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Anthropic Principle musings and questions

  1. Jul 16, 2005 #1
    I just listened to a talk by Leonard Susskind on "Landscape" ideas. He obviously is a big believer in these ideas, and also clearly he knows much more physics than I do by an order of magnitude comparable to electromagnetism versus gravity:) So I'm interested in why people, especially brilliant scientists, might believe in these ideas as something significant.

    Now, I take it as given that I exist and wonder about the universe. Also, it obviously (?) follows that the conditions are such that I could exist and ask these questions. My first problem is introducing the idea of "because" anywhere in there. What I'm talking about, of course, is an idea like "The conditions of the universe are what they are because we exist to ask the question". Isn't "because" a concept that involves events within our universe, and in particular time? Why would anyone think that you can reason about the universe using terms that are only defined within it? As far as I can see, the idea is purely semantically meaningless, like asking for "first cause" of time and space. (Since cause involves time, asking what caused time would be like asking what is higher than the y axis on a Cartesian plane.)

    As far as I can follow, one of Susskind's analogies involves intelligent fish, who can't observe outside the water they live in, wondering why the water is the right temperature for them to live in. And if they can't see any reason for the water to be the way it is, they might wonder if there is water elsewhere they don't live in. (Whereas if they saw that it was exactly halfway between boiling and freezing: 50.00000000... degrees C, to the limit of their measurements, they could suppose there was another principle involved.)

    I don't think anyone has a problem with saying we live on the Earth, rather than non-habitable places like on stars or on Mercury. Is the structure of the anthropic argument basically that because certain features of the Earth are arbitrary, e.g. the laws of physics don't say its size has to be what it is, that this could suggest that the Earth is part of a "landscape" of other planets? This seems to be what Susskind is saying, to the best of my ability to tell. (I'm also referring to this web debate between Susskind and Lee Smolin from last year: http://edge.org/documents/archive/edge145.html )

    Of course, because of what we can observe, namely other galaxies and stars, this is correct for the Earth. The best guess has to be that there are many planets, and some subset are Earth-like planets. (And we don't have much clue about just how rare they could be, but the chance probably isn't vanishingly small.)

    So maybe, in analogy, the seeming arbitrariness of things like the Cosmological Constant could suggest other values "somewhere else". But, does this really follow? This is the part I have trouble with. It seems to be introducing things that may not be elegant, simplifying, or relevant to anything in the real world. Am I wrong?

    Take idea A: we live in a universe with some arbitrary constants, and their values don't follow from any deeper physics. This "just is", and there is nothing else out there (whatever "out there" might mean for something we can't ever observe or see any effects of.)

    Then idea B: we live in a pocket universe among many possible sets of values, and in particular, we are in a set that admits the possibility of life.

    (It still could be possible that all constants can be explained by some elegant theory. Or there could be weirder Science Fiction ideas, e.g. intelligent life came from a really elegant set of physical laws, and then our universe is a Rube-Goldberg-like simulation on one of their "computers". Or some other creation idea.)

    But is there any reason at all for preferring idea B from idea A above? It seems to me like Susskind clearly does prefer B, but why? Is it more elegant or simple somehow to say that a whole bunch of things exist, rather than just one which is tuned right? Is there anything intelligent that can be said further about this?

    I think one other thing he points out is that there is reason to believe that exponential inflation happened with the universe, so there seems to be a lot of stuff that is outside our "pocket universe" anyway. But does this strengthen idea B over idea A at all?

    It's pretty clear that no measurement can distinguish B from A, or is it? So we either have to conclude that the distinction is meaningless, unknowable, or decide in some other way based on ideas like Occam's Razor? (As we would not take seriously a theory that the universe was created as it was 6000 years ago with planets, isotopes, and dinosaur bones intact.)
  2. jcsd
  3. Jul 16, 2005 #2


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    Before going overboard on what Susskind says, check out http://www.math.columbia.edu/~woit/blog/, especially the archives, where Susskind is much discussed, not often favorably. Can't tell the players without a program.
  4. Jul 17, 2005 #3
    Thanks for the pointer. I've been reading Peter Woit's blog for a few months, but not far back enough to see much discussion on anthropic ideas. I also read Lubos' blog, or what I can understand of it.

    In his talk, Susskind seemed pretty fair about stressing that there was heavy debate among physicists about the subject, and at the end of the talk he said we had only heard his side of the story.

    I'm just wondering if there is anything intelligent out there about the anthropic principle in physics, that doesn't boil down to a non-sequitur when expressed in succinct terms.

    I don't mind not having something be scientific, if in some sense more comes out of the idea that goes in. (E.g. anthropic reasoning would be interesting to me if it presents a simpler view of things.)
    Last edited: Jul 17, 2005
  5. Jul 17, 2005 #4
    His entire philosophy is wrong, he wants us to discover things which are physically impossible to prove. He refuses to engage in rational debate on the same basis and from what I hear he does this to vent his sexual repression.

    Worth a read if you can be botherred to plough through the acres and acres of ambiguous corrupt logic which forces you to study each point for 5 minutes before realising that it is fallaciousand you have wasted your time.
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