In the first part of ‘David Lewis and Science Fiction’ I explored how Lewis’ reading of science fiction influenced his four-dimensionalist tendencies. In the second part I will explore the connection between Lewis’ reading of science fiction and his espousal of counterpart theory and the doctrine of life-everlasting.


Counterpart Theory

One of Lewis’ signature doctrines is counterpart theory. His seminal article on the topic is ‘Counterpart Theory and Quantified Modal Logic’, Journal of Philosophy, 1968. According to counterpart theory (roughly speaking), each thing exists in only one world; nothing exists in two or more worlds. Two things of two distinct worlds are counterparts if they resemble each other in some respect picked out by the context of the sentence in which one of them is characterised, described, referred to, etc. To say ‘I might have been a mechanic’ is to say that ‘some counterpart of mine in some other world is a mechanic’, rather than (as Kripke says) ‘there is a world where (or according to) I, the very same person, has the property of being a mechanic’. In ‘Counterpart Theory and Quantified Modal Logic’ Lewis says that counterpart relations take the place of identity across worlds. I am not in many worlds. I am in just one, but have counterparts in other worlds. We might say in a loose sense that I am in many worlds or that me and my counterparts are the same, just like we might say in a loose sense that me today and me yesterday are the same. Again, given Lewis’ four-dimensionalist tendencies, the analogy of time and modality makes perfect sense here and it seems Lewis was drawn to counterpart theory because of his commitment to four-dimensionalism.

Now, Lewis thinks a better way to talk about the sameness between me and my counterparts in other worlds is to say that my counterparts are persons I would have been had the world been otherwise (see Lewis 1968, 115). This way of talking about my counterparts is understood counterfactually, about ways I could have been had the world been otherwise, although it does not commit us to trans-world identity. In a footnote Lewis references a science fiction story from the mid-twentieth century, a story we can suppose he read as a teenager or as a student. In footnote 3 he says ‘this way of describing counterparts is due to L. Sprague de Camp, “The Wheels of If”, Unknown Fantasy Fiction, October 1940’ (Lewis 1968, p. 115, n. 3).

The Wheels of If is a story about Allister Park, a New York attorney hoping to rise to the top in Manhattan law. However, one day he wakes up and everything seems a bit different. The year was the same, but he noticed his clothes were different and so were his eyebrows, nose, etc. He was in someone else’s body and in a world that was much like ours but diverged at key places in history. Park wasn’t in New York. He was in New Belfast! As the story unfolds Park finds out that he is an important figure in this alternate universe and he uses his power to great effect. I won’t ruin the whole story for you. What is of interest is the conceptual apparatus Sprague de Camp uses to describe the story.

Early on, as Park is learning about his predicament, he is told by Rufus Callahan about how Joe Noggle was responsible for swapping his mind with the person he inhabits in this alternate universe:

‘When Callahan agreed to tell Park all he wanted to know, Park told his story. Callahan looked thoughtful. He said: “I’m nay brain-wizard, but they do say there’s a theory that every time the history of the world hinges on some decision, there are two worlds, one that which would happen if the card fell one way, the other that which would follow fro the other”.

“Which is the real one?”

“That I can’t tell you. But they do say Noggle can swap minds with his thocks, and I don’t doubt it’s swapping between one of these possible worlds and another they mean.” (1990 edition, Tom Doherty Assoc., p. 30).

A bit later Park confronts Noggle. Noggle explains to Park the concept of the ‘wheels of if’. The concept for any given individual is of a wheel with six persons on it. Noggle, for instance, is on a wheel with five other people. If the wheel is moving, then Noggle inhabits one of the six bodies each day and the other five do likewise. Every person on this wheel has a turn in each body. Noggle explains thus:

“I call it my wheel of if. Each of the other five men on it are the men I should most likely have been if certain things had been otherwise. For instance, the man in whose body my mind dwelt yesterday was the man I should most likely have been if King Egbert had fallen off his horse in 1781.” (1990 edition, Tom Doherty Assoc., p. 42).

