Long ago I read a book that asked the question “Why is there something rather than nothing?” Contemplating this question, I asked “What if there really is nothing?” Eventually I concluded that there really isn’t – reality is just fiction as seen from the inside.
Much later, I learned that this idea had a name: modal realism. After I read some about David Lewis’s views on the subject, it became clear to me that this was obviously, even trivially, correct, but since all the other worlds are causally unconnected, it doesn’t matter at all for day-to-day life. Except as a means of dissolving the initial vexing question, it was pointless, I thought, to dwell on this topic any more.
Later on I learned about the Cold War and the nuclear arms race and the fears of nuclear annihilation. Apparently, people thought this was a very real danger, to the point of building bomb shelters in their backyards. And yet somehow we survived, and not a single bomb was dropped. In light of this, I thought, “What a bunch of hype this all is. You doomsayers cried wolf for decades; why should I worry now?”
But all of that happened before I was born.
If modal realism is correct, then for all I know there was* a nuclear holocaust in most world-lines; it’s just that I never existed there at all. Hence I cannot use the fact of my existence as evidence against the plausibility of existential threats, any more than we can observe life on Earth and thereby conclude that life is common throughout the universe.
(*Even setting aside MWI, which of course only strengthens the point.)
Strange how abstract ideas come back to bite you. So, should I worry now?
If you think doom is very probable and we only survived due to the anthropic principle, then you should expect doom any day now, and every passing day without incident should weaken your faith in the anthropic explanation.
If you think all possible worlds exist, then you should expect our small bubble of ordered existence to erupt into chaos any day now, because way more copies of it are contained in chaotic worlds than in ordered ones. Every day you spend without spontaneously turning into a pheasant should weaken your faith in the multiverse.
(These arguments are not standard LW fare, but I’ve floated them here before and they seem to work okay.)
If you think all possible worlds exist, then you should expect our small bubble of ordered existence to erupt into chaos any day now, because way more copies of it are contained in chaotic worlds than in ordered ones. Every day you spend without spontaneously turning into a pheasant should weaken your faith in the multiverse.
This depends on which level of the Tegmark classification you are talking about. Level III for example, quantum MWI, gives very low probabilities for things like turning into a pheasant, since those evens while possible, have tiny chances of occurring. Level IV, the ultimate ensemble, which seems to the main emphasis of the poster above, may have your argument as a valid rebuttal, but since level IV requires consistency, it would require a much better understanding of what consistent rule systems look like. And it may be that the vast majority of those universes don’t have observers, so we actually would need to look at consistent rule systems with observers. Without a lot more information, it is very hard to examine the expected probabilities of weird even events in a level IV setting.
Yeah, that’s a good point. Hardcoding complicated changes is consistent. So any such argument of this form about level IV fails. I withdraw that claim.
Tegmark level IV is a very useful tool to guide one’s intuitions, but in the end, the only meaningful question about Tegmark IV universes is this: Based on my observations, what is the relative probability that I am in this one rather than that one? And this, of course, is just what scientists do anyway, without citing Tegmark each time. Hardcoded universes are easily dealt with by the scientists’ favorite tool, Occam’s Razor.
Consistency is about logics, while Tegmark’s madness is about mathematical structures. Whenever you can model your own actions (decision-making algorithm) using huge complicated mathematical structures, you can also do so with relatively simple mathematical structures constructed from the syntax of your algorithm (Lowenheim-Skolem type constructions). There is no fact of the matter about whether a given consistent countable first order theory, say, talks about an uncountable model or a countable one.
I don’t follow. Many low probability and unordered worlds are highly preferable. Conversely, many high probability worlds are not. I don’t see a correlation.
It’s a simplification. If preference satisfies expected utility axioms, it can be decomposed on probability and utility, and in this sense probability is a component of preference and shows how much you care about a given possibility. This doesn’t mean that utility is high on those possibilities as well, or that the possibilities with high utility will have high probability. See my old post for more on this.
