What Created the Dome in Under the Dome?

In Season 2 episode In the Dark it's revealed that there is a mysterious tunnel below the Dome. ... In episode Caged it's revealed that the Dome came down on Chester's Mill town because of Christine Price's interaction with the egg.

Where does the dome come from?

dome, in architecture, hemispherical structure evolved from the arch, usually forming a ceiling or roof. Domes first appeared as solid mounds and in techniques adaptable only to the smallest buildings, such as round huts and tombs in the ancient Middle East, India, and the Mediterranean.

Where did the egg come from under the dome?

In Curtains, when a monarch butterfly starts to smash into the mini-dome and leaving black patches, the same thing happens to the larger dome. When Julia drops the Egg into lake, it causes the Dome to become completely white. It's revealed in Alaska that the egg is indeed the power source of the Dome.