     private let playerNode: PlayerNode = PlayerNode()
     private let enemies =  SKNode()
     private let playerBullets = SKNode()
+    private let forceFields = SKNode()
     
     class func scene(size:CGSize, levelNumber:UInt) -> GameScene {
         return GameScene(size: size, levelNumber: levelNumber)

        view!.presentScene(gameOver, transition: transition)
    }
    
    
}

        
        // Player bullets
        addChild(playerBullets)
        
        // Force Fields
        addChild(forceFields)
        createForceFields()
        
        // Physics body delegate
        physicsWorld.gravity = CGVectorMake(0, -1)