I understand this move but I don’t like it. I think that in the fullness of time, we’ll see that probability is not a kind of preference, and there is a “fact of the matter” about the effects that actions have, i.e. that reality is objective not subjective.
But I don’t like arguments from subjective anticipation, subjective anticipation is a projective error that humans make, as many worlds QM has already proved.
Indeed MW QM combined with Robin’s Mangled Worlds is a good microcosm for how the multiverse at other levels ought to turn out. Subjective anticipation out, but still objective facts about what happens.
I note that since the argument from subjective anticipation is invalid, there is still the possibility that we live in an infinite structure with no canonical measure, in which case Vladimir would be right.
I understand this move but I don’t like it. I think that in the fullness of time, we’ll see that probability is not a kind of preference, and there is a “fact of the matter” about the effects that actions have, i.e. that reality is objective not subjective.
I think that probability is a tool for preference, but I also think that there is a fact of the matter about the effects of actions, and that reality of that effect is objective. This effect is at the level of the sample space (based on all mathematical structures maybe) though, of “brittle math”, while the ways you measure the “probability” of a given (objective) event depend on what preference (subjective goals) you are trying to optimize for.
If you think doom is very probable and we only survived due to the anthropic principle, then you should expect doom any day now, and every passing day without incident should weaken your faith in the anthropic explanation.
What if you can see the doom building up, with every passing day? :-)
If you think all possible worlds exist, then you should expect our small bubble of ordered existence to erupt into chaos any day now, because way more copies of it are contained in chaotic worlds than in ordered ones.
I think this one is deeper. It is a valid criticism of quantum MWI, for example. If all worlds exist equally then naively all this structure around us should dissolve immediately, because most physical configurations are just randomness. Thus the quest to derive the Born probabilities…
I don’t believe MWI as an explanation of QM anyway, so no big deal. But I am interested in “level IV” thinking—the idea that “all possible worlds exist”, according to some precise notion of possibility. And yes, if you think any sequence of events is equally possible and hence (by the hypothesis) equally real, then what we actually see happening looks exceedingly improbable.
One pragmatist response to this is just to say “only orderly worlds are possible”, without giving a further reason. If you actually had an “orderly multiverse” theory that gave correct predictions, you would have some justification for doing this, though eventually you’d still want to know why only the orderly worlds are real.
A more metaphysical response would try to provide a reason why all the real worlds are orderly. For example: Anything that exists in any world has a “nature” or an “essence”, and causality is always about essences, so it’s just not true that any string of events can occur in any world. Any event in any world really is a necessary product of the essences of the earlier events that cause it, and the appearance of randomness only happens under special circumstances (e.g. brains in vats) which are just uncommon in the multiverse. There are no worlds where events actually go haywire because it is logically impossible for causality to switch off, and every world has its own internal form of causality.
Then there’s an anthropic variation on the metaphysical response, where you don’t say that only orderly worlds are possible, but you give some reason why consciousness can only happen in orderly worlds (e.g. it requires causality).
If you think all possible worlds exist, then you should expect our small bubble of ordered existence to erupt into chaos any day now, because way more copies of it are contained in chaotic worlds than in ordered ones. Every day you spend without spontaneously turning into a pheasant should weaken your faith in the multiverse.
It’s not clear to me that this is correct. Also, even if it is, then coherent memories (like what we’re using to judge this whole scenario) only exist in worlds where this either hasn’t happened yet or won’t ever.
Well, we even had a law which required to have one if you built a new house (see an article in German). This law is long since extinct, but according to the link above, there were 2.5 million such rooms, for a population of just 8 million people… Please note that in case of a real emergency most of those would probably have been extremely under-equipped. So,built—yes, correctly—no, and nowadays not even thought about.
What I’d heard was a bit on NPR which claimed there were only a handful of bomb shelters built in the US, and I admit I wasn’t thinking about the rest of the world.
I’m probably born a little late (1953) for the height of bomb-shelter building, but I’ve never heard second or third-hand about actual bomb shelters in the US, and I think I would have (as parts of basements or somesuch) if they were at all common.
