There's apparently a giant void in the Great Pyramid. Here's why we don't know what's in there.

In the upper reaches of Earth's atmosphere, a rain of high-energy radiation slams into the thin air. The impact creates a second shower of charged subatomic particles, like muons, which fall towards Earth, and then fall into it. They drift down through clouds and then through stone, with most halting in the sculpted, lithified skeletons of long-dead sea creatures. Others press on, passing again through air, through rock once more, and then through a photographic film.