Is our continued existence evidence that Mutually Assured Destruction worked?

Why are "observers" ontologically fundamental in these anthropic arguments? Is there somewhere an analysis of this assumption? I know that there is SSA and SIA, but I don't really understand them.

How do you assign probability over worlds with different numbers of observers?

There is empirical evidence against the MAD hypothesis.

During the Cuban Missile Crisis, a Russian submarine believed that nuclear war had broken out. Three officers on board the submarine were authorised to unanimously launch a nuclear torpedo. An argument broke out among the three, in which http://en.wikipedia.org/wiki/Vasili_Arkhipov was against the launch, preventing a nuclear missile from being launched (and presumably a nuclear retaliation would not be unlikely).

Let's assign a probability that one of the officers would be in favour of launching a missile. Given that 2/3 in our sample were in favour of launching the missile, let's assign the probability to be 2/3 for any single officer. Therefore, the chance that a missile would have been launched is (2/3)^3 - 27%. Even if the probability was less than 2/3 (and people's opinions are interdependent - one person could convince another, or one person could take a contrarian stand), nevertheless it still could have happened. And this wasn't the only time that there almost was a nuclear war. (Incidentally I believe these cases show that an individual effort can at certain points have a huge impact - proof of both the butterfly effect or the 'great man theory' - as long as you redefine 'Great Man' to be a person in the right time and place).

As to the question of whether MAD worked - well it can be certainly argued to have helped, but it demonstrably did not prevent circumstances that could lead to a nuclear war.

Ultimately, I think what this question boils down to is whether to expect "a sample" or "a sample within which we live" (i.e. whether or not the anthropic argument applies). Under MWI, anthropics would be quite likely to hold. On the other hand, if there is only a single world, it would be quite unlikely to hold (as you not living is a possible outcome, whether you could observe it or not). In the former case, we've received no evidence that MAD works. In the latter, however, we have received such evidence.

Something that doesn't often get remarked upon is that the Cold War wasn't the first instance of the strategy of MAD. World War 1 was the culmination of a MAD strategy gone awry.

One difference between the Cold War and World War 1, however, is that in the Cold War at least one of the nations involved was actually employing people to study the mathematics behind the strategy.

(A consideration that people often miss: just because MAD nearly failed doesn't mean it wasn't better than politically feasible (quantum-probable) counterfactually enacted policies.)

Suppose you're on a game show, and you're given a choice between three doors, One has a car, one has a goat, and one has a tiger. You pick a door, and you figure it has 1/3 chance of having the car. The host tells you to stand in front of your chosen door. He presses a button, and one of the doors you didn't choose swings open and a tiger jumps out. Should you update your previous belief that the door you chose has a 1/3 chance of having the car? Your only new evidence was that you've seen that the door you chose didn't have the tiger. But if the door had had the tiger, you wouldn't have seen that evidence, because the tiger would have killed you.

Yes, assuming post-Everett quantum mechanics, our continued existence needn't be interpreted as evidence that Mutually Assured Destruction works, but rather as an anthropic selection effect. It's unclear why (at least in our family of branches) Hugh Everett, who certainly took his own thesis seriously, spent much of his later life working for the Pentagon targeting thermonuclear weaponry on cities. For Everett must have realised that in countless world-branches, such weapons would actually be used. Either way, the idea that Mutually Assured Destruction works could prove ethically catastrophic this century if taken seriously.

MAD didn't work; we were simply lucky: http://cornerstone.gmu.edu/articles/4198

I don't think you need to invoke the anthropomorphic principle here.

The fact that we survived the cold war without a nuclear war doesn't really tell us that much about the odds of doing so. It is basically impossible to estimate the probability of something with a sample size of 1. It could be that we had a 90% chance of getting through the cold war without a nuclear war, or it could be that we only had a 10% chance and just got lucky; based on our current data, either seems quite plausible.

So, for your question "did MAD work"; well, in some sense, either it worked or we got lucky or some combination of the two. But we don't really have enough information to know if it's a good policy to follow or not.

Maybe MAD is the great filter

Applying the anthropic principle here, however, requires that a failure of MAD really would have killed everyone.

No, it doesn't.

People understand very well that they can't draw valid conclusion from experiments with few measurements in domains where it's possible to make a lot of measurements.

They usually don't understand that the same is true with nuclear war. One observation of a strategy working doesn't provide evidence that the strategy works.

If I would tell you that I started doing Forex trading and I turned 100$ into 150$ in a few days, you would think that I'm a good Forex trader even if I could prove to you that I really turned 100$ into 150$ and those were the only Forex trades I did in my life. It would not rational for you to give me your money to invest on your behalf.

If your data set has only one observation it doesn't provide much evidence. That's what the core of the anthropic principle is about.

If we imagine mutually assured destruction as if it was a policy option in a strategy game, it would have statistics along the lines of:

-20% chance of nuclear war, +40% nuclear war intensity.