God created the universe and the Sky ( Home of God ) and the Hell existed before our universe created.
My idea is that the Sky and the Hell are made by antimatter particles. Not only these two worlds but also God and spirits ( ghosts ) are made of some kind of plasma that is formed with antimatter. The spiritual world is made of antimatter.
Ghosts pass through walls because they are invisible, right? I think that this kind of plasma cannot connect with the fisical universe, and the type of body that they are made is invisible to us ( not all of us, because some people can see and talk with spirits ). Only a spirit that is strong enough can connect with fisical worlds.
I think that one day we will invent some kind of machine that can detect spirits and the spiritual world. All people in the world will have a chance to talk with and see their died parents and friends. And we will finally know what type of particle spirits are made.