I read the first link, and to me it seems that the author actually stumbles upon the right answer in the middle of the paper, only to dismiss it immediately with "we have no good way to justify it" and proceed towards things that make less sense. I am talking about what he calls the "intensity rule" in the paper.

Assuming a non-collapse interpretation, the entire idea is that literally everything happens all the time, because every particle has a non-zero amplitude at every place, but it all adds up to normality anyway, because what matters is the actual value of the amplitude, not just the fact whether it is zero or non-zero. (Theoretically, epsilon is not zero. Practically, the difference between zero and epsilon is epsilon.) Outcomes with larger amplitudes are the normal ones; the ones we should expect more. Outcomes with epsilon amplitudes are the ones we should only pay epsilon attention to.

It is possible that the furniture in my room will, due to some very unlikely synchronized quantum tunneling, transform into a hungry tiger? Yes, it is theoretically possible. (Both in Copenhagen and many-worlds interpretations, by the way.) How much time should I spend contemplating such possibility? Just by mentioning it, I already spent many orders of magnitude more than would be appropriate.

The paper makes some automatic assumption about time, which I am going to ignore for the moment. Let's assume that, because of quantum immortality, you will be alive 1000000 years from now. Which path is most likely to get you from "here" to "there"?

In any case, some kind of miracle is going to happen. But we should still expect the smallest necessary miracle. In absolute numbers, the chances of "one miracle" and "dozen miracles" are both pretty close to zero, but if we are going to assume that some miracle happened, and normalize the probabilities accordingly, "one miracle" is almost certainly what happened, and the probability of "dozen miracles" remains pretty close to zero even after the normalization. (Assuming the miracles are of comparable size, mutually independent, et cetera.)

Comparing likelihoods of different miracles is, by definition, outside of our usual experience, so I may be wrong here. But it seems to me that the horror scenario envisioned by the author requires too many miracles. (In other words, it seems optimized for shock value, not relative probability.) Suppose that in 10 years you get hit by the train, and by a miracle, a horribly disfigured fragment of you survives in an agony beyond imagination. Okay, technically possible. So, what is going to happen during the following 999990 years? It seems that further surviving in this state would require more miracles than further surviving as a healthy person. (The closer to death you are, the more unlikely it is for you to survive another day, or year.) And both these paths seem to require more miracles than being frozen now, and later resurrected and made forever young using advanced futuristic technology. Even just dying now, and being resurrected 1000000 years later, would require only one miracle, albeit a large one. If you are going to be alive in 1000000 years, you are most likely to get there by a relatively least miraculous path. I am not sure what exactly it is, but being constantly on the verge of death and surviving anyway seems too unlikely (and being frozen and later unfrozen, or uploaded to a computer, seems almost ordinary in comparison).

Now, let's take a bit more timeless perspective here. Let's look at the universe in its entirety. According to quantum immortality, there are you-moments in the arbitrarily distant future. Yes; but most of them are extremely thin. Most of the mass of the you-moments is here, plus or minus a few decades. (Unless there is a lawful process, such as cryonics, that would stretch a part of the mass into the future enough to change the distribution significantly. Still not as far as quantum immortality, which can probably overcome even the death heat of the universe and get so far that the time itself stops making sense.) So, according to anthropic principle, whenever you find yourself existing, you most likely find yourself in the now -- I mean, in your ordinary human lifespan. (Which is, coincidentally, where you happen to find yourself right now, don't you?) There are a few you-moments at a very exotic places, but most of them are here. Most of your life happens before your death; most instances of you experiencing yourself are the boring human experience.

[Note: potential info hazard, but probably good to read if you already read the question.]

[Epistemic status: this stuff is all super speculative due to the nature of the scenarios involved. Based on my understanding of physics, neuroscience, and consciousness, I haven't seen anything that would rule this possibility out.]

All I want to know is, is this stuff just being pulled out of his butt? Like, an extremely unlikely hypothetical that nonetheless carries huge negative utility? I'd be okay with that, as I'm not a utilitarian. Or have these scenarios actually been considered plausible by AI theorists?