In Lewis’ eyes, Park’s wheel of if is a set of possible worlds that contain individuals much like Park and are individuals Park would have been had the world been otherwise. The comparison here is striking. It is reasonable to suppose that this story was in the back of Lewis’ mind when he was developing his counterpart theory in 1965-66, especially since he took the trouble to cite it in ‘Counterpart Theory and Quantified Modal Logic’.



The final comparison I’d like to make between Lewis’ philosophy and science fiction concerns Everett’s no-collapse interpretation of quantum mechanics. I cannot do justice to such a technical and scientific topic, but I will do my best to make the relevant notions clear enough for our purposes. In quantum mechanics it is supposed that things in nature are in superpositions. A superposition is some kind of indeterminate state of any given thing. To illustrate, take a particle like a photon. If we set up an experiment where we intend to throw the photon at a beam splitter it would deflect in a certain way. The photon, therefore, is in a superposition of deflected versus undeflected: there is deflected-and-undeflected-branching. If the superposition collapses, we are left with a ‘sharp’ state that corresponds to one of the branches. According to the no-collapse interpretation, superpositions never collapse. We never reach a sharp state that corresponds to one of the branches. We always have a plethora of coexisting actual superpositions interacting with each other in a myriad of ways.

Towards the end of his life Lewis wrote a paper on quantum mechanics and Schrodinger’s cat. It was called ‘How Many Lives has Schrodinger’s Cat?’. He read it in June 2001 in Australia in honour of Jack Smart. It was posthumously published in 2004 (Australasian J. Phil., vol. 82). In this paper he considers the consequences of the no-collapse interpretation when applied to the thought experiment known as Schrodinger’s cat. In this experiment a cat is placed in a box with a vial of poison, a hammer, and a radioactive detector. If an atom or particle decays, the detector smashes the vial, releases the poison and the cat dies. So we have a jumble of superpositions, the final one being the superposition of alive versus dead for the cat. From the perspective of the cat we can ask ‘what should it expect to experience?’ It is nonsense to suggest, Lewis argues, that the cat should expect either life-or-death because the experience of being dead is not to be expected. Such an experience doesn’t exist. Therefore, the cat should forget the death-branches and calculate its expectations using the non-death-branches. Schrodinger’s cat should be confident that it will survive the episode of life-and-death-branching. Surviving branches are good enough to constitute survival. Lewis thinks the same applies to us. We should expect to live forever through this same form of survival regardless of what bad things we might come across.

Despite the fact that Lewis wrote on this topic late in life he arrived at some of the core ideas of ‘How Many Lives has Schrodinger’s Cat?’ in the 1960s. In a letter to Peter J. Lewis he explains how he arrived at the doctrine of life-everlasting from his reading of science fiction. He says:

‘I’ve long thought that someone who anticipates life-and-death branching ought to be confident that he will survive. (One surviving branch is good enough. Who needs two?) See my Philosophical Papers, Vol. I (OUP 1983), pp. 73-76; but in fact I’ve thought so since very roughly 1960, which is when I read the story about the nefarious company that I mention in the first paragraph of the attached draft. (Alas, there’s now no way I can find that story again. I read lots of science fiction mags at about that time.)’ (Letter to Peter J. Lewis, 7 April 2001, his italics).

The first paragraph of the ‘attached draft’ (dated 1998) of ‘How Many Lives has Schrodinger’s Cat?’ is as follows:

‘I once read a story about a nefarious company that claimed to sell travel by matter-transmitter; but really all they had was a matter-duplicator, and they killed off the original. Now it always seemed to me that, provided the original was killed off without any unpleasantness, this wasn’t very nefarious at all. If I’m going to branch, and one branch will get to Melbourne without any 17-hour plane flight, and the other branch will be killed immediately (and it’s all very reliable) I reckon it’s the way to go. I should anticipate having the experiences of the surviving branch, because the dead-end branch won’t have any experiences’.

This passage did not make it into the final version of the paper.

