If your more scientific you might say that "sin" is an inheiritted disease of mankind and that it will eventually be cured.
now for that I have to say humans are born with sin. For them to be "cured" or in other words go to heaven they have to do that through jesus or somethin like that now if you think about it he is dead so what I'm trying to say is this "darkness" or "sin" if you like to put it that way will never be cured and it will always be with humans....