My impression is that the real attitude wasn’t so much that a big nuclear war was unlikely as that people thought that if it happened, it wouldn’t be worth living through.
Long ago I read a book that asked the question “Why is there something rather than nothing?” Contemplating this question, I asked “What if there really is nothing?” Eventually I concluded that there really isn’t – reality is just fiction as seen from the inside.
Much later, I learned that this idea had a name: modal realism. After I read some about David Lewis’s views on the subject, it became clear to me that this was obviously, even trivially, correct, but since all the other worlds are causally unconnected, it doesn’t matter at all for day-to-day life. Except as a means of dissolving the initial vexing question, it was pointless, I thought, to dwell on this topic any more.
Later on I learned about the Cold War and the nuclear arms race and the fears of nuclear annihilation. Apparently, people thought this was a very real danger, to the point of building bomb shelters in their backyards. And yet somehow we survived, and not a single bomb was dropped. In light of this, I thought, “What a bunch of hype this all is. You doomsayers cried wolf for decades; why should I worry now?”
But all of that happened before I was born.
If modal realism is correct, then for all I know there was* a nuclear holocaust in most world-lines; it’s just that I never existed there at all. Hence I cannot use the fact of my existence as evidence against the plausibility of existential threats, any more than we can observe life on Earth and thereby conclude that life is common throughout the universe.
(*Even setting aside MWI, which of course only strengthens the point.)
Strange how abstract ideas come back to bite you. So, should I worry now?
If you think doom is very probable and we only survived due to the anthropic principle, then you should expect doom any day now, and every passing day without incident should weaken your faith in the anthropic explanation.
If you think all possible worlds exist, then you should expect our small bubble of ordered existence to erupt into chaos any day now, because way more copies of it are contained in chaotic worlds than in ordered ones. Every day you spend without spontaneously turning into a pheasant should weaken your faith in the multiverse.
(These arguments are not standard LW fare, but I’ve floated them here before and they seem to work okay.)
This depends on which level of the Tegmark classification you are talking about. Level III for example, quantum MWI, gives very low probabilities for things like turning into a pheasant, since those evens while possible, have tiny chances of occurring. Level IV, the ultimate ensemble, which seems to the main emphasis of the poster above, may have your argument as a valid rebuttal, but since level IV requires consistency, it would require a much better understanding of what consistent rule systems look like. And it may be that the vast majority of those universes don’t have observers, so we actually would need to look at consistent rule systems with observers. Without a lot more information, it is very hard to examine the expected probabilities of weird even events in a level IV setting.
Wha? Any sequence of observations can be embedded in a consistent system that “hardcodes” it.
Yeah, that’s a good point. Hardcoding complicated changes is consistent. So any such argument of this form about level IV fails. I withdraw that claim.
Tegmark level IV is a very useful tool to guide one’s intuitions, but in the end, the only meaningful question about Tegmark IV universes is this: Based on my observations, what is the relative probability that I am in this one rather than that one? And this, of course, is just what scientists do anyway, without citing Tegmark each time. Hardcoded universes are easily dealt with by the scientists’ favorite tool, Occam’s Razor.
Consistency is about logics, while Tegmark’s madness is about mathematical structures. Whenever you can model your own actions (decision-making algorithm) using huge complicated mathematical structures, you can also do so with relatively simple mathematical structures constructed from the syntax of your algorithm (Lowenheim-Skolem type constructions). There is no fact of the matter about whether a given consistent countable first order theory, say, talks about an uncountable model or a countable one.
Not if you interpret your preference about those worlds as assigning most of them low probability, so that only the ordered ones matter.
I don’t follow. Many low probability and unordered worlds are highly preferable. Conversely, many high probability worlds are not. I don’t see a correlation.
It’s a simplification. If preference satisfies expected utility axioms, it can be decomposed on probability and utility, and in this sense probability is a component of preference and shows how much you care about a given possibility. This doesn’t mean that utility is high on those possibilities as well, or that the possibilities with high utility will have high probability. See my old post for more on this.