I have looked through several science fiction magazines from the 1950s and 1960s and have yet, in my view, to find the story Lewis is thinking of (alas, indeed!). However, the idea of matter-transmission and matter-duplication was common among science fiction writers. Many science fiction stories take either process or both as its central theme. In ‘Here Gather The Stars’ by Clifford D. Simak (Galaxy Science Fiction, June-August 1963), Enoch Wallace is the galactic conductor of a way station on Earth that transmits aliens throughout the universe via matter-duplication. In the basement of Wallace’s house are special facilities for storing and destroying the dead-copies of the aliens who pass through the way station on Earth. In ‘Now is Forever’ by Dobbin Thorpe (Amazing Stories, March 1964), the Reprostat is a matter-duplicator device that affords one the opportunity to continue living by duplicating oneself – in the story it is touted as a form of immortality (1964, p. 95). Then there is Rogue Moon (1960) by Algis Budrys, which involves matter-duplication as a form of travel from Earth to the Moon. Finally, in ‘All The Myriad Ways’ by Larry Niven (Galaxy Science Fiction, October 1968), Detective-Lieutenant Gene Trimble is trying to solve the mystery of the recent spate of senseless suicides and criminal acts in his city. It is stipulated in the story that there is an infinity of branching universes based on the decisions of each individual. Every time someone makes a decision the universe splits. This is very much like quantum branching. In one scene Trimble is deciding to get a cup of coffee:

All The Myriad Ways, Galaxy October 1968

‘The image came to him in an endless row of Trimbles, lined up like the repeated images in facing mirrors. But each image was slightly different. He would go get the coffee and he wouldn’t and he would send somebody for it, and someone was about to bring it without being asked. Some of the images were drinking coffee, a few had tea or milk, some were smoking, some were leaning too far back with their feet on the desks (and a handful of these were toppling helplessly backward), some were, like this present Trimble, introspecting with their elbows on the desk. Damn Crosstime anyway’ (1968, p. 36, emphasis in original).

Crosstime is a business corporation that discovered a way to travel to these other possible worlds and begins to bring back new technologies from the worlds it visits and patents them, but it is not clear that Crosstime is selling travel or that in bringing back artefacts it is using matter-duplication. So I’m doubtful that this is the story Lewis is referring to in his letter to Peter J. Lewis. At any rate, the gist of the story is that given the multitude of possible worlds every choice that might have been made was made in some world. One of the suicidal individuals of the story reasons thus:

‘Watching the dawn, thinking of all the Ambrose Harmons on that roof. Some were penniless this night, and they had not come out to watch the dawn.

Well, why not? If he stepped over the edge, here and now, another Ambrose Harmon would only laugh and go inside.

If he laughed and went inside, other Ambrose Harmons would fall to their deaths. Some were already on their way down. One changed his mind too late, another laughed as he fell…

Well, why not? …’ (1968, p. 39).

Given that all of these possibilities are equally real, as Niven tells the story, there’s no reason not to go ahead and commit suicide. If you die in this branch, you will survive in another and if you live in this branch, you will die in another.

Lewis discusses ‘All The Myriad Ways’ in On the Plurality of Worlds, pp. 124-25. He rejects Niven’s argument that Trimble and the other characters in this story should be indifferent about what happens to them. ‘All The Myriad Ways’ is not exactly a story of immortality through branching. But bracketing the philosophical argument I believe we have evidence to support the claim that Lewis’ reading of science fiction during his formative years played some role in shaping some of his most important and well-known philosophical doctrines such as the doctrine of life-everlasting.

Talk of possible worlds, alternate timelines, branching universes, counterparts in other spacetimes, not to mention time travel, are well-traced ideas in science fiction of the mid-twentieth century. It seems this is one place where he was acquainted with such ideas and through his genius developed and improved some of the concepts expressed in these stories in his philosophical system. It is no wonder that Lewis was happy to posit possible worlds equally concrete and real as this one. He might have thought (like us) that modal realism was bizarre, but it was certainly familiar to him and therefore not repugnant. This, I infer, is probably due to his reading of science fiction as a teenager and as a student during those formative years in the 1960s.