Late Great Filter Is Not Bad News

byWei_Dai9y4th Apr 201082 comments


But I hope that our Mars probes will discover nothing. It would be good news if we find Mars to be completely sterile. Dead rocks and lifeless sands would lift my spirit.

Conversely, if we discovered traces of some simple extinct life form—some bacteria, some algae—it would be bad news. If we found fossils of something more advanced, perhaps something looking like the remnants of a trilobite or even the skeleton of a small mammal, it would be very bad news. The more complex the life we found, the more depressing the news of its existence would be. Scientifically interesting, certainly, but a bad omen for the future of the human race.

— Nick Bostrom, in Where Are They? Why I hope that the search for extraterrestrial life finds nothing

This post is a reply to Robin Hanson's recent OB post Very Bad News, as well as Nick Bostrom's 2008 paper quoted above, and assumes familiarity with Robin's Great Filter idea. (Robin's server for the Great Filter paper seems to be experiencing some kind of error. See here for a mirror.)

Suppose Omega appears and says to you:

(Scenario 1) I'm going to apply a great filter to humanity. You get to choose whether the filter is applied one minute from now, or in five years. When the designated time arrives, I'll throw a fair coin, and wipe out humanity if it lands heads. And oh, it's not the current you that gets to decide, but the version of you 4 years and 364 days from now. I'll predict his or her decision and act accordingly.

I hope it's not controversial that the current you should prefer a late filter, since (with probability .5) that gives you and everyone else five more years of life. What about the future version of you? Well, if he or she decides on the early filter, that would constitutes a time inconsistency. And for those who believe in multiverse/many-worlds theories, choosing the early filter shortens the lives of everyone in half of all universes/branches where a copy of you is making this decision, which doesn't seem like a good thing. It seems clear that, ignoring human deviations from ideal rationality, the right decision of the future you is to choose the late filter.

Now let's change this thought experiment a little. Omega appears and instead says:

(Scenario 2) Here's a button. A million years ago I hid a doomsday device in the solar system and predicted whether you would press this button or not. Then I flipped a coin. If the coin came out tails, I did nothing. Otherwise, if I predicted that you would press the button, then I programmed the device to destroy Earth right after you press the button, but if I predicted that you would not press the button, then I programmed the device to destroy the Earth immediately (i.e., a million years ago).

It seems to me that this decision problem is structurally no different from the one faced by the future you in the previous thought experiment, and the correct decision is still to choose the late filter (i.e., press the button). (I'm assuming that you don't consider the entire history of humanity up to this point to be of negative value, which seems a safe assumption, at least if the "you" here is Robin Hanson.)

So, if given a choice between an early filter and a late filter, we should choose a late filter. But then why do Robin and Nick (and probably most others who have thought about it) consider news that imply a greater likelihood of the Great Filter being late to be bad news? It seems to me that viewing a late Great Filter to be worse news than an early Great Filter is another instance of the confusion and irrationality of SSA/SIA-style anthropic reasoning and subjective anticipation. If you anticipate anything, believing that the great filter is more likely to lie in the future means you have to anticipate a higher probability of experiencing doom.

(This paragraph was inserted to clarify in response to a couple of comments. These two scenarios involving Omega are not meant to correspond to any actual decisions we have to make, but just to establish that A) if we had a choice, it would be rational to choose a late filter instead of an early filter, therefore it makes no sense to consider the Great Filter being late to be bad news (compared to it being early), and B) human beings, working off subjective anticipation, would tend to incorrectly choose the early filter in these scenarios, especially scenario 2, which explains why we also tend to consider the Great Filter being late to be bad news. The decision mentioned below, in the last paragraph, is not directly related to these Omega scenarios.)

From an objective perspective, a universe with a late great filter simply has a somewhat greater density of life than a universe with an early great filter. UDT says, let's forget about SSA/SIA-style anthropic reasoning and subjective anticipation, and instead consider yourself to be acting in all of the universes that contain a copy of you (with the same preferences, memories, and sensory inputs), making the decision for all of them, and decide based on how you want the multiverse as a whole to turn out.

So, according to this line of thought, we're acting in both kinds of universes: those with early filters, and those with late filters. If, as Robin Hanson suggests, we were to devote a lot of resources to projects aimed at preventing possible late filters, then we would end up improving the universes with late filters, but hurting the universes with only early filters (because the resources would otherwise have been used for something else). But since copies of us occur more frequently in universes with late filters than in universes with early filters, such a decision (which Robin arrives at via SIA) can be justified on utilitarian grounds under UDT.