FWIW, I've thought about this a lot and independently came up with and considered all the scenarios mentioned in the Turchin excerpt. It used to really really freak me out, and I believed it on a gut level. Avoiding this kind of outcome was my main motivation for actually getting the insurance for cryonics (the part I was previously cryocrastinating on). However, I now believe that QI is not an s-Risk and don't feel personally worried about the possibility anymore.

One thing to note is that this is a potential problem in any sufficiently large universe, and doesn't depend on a many-worlds style interpretation being correct. Tegmark has a list of various multiverses, which are different and affect what scenarios we might face. I do believe in many-worlds (as a broad category of interpretations) though.

Lots of the comments here seem confused about how this works, so I'll recap. If I'm at the point of death where I'm still conscious, the next moment I'll experience will be (in expectation) whatever conscious state has the highest probability mass in the multiverse, which is also a valid next conscious moment from the previous moment. Note that this next conscious moment is not necessarily in the future of the previous moment. If the multiverse contains no such moments, then we would just die the normal way. If the multiverse includes lots of humans doing ancestor simulations, you potentially could end up in one of those, etc... The key is that out of all conscious beings in the multiverse who feel like this just happened to them, those are (tautologically) the ones having the subjective experience of the next valid conscious moment. And it's valid to care about these potential beings, and is AFAICT the reason I care about my future selves (who do not exist yet) in the normal sense.

Regarding cryonics, it seems like the best way to preserve a significant amount of information about my last conscious moment. To whatever extent information about this is lost, a civilization that cares about this could optimize for likelihood of being a valid next conscious moment. I think this is the main actionable thing you can do for this. Of course, this only passes the buck to the future, since there is still the inevitable heat death of the universe to contend with.

Another thing that seems especially plausible for sudden deaths Aranyosi's 1 scenario. In this case, the highest probability mass next conscious moment will be a moment based on the moment from a few seconds before, but with a "false" memory of having survived a sudden death. This has relatively high probability because people sometimes report having kind of experience when they have a close call. But this again simply passes the buck to the future, where you're most likely to die from a gradual decline.

However, I think that by far, the most likely situation is common to death by aging, illness, or heat death of the universe. At the last moment of consciousness, the only next conscious moments that will be left will be in highly improbable worlds. But which world you are most likely to "wake up" in is still determined by Occam's razor. People seem to imagine that these improbable worlds will be ones where your consciousness remains in a similar state to the one you died in, but I think this is wrong.

Think carefully about what things are actually happening to support a conscious experience. Some minimal set of neurons would need to be kept functional -- but beyond that, we should expect entropy to effect things which are not causally upstream of the functionality of this set of neurons. Since strokes happen often, and don't always cause loss of consciousness, we can expect them to eventually occur for every non-essential (for consciousness) region of the brain. Because people can experience nerve damage to their sensory neurons without losing consciousness, we can expect that the ability to experience physical pain will decay. Emotional pain doesn't seem to be that qualitatively different from physical pain (e.g. is also mitigated by NSAIDs), so I expect this will be true for pain in general.

So most of your body and most of your mind will still decay as normal, only the absolutely essential neuronal circuitry (and whatever else, perhaps blood circulation) to induce a valid next conscious moment will miraculously survive. Anesthesia works by globally reducing synapse activity. So the initial stages this would likely feel like going under anesthesia, but where you never quite go out. Because anesthetics stop pain (remember this is still true if applied locally), and because by default, we do not experience pain, I'm now pretty sure that given QI being real: infinite agony is very unlikely.

I wrote the article quoted above. I think I understand your feelings as when I came to the idea of QI, I realised - after first period of excitement - that it implies the possibility of eternal sufferings. However, in current situation of quick technological progress such eternal sufferings are unlikely, as in 100 years some life extending and pain reducing technologies will appear. Or, if our civilization will crash, some aliens (or owners of simulation) will eventually bring pain reduction technics.

If you have thoughts about non-existence, it may be some form of suicidal ideation, which could be side effect of antidepressants or bad circumstances. I had it, and I am happy that it is in the past. If such ideation persists, ask professional help.

While death is impossible in QI setup, a partial death is still possible, when a person forgets those parts of him-her which want to die. Partial death has already happened many times with average adult person, when she forgets her childhood personality.

