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Oct 08

The Anthropic Principle

The Anthropic Principle has had a long and sordid history among cosmologists and others.  In essence, the principle asserts that the fine-tuning of the physical constants that allow for the formation of conscious life requires some sort of explanation.  As an example, some physicists try to argue for the existence of multiple universes in order to account for the precise values of physical laws, like the cosmological constant.  However, this reasoning seems to be a bit flawed.

Many writers who invoke the Anthropic Principle speak of the principle as if it somehow demonstrates some sort of strange fact about the universe.  But the Anthropic Principle doesn’t really demonstrate anything.  It merely presents a problem, not an explanation.  The principle can’t be used to justify a hypothesis if there is no other additional evidence for the hypothesis in question.  As such, I don’t quite understand the fascination with the Anthropic Principle exhibited by many physicists.

Consider someone who has won a lottery.  Such an event is quite improbable.  According to anthropic reasoning, this improbable event would require some sort of explanation.  Suppose a cosmologist argued that he could explain this event by invoking multiple universes where the person plays the lottery.  The person loses in most of the universes, but happens to have won in our own.  In this sense, the improbability is explained away.  The cosmologist can further argue that the mathematical model of this multiverse is consistent and trumpet this as some saving grace of his hypothesis.  But in the end, if there is no additional evidence of these multiple universes, mere mathematical consistency is not enough to support such a hypothesis, nor is the improbability of winning the lottery reason enough to assert such a bizarre hypothesis.

The problem with such anthropic reasoning, as I see it, is that there are a variety of other potential explanations, and without additional evidentiary support they can’t be ruled out.  Beyond that, it doesn’t even seem as if improbable events necessarily require explanations beyond chance.  By definition, even very unlikely events can still occur, as they are only unlikely, not impossible.  Aside from chance occurences and multiverses, there are a number of other possible explanations, ranging from benevolent deities creating things in this way to “evolutionary” mechanisms that select for universes that promote life or perhaps universe characteristics that correlate with the formation of life.  Without any sort of additional evidence for benevolent deities, or multiple universes, or evolutionary selection mechanisms for universes, though, such explanations are only baseless conjecture.  I don’t think it is enough for String Theorists to talk as if the precise values of the physical constants, in tandem with the mathematical consistency of their models, is evidence for such a conjecture.

Of course, I am not terribly well-read on the subject, and if anyone has any resources that present any additional evidence for such explanations, I’d gladly look into it.  But it seems to me that the Anthropic Principle is highly questionable as a “scientific” principle.

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About the author

Dustin Martinez

I'm a laid back guy. I love pizza! I never know what to write in these things! I constantly think of suicide and stand perilously before the ominous void of nonexistence. I have two dogs and I love tennis!

8 comments

  1. Unbeliever

    I’ve heard the Anthropic Principal used as an argument for the existence of God, by a professor here at Oregon State University.

    I hadn’t heard the argument prior to this, but my thought then, and now, is:

    There’s nothing especially surprising in a flipped coin landing on “heads”, a thousand times in a row — if the only time you observe the result of a coin toss is when it lands on heads.

    In other words, if the physical constants WEREN’T just right for the development of intelligent life, we wouldn’t be here to notice it. So the fact that, when we ARE here to notice it, the constants ARE just right, isn’t really all that remarkable…

  2. Flavin

    “Without any sort of additional evidence for benevolent deities, or multiple universes, or evolutionary selection mechanisms for universes, though, such explanations are only baseless conjecture.”

    I think the “universe evolution” idea presupposes the “multiple universe” idea. They aren’t quite on equal footing, as you seem to present it here.

    I’m not sure the problem posed even exists. We’re presented as having won the cosmic lottery, our universe being one favorable environment in an unlivable sea of parameter space. But is there a lottery? Could these favorable parameters have been any different? I think until we know how some of these parameters come about (and, no slight to you, but we haven’t made explicit what exactly we’re talking about) we won’t know how or if they might be different.

    Until then, I find the anthropic principle to be angels-on-the-head-of-a-pin navel gazing. (This being similar to, but a bit harsher than, your conclusion. Fuck you for making me agree.)

