What is under the dome by Stephen king about?

Answer 1

On an entirely normal, beautiful fall day in Chester's Mill, Maine, the town is inexplicably and suddenly sealed off from the rest of the world by an invisible force field. Planes crash into it and fall from the sky in flaming wreckage, a gardener's hand is severed as "the dome" comes down on it, people running errands in the neighboring town are divided from their families, and cars explode on impact. No one can fathom what this barrier is, where it came from, and when-or if-it will go away.