What you are talking about is known as Quantum Suicide/Quantum Immortality. And yes, MWI is not just an interpretation, it's a testable model, though the tests are either unfeasible or drastic. Whether the tests have been accidentally performed during the Cold War, or even that MWI is the resolution of the Fermi paradox (one civilization per timeline survives), is quite speculative.
I think the MWI is already almost certainly true (95%+), and Eliezer agrees with this. So I'd just accept MW and move on. What then?
If you just want assurance that humanity will continue on some branches, then yes, I basically don't doubt this.
(I think it's wrong that it's a fringe theory in the mainstream, afaik it's pretty on par with Copenhagen, but I don't think it matters what the average physicist thinks to this isn't that important.)
Although you didn't explicitly say it, the fact that you decided that this was worth bringing to our attention strongly suggests that you hope that if Many Worlds is true, then no matter what happens, humanity will continue (avoid becoming extinct) in at least one future branch.
Is that in fact your belief?
Yes, though I actually think "belief" is more correct here. I assume that if MWI is correct then there will always exist a future branch in which humanity continues to exist. This doesn't concern me very much, because at this point I don't believe humanity is nearing extinction anyway (I'm a generally optimistic person). I do think that if I would share MIRI's outlook on AI risk, this would actually become very relevant to me as a concrete hope since my belief in MWI is higher than the likelihood Eliezer stated for humanity surviving AI.
It might interest you to know that Eliezer considers MWI to be obviously true:
We have embarrassed our Earth long enough by failing to see the obvious. So for the honor of my Earth, I write as if the existence of many-worlds were an established fact, because it is. The only question now is how long it will take for the people of this world to update.
Source. More on MWI by Eliezer..
The reason he is pessimistic about humanity's survival even though he believes in MWI is because MWI's being true does not save us.
Although it is possible to set up a special situation (e.g., by connecting a quantum-measurement device to a bomb) in which you will die in one branch, but live in a different branch, most situations aren't like that. Most situations have you surviving in both branches or dying in both branches.
This seems silly to me - it is true that in a single instance, a quantum coin flip probably can't save you if classical physics has decided that you're going to die. But the exponential butterfly effect from all the minuscule changes that occur between splits from now should add up to providing us a huge possible spread of universes by the time AGI will arrive. In some of which the AI will be deadly, and in others, the seed of the AI will be picked just right for it to turn out good, or the exact right method for successful alignment will be the first one discovered.
"every possible universe exists"
Under what kind of metaphysics or semantics could this sentence not be a tautology?
There were real activist groups worried about black hole production. To my mind this is comparable to flat earthers.
At some point if the coins have landed constantly in a particular direction we would have done an inductive reasoning of the pattern and just called it a law. In order for the occurence to be "anamolous" we need some theory of what "should" have happened. So why are we more confident in the inductive reasoning of that "should" law over the apparent "coinflip law" (and how can we tell them appart)?
Many worlds does not say that anything can happen, it has proportions to the chances.
Wrong coin flips don't normally destroy the observer, but if you keep winning in the (guaranteed to kill but not maim if you lose) Russian roulette, then it would be evidence for MWI. This is endlessly discussed online and in literature, by the way.
I get that having a strong anthropic effect suggest there is something going on. It is not immidietly obvious to me that it favours MWI in particular. Would it or why would it not favour the hypotheses that you are gods chosen protagonist?
I am assuming in that the russian roulette the guns works "correct", that there is no violation of orderliness in the physical causation. The scenario where I am imagining "coin flips run out" is like gravity just stops because gravity was just a very big coincidence of quantum improbability. I could see that "world selection" could be meanigful in tippping points but if one is to extract whole structures and mechanics that is a way stingier bullet to swallow.
The Many-Worlds Interpretation is an interpretation of Quantum Mechanics, that says that the wave function never collapses - every possible universe exists, every quantum coin flip falls both ways. As far as I'm aware, this interpretation is usually (a) regarded to be just a philosophical interpretation, with no practical effect on the physical world, and (b) is usually believed to be false.
But there is a world in which we would all be convinced that this interpretation is correct. Imagine that tomorrow a paper comes out, and it says that actually, the LHC should have killed us all. Colliding protons at the speed and quantity that the LHC does should create an average of 1.2 black holes capable of destroying the planet every month. But the LHC has been running, colliding a billion protons per second for years, and we are still here. Say that paper has been peer-reviewed, the math checked and rechecked, mini black holes created up to the point where they would actually destroy the earth, etcetera. What would this mean? It would mean the Many-Worlds Interpretation is reality, and that we are only alive thanks to there existing an incredibly improbable universe - some universe from the infinite universes - where all the quantum flips came in our favor, and we are there, still alive.
So the Many-Worlds Interpretation should eventually reveal itself as correct in any universe (in this case, multiverse) where the probabilistic tendency in any given universe is for humanity to die out. Or in other words, any universe with a great filter. Is our universe such a universe?
What does Eliezer think? He just made a post called Death with Dignity. He believes, it is incredibly likely, 99.9%+ likely, that humanity will soon die out because of AI. I may not personally agree with this assessment, but from his perspective, if 50 years pass and humanity is still here, this should make him update significantly whatever his current belief is in the different interpretations of quantum mechanics. The same goes for anyone else who believes humanity is faced with a nearly impassable great filter.
Well, but, it would be annoying to wait to become convinced that this interpretation is correct. Is there anyone who has made predictions like these in the past? Have there ever been doomsayers? Interestingly, yes. How many intelligent people, in the peak of the cold war, believed with high certainty we would be extinct by now? Any one of them still alive should update in favor of the Many-Worlds Interpretation. How many nuclear close calls have we had? How many more we don't know about? And how likely was each of them to resolve as nicely as they did? I don't know, but I would be interested in an in-depth analysis by an expert.
I'm a lurker inspired by the "recent changes" to make a post (as intended!), suggestions and comments would be much appreciated.