It's a back-of-the-envelop calculation on vast unknowns. I wrote it up because it seemed pointless to try making a decision if we weren't even going to involve numbers. I happily concede that it is deeply speculative.
First, given it's a back-of-the-envelop calculation, I assume that anything LESS than a 100% difference (2:1 value ratio) can effectively be treated as within the margin of error. So if the ratio I got was 1.5 : 1, I'd still say they were approximately equal. I can't off-hand defend this intuition, beyond that it's sloppy math so we have to assume I made at least a few mistakes.
Calculating for your life-extension black swan, the math works out to a ratio of 27X + 1 : 1, where X = the chance of such a radical life extension event (i.e. within the next 50 years, the entire world is effectively immortal). At 4%, that's about a 2:1 ratio, so the point where I'd call it a significant difference. At 33%, it's a 10:1 ratio, which is the point where I'd concede it's clearly the correct decision. I personally assume this is < 1%, which means it doesn't affect the result.
(Math note: 27X+1 is because of the 28:1 cost ratio with cryonics. If the black swan occurs, we're 28 times more efficient. If it doesn't occur, our original equation says we're still equally efficient. Thus we get a ratio of (28 X) + (1 (1-X)) : 1, which simplifies to 27X+1 : 1.)
(Stylistic note: For back of the envelope calculations, as you can see, even astounding events like "radical life extension" require fairly solid odds before they affect things. We can reasonably ignore anything 1% or less, since there's probably other black swans pointed the other direction, and we need at least a 2:1 difference before we stop calling it "approximately equal" :))
As to compounding effects, well... yeah, I have to concede that QALY doesn't cover that. If you have research that says this should specifically bias our calculations one way or another, that's useful information. Otherwise I'd just have to conclude insufficient information, or assume that any given QALY compounds approximately identically to any other QALY.
From here, while you may well still disagree with me, I think my methods and assumptions are open enough that you can just plug in your own numbers and get your own results.
Feel free to post your own revised estimates if you do disagree, but I'd appreciate you actually running the numbers first - it's much easier to discuss if I can tell we disagree because you think the black swan has 25% odds and I think it's <1%.
It's also a good way to notice how even radical black swans still require decent odds before they affect the calculations at all, which is important to understand when using a tool like this (I still sometimes find it surprising myself! Which is why I like doing these :))
Cryonics working requires most of the same "black swan," and providing large lifespans is heavily correlated with large lifespans for ordinary people. The chance of cryonic organizations failing increases with time (among other things, their financials are rickety, and there have been past failures), so the much of the chance of cryonics working depends on big technological advances happening within a century.
I would say that conditional on cryonics working (which is a major thing to condition on), the chance of the "black swan" (which ...
I am not currently signed up for cryonics. I am considering it, but have not yet decided whether it is the right choice. Here's my reasoning.
I am very sure of the following:
1. Life is better than death. For any given finite lifespan, I'd prefer a longer one, at least within the bounds of numbers I can reasonably contemplate.
2. Signing up for cyronics increases the expected value of my lifespan.
But then I also believe the following:
3. I am not particularly exceptional among the set of human beings, and so should not value my lifespan much more than that of other humans. I obviously fail at this in practice, but I think the world would be a much better place if I and others didn't fail so often.
4. The money it would take to sign up for cryonics, though not large, is enough to buy several centuries of healthy life each year if given to givewell's top malaria charities. Since on average I expect to live another 50-60 years without cryonics, the investment would need to increase the expected value of my lifespan by at least 5,000 years at minimum to be morally acceptable to me.
5. There is a chance we'll discover immortality in my lifetime. If so, then if I signed up for cryonics the payout is 0, and the people who died because I bought insurance instead of charity are people I could have saved for far longer.
So, what do you think is the probability that immortality will be discovered in my lifetime? What about the probability that, if signed up for cryonics, I will live into the far future? These priors would seem to be the key for me to decide whether signing up for cryonics is morally acceptable to me.