Splitting the timeline as an extinction risk intervention

Thanks for writing this — in general I am pro thinking more about what MWI could entail!

But I think it's worth being clear about what this kind of intervention would achieve. Importantly (as I'm sure you're aware), no amount of world slicing is going to increase the expected value of the future (roughly all the branches from here), or decrease the overall (subjective) chance of existential catastrophe.

But it could increase the chance of something like "at least [some small fraction]% of'branches' survive catastrophe", or at the extreme "at least one 'branch' survives catastrophy". If you have some special reason to care about this, then this could be good.

For instance, suppose you thought whether or not to accelerate AI capabilities research  in the US is likely to have a very large impact on the chance of existential catastrophe, but you're unsure about the sign. To use some ridiculous play numbers: maybe you're split 50-50 between thinking investing in AI raises p(catastrophe) to 98% and 0 otherwise, or investing in AI lowers p(catastrophe) to 0 and 98% otherwise. If you flip a 'classical' coin, the expected chance of catastrophe is 49%, but you can't be sure we'll end up in a world where we survive. If you flip a 'quantum' coin and split into two 'branches' with equal measure, you can be sure that one world will survive (and another will encounter catastrophe with 98% likelihood). So you've increased the chance that 'at least 40% of the future worlds will survive' from 50% to 100%.^[1]

In general you've moving from more overall uncertainty about whether things will turn out good or bad, to more certainty that things will turn out in some mixture of good and bad.

Maybe that sounds good, if for instance you think the mere fact that something exists is good in itself (you might have in mind that if someone perfectly duplicated the Mona Lisa, the duplicate would be worth less than the original, and that the analogy carries).^[2]

But I also think it is astronomically unlikely that a world splitting exercise like this would make the difference^[3] between 'at least one branch survives' and 'no branches survive'. The reason is just that there are so, so many branches, such that —

1. It just seems very likely that at least some branches survive anyway;
2. Even if you thought there was a decent chance that no branches survive without doing the world splitting, then you should have such a wide uncertainty over the number of branches you expect to survive that (I claim) your odds on something like [at least one branch will survive if we do split worlds, and no branches will survive if we don't] should be very very low.^[4] And I think this still goes through even if you split the world many times.

1. ^{^}

   It's like choosing between [putting $50 on black and 50% on red] at a roulette table, and [putting $100 on red].

2. ^{^}

   But also note that by splitting worlds you're also increasing the chance that 'at least 40% of the future worlds will encounter catastrophe' from 48% to 99%. And maybe there's a symmetry, where if you think there's something intrinsically good about the fact that a good thing occurs at all, then you should think there's something intrinsically bad about the fact that a bad thing occurs at all, and I count existential catastrophe as bad!

3. ^{^}

   Note this is not the same as claining it's highly unlikely that this intervention will increase the chance of surviving in at least one world.

4. ^{^}

   Because you are making at most a factor-of-two difference by 'splitting' the world once.

I think this somehow assumes two types of randomness: quantum randomness and some other (non-quantum) randomness, which I think is an inconsistent assumption.
In particular, in a world with quantum-physics, all events either depend on "quantum" random effects or are (sufficiently) determined*. If e.g. extinction is uncertain, then there will be further splits, some branches avoiding extinction. In the other (although only hypothetical) case of it being determined in some branch, the probability is either 0 or 1, voiding the argument.

*) In a world with quantum physics, nothing is perfectly determined due to quantum fluctuations, but here I mean something practically determined (and also allowing for hypothetical world models with some deterministic parts/aspects).

I think it is confusing to think about quantum randomness as being only generated in special circumstances - to the contrary, it is extremely common. (At the same time, it is not common to be certain that a concrete "random" bit you somehow obtain is quantum random and fully independent of others, or possibly correlated!)

To illustrate what I mean by all probability being quantum randomness: While some coin flips are thrown in a way that almost surely determines the result (even air molecule fluctuations are very unlikely to change the result - both in quantum and classical sense) - some coin flips are thrown in such a way that the outcome is uncertain to the extent to be mostly dependent on the air particles bumping into the coin (imagine a really long throw); lets look at those. 
The movements of individual particles are to large extent quantum random (on the particle level, also - the exact micro-state of individual air molecules is to a large extent quantum-random), and moreover influenced by quantum fluctuations. As the coin flies through the air, the quantum randomness influence "accumulates" on the coin, and the flip can be almost-quantum-random without any single clearly identifiable "split" event. There are split events all along the coin movement, with various probabilities and small influences on the outcome - each contributing very small amounts of entropy to the target distribution. (In a simplified "coin" model, each of the quantum-random subatimic-level events would directly contribute a small amount of entropy (in bits) to the outcome.)

With this, it is not clear what you mean "one branch survives", as in fully quantum world, there are always some branches always survive; the probability may just be low. My point is that there (fundamentally) is no consistent way to say what constitutes the branches we should care about. 

If you instead care about the total probability measure of the branches with an extinction event, that should be the same as old-fashioned probability of extinction - my (limited) understanding of quantum physics interpretations is that by just changing the interpretation, you won't get different expected results in a randomly chosen timeline. (I would appreciate being corrected here if my general understanding is lacking or missing some assumption.)

It seems to me like quantum randomness can be a source of creating legitimate divergence of outcomes. Lets call this "bifurcation". I could imagine some utility functions for which increasing the bifurcation of outcomes is beneficial. I have a harder time imagining situations where it's negative. 

I'd expect that interventions that cause more quantum bifurcation generally have other costs. Like, if I add some randomness to a decision, the decision quality is likely to decrease a bit on average.

So there's a question of the trade-offs of a decrease in the mean outcome, vs. an increase in the amount of bifurcation.

There's a separate question on if EAs should actually desire bifurcation or not. I'm really unsure here, and would like to see more thinking on this aspect of it.
 

Separately, I'd note that I'm not sure how important it is if there's already a ton of decisive quantum randomness happening. Even if there's a lot of it, we might want even more.

This second option doesn't buy you a greater overall measure. Or, in other words, if you're inside a branch, it doesn't increase your probability of survival. But it does increase the probability that at least one branch will survive (For instance, if the probability of x-risk is 50%, it increases it from 50% to 75%).

My intuitions don't tell me to care about the probability that at least one branch survives.

I don't really buy the "butterfly effect" as it corresponds to extinction risk. That is, I think that to meaningfully affect chances of survival, you can't just quantum-randomize small-scale events.

This seems like a quite strong empirical claim. It may be the case that tiny physical differences eventually have large counterfactual effects on the world. For example, if you went back in time 1000 years and painted someone's house a different color, my probability distribution for the weather here and now would look like the historical average for weather here, rather than the weather in the original timeline. Certainly we don't have reason to believe in a snowball effect, where if you make a small change, the future tends to look significantly different in (something like) the direction of that change -- but I think we do have reason to believe in a butterfly effect, in which small changes have unpredictable, eventually-large effects. The alternative is a strong empirical claim that the universe is stable (not sure how to make this precise), I think.

From this Twitter thread, maybe one thinks that the world is net-good, and one wants to have more branches (would be the same as a clone of Earth). Like, it isn't clear to me why one should value worlds according to their quantum-probability mass.