Tintinimaginatio
In 2017, on the other hand, the researchers from France and Japan that we were talking about at the beginning of this article, were able to highlight a void inside the Great Pyramid of Giza. Further studies are underway to understand what this void is made of, one or more chambers, and whether it contains objects of different materials.
Figure 2 : Illustration of muography principle. Adapted from K. Jourde.

Probing the pyramids, but not only!

Muography has proven to be an incredible tool for Egyptologists and is now being used to study other sites, such as volcanoes!
Belgian teams, for example, are part of the MURAVES Collaboration, which studies Mount Vesuvius, the famous Italian volcano that destroyed Pompeii and its surroundings in the year 79 AD.
This team uses muon telescopes as illustrated in Figure 3. This study will allow them to study the different densities of the upper part of Mount Vesuvius in which the different eruptive phases have created volumes of different density. After Egyptology, muography is therefore at the service of volcanology! For the curious, it's here!
Figure 3: Muon telescope used to study Mount Vesuvius. Credits: MURAVES Collaboration

Want to play the muographer?

Another team is studying the Grande Soufrière volcano in Guadeloupe. The success of muography depends on the ability to precisely reconstruct the path of muons with the telescope. Remember, however, that these researchers are trying to probe geological or archaeological sites using elementary particles naturally produced in our atmosphere! he DIAPHANE and REINFORCE collaborations need you to help them in this task. Do you want to become a muographer too? Join the team here!
Many thanks to Andrea Giammanco and Theodore Avgitas for their insightful comments!
About the author :
Gwenhaël W. De Wasseige is assistant professor at UCLouvain in astroparticle physics. Each month, Gwenhaël will tell us through her Little Story of Infinity the latest news about the universe and the domain of the infinitely small.
Gwenhaël W. De Wasseige
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