A Signal from Above
The most common theory is that aliens used these pyramids as a waypoint beacon to navigate themselves back to, or away from the Earth. Some think that the stone spheres around the world served similar purposes, acting as waypoints or transceivers to send and receive messages from the stars above. Scientifically, this is absolutely preposterous, but, since there is no way to disprove these theories, people actually believe that aliens will use these objects to return to the Earth someday.