If the Many Worlds interpretation of quantum mechanics is true, I think it follows that falling asleep and death are not very different events. This causes me anxiety.
The Many Worlds interpretation of QM implies that at every moment ‘you’ are splitting into a vast number of copies of you in different worlds. From the point of view of your individual subjective experience, this may not seem like a plausible view, but once you understand the details of the view, you see that it doesn’t pose any direct inconsistency with this experience. There’s a famous Wittgenstein anecdote (due to Elizabeth Anscombe, a participant in the alleged conversation) that’s relevant to this:
“Tell me," Wittgenstein asked Elizabeth Anscombe, "why do people always say, it was natural for man to assume that the sun went round the earth rather than that the earth was rotating?" She replied, "Well, obviously because it just looks as though the Sun is going round the Earth." Wittgenstein replied, "Well, what would it have looked like if it had looked as though the Earth was rotating?”
Subjectively, you only inhabit one stream of thoughts and consciousness that seems unbroken and whole because you are a pattern along a path through the infinitely branching universes. But in the broader context of reality, there are infinite copies of patterns very similar to the pattern that characterises you.
When you wake up in the morning, what makes it seem that you are ‘continuing on’ from yesterday as a single being is that you have a flood of memories of ‘your life’, of the things you have to do during the current day and of the night before. Again, it may feel to you that there is one and only you, but in fact there is nothing in this experience that is logically contradictory with the idea that while you were sleeping there was a gargantuan number of branchings, and the specific you that is most particularly you is just one of many yous who are a little different.
You might find it a little baffling that you - each version of you - only ever experiences one arbitrary pattern of a vast multitude of similar pattens. Why don’t I experience multiple consciousnesses at once? That is because the emergent ontology which includes human beings and experience only emerges at each ‘moment’ of decoherence (wave function collapse), so it makes no sense to suppose that one could have experience of multiple decohered worlds at once.
How does this bear on death? Well, it implies that death perhaps doesn’t even matter all that much in the grand scheme of things, because it’s just death relative to a world. There will be plenty of other worlds where you don’t die at that moment you die relative to the particular one your pattern is experiencing. And so, likely, a pattern extremely similar to yours will be isomorphic to conscious experience in another world. What’s scary is that this conscious experience in this other world may very well be associated with significant physical and/or mental suffering, which is certainly a common thing among moribund people.
As I’ve written about previously, the great philosopher David Kellogg Lewis cooked up an unimaginably horrific scenario out of this, suggesting that the ultimate implication was that, at any moment, in any universe, ‘you’ should expect to live eternal life in likely massively decreased health and therefore more suffering. All injuries, accidents and diseases will be outlasted on a multitude of branches, simply because there are so vastly many. And in many of these you will retain a lively mind, full-bodied consciousness, and therefore a full capacity to suffer. In those, the pattern of existence most similar to your own consciousness will live on, endlessly.
This is the thing that causes me anxiety. And not even necessarily for selfish reasons, either; it just suggests, in general, that the multiverse might be full of terrible suffering.
Luckily, there are a number of responses to this. It would seem that many Many Worlds proponents do not believe (though I don’t think anyone is quite sure) that at each, say, 100-year time-slice of the overall tree of worlds, there is an infinite number of branches containing at least one pattern that is very similar to you as an adult person, at some point during your adult life as you remember it. Instead, there is probably only a very large finite number of such branches and such consciousness-associated patterns at each time-slice. And if this number is finite, this opens the possibility for variation between such time-slices. In particular, it seems plausible to think that the number of such patterns in the overall multiverse might start to decay at a certain point, as you die or decay along most branches.
You might also think that physical decay should statistically be associated with decay in consciousness, so that the combination of physical suffering with full-bodied consciousness is less probable.
You might also ask: Does probability even matter? Once you start thinking objectively about suffering, beyond the fear of subjective suffering, it would seem that the answer is Yes, because the less suffering in the overall multiverse, the better. But just so long as there are always a vast number of consciousnesses experiencing great suffering, some element of fear or foreboding seems natural.
