## LESSWRONGLW

What are your stances on the Doomsday Argument?

The doomsday argument strikes me as complete and utter misguided bullshit, notwithstanding the fact that smart and careful physicists have worked on it, including J. Richard Gott and Brandon Carter, whose work in actual physics I had used extensively in my research. There are plenty of good reasons for x-risk work, no need to invoke lousy ones. The main issue with the argument is the misuse of probability.

First, the argument assumes a specific distribution (usually uniform) a priory without any justification. Indeed one needs a probability distribution to meaningfully talk about probabilities, but there is no reason to pick one specific distribution over another until you have a useful reference class.

Second, the potential infinite expectation value makes any conclusions from the argument moot.

Basically, the Doomsday argument has zero predictive power. Consider a set of civilizations with a fixed number of humans at any given time, each existing for a finite time T, randomly distributed with a distribution function f(T), which does not necessarily have a finite expectation value, standard deviation or any other moments. Now, given a random person from a random civilization at the time t, the Doomsday argument tells them that their civilization will exist for about as long as it had so far. It gives you no clue at all about the shape of f(t) beyond it being non-zero (though maybe measure zero) at t.

Now, shall we lay this nonsense to rest and focus on something productive?

1maximkazhenkov2moNitpick: I was arguing that the Doomsday Argument would actually discourage x-risks related work because "we're doomed anyway".

Right. Either way, it's not a good argument to base one's decisions on.

# 5

Lesswrong contains a large intersection of people who are interested in x-risk reduction and people who are aware of the Doomsday Argument. Yet these two things seem to be incompatible with each other, so I'm going to ask about the elephant in the room:

What are your stances on the Doomsday Argument? Does it encourage or discourage you from working on x-risks? Is it a significant concern for you at all?

Do most people working on x-risks believe the Doomsday Argument to be flawed?

If not, it seems to me that avoiding astronomical waste is also astronomically unlikely, thus balancing out x-risk reduction to a moderately important issue for humanity at best. From an individual perspective (or altruistic perspective with future discounting), we perhaps should focus on having a good time before inevitable doom? What am I missing?

New Comment

Donald Hobson

### Apr 03, 2020

9

Suppose we ignore the simulation argument and take the evidence of history and astronomy at face value. The doomsday argument provides a good prior. However, the evidence that shows we are on early earth is really strong, and the prior is updated away. If we take the simulation hypothesis into account, then there could be a version of us in reality, and many in simulations. The relative balance of preventing X risk vs having a good time is swung, but still strongly cares about X risk. Actually, the doomsday argument puts the probability that infinitely many people will exist, but only finitely many have existed so far at 0, so I'm don't think I believe it.

Charlie Steiner

### Apr 03, 2020

7

People are bad at interpreting the Doomsday Argument, because people are bad at dealing with evidence as Bayesian evidence, rather than a direct statement of the correct belief.

The Doomsday Argument is evidence that we should update on. But it is not a direct statement of the correct belief.

A parable:

On a parallel earth, humanity is on the decline. Some disaster has struck, and the once-billions of proud humanity have been reduced to a few scattered thousands. Now the last exiles of civilization hide in sealed habitats that they no longer have the supply chains to repair, and they know that soon enough the end will come for them too. But on the other hand, the philosophers among them remark, at least there's the Doomsday Argument, which says that on average we should expect to be in the middle of humanity. So if the DA is right, the current crisis is merely a bottleneck in the middle of humanity's time, and everything will probably work itself out any day now. The last philosopher dies after breathing in contaminated air, with the last words "No! The position I occupy is... very unlikely!"

Moral:

Your eyes and ears also provide you evidence about the expected span of humanity.

Daniel Kokotajlo

### Apr 03, 2020

7

I'd like to see someone explore the apparent contradiction in more detail. Even if I were convinced that we will almost certainly fail, I might still prioritize x-risk reduction, since the stakes are so high.

Anyhow, my guess is that most people think the doomsday argument probably doesn't work. I am not sure myself. If it does work though, its conclusion is not that we will all go extinct soon, but rather that ancestor simulations are one of the main uses of cosmic resources.

avturchin

### Apr 04, 2020

6

There is an uncertainty if DA valid or not. Around 40 per cent of scientists who analysed it, think that some version of DA is true, and if we treat as a prediction market, it is a 40 per cent bet. So there is a 60 per cent chance that DA is not valid and thus we should continue to work on x-risks prevention.

Also, it is possible to cheat DA, if we precomit to forget our position number in the future (may be via creating enough simulations of early past).

shminux

### Apr 03, 2020

6
What are your stances on the Doomsday Argument?

The doomsday argument strikes me as complete and utter misguided bullshit, notwithstanding the fact that smart and careful physicists have worked on it, including J. Richard Gott and Brandon Carter, whose work in actual physics I had used extensively in my research. There are plenty of good reasons for x-risk work, no need to invoke lousy ones. The main issue with the argument is the misuse of probability.

First, the argument assumes a specific distribution (usually uniform) a priory without any justification. Indeed one needs a probability distribution to meaningfully talk about probabilities, but there is no reason to pick one specific distribution over another until you have a useful reference class.

Second, the potential infinite expectation value makes any conclusions from the argument moot.

Basically, the Doomsday argument has zero predictive power. Consider a set of civilizations with a fixed number of humans at any given time, each existing for a finite time T, randomly distributed with a distribution function f(T), which does not necessarily have a finite expectation value, standard deviation or any other moments. Now, given a random person from a random civilization at the time t, the Doomsday argument tells them that their civilization will exist for about as long as it had so far. It gives you no clue at all about the shape of f(t) beyond it being non-zero (though maybe measure zero) at t.

Now, shall we lay this nonsense to rest and focus on something productive?

Rafael Harth

### Apr 03, 2020

2

I confidently reject the Doomsday argument, so it doesn't have any implications.