  3. Liew

    The anthropic principle always makes me want to go “Well, DUHHHH.” I mean, if “the fine-tuning of the physical constants that allow for the formation of conscious life” weren’t tuned in such a way that allowed for the formation of conscious life then we wouldn’t even be here to be conscious of the fine-tuning of the physical constants that allow for the formation of conscious life.

  4. UnBeguiled

    Flavin has it right.

    Theists frequently say something like this: “Our universe has all these constants fine tuned for life. This combination of constants is highly improbable. This improbability cries out for an explanation.”

    But wait. We have an N of one!

    You cannot make any comment about probabilities, other than to say that the probability of our universe having the constants it does is not zero. With an N of one, that is all you can say.

    My own analogy. Suppose I showed a guy a zebra with 20 stripes. This guy had never seen a zebra, nor did he even know if other zebras existed. Then suppose he said: “The probability of this zebra having exactly 20 stripes is highly improbable.”

    I hope we can see that this guy is a twit. And so with theists.

  5. Zi

    The problem with the anthropic principle is that it’s a “Shut up, that’s why” explanation of phenomena. While there’s nothing -technically- wrong about that, and it does logically make sense, the fact that it can be used to explain anything renders it an informationally useless explanation.

    When every question of “Why is X like this” is answered by “Because if X wasn’t like this, you wouldn’t have asked that question”, discourse and intellectual progress starts going nowhere.

    It’s only a valid answer because we don’t yet have a better one. Those damn theoretical physicists better get to work.

  6. Lizz

    Wait. There are zebras with MORE than twenty stripes???? Damn.

    I think scientists just like to explain things – even concepts that we can’t really explain. Science has made lots of claims over the years that have turned out later to be total bunk. We just want to know everything because we do. And if we don’t, we make shit up that sounds good.

    Arm-chair analysis of the anthropic principle – B.S. to cover what we can’t figure out. <—- and that is why I should be a physicist – somebody get me an honorary degree of some sort so I can go hang out with Hawking.

  7. Flavin

    Let me pick apart unbeguiled’s argument.

    Theists frequently say something like this: “Our universe has all these constants fine tuned for life. This combination of constants is highly improbable. This improbability cries out for an explanation.”

    But wait. We have an N of one!

    You cannot make any comment about probabilities, other than to say that the probability of our universe having the constants it does is not zero. With an N of one, that is all you can say.

    Now I will paraphrase.

    In the “theist’s” argument, the unstated premise is that the values of these constants are randomly distributed among all real numbers. Were that true, yes, it would be highly unlikely to have arrived at the narrow range of these constants capable of supporting macroscopic complexity, including but not limited to life.

    In your response you say, in effect, “We don’t know if this distribution is random. In order to discover the distribution of these constants, we must take a statistical sampling and perform an analysis. Only then will we be equipped to make definitive statements about the probabilities involved. Until that time, your unstated premise is assumed false.”

    Nothing about this is incorrect, and it would be a fruitful line of discovery if we did have more than one universe to study. But we might not need to use that evidence even if we had it, because we may be able to explain these seeming mysteries theoretically.

    It is possible that some unifying theory will be written in the future that is able to produce values for these mysterious constants with minimal assumptions. If that were the case, then there would be no need to assess how probable it is that we got the constants we have, because it would have been shown that the particular values we find are necessarily true in 100% of possible universes.

    We certainly have not done this, which is why a fake mystery still exists to some. However, the fact that we one day might makes this debate, to me, a nonstarter.

  8. quodlibetor

    The anthropic principle says that we are observing a universe that is fit for life because if the universe was not fit for life we would not be in it.

    Everything else — multiple universes, changing physical laws — is different methods of making that (incredibly circular) claim more palatable.

    In the metaphor of the lottery winner multiple universes don’t enter into it, really the role of multiple universes is played by all of the people who don’t win. They are the universes wherein the finely-tuned physical constants aren’t finely tuned, and so they don’t support life. But, with enough people, (universes,) and variation from person-to-person (universe-to-universe) about how the physical constants are set (which lottery numbers they choose) it is fairly definite that eventually one person will support life (win the lottery).

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