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I don't see why there needs to be other universes that actually exist in order for the anthropic principle to apply. It seems to make perfect sense to apply it

by baddox 11y ago

I don't see why there needs to be other universes that actually exist in order for the anthropic principle to apply. It seems to make perfect sense to apply it to a set of conceivable universes, even if such universes don't actually exist and even if it's not physically possible for them to exist.

ncallaway 11y ago
Again, I could easily be wrong about all this. I think this entire discussion is sensitive to exactly what one means by "The Anthropic Principle". If one's definition of the Anthropic Principle in this context simply means that an observed universe will be consistent with a universe that can be observed, then I find it to be trivially true and applicable to a single universe scenario. I subscribe to a definition of the anthropic principle that invokes selection bias as its core mechanism. I think that, in order to have a selection bias, one needs to actually be selecting from a population. Hence my assertion that you need a multi-verse (with different constants in each universe) or a constant that is variable in space or time [2]. The difference, to me, is this: If you are selecting from a population the Anthropic Principle can actually help explain why a value is what it is. Under our understanding of planetary bodies, we often invoke the Anthropic Principle to explain why the earth falls in the habitable-zone. Earth falls in the habitable-zone because — we think — life is most likely to arise on a planet in that zone. However, if you are not selecting from a population, I don't find that the Anthropic Principle explains why a value is what it is. In the scenario where there is only a single value, I think the Anthropic Principle simply demonstrates that that particular value must support life. Put another way, if all planets we observed were the exact same distance from their star as Earth [1], then we couldn't use the Anthropic Principle to explain why Earth is that particular distance from the sun. We would have to find other astronomical reasons to explain why planets form at that specific distance from a star. In this single-distance scenario the only thing the Anthropic Principle actually does for us is confirm that such a distance supports life. [1] Well, not distance per se, but placed such that they received the same amount of stellar energy in their orbits. [2] This final sentence of the introduction of the Anthropic Principle also makes some reference to this saying: "Most often such arguments draw upon some notion of the multiverse for there to be a statistical population of universes to select from and from which selection bias (our observance of only this universe, compatible with life) could occur."
- baddox 11y ago
  > If one's definition of the Anthropic Principle in this context simply means that an observed universe will be consistent with a universe that can be observed, then I find it to be trivially true and applicable to a single universe scenario. It is "trivially" true in a sense. It's a tautology. But it's still useful for thinking about things. I think it applies just as well to a single universe or a multiverse, because even with a single universe you can at least hypothesize about other ways the single universe could behave. > However, if you are not selecting from a population, I don't find that the Anthropic Principle explains why a value is what it is. In the scenario where there is only a single value, I think the Anthropic Principle simply demonstrates that that particular value must support life. It might not answer the extremely broad and ill-defined question "why" to your satisfaction, but I find it fairly satisfying. If things were another way, then I wouldn't be observing the universe because I wouldn't exist. So it's not strange that the universe is this way, given that I exist.
mc808 11y ago
If something is truly a universal constant, then it's part of the definition of what it is to be the universe. That we can imagine the constant being different is really just an artifact of the imperfect symbolic language we've developed to describe the universe. Edit: It's hard to come up with a good analogy because obviously I don't have that "perfect" language at my disposal. But for example, a triangle fundamentally has 3 angles. We can imagine polygons with more angles, but it doesn't make sense to imagine a triangle with any other number of angles. If "the whole universe" were synonymous with "triangle", the notion of "universe with 4 angles" would be absurd. The ideal description would not even allow for that possibility.
- deleted 11y ago
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tbabb 11y ago
The goal is to explain "why is the number this value and not some other value". Unless the number actually takes on multiple values, the anthropic principle has no explanatory power. If there is only one value, the universe can't "plan" or "choose" a value that is conducive to life, and so pointing to its suitability for life is a teleological argument-- it explains a cause (the value of the constant) in terms of its effect (the eventual existence of life). That's backwards and circular-- causes come before effects.
- Houshalter 11y ago
  Think of it in terms of Bayes theorem. The probability of observing a constant that doesn't support life is 0, since we wouldn't exist. So the probability of observing constants that just happen to support life is 1, and so it shouldn't be surprising at all. If it wasn't that way, we just wouldn't exist to ask the question.
  - tbabb 11y ago
    What on Earth has that got to do with Bayes' theorem? What's your prior? All you did was re-state the anthropic principle.
    - fenomas 11y ago
      I think the point is that there's no question of causality between values of constants and the existence of life, just conditionality, which is what Bayes knows how to talk about. That is, the anthropic principle doesn't try to "explain" why a constant takes a value. It just notes that the conditional property of us observing that value (given that we exist) is 1, regardless of what the unconditional property might be (or even whether it's variable to begin with).
      - tbabb 11y ago
        If this is Bayes, then what is the prior probability distribution over the values the fine structure constant could take?