There’s a lot of fascinating commentary on this issue on Wikipedia:
https://en.wikipedia.org/wiki/Quantum_suicide_and_immortality
Analysis of real-world feasibility[edit]
In response to questions about "subjective immortality" from normal causes of death, Max Tegmark suggested that the flaw in that reasoning is that dying is not a binary event as in the thought experiment; it is a progressive process, with a continuum of states of decreasing consciousness. He states that in most real causes of death, one experiences such a gradual loss of self-awareness. It is only within the confines of an abstract scenario that an observer finds they defy all odds.[1] Referring to the above criteria, he elaborates as follows: "[m]ost accidents and common causes of death clearly don't satisfy all three criteria, suggesting you won't feel immortal after all. In particular, regarding criterion 2, under normal circumstances dying isn't a binary thing where you're either alive or dead [...] What makes the quantum suicide work is that it forces an abrupt transition."[14]
David Lewis' commentary and subsequent criticism[edit]
Philosopher David Lewis explored the possibility of quantum immortality in a 2001 lecture titled How Many Lives Has Schrödinger's Cat?, his first - and last, due to his death less than four months afterwards - academic foray into the field of the interpretation of quantum mechanics. In the lecture, published posthumously in 2004, Lewis rejected the many-worlds interpretation, allowing that it offers initial theoretical attractions, but also arguing that it suffers from irremediable flaws, mainly regarding probabilities, and came to tentatively endorse the Ghirardi-Rimini-Weber theory instead. Lewis concluded the lecture by stating that the quantum suicide thought experiment, if applied to real-world causes of death, would entail what he deemed a "terrifying corollary": as all causes of death are ultimately quantum-mechanical in nature, if the many-worlds interpretation were true, in Lewis' view an observer should subjectively "expect with certainty to go on forever surviving whatever dangers [he or she] may encounter," as there will always be possibilities of survival, no matter how unlikely; faced with branching events of survival and death, an observer should not "equally expect to experience life and death," as there is no such thing as experiencing death, and should thus divide his or her expectations only among branches where he or she survives. If survival is guaranteed, however, this is not the case for good health or integrity. This would lead to a cumulative deterioration that indefinitively stops just short of death.[2][15]
Interviewed for the 2004 book Schrödinger's Rabbits, Max Tegmark rejected this scenario for the reason that "the fading of consciousness is a continuous process. Although I cannot experience a world line in which I am altogether absent, I can enter one in which my speed of thought is diminishing, my memories and other faculties fading [...] [Max Tegmark] is confident that even if he cannot die all at once, he can gently fade away." In the same book, philosopher of science and many-worlds proponent David Wallace[16] undermines the case for real-world quantum immortality on the basis that death can be understood as a continuum of decreasing states of consciousness not only in time, as argued by Tegmark, but also in space: "our consciousness is not located at one unique point in the brain, but is presumably a kind of emergent or holistic property of a sufficiently large group of neurons [...] our consciousness might not be able to go out like a light, but it can dwindle exponentially until it is, for all practical purposes, gone."[17]
Directly responding to David Lewis' lecture, British philosopher and many-worlds proponent David Papineau, while finding Lewis' other objections to the many-worlds interpretation lacking, strongly denies that any modification to the usual probability rules is warranted in death situations. Assured subjective survival can follow from the quantum suicide idea only if an agent reasons in terms of "what will be experienced next" instead of the more obvious "what will happen next, whether will be experienced or not". He writes: "[...] it is by no means obvious why Everettians should modify their intensity rule[note 3] in this way. For it seems perfectly open for them to apply the unmodified intensity rule in life-or-death situations, just as elsewhere. If they do this, then they can expect all futures in proportion to their intensities, whether or not those futures contain any of their live successors. For example, even when you know you are about to be the subject in a fifty-fifty Schrödinger’s experiment, you should expect a future branch where you perish, to just the same degree as you expect a future branch where you survive."[15]
