Science fiction will sometimes address the topic of religion. Often religious themes are used to convey a broader message, but others confront the subject head-on—contemplating, for example, how attitudes towards faith might shift in the wake of ever-advancing technological progress, or offering creative scientific explanations for the apparently mystical events related in religious texts (gods as aliens, prophets as time travelers, etc.). As an exploratory medium, science fiction rarely takes religion at face value by simply accepting or rejecting it; when religious themes are presented, they tend to be investigated deeply. Some science fiction works portray invented religions, either placed into a contemporary Earth society (such as the Earthseed religion in Octavia Butler's Parable of the Sower), or in the far future (as seen in Dune by Frank Herbert, with its Orange Catholic Bible). Other works examine the role of existing religions in a futuristic or alternate society. The classic A Canticle for Leibowitz explores a world in which Catholicism is one of the few institutions to survive an apocalypse, and chronicles its slow re-achievement of prominence as civilisation returns. Christian science fiction also exists, sometimes written as allegory for inspirational purposes. Orson Scott Card has criticized the genre for oversimplifying religion, which he claims is always shown as "ridiculous and false". Afterlife The Palace of Eternity (1969) by Bob Shaw The Riverworld series, by Philip José Farmer Ubik (1969) by Philip K. Dick — In the novel, companies use a form of cryonic suspension ("cold-pac chambers") to preserve the deceased in a state of "half-life" which allows for limited consciousness and the ability to communicate with both the living world and others in half-life. (The half-life concept was first explored in Dick's novella, "What the Dead Men Say" (1964)) The Divine Invasion (1981) by Philip K. Dick — Dick revisits cryonic suspension in this novel, with two principal differences being that, here, (A) the clinically dead can be brought back to life with proper medical procedures (provided they do not lose brain function for too long a period before being suspended) and (B) the dreamlike state of one in cryonic suspension often takes the form of extended memories from the person's life. The Divine Invasion also explores more traditionally religious visions of afterlife; e.g., deities discuss a sifting bridge that must be crossed by the souls of the newly dead to be judged and the coming-about of an "Advocate"