At the end of Section 5.3 the authors write “So far, we have assumed that we can derive no information on the probability of intelligent life from our own existence, since any intelligent observer will inevitably find themself in a location where intelligent life successfully emerged regardless of the probability. Another line of reasoning, known as the “Self-Indication Assumption” (SIA), suggests that if there are different possible worlds with differing numbers of observers, we should weigh those possibilities in proportion to the number of observers (Bostrom, 2013). For example, if we posit only two possible universes, one with 10 human-like civilizations and one with 10 billion, SIA implies that all else being equal we should be 1 billion times more likely to live in the universe with 10 billion civilizations. If SIA is correct, this could greatly undermine the premises argued here, and under our simple model it would produce high probability of fast rates that reliably lead to intelligent life (Fig. 4, bottom)...Adopting SIA thus will undermine our results, but also undermine any other scientific result that would suggest a lower number of observers in the Universe. The plausibility and implications of SIA remain poorly understood and outside the scope of our present work.”
I’m confused, probably because anthropic effects confuse me and not because the authors made a mistake. But don’t the observer selection effects the paper uses derive information from our own existence, and if we make use of these effects shouldn’t we also accept the implications of SIA? Should rejecting SIA because it results in some bizarre theories cause us to also have less trust in observer selection effects?
When using SSA (which I think the authors do implicitly), you can exclude worlds which contain no observer “like you”, but there’s no anthropic update to the relative probabilities of the worlds that contain at least one observer “like you”. When using SIA, the probability of each worlds gets updates in proportion to the number of observers.
Consider a variant of “god’s coin toss”. God has a device that outputs A, B, or C with equal probability. When seeing A, god creates 0 humans, when seeing B god creates 1 human, and when seeing C god creates 2 humans. You’re one of the humans created this way and don’t know how many other humans have been created. What should be your probability distribution over {A, B, C}? According to SSA, B and C should have probability 1⁄2 each, while according to SIA, B has probability 1⁄3 and C has probability 2⁄3.
The fact that SSA has a discontinuity between zero and any positive number of observers is one of the standard arguments against SSA, see e.g. argument 4 against SSA here:
SIA also implies that we are likely live in the world with interstellar panspermia and many inhabitable planets in our galaxy, as I explored here. In that case, the difficulty of abiogenesis is not a big problem as there will be many planets inseminated with life from one source.
Moreover, SIA and SSA seems to converge in very-very large universe where all possible observers exist: in it I will find myself in the region where most observers exist, and it—with some caveats—will be a region with the high concentration of observers.
Yes for high concentration of observers, and if high tech civilizations have strong incentives to grab galactic resources as quickly as they can thus preventing the emergence of other high tech civilizations, most civilizations such as ours will exist in universes that have some kind of late great filter to knock down civilizations before they can become spacefaring.
Berezin suggested that if the first civilisation will kill all other civilizations, than we are this first civilisation.
Also, if panspermia is true, the age of civilizations will be similar, and several civilizations could become first almost simultaneously in one galaxy, which creates interesting colonisation dynamics.
At the end of Section 5.3 the authors write “So far, we have assumed that we can derive no information on the probability of intelligent life from our own existence, since any intelligent observer will inevitably find themself in a location where intelligent life successfully emerged regardless of the probability. Another line of reasoning, known as the “Self-Indication Assumption” (SIA), suggests that if there are different possible worlds with differing numbers of observers, we should weigh those possibilities in proportion to the number of observers (Bostrom, 2013). For example, if we posit only two possible universes, one with 10 human-like civilizations and one with 10 billion, SIA implies that all else being equal we should be 1 billion times more likely to live in the universe with 10 billion civilizations. If SIA is correct, this could greatly undermine the premises argued here, and under our simple model it would produce high probability of fast rates that reliably lead to intelligent life (Fig. 4, bottom)...Adopting SIA thus will undermine our results, but also undermine any other scientific result that would suggest a lower number of observers in the Universe. The plausibility and implications of SIA remain poorly understood and outside the scope of our present work.”
I’m confused, probably because anthropic effects confuse me and not because the authors made a mistake. But don’t the observer selection effects the paper uses derive information from our own existence, and if we make use of these effects shouldn’t we also accept the implications of SIA? Should rejecting SIA because it results in some bizarre theories cause us to also have less trust in observer selection effects?
When using SSA (which I think the authors do implicitly), you can exclude worlds which contain no observer “like you”, but there’s no anthropic update to the relative probabilities of the worlds that contain at least one observer “like you”. When using SIA, the probability of each worlds gets updates in proportion to the number of observers.
Consider a variant of “god’s coin toss”. God has a device that outputs A, B, or C with equal probability. When seeing A, god creates 0 humans, when seeing B god creates 1 human, and when seeing C god creates 2 humans. You’re one of the humans created this way and don’t know how many other humans have been created. What should be your probability distribution over {A, B, C}? According to SSA, B and C should have probability 1⁄2 each, while according to SIA, B has probability 1⁄3 and C has probability 2⁄3.
The fact that SSA has a discontinuity between zero and any positive number of observers is one of the standard arguments against SSA, see e.g. argument 4 against SSA here:
https://meteuphoric.com/anthropic-principles/
Thanks, that’s a very clear explanation.
SIA also implies that we are likely live in the world with interstellar panspermia and many inhabitable planets in our galaxy, as I explored here. In that case, the difficulty of abiogenesis is not a big problem as there will be many planets inseminated with life from one source.
Moreover, SIA and SSA seems to converge in very-very large universe where all possible observers exist: in it I will find myself in the region where most observers exist, and it—with some caveats—will be a region with the high concentration of observers.
Yes for high concentration of observers, and if high tech civilizations have strong incentives to grab galactic resources as quickly as they can thus preventing the emergence of other high tech civilizations, most civilizations such as ours will exist in universes that have some kind of late great filter to knock down civilizations before they can become spacefaring.
Berezin suggested that if the first civilisation will kill all other civilizations, than we are this first civilisation.
Also, if panspermia is true, the age of civilizations will be similar, and several civilizations could become first almost simultaneously in one galaxy, which creates interesting colonisation dynamics.