Parallel Universes and Eternal Return Again

by Tim Sommers

Suppose you had some undeniable proof of the Everettian or Many-Worlds Interpretation (MWI) of quantum mechanics. You would know, then, that there are very many, uncountably many, parallel worlds and that in very many of these there are many, many nearly identical versions of you – as well as many less-closely related “you’s” in still other worlds. Would this change the way you think about yourself and your life? How? Would you take the decisions that you make more or less seriously?

Consider Larry Niven’s 1971 take on that question. In a fitting contrast to the infinite multiplication of actions implied by the existence of a quantum multiverse, his story, “All the Myriad Ways”, consists entirely of a solitary police detective sitting alone and trying to puzzle out why a rash of unexplained suicides has accompanied the discovery of multiple, parallel universes. He begins to think that people see the existence of a world corresponding to every possible choice they might make as undermining the idea that they have any choice at all. In the end, he puts his own gun to his head – and all of the possible outcomes of that occur at once. I think there is more than one way of understanding this story. It’s not necessarily that people are inspired to take a fatalistic attitude by the knowledge of other worlds, it’s that just by recognizing that suicide is one of the possible outcomes, it becomes one of the things that will happen in some world or another.

But there may be a basic misunderstanding about quantum parallel universes lurking there. The splitting of universes has nothing to do with you and your decisions. Subatomic quantum events cause the universe to split, not you. You can, however, cause the universe to split whenever you make a decision by tying that decision to a quantum event. There’s an app for that. (Warning! This app only works if the MWI of Quantum Mechanics is correct.) Anyway, in the end, it’s not clear that it matters what causes the universe to split since it is splitting so often and so fast that it should create plenty enough parallel universes to cover all the decisions you could possibly make.

How should you feel about this?

Does it make everything we do meaningless, somehow insubstantial, to have it endlessly multiplied in this way? Or is reassuring to think that no matter what happens to you there are other you’s, or at least near you’s, out there? Does it depend on what is happening with them (or most of them? or some of them?)? I can tell you what is happening with them if the MWI is correct. Everything.

Maybe, all these are not really you’s since you have no access to their experiences and so what they do or what happens to them is unknown to you. But elsewhere, I have argued that it could be better for you if there were more of you even if you don’t have access to the experiences of other you’s (“Would it be Better for You if there were More of You?”/3 Quarks Daily, 10/8/18). And consider this.

The great innovation of Christianity was not life after death. Many religions and cultures have believed that something like a spirit persists after we die – in this or (more often) some other world. The great innovation of Christianity was bodily resurrection. It seems to me that if you deny that an exact copy of you is you (for example, if you think teleportation kills you and the copy it makes is not you) or deny that you should ever care about other versions of you because you have no direct access to their experiences, then you should also deny that you can be bodily resurrected in the Christian sense, or, at least, you should deny that an exact copy of you raised from the dead (by Jesus, for example) is you. (Unless, I guess, it’s you because Jesus, or whoever, also puts the same mysterious spirit back inside of the new body that was in the old body. But then your resurrection isn’t really bodily, is it?

For my part, I think it is hard to dismiss the idea that you should care about all these other selves. So, suppose most of them are serial killers. Should you feel great about having avoided that fate (if you have) – or despair about all the other near you’s out there doing terrible things? Or suppose that most of them are more successful than you. Should you feel bad about yourself?

Of course, the Everettian interpretation may not be true. Here are three reasons to that think that it isn’t. First, it’s just an interpretation of quantum mechanics. There are other interpretations that do not multiply worlds. The metaphysical version of Ockham’s Razor says to avoid postulating more entities than are strictly necessary to explain the phenomenon in question. The MWI solves the “measurement problem” in quantum mechanics by postulating a nearly or potentially infinite number of parallel universes. Hence the MWI is, at least at this point, the greatest violation of Ockham’s Razor in the history of the world. Not everybody buys into the Razor, so here’s a second objection. Strictly speaking, since we have no access to other worlds, there’s no empirical evidence of their existence. As with string theory, we might doubt that MWI is really (at least at this point) a scientific theory at all.

