Thursday, 17 July 2014

Multiverses And Anthropic Reasoning

I liked this article summarizing the current state of science regarding multiverse theories. It's very clear and well-illustrated, and, as far as I know, accurate.

This quote is particularly interesting:

So as appealing as the idea is that there are other Level 1 Multiverses out there with different constants than our own, we have good physical reasons based on observable evidence to think it’s unlikely, and zero good reasons (because wanting it to be so is not a good reason) to think it’s likely.

He doesn't mention why anyone would "want it to be so", i.e. believe that other universes of a "Level 1 Multiverse" could have different constants to our own. However, I'm pretty sure he had in mind the selection-bias explanation for the anthropic coincidences. That is, if we accept that only a narrow range of possible values for the fundamental physical constants are compatible with the existence of intelligent life (and most scientists do, I think), then we would like to be able to explain why our universe's constants are in that range. If there are an abundance of different universes, each with different values for the physical constants, then most of them would be dead but a lucky few would sustain intelligent life, and naturally we can only observe one of those latter.

This reasoning relies on the assumption that there are abundance of different universes with different values for the physical constants. Scientists obviously would prefer to be able to deduce this from observations rather than pull it out of thin air. As discussed in the above article, theories of chaotic inflation --- which are reasonably well-grounded in observations of our own universe --- predict the existence of alternate universes. If those universes could have different values for physical constants (or even different physical laws), we'd have an observationally-grounded theory that predicts exactly the kind of multiverse needed to power the selection-bias explanation for the anthropic coincidences. Unfortunately for proponents of that explanation, the science isn't working out.

Of course, the selection-bias explanation could still be valid, either because new information shows that chaotic-inflation universes can get different constants after all, or because we assume another level of multiverse, whose existence is not due to chaotic inflation. However, many scientists (such as in the article above) find the assumption of a higher-level multiverse quite unsatisfactory.

Unsurprisingly, I'm comfortable with the explanation that our universe was intentionally created for intelligent life to live in. Incidentally, you don't need to be a classical theist to adopt this explanation; some atheist philosophers argue with varying degrees of seriousness that we are (probably) living in a simulation.

6 comments:

  1. Le Dahu Lévogyre17 July 2014 04:00

    Obviously, if the constants could be different in other multiverses, the anthropic coincidence wouldn't be a valid argument in favor of creationist theories.
    But the anthropic "coincidence" is not a very good term anymore if the constants are the same in every other multiverses. Because it means they cannot be different than what they are here (for some reason). Then it can't be called a coincidence.
    A coincidence only makes sense if there are multiple possibilities.

    So, I always fail to understand that anthropic coincidence as an argument in favor of creationism. (Maybe you can help me understand ?)


    A second point : even if this universe was created, the questions remains. Who created the creator ? What is the simulation container ?
    Don't the religious people ask themselves these questions ?

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    1. People who use the word "coincidences" here are comparing to hypothetical alternative universes that are much like our own but don't support life. Even if some deeper theory of physics constraints parameters to have our values, it would still be surprising that those values should be precisely the values that support life ... to me, and I expect also to other thinkers of all kinds.

      I'm not sure anthropic coincidences point directly to a creator, but if you think they demand an explanation then a creator is one explanation (and multiverses are another). I prefer the creator explanation because I believe it explains other evidence as well.

      Religious people certainly do ask questions like yours! The classical answer is that God is the only uncreated entity. In fact, that could almost be the definition of God. People complain that's special pleading, but I think that's somewhat subjective.

      Even if we ignore theism for a moment, I think it might be possible to explain the anthropic coincidences via a simulation argument that doesn't trigger infinite regress. For example the creator(s) might live in a universe that is nothing like ours and has no tunable parameters.

      Sorry about the delayed response, I had written a comment earlier but Google ate it.

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    2. Le Dahu Lévogyre12 August 2014 00:45

      > Even if some deeper theory of physics constraints parameters to have our values, it would still be surprising that those values should be precisely the values that support life

      It would be interesting and exciting. But not really surprising. Because I believe it might be possible that we overlook other form of life with other parameters.
      I mean, predicting life just by looking at the physics parameters is hard.

      > The classical answer is that God is the only uncreated entity

      I see.
      You're close to convert an atheist into Christianity :-)
      But I still find it very unlikely, Sorry.
      I'm also curious about those "other evidences" you write about. Don't you think there are many hints that there's no creator caring about life at all ?


      > I had written a comment earlier but Google ate it.

      Talking about God... we are only the object of Google's simulation, anyway. You know. ;-)

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    3. > Because I believe it might be possible that we overlook other form of life with other parameters.

      That is possible, but a lot of scientists find it very difficult to believe that intelligent life could exist in, for example, a universe that has no atoms more complex then hydrogen (and therefore no interesting chemistry). We presume intelligent life needs some kind of structure capable of computation. And if you're going to avoid a creator, you also need enough structure to drive selection of heritable traits so you can have evolution.

      > I'm also curious about those "other evidences" you write about.

      I've written about some of that in my blog in the past, and I'll write more later.

      > Don't you think there are many hints that there's no creator caring about life at all ?

      Yes and no. I think God has worked in history to reveal information about himself, and is still doing so --- he is not silent or inactive. But a lot of his interactions with people are subjective, and I do wish he would do more to show himself. Then again, he's God and I have no right to impose my expectations on him.

      > Talking about God... we are only the object of Google's simulation, anyway.

      Haha, that's relevant to my blog too :-).

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    4. Le Dahu Lévogyre13 August 2014 04:04

      Yes, a lot of scientists lack imagination, IMO. :-)

      Look around you (I mean "up"). Life does not seem to be the rule in this universe. If it is intended, then the creator really missed the point. He triggered a zillion missing arrows for just one right on.

      I can't see God's work anywhere. I'm sorry.
      Nature is sometimes very beautiful. But it's a totally subjective point of view, in a universe ruled by physics, it seems.
      Why do you have no right to impose your expectations on him ? Why the submission ?
      So you think he's omnipotent (but I've never seen him intervene), and benevolent (then look around, he's incompetent, sorry for the heresy). These are the main characteristics that I don't understand in monotheisms.

      I hope you're not bothered by my naive atheist/agnostic questions. I don't intend to make you doubt. I just like reading your points.

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    5. > Why do you have no right to impose your expectations on him ? Why the submission ?

      I think God objectively exists, so like any other part of reality, if he doesn't match my expectations that's my problem, not reality's problem.

      On top of that, God being the creator and me the created, it seems reasonable to submit to him.

      > So you think he's omnipotent (but I've never seen him intervene)

      Omnipotence just means God can do everything he wants to do. If what he wants is generally to have the universe follow predictable laws (which I think is necessary for intelligent beings to be morally responsible), then that doesn't contradict his omnipotence.

      > and benevolent (then look around, he's incompetent, sorry for the heresy).

      I look around and mourn the evil of man spoiling the good gifts of God. And I feel thankful that God has provided a way for sins to be forgiven.

      > I hope you're not bothered by my naive atheist/agnostic questions. I don't intend to make you doubt. I just like reading your points.

      I'm glad to hear it. Thanks.

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