What is death really?
Death is the separation of the body and soul. The body has the ability through its brain connections to form complex shapes in the neurons. These shapes are so complex and tiny, that they affect the aether (which we call empty space). In their affecting of the aether, they actually reach outside the universe.
Death of the body allows the soul (the shapes) to fly away. The problem is that the soul has no method for operating if it doesn't have a body. It simply exists.
People who believe in Jesus salvation are given a new, temporary body at death. This new body allows them to be active within the universe. Remember the thief on the cross who asked Jesus to remember him when Jesus came into His kingdom? Jesus said, "Today you will be with me in paradise," not Heaven. He received a new, temporary body from God... one which has been holding him alive to fly around the universe for the last 2,000 years.
Why is the body temporary? Because at the Judgment Day, God will start a destruction of this universe, and start a new universe for His saved people. The new universe will have no imperfection in it. God's people will be raised from the dead to a new perfect body to live in the new universe forever.
What happens to the people who die without believing in Jesus salvation? They simply float out of control in the vast voids of space, never seeing or understanding anything... because they have not been given a new, temporary body. At the Judgment Day they will be raised from the dead to go to their destruction along with this universe. They will never die. They will continue on to eternity in their continual destruction.
How can they be continually destroyed without dying? When Jesus did His work on the cross, He won a new body for everybody... not only the people who would be saved. The new body is not able to die any longer, just like Jesus was raised from the dead, and lives forever. Since Jesus won a new body even for the evil people, they won't be able to die. But not being taken into the new universe with the saved, they will continue on forever in the destruction of this universe, because everything in this universe will be destroy, even if it takes to eternity to do it.