I understand this move but I don’t like it. I think that in the fullness of time, we’ll see that probability is not a kind of preference, and there is a “fact of the matter” about the effects that actions have, i.e. that reality is objective not subjective.
But I don’t like arguments from subjective anticipation, subjective anticipation is a projective error that humans make, as many worlds QM has already proved.
Indeed MW QM combined with Robin’s Mangled Worlds is a good microcosm for how the multiverse at other levels ought to turn out. Subjective anticipation out, but still objective facts about what happens.
I note that since the argument from subjective anticipation is invalid, there is still the possibility that we live in an infinite structure with no canonical measure, in which case Vladimir would be right.
I think that probability is a tool for preference, but I also think that there is a fact of the matter about the effects of actions, and that reality of that effect is objective. This effect is at the level of the sample space (based on all mathematical structures maybe) though, of “brittle math”, while the ways you measure the “probability” of a given (objective) event depend on what preference (subjective goals) you are trying to optimize for.
To rephrase, “unless you interpret your preference as denying the multiverse hypothesis” :-)
You don’t have to assign exactly no value to anything, which makes all structures relevant (to some extent).
What if you can see the doom building up, with every passing day? :-)
I think this one is deeper. It is a valid criticism of quantum MWI, for example. If all worlds exist equally then naively all this structure around us should dissolve immediately, because most physical configurations are just randomness. Thus the quest to derive the Born probabilities…
I don’t believe MWI as an explanation of QM anyway, so no big deal. But I am interested in “level IV” thinking—the idea that “all possible worlds exist”, according to some precise notion of possibility. And yes, if you think any sequence of events is equally possible and hence (by the hypothesis) equally real, then what we actually see happening looks exceedingly improbable.
One pragmatist response to this is just to say “only orderly worlds are possible”, without giving a further reason. If you actually had an “orderly multiverse” theory that gave correct predictions, you would have some justification for doing this, though eventually you’d still want to know why only the orderly worlds are real.
A more metaphysical response would try to provide a reason why all the real worlds are orderly. For example: Anything that exists in any world has a “nature” or an “essence”, and causality is always about essences, so it’s just not true that any string of events can occur in any world. Any event in any world really is a necessary product of the essences of the earlier events that cause it, and the appearance of randomness only happens under special circumstances (e.g. brains in vats) which are just uncommon in the multiverse. There are no worlds where events actually go haywire because it is logically impossible for causality to switch off, and every world has its own internal form of causality.
Then there’s an anthropic variation on the metaphysical response, where you don’t say that only orderly worlds are possible, but you give some reason why consciousness can only happen in orderly worlds (e.g. it requires causality).
It’s not clear to me that this is correct. Also, even if it is, then coherent memories (like what we’re using to judge this whole scenario) only exist in worlds where this either hasn’t happened yet or won’t ever.
We use markdown syntax. An > at the start of the paragraph will make it a quote,
I know, I was just being too lazy to look up the syntax :/.
If you click “Help” when writing a comment, it will appear in a handy box right next to where you are writing.
What is this subjective expectation that you speak of?
http://www.nickbostrom.com/papers/anthropicshadow.pdf
From what I’ve heard, there was a lot of talk about bomb shelters, but very few of them were built.
Well, we even had a law which required to have one if you built a new house (see an article in German). This law is long since extinct, but according to the link above, there were 2.5 million such rooms, for a population of just 8 million people… Please note that in case of a real emergency most of those would probably have been extremely under-equipped. So,built—yes, correctly—no, and nowadays not even thought about.
What I’d heard was a bit on NPR which claimed there were only a handful of bomb shelters built in the US, and I admit I wasn’t thinking about the rest of the world.
I’m probably born a little late (1953) for the height of bomb-shelter building, but I’ve never heard second or third-hand about actual bomb shelters in the US, and I think I would have (as parts of basements or somesuch) if they were at all common.
My impression is that the real attitude wasn’t so much that a big nuclear war was unlikely as that people thought that if it happened, it wouldn’t be worth living through.