How Subatomic Cosmic-Ray Muons Pierced 4,500 Years of Solid Pyramid Stone
Constructed around $2560\text{ BCE}$ for Pharaoh Khufu, the Great Pyramid of Giza ($146.6\text{ meters}$ original height) contains approximately $2.3\text{ million}$ limestone and granite blocks weighing over $6\text{ million tons}$. Conventional ground-penetrating radar (GPR) cannot penetrate more than a few meters of moisture-bearing limestone.
To see deep inside without drilling a single hole, the international ScanPyramids mission deployed cosmic-ray muon radiography. When cosmic rays collide with Earth's stratosphere, they generate relativistic muons that rain down at nearly the speed of light. By placing nuclear emulsion films inside the Queen's Chamber and gas-based micromegas telescopes outside the pyramid, physicists detected an excess of muons passing through two previously unknown cavities: the 9-meter North Face Corridor (NFC) behind the entrance chevrons (confirmed via endoscopic camera) and the massive 30-meter Big Void above the Grand Gallery.