There is a very interesting documentary called "Afterlife" which interview people who died and came back to life. I suppose you can argue that the images that they saw were caused my the brain shutting down, but who knows. We can really know until it happens to us. The existentialist thought goes that there is no meaning to the world other than the meaning we give it. We create our own realities, therefore heaven and hell or any sort of afterlife is a creation of our own.
Although the nature of the universe is linear that does not mean it has a beginning and an end. For their to be nothing there has to be something. In order for there to be something there has to be nothing. Hinduism talks of different stages of the universe, called yuga's. At the end of the fourth yuga Brahma, the god of creation, destroys the universe and recreates it. In some school's of thought there is an extended period of time where there is nothingness between cycles.
I personally do not believe in a fire and brimstone, endless torture kind of hell. That image was largely created by Dante in "The Inferno". Hell is simply knowing there was a God and a heaven, and you must spend eternity knowing that you failed to accept him or did not repent for your misdeeds in life. I choose to believe in some sort of "afterlife". But I also chose to believe in ghosts, so....
Who knows, we may or may not have an eternal soul that transcends this world. Or maybe not. Maybe we're stuck in a constant cycle of reincarnation that can only be purged by Nirvana. Maybe we are in hell. Maybe we're in heaven. Who knows. Unless their is a heaven or a hell, we'll probably never know.