The survivors are living in an area that shatters the illusion of classical reality. The survivor probabilities favour classical probabilities so you should be able to expect for things to get classical. In a non-classical universe it might be possible to get a very rapid regeneration that might bounce you far from the torment zone for a long time. Even if you do not get a particuarly stellar regeneration you will constantly be tunneling out of the torment zone too. At some point the tunneling to torment and tunneling to relief should balance out where you have 50% chance of being in a bad scenario and 50% chance of being in a good scenario. That is if you are sustained longer in a scenario that classically would be considered bad the less faith you can have that the mechanics of the scenario continue to work. It will either resolve to a classical situation different from current or it is such a jumbled mess that "being stuck in a bad place" is not representative.

In general the jumbling might also target your personality and then the question of how much of your alteration really counts as you starts to get relevant. If you escape with a cunning deduction you made because you tought you were Sherlock Holmes because cosmic rays fabricated your memories for it does that count as Sherlock Holmes or you waking up or both? One might need classical mechanics to maintain a sense of identity stability (that is the you on the next second has very similar personality) and when that is taken away it is not sure the concept applies with the same strength. Sure somebody concious will get to expererience a bunch of stuff and it will be structurally reminicient of you. But will it really be you?

I used to be heavily into this area, and after succumbing somewhat to an 'it all adds up to normality' shoulder-shrugging, my feeling on this is that it's not just the 'environment' that is subject to radical changes, but the mind itself. It might be that there's a kind of mind-state attractor, by which minds tend to move along predictable paths and converge upon weirdness together. All of consciousness may, by different ways of looking at it, be considered as fragments of that endstate.

You've been basilisked. There is no empirical evidence for MWI, but a number of physicists do believe that it can be something related to reality, with some heavy modifications, since, as stated, it contradicts General Relativity. Sean Carroll, an expert in both Quantum Mechanics and General Relativity, is one of them. Consider reading his blog. His latest article about the current (pitiful) state of fundamental research in Quantum Mechanics, can be found in the New York Times. His book on the topic is coming out in a couple of days, and it is guaranteed to be a highly entertaining and insightful read, which might also alleviate some of your worries.

Some thought experiments that can contradict QI:

1. Quantum anesthesia. If the premise in QI is that you can't branch out into a non-conscious state, then anesthesia would be impossible as well. And mind you: anesthesia is not sleep, where consciousness is simply diminished. Anesthesia is total anihilation of consciousness (when properly given at least). Those of us who have had surgery know this: you don't feel any passage of time during anesthesia. When you wake up, after several hours, you feel like you had just been put under a second ago.

1b) Quantum temporary-death. Coming out of temporary unconscious states like temporary death (where your heart can stop beating (and you remain unconscious) for up to several hours) would be impossible, since you would also branch out into states of consciousness before any unconsciousness would settle in.

2. Entropy. Dodging death infinitely is impossible. There might be branches where you die and others where you survive, but even then, on the ones where you survive, your body is still decaying. To keep decaying forever and never die would simply contradict biology. After a certain threshold of damage, death is inevitable. But would this prolong itself for thousands of years of agony? No. It would occur under normal timelines. Maybe, say, if you get headshot, you die instantly in branch A and survive damaged on branch B, but it doesn't mean that you're not on your way to death on branch B if the damage is severe enough. If it isn't, you go to the hospital and make a recovery. In short: to keep suffering forever for eternity simply contradicts biology - no one can live forever, and damage will always lead to death (sooner or later, BUT on a normal biological timescale related to the different degrees of damage in each branch).

3. Maybe MWI is just bs, lol.

I think in short QI is Zeno's Paradox. Ancient Greek philosopher Zeno concluded that for each distance between A and B, you first have to reach halfway between A and B before getting to B. Therefore, you can never reach B, since you always have to reach the halfway point first, and there is always a halfway point, no matter how small the distance. This led Zeno into concluding that movement is impossible. In reality, we know that it isn't, you eventually will reach B, and in a normal timescale.

Even if MWI is true, you eventually will die (in normal timescales), just as you will eventually reach point B (in normal timescales).