On a similar note, quoting David Lewis' position that death should not be expected as an experience, philosopher of science Charles Sebens concedes that, in a quantum suicide experiment, "[i]t is tempting to think you should expect survival with certainty." However, he remarks that expectation of survival could follow only if the quantum branching and death were absolutely simultaneous, otherwise normal chances of death apply: "[i]f death is indeed immediate on all branches but one, the thought has some plausibility. But if there is any delay it should be rejected. In such a case, there is a short period of time when there are multiple copies of you, each (effectively) causally isolated from the others and able to assign a credence to being the one who will live. Only one will survive. Surely rationality does not compel you to be maximally optimistic in such a scenario." Sebens also explores the possibility that death might not be simultaneous to branching, but still faster than a human can mentally realize the outcome of the experiment. Again, an agent should expect to die with normal probabilities: "[d]o the copies need to last long enough to have thoughts to cause trouble?[note 4] I think not. If you survive, you can consider what credences you should have assigned during the short period after splitting when you coexisted with the other copies."[18]
Writing in the journal Ratio, philosopher István Aranyosi, while noting that "[the] tension between the idea of states being both actual and probable is taken as the chief weakness of the many-worlds interpretation of quantum mechanics," summarizes that most of the critical commentary of David Lewis' immortality argument has revolved around its premises. But even if, for the sake of argument, one were willing to entirely accept Lewis' assumptions, Aranyosi strongly denies that the "terrifying corollary" would be the correct implication of said premises. Instead, the two scenarios that would most likely follow would be what Aranyosi describes as the "Comforting Corollary," in which an observer should never expect to get very sick in the first place, or the "Momentary Life" picture, in which an observer should expect "eternal life, spent almost entirely in an unconscious state," punctuated by extremely brief, amnesiac moments of consciousness. Thus, Aranyosi concludes that while "[w]e can’t assess whether one or the other [of the two alternative scenarios] gets the lion’s share of the total intensity associated with branches compatible with self-awareness, [...] we can be sure that they together (i.e. their disjunction) do indeed get the lion’s share, which is much reassuring."[19]
Analysis by other proponents of the many-worlds interpretation[edit]
Physicist David Deutsch, though a proponent of the many-worlds interpretation, states regarding quantum suicide that "that way of applying probabilities does not follow directly from quantum theory, as the usual one does. It requires an additional assumption, namely that when making decisions one should ignore the histories in which the decision-maker is absent....[M]y guess is that the assumption is false."[20]
Tegmark now believes experimenters should only expect a normal probability of survival, not immortality. The experimenter's probability amplitude in the wavefunction decreases significantly, meaning they exist with a much lower measure than they had before. Per the anthropic principle, a person is less likely to find themselves in a world where they are less likely to exist, that is, a world with a lower measure has a lower probability of being observed by them. Therefore, the experimenter will have a lower probability of observing the world in which they survive than the earlier world in which they set up the experiment.[14] This same problem of reduced measure was pointed out by Lev Vaidman in the Stanford Encyclopedia of Philosophy.[21] In the 2001 paper, "Probability and the many-worlds interpretation of quantum theory", Vaidman writes that an agent should not agree to undergo a quantum suicide experiment: "The large "measures" of the worlds with dead successors is a good reason not to play." Vaidman argues that it is the instantaneity of death that may seem to imply subjective survival of the experimenter, but that normal probabilities nevertheless must apply even in this special case: "[i]ndeed, the instantaneity makes it difficult to establish the probability postulate, but after it has been justified in the wide range of other situations it is natural to apply the postulate for all cases."[22]
In his 2013 book The Emergent Multiverse, David Wallace opines that the reasons for expecting subjective survival in the thought experiment "do not really withstand close inspection," although he concedes that it would be "probably fair to say [...] that precisely because death is philosophically complicated, my objections fall short of being a knock-down refutation." Besides re-stating that there appears to be no motive to reason in terms of expectations of experience instead of expectations of what will happen, he suggests that a decision-theoretic analysis shows that "an agent who prefers certain life to certain death is rationally compelled to prefer life in high-weight branches and death in low-weight branches to the opposite."[3]
Physicist Sean M. Carroll, another proponent of the many-worlds interpretation, states regarding quantum suicide that neither experiences nor rewards should be thought of as being shared between future versions of oneself, as they become distinct persons when the world splits. He further states that one cannot pick out some future versions of oneself as "really you" over others, and that quantum suicide still cuts off the existence of some of these future selves, which would be worth objecting to just as if there were a single world.[23]
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