by baddox 11y ago

ncallaway 11y ago

Again, I could easily be wrong about all this. I think this entire discussion is sensitive to exactly what one means by "The Anthropic Principle". If one's definition of the Anthropic Principle in this context simply means that an observed universe will be consistent with a universe that can be observed, then I find it to be trivially true and applicable to a single universe scenario. I subscribe to a definition of the anthropic principle that invokes selection bias as its core mechanism. I think that, in order to have a selection bias, one needs to actually be selecting from a population. Hence my assertion that you need a multi-verse (with different constants in each universe) or a constant that is variable in space or time [2]. The difference, to me, is this: If you are selecting from a population the Anthropic Principle can actually help explain why a value is what it is. Under our understanding of planetary bodies, we often invoke the Anthropic Principle to explain why the earth falls in the habitable-zone. Earth falls in the habitable-zone because — we think — life is most likely to arise on a planet in that zone. However, if you are not selecting from a population, I don't find that the Anthropic Principle explains why a value is what it is. In the scenario where there is only a single value, I think the Anthropic Principle simply demonstrates that that particular value must support life. Put another way, if all planets we observed were the exact same distance from their star as Earth [1], then we couldn't use the Anthropic Principle to explain why Earth is that particular distance from the sun. We would have to find other astronomical reasons to explain why planets form at that specific distance from a star. In this single-distance scenario the only thing the Anthropic Principle actually does for us is confirm that such a distance supports life. [1] Well, not distance per se, but placed such that they received the same amount of stellar energy in their orbits. [2] This final sentence of the introduction of the Anthropic Principle also makes some reference to this saying: "Most often such arguments draw upon some notion of the multiverse for there to be a statistical population of universes to select from and from which selection bias (our observance of only this universe, compatible with life) could occur."

baddox 11y ago
> If one's definition of the Anthropic Principle in this context simply means that an observed universe will be consistent with a universe that can be observed, then I find it to be trivially true and applicable to a single universe scenario. It is "trivially" true in a sense. It's a tautology. But it's still useful for thinking about things. I think it applies just as well to a single universe or a multiverse, because even with a single universe you can at least hypothesize about other ways the single universe could behave. > However, if you are not selecting from a population, I don't find that the Anthropic Principle explains why a value is what it is. In the scenario where there is only a single value, I think the Anthropic Principle simply demonstrates that that particular value must support life. It might not answer the extremely broad and ill-defined question "why" to your satisfaction, but I find it fairly satisfying. If things were another way, then I wouldn't be observing the universe because I wouldn't exist. So it's not strange that the universe is this way, given that I exist.

mc808 11y ago

If something is truly a universal constant, then it's part of the definition of what it is to be the universe. That we can imagine the constant being different is really just an artifact of the imperfect symbolic language we've developed to describe the universe. Edit: It's hard to come up with a good analogy because obviously I don't have that "perfect" language at my disposal. But for example, a triangle fundamentally has 3 angles. We can imagine polygons with more angles, but it doesn't make sense to imagine a triangle with any other number of angles. If "the whole universe" were synonymous with "triangle", the notion of "universe with 4 angles" would be absurd. The ideal description would not even allow for that possibility.

deleted 11y ago
[deleted]

tbabb 11y ago

The goal is to explain "why is the number this value and not some other value". Unless the number actually takes on multiple values, the anthropic principle has no explanatory power. If there is only one value, the universe can't "plan" or "choose" a value that is conducive to life, and so pointing to its suitability for life is a teleological argument-- it explains a cause (the value of the constant) in terms of its effect (the eventual existence of life). That's backwards and circular-- causes come before effects.

Houshalter 11y ago
Think of it in terms of Bayes theorem. The probability of observing a constant that doesn't support life is 0, since we wouldn't exist. So the probability of observing constants that just happen to support life is 1, and so it shouldn't be surprising at all. If it wasn't that way, we just wouldn't exist to ask the question.
- tbabb 11y ago
  What on Earth has that got to do with Bayes' theorem? What's your prior? All you did was re-state the anthropic principle.
  - fenomas 11y ago
    I think the point is that there's no question of causality between values of constants and the existence of life, just conditionality, which is what Bayes knows how to talk about. That is, the anthropic principle doesn't try to "explain" why a constant takes a value. It just notes that the conditional property of us observing that value (given that we exist) is 1, regardless of what the unconditional property might be (or even whether it's variable to begin with).
    - tbabb 11y ago
      If this is Bayes, then what is the prior probability distribution over the values the fine structure constant could take?