I do mean to dissolve the Doomsday Argument with a mind-bending reinterpretation of the philosophy involved.
It used to be fashionable to argue whether Bayesian probability is objective or subjective. I think that has died down and that people vaguely get that probability is situational.
When you are forced to reason probabilistically, due to having incomplete information, you are in a situation defined by the information you actually have. You have to use all of information. If you leave some out, you end up computing the probability for a different situation. If that changes the answer, you’ve done it wrong. You have computed the probability for somebody else’s situation, not yours.
Let me highlight the issue: probability is not a single number.
Ponder the situation of a space alien in the Andromeda Galaxy. His galaxy is on a collision course with the Milkyway. His anxious scanning of our Galaxy has revealed the planet Earth, and he has learned three basic facts. 60 billion humans so far. Some maybe 60 billion to come. Population of 10 billion, life expectancy of 80 years.
Since that is all he knows (Earth is a long way away, it is surprising he knows even that much) those 60 billion probably come over the next 480 years. That is the correct calculation for his situation. He doesn’t take that number very seriously. He has done a course in Bayesian reasoning and remembers the stuff about how probabilities lurch abruptly when a killer fact comes in. He remembers the set up for probability lurches: too little information. He notices that he has too little information about Earth, and expects the number to change dramatically if he got a little more.
Notice how different his situation is from ours. We know vastly more and have to do a vastly more complicated calculation. There are all sorts of relevant considerations.
When nuclear weapons are invented, we have to update by reducing our guess of the life time of the the human race, because we might blow ourselves up.
When we land on the moon, we should raise our guess a little, because of the hope of becoming an interplanetary species, and thus a little safer from meteorite wipe out.
Antibiotics—longer duration, we are not going to be wiped out by the Black Death.
Discover viruses—shorter duration, since antibiotics don’t work for viruses
Invent anti-viral medicines—longer duration, we aren’t going to be wiped out by HIV.
We suffer from an embarrassment of riches. We know a great deal that is relevant to how long the human race will last, we just don’t know what to do with all that information.
We could throw nearly all of it away and just use the most most basic facts. That allows us to calculate the probability of human extinction for an observer 10 million light years away, who knows only the most basic facts. But that is not a very interesting calculation, for we are here, not there, and know too much, not too little. Failing to use the information we have is a different situation from being too far away to see anything much.
I would also point out that, I do actually kind of know facts like (1) The population is growing and (2) its like 8 Billion or something, (3) Nuclear weapons are scary. But, I didn’t know my approximate position in the human birth order (how many people have come before), I had to look that up. So its an especially artificial situation, I am not just interpolating based on a tiny subset of the information available, but I am actually seeking out some new information (me in the birth order) and then interpolating based only on that thing I previously didn’t know.
I do mean to dissolve the Doomsday Argument with a mind-bending reinterpretation of the philosophy involved.
It used to be fashionable to argue whether Bayesian probability is objective or subjective. I think that has died down and that people vaguely get that probability is situational.
When you are forced to reason probabilistically, due to having incomplete information, you are in a situation defined by the information you actually have. You have to use all of information. If you leave some out, you end up computing the probability for a different situation. If that changes the answer, you’ve done it wrong. You have computed the probability for somebody else’s situation, not yours.
Let me highlight the issue: probability is not a single number.
Ponder the situation of a space alien in the Andromeda Galaxy. His galaxy is on a collision course with the Milkyway. His anxious scanning of our Galaxy has revealed the planet Earth, and he has learned three basic facts. 60 billion humans so far. Some maybe 60 billion to come. Population of 10 billion, life expectancy of 80 years.
Since that is all he knows (Earth is a long way away, it is surprising he knows even that much) those 60 billion probably come over the next 480 years. That is the correct calculation for his situation. He doesn’t take that number very seriously. He has done a course in Bayesian reasoning and remembers the stuff about how probabilities lurch abruptly when a killer fact comes in. He remembers the set up for probability lurches: too little information. He notices that he has too little information about Earth, and expects the number to change dramatically if he got a little more.
Notice how different his situation is from ours. We know vastly more and have to do a vastly more complicated calculation. There are all sorts of relevant considerations.
When nuclear weapons are invented, we have to update by reducing our guess of the life time of the the human race, because we might blow ourselves up.
When we land on the moon, we should raise our guess a little, because of the hope of becoming an interplanetary species, and thus a little safer from meteorite wipe out.
Antibiotics—longer duration, we are not going to be wiped out by the Black Death.
Discover viruses—shorter duration, since antibiotics don’t work for viruses
Invent anti-viral medicines—longer duration, we aren’t going to be wiped out by HIV.
We suffer from an embarrassment of riches. We know a great deal that is relevant to how long the human race will last, we just don’t know what to do with all that information.
We could throw nearly all of it away and just use the most most basic facts. That allows us to calculate the probability of human extinction for an observer 10 million light years away, who knows only the most basic facts. But that is not a very interesting calculation, for we are here, not there, and know too much, not too little. Failing to use the information we have is a different situation from being too far away to see anything much.
I argued something similar to your position in a recent post. https://www.lesswrong.com/posts/LhsteuSNFfWRoXBjz/randomness-and-doomsday-for-weak-agents
I would also point out that, I do actually kind of know facts like (1) The population is growing and (2) its like 8 Billion or something, (3) Nuclear weapons are scary. But, I didn’t know my approximate position in the human birth order (how many people have come before), I had to look that up. So its an especially artificial situation, I am not just interpolating based on a tiny subset of the information available, but I am actually seeking out some new information (me in the birth order) and then interpolating based only on that thing I previously didn’t know.