Here’s a third more technical reason to doubt the MWI. It makes nonsense of the probabilities it was meant to explain. Suppose there’s a quantum event where particle X has a 30% chance of being positively charged and a 70% chance of being negatively charged. The MWI says the universe always splits and that both events always happen. But then what was that probability? It was supposed to be more likely that X would be positively charged, but really (as with every quantum event on this interpretation) it was always going to be both positively charged in one world and negatively charged in another. The outcome isn’t probabilistic, it’s certain. But if the notion of probability makes any sense at all here, isn’t there a 50/50 chance you will be in one world or another – not a 30/70 one? I think there’s supposed to be something about how the less probable universes are “thinner” than the more probable ones, but the physics of this is way above my pay-grade. Go listen to Sean Carroll’s Mindscape podcast with David Alpert if you want to hear about it from people who know what they are talking about. (

It occurs to me that there is a philosophical precedence for MWI in Nietzsche’s idea of eternal return or the eternal reoccurrence of the same. “What, if some day or night,” Nietzsche wrote, “a demon were to steal after you into your loneliest loneliness and say to you: ‘This life as you now live it and have lived it, you will have to live once more and innumerable times more; and there will be nothing new in it, but every pain and every joy and every thought and sigh and everything unutterably small or great in your life will have to return to you, all in the same succession and sequence—even this spider and this moonlight between the trees, and even this moment and I myself.”

“Would you not throw yourself down and gnash your teeth and curse the demon who spoke thus?”

But elsewhere he said, “The ideal of the most high spirited, alive, and world affirming human being”, is the one “who has not only come to terms and learned to get along with whatever was and is, but who wants to have what was and is repeated into all eternity, shouting insatiably ‘da capo [from the beginning]’!”

There are two ways of understanding Nietzsche on eternal return. There’s the hypothetical, aesthetic interpretation. The idea is that having thrown off the shackles of religion and morality and gone, as it were, beyond good and evil, and having recognized that the only way to justify and give meaning to our existence is aesthetically, Nietzsche needs a nonmoral normative standard to judge our lives by. On this reading, the way to judge our life is to ask, “Would I want to repeat it again and again down to every last detail – or not?” On this interpretation, it doesn’t really matter if the universe or your life actually reoccurs again and again, it’s just a thought-experiment, a counterfactual way of measuring the value that your life has here and now.

On the other hand, the cosmological interpretation takes seriously the idea that eternal return really occurs. Why think that? Well, if there are a finite number of ways that matter can be arranged – and the universe lasts an infinite amount of time – then every possible combination will reoccur again and again. Right?

I have some doubts about this. It doesn’t really follow just from the fact there are a finite number of ways the universe can be arranged, and that the universe will go on forever, that every way that things could be will even occur once, much less again and again. Maybe, one thing is happening now (including your life), but immediately after this something completely different (which doesn’t include you) will happen and then that will reoccur forever. You need some reason to believe that dice are being rolled here, that things will occur in a variety of different ways – not just that they can so occur or reoccur.

But, more importantly, and as with parallel universes, you need to ask yourself if a physically exact version of you reoccurring a trillion years from now is really you or not. If after every turn of the wheel there is a new you that you really are not, maybe you shouldn’t care either way. But if it is you, how should you feel about that?

In Milan Kundera’s “The Unbearable Lightness of Being”, the protagonist, Tomas, is haunted by the German adage “Einmal is Kleinman” – “once is not at all”. “If we have only one life to live,” Tomas thinks “we might as well have not lived at all.” There is no way of knowing if a decision is better or worse since we have nothing to compare it with.

We seem to think, Kundera writes, that “The heavier the burden, the closer our lives come to the earth, the more real and truthful they become. Conversely, the absolute absence of burden causes man to be lighter than air, to soar into heights, take leave of the earth and his earthly being, and become only half real, his movements as free as they are insignificant. What shall we choose? Weight or lightness?”

So, one last time, should we be comforted by the thought that our life is, in some sense, multiplied across many universes or destined to occur again and again? Or should we be terrified by it?

Here’s what I think. Don’t look to metaphysics for solace – nor let it cause you grief. “Philosophy,” Wittgenstein said, “just puts everything before us, and neither explains nor deduces anything.” The facts of your life are already before you. The meaning of your life is in your hands. Cosmology and metaphysics have nothing to do with it.

Even though my profession is philosophy, I mostly avoid metaphysics. On the other hand, I have a keen, if amateur’s, interest in cosmology (the branch of astronomy and physics that studies the end, the beginning, and the large-scale structure of the universe). Knowing that, my wife Stacey once asked me what cosmology is good for. I told her what I am telling you now. Nothing. It’s not good for anything. It’s of no use. It’s just interesting. Right?