[csours]

https://en.wikipedia.org/wiki/Luis_Walter_Alvarez

Alvarez proposed muon tomography in 1965 to search the Egyptian pyramids for unknown chambers. Using naturally occurring cosmic rays, his plan was to place spark chambers, standard equipment in the high-energy particle physics of this time, beneath the Pyramid of Khafre in a known chamber. By measuring the counting rate of the cosmic rays in different directions the detector would reveal the existence of any void in the overlaying rock structure.[48]

[kulahan]

They were indeed able to do this after all [1], and found some unknown voids.

[1] https://spectrum.ieee.org/muon-imaging-finds-hidden-chamber-...

[lazide]

At least one was confirmed to indeed be exist - quite fascinating.

One day hopefully we can find out if the remaining giant looking open area exists too!

[Cthulhu_]

Wouldn't there be other ways to detect voids? Strong X-Rays, penetrating radar, or sound wave / seismic measurements taken from every outside and accessible inside space, combined into a 3d model / visualisation. Or is the stone used that impenetrable? I have no idea about these things.

[lazide]

Those other methods do get used, but are of limited utility because the stone is that impenetrable - and it’s a masonry structure with a significant amount of joints, random small voids, etc.

It really does benefit from something like muon/neutron radiation, where absorption is quite low/penetration quite high, so we can ‘see’ pass the first couple centimeters to meters.