Except I don’t think this works. The answer to the question “why did X happen” should not depend on who is asking. Martian historians observing the Earth and asking “how did they avoid blowing themselves up?” are not in a position to answer the question anthropically(1), without going all the way to the absurdity of answering every question “why X?” with “otherwise, you would not be asking why X”.
I disagree. Most observers will have found that their planet was not blown up, but if they look at other planets, they will find that most of them blew up. As such, it would be surprising to find another planet that didn’t blow up, but not surprising that yours did not.
The difference in surprise is due to the unlikeliness of being from Earth. Being from Earth is evidence that it did not blow itself up. The aliens don’t have this evidence, so they’re more surprised than an Earthling.
I think this is confusing priors and posteriors. Since we have not blown ourselves up, the probability that we have not blown ourselves up is 1. That does not affect the answer to the question, “how likely was it in 1950 that we would?”.
Here’s another extreme and hypothetical problem (hence of little interest to me, but others may find themselves drawn to thinking about it). A physicist deduces from currently known physics the existence of a process whereby there is a calculable probability per unit of space-time volume of a spontaneously created singularity that will spread outwards at the speed of light, instantaneously turning everything it hits to a state incapable of the complexity required to support any sort of life. The probability works out to about 1-10^(-20) per Planck volume per Planck time. Should that suggest that his conclusion is wrong?
Anthropics seems to be built around the idea of using who you are as evidence. P(humans have not blown ourselves up|I am a human) is high, so long as you accept that “I am a human” is a meaningful observation.
For the way you phrased it, “at least one human exists” would give the same answer, but imagine that not everyone would die. There being at least one human is a given.
Should that suggest that his conclusion is wrong?
There’s a few distinct possibilities to consider:
The physicist is a human, and his theory is wrong. (Moderate prior)
The physicist is a human, and his theory is right. (Exponentially tiny prior)
The physicist is a Boltzmann brain, and his theory is wrong. (Tiny prior)
The physicist is a Boltzmann brain, and his theory is right. (Very tiny prior)
If he’s right, he’s almost certainly a Boltzmann brain, since an actual human evolving in that universe requires far too many coincidences. But if he’s a Boltzmann brain, he has no reason to believe that theory, since it’s based on a chance hallucinated memory rather than actual experiments, and the theory is most likely wrong. And if the theory is wrong, it would be pretty surprising to hallucinate something like humanity, so he probably is a real person.
Thus, the most likely conclusion is that his theory is wrong, and he’s a human.
I disagree. Most observers will have found that their planet was not blown up, but if they look at other planets, they will find that most of them blew up. As such, it would be surprising to find another planet that didn’t blow up, but not surprising that yours did not.
The difference in surprise is due to the unlikeliness of being from Earth. Being from Earth is evidence that it did not blow itself up. The aliens don’t have this evidence, so they’re more surprised than an Earthling.
I think this is confusing priors and posteriors. Since we have not blown ourselves up, the probability that we have not blown ourselves up is 1. That does not affect the answer to the question, “how likely was it in 1950 that we would?”.
Here’s another extreme and hypothetical problem (hence of little interest to me, but others may find themselves drawn to thinking about it). A physicist deduces from currently known physics the existence of a process whereby there is a calculable probability per unit of space-time volume of a spontaneously created singularity that will spread outwards at the speed of light, instantaneously turning everything it hits to a state incapable of the complexity required to support any sort of life. The probability works out to about 1-10^(-20) per Planck volume per Planck time. Should that suggest that his conclusion is wrong?
Anthropics seems to be built around the idea of using who you are as evidence. P(humans have not blown ourselves up|I am a human) is high, so long as you accept that “I am a human” is a meaningful observation.
For the way you phrased it, “at least one human exists” would give the same answer, but imagine that not everyone would die. There being at least one human is a given.
There’s a few distinct possibilities to consider:
The physicist is a human, and his theory is wrong. (Moderate prior)
The physicist is a human, and his theory is right. (Exponentially tiny prior)
The physicist is a Boltzmann brain, and his theory is wrong. (Tiny prior)
The physicist is a Boltzmann brain, and his theory is right. (Very tiny prior)
If he’s right, he’s almost certainly a Boltzmann brain, since an actual human evolving in that universe requires far too many coincidences. But if he’s a Boltzmann brain, he has no reason to believe that theory, since it’s based on a chance hallucinated memory rather than actual experiments, and the theory is most likely wrong. And if the theory is wrong, it would be pretty surprising to hallucinate something like humanity, so he probably is a real person.
Thus, the most likely conclusion is that his theory is wrong, and he’s a human.