Fun with physics

Fun fact:

The earth is so large that if it were hollow, and two lights on the surface were pointed at the center from the surface, which were set two miles apart, a human eye at the center could not possibly tell them apart.

(Assumptions: The human eye's angular resolution is .03 degrees; the radius of the earth is 6378.1km. The minimum distance to be able to resolve the difference would be just over two miles (about 3 1/3 km))