This post describes variations on a thought experiment involving the anthropic principle. The variations were developed through discussion with Andreas Albrecht, Charles Bennett, Leonid Levin, and Andrew Arrasmith at a conference at the Neils Bohr Institute in Copenhagen in October of 2019. I have not yet finished reading Bostrom’s “Anthropic Bias“, so I don’t know where it fits in to his framework. I expect it is subsumed into such existing discussion, and I would appreciate pointers.
The point is to consider a few thought experiments that share many of the same important features, but for which we have very different intuitions, and to identify if there are any substantive difference that can be used to justify these intuitions.
I will use the term “shocked” (in the sense of “I was shocked to see Bob levitate off the ground”) to refer to the situation where we have made observations that are extremely unlikely to be generated by our implicit background model of the world, such that good reasoners would likely reject the model and start entertaining previously disfavored alternative models like “we’re all brains in a vat”, the Matrix, etc. In particular, to be shocked is not supposed to be merely a description of human psychology, but rather is a normative claim about how good scientific reasoners should behave.
Here are the three scenarios:
Scenario 2: Terrorists release a carefully engineered virus that wouldn’t naturally arise and has a vastly higher fatality rate than natural pathogens. In fact, it is designed to incubate for several years, infect every human on the planet, and then kill each host unless the host has a randomly chosen precise selection of genetic variants, which is expected to occur only once per 4 billion people. (There are 7 billion people on the planet at the time.) One of the following takes place:
- 2(a): Two people, a man and a woman, are the lone survivors with the correct genetic variants. They find each after everyone else is wiped out by quickly getting on Twitter (before the power goes down) and agreeing on somewhere to meet. They fall in love, have a child, and that child is you.
- 2(b): You are an infant when the pandemic hits, and you are the lone survivor. You are raised by the terrorists and grow up.
- 2(c): You are an adult when the pandemic hits, and you are the lone survivor.
In all versions of this scenario, having one or two people worldwide survive is a probabilistically reasonable outcome.
Scenario 3: You live 50 years in the future when there are lots of highly agile robots; however, like today, they are very dumb with no signs of anything we might call intelligence of consciousness. One day you are abducted by evil robots to an underground lair and subjected to a cruel punishment: You are given a fair coinThis could be a quantum coin if you know what that means and you prefer.b , which you inspect very carefully, and you are forced to flip it 33 times. If you flip 33 heads in a row (a chance of 1 in 233 = 8,589,934,592 ≈ 8.6 billion), you will be released unharmed. But if any of the flips land tails up, then on the following day you will be…
- 3(a): …executed.
- 3(b): …given a very intense noogie.
You proceed to flip 33 heads in a row, and the robots release you alive and with a comfortable scalp. You later find out that Earth was taken over by an insane dictator with robot armies who rounded up everyone and subjected them to the same cruel experiment, and that you were the lone winner.
In all cases, we are reasoning from a situation where our past contains an extremely unlikely event that was necessary (except for Scenario 3(b)) for us to exist in the present when we are doing our reasoning. Furthermore, the event, though extremely unlikely considered in isolation, was likely to occur somewhere because it was attempted a very large number of times.
In Scenario 1, it’s seems we should not be shocked. Abiogenesis may be extremely rare in any given galaxy, but we are not bothered by finding evidence for such an event in our past because it is necessary (given the laws of physics in our universe) for an intelligent observers to trace their origins to such an event, and the universe is big enough that this should have happened at least once.
In Scenario 3, it seems you should be shocked, and should conclude that the coin must have been rigged, or something. For Scenario 3(b), it’s pretty obvious that you personally have been singled out beyond all reasonable odds. And to see that Scenario 3(a) is equivalent, just consider how you should react immediately after flipping the coins, before the time you were scheduled to be executed had you not succeeded. At that point in time, the unlikely event is not necessary for you to exist.This is the modification to the quantum suicide thought experiment that in the past always convinced me there was no quantum immortality. That is, if there is a delay between the quantum measurement event and the potential mortal blow, then you should expect to exist no matter what the measurement outcome was, and the measurement out statistics should be normal, i.e., you should be shocked to see an extremely rare event.c And if flipping all those heads in a row is shocking immediately after it happens, how could it suddenly become un-shocking later, after the execution would have taken place?
In Scenario 2, I am confused. In all of these cases, the unlikely event can be said to take place before you’re bornThat event is either (a) the initial formation of a zygote’s genome, whether you or your parents, or (b) the choice of which genetic variant the virus should allow to live, which for the sake of argument we can assume was randomly chosen by the terrorists before you were born in all three versions of the scenario. And of course, events (a) and (b) could be spacelike separated!d , and you wouldn’t be around to do the reasoning unless the unlikely event had happened. Scenario 2(a) is especially close to Scenario 1 on the key factors. Yet, there also don’t seem to be any substantive differences between Scenarios 2(c) and Scenario 3(a).
(↵ returns to text)
- In particular, we assume primordial life was not carried to Earth by an asteroid.↵
- This could be a quantum coin if you know what that means and you prefer.↵
- This is the modification to the quantum suicide thought experiment that in the past always convinced me there was no quantum immortality. That is, if there is a delay between the quantum measurement event and the potential mortal blow, then you should expect to exist no matter what the measurement outcome was, and the measurement out statistics should be normal, i.e., you should be shocked to see an extremely rare event.↵
- That event is either (a) the initial formation of a zygote’s genome, whether you or your parents, or (b) the choice of which genetic variant the virus should allow to live, which for the sake of argument we can assume was randomly chosen by the terrorists before you were born in all three versions of the scenario. And of course, events (a) and (b) could be spacelike separated!↵