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What do you know? – A Fine-Tuned Critique of Ikeda and Jefferys (Part 2)

This is my second critique of the work of Ikeda and Jefferys (IJ) on the fine-tuning of the universe for intelligent life. IJ insist that we must always condition on everything that we know is true. Here, I’ll raise a few case studies in need of clarification. I should warn that I’m somewhat less certain about this part than the previous one. The fog is probably in my own head.

A. Magneto saves the day

This is a variation on John Leslie’s firing squad parable. You are sitting with your grandpa on his porch. Grandpa says, “I have a confession. I’m Magneto.” You: “What? You’re one of the Xmen? You can manipulate metals at will?” Grandpa: “Yes. That’s right”. You: “Right. Sure. Prove it.”

Grandpa pulls a set of keys from his pocket and makes them levitate two inches above his hand. “Yeah, nice magic trick, Grandpa”, you say. But then, up on the hill overlooking the porch, a freight train derails! Its carriages tumble toward the house. And, just your luck, this train happened to be loaded with TNT and samurai swords. The ensuing explosion sends several tonnes of rather pointy metal hurtling towards the porch. You instinctively flinch. A few seconds later … you’re alive! You turn in shock to see that every inch of your Grandpa’s house has shards of metal sticking out of it, except for two perfect silhouettes of you and your Grandpa. He looks at you, and smiles. “Not bad, huh?”

Now, like the nerd you are (you’re reading a science-themed blog, so there’s no point denying it), you want to formalise your conclusion.

$L$ = you are alive

$F$ = all the shards of metal from the explosion followed paths that were “you-friendly”.

$N$ = the shards of metal followed essentially straight paths from the explosion to their final resting place. The “Grandpa is Magneto” hypothesis implies that Grandpa can violate $N$.

Now, the fact that you are alive means that all the shards missed you.

$P(F|NL) = 1$        (1)

Also, the probability that all the shards missed your body, given that they travelled in straight lines from the explosion, is very small:$P(F|N) \ll 1$. But, according to IJ, we must condition on L. Thus, we find:

$P(N|FL) = \frac{P(F|NL) P(N|L)} {P(F|L)}$       (Bayes theorem)

$= \frac{P(N|L)} {P(F|L)}$                   (using 1)

$\ge P(N|L)$                               (since $P(F|L) \le 1$)

It follows that you cannot conclude anything at all about your Grandpa’s abilities. Observing that all the shards of metal missed my body has somehow made it not less likely that they simply followed ballistic paths from the explosion. This conclusion holds independently of the extent and violence of the explosion: suppose another train hits the wreckage and the whole debacle happens again, suppose a malfunctioning tank wanders past, the monthly meeting of the society for blind snipers gets out of hand, several satellites fall out of orbit, an angry neighbour throws a frying pan. And still you have no evidence at all of your Grandpa’s ability. Surely, this is nuts. If you see Grandpa Magneto cause a shard of metal to swerve wildly so that it hits the door instead of the window, then this is evidence of his abilities. But if it hits the door instead of your head, then you can’t conclude anything, even if Grandpa makes the shards in the door spell out the sentence: “I’d like to see Rev. Bayes do this!”.

I’m not sure if the problem here is that we are conditioning on $L$, or if this formulation is incomplete, as I alleged of IJ’s formulation of the fine-tuning argument (see part 1).

(Note that we might wonder why Grandpa didn’t stop all the shards of metal from hitting his house. This is a good question, but it isn’t an objection: it does nothing to reduce the strength of our conclusion that Grandpa has the abilities he claims. Neither can we object that any arrangement of metal shards is improbable.)

It’s 3042 and the annual universe building competition is about to kick off. First prize goes to the universe which first produces life intelligent enough to speculate that it was created as a result of a universe building competition1. You are going to compete, having spent years up to your eyeballs in equations, sorting through all the possible physics of your universe, trying to find the ones that will support the evolution of intelligent life. (No cheating! You can’t put intelligent organisms into the initial conditions.) Nervously, you hit the big red button and your universe (call it Lucia) has its “In the beginning …” moment. Success!!! Intelligent life forms – we shall call them Lucians. Soon enough, they speculate on all manner of theories of the origin of Lucia.

Now, in such a universe, the fact that physics permits the evolution of life is the direct result of your hard work and ingenuity. You sit back and wait for the Lucians to develop science, discover the laws of nature and marvel at the cleverness of your physics (where physics = physical laws + initial conditions + constants of nature).

But what’s this? One rowdy Lucian is trying to convince them that the fine-tuning evident in the laws of nature is no evidence at all that physics has been carefully chosen to permit the evolution of life. Given that life exists, he argues, the fact that the physics of Lucia supports life follows inevitably. Thus, life-friendliness supports (or at least does not undermine) the hypothesis that Lucia is governed by naturalistic law.

Fuming, you hit the small white button next to the big red one – the intercom. A heavenly voice booms across the Lucian cosmos.

What do you mean, “given that life exists”?! Talk about being taken for granted – I’ve been working my fingers to the bone up here, you ungrateful sods. Do you think this is just any old universe? That I just closed my eyes and picked at random? Do you have any idea how hard it is to blow up a star and make the remains into DNA? Of course you’re governed by naturalistic laws – they’re my sodding laws! Unbelievable. And to think I was going to introduce you to my son.

Someone who merely stumbled into your basement and found Lucia could reasonably conclude that it is unlikely that its physics were chosen at random. The Lucians have exactly the same information, and should be able to make exactly the same inference.

______________________________

I’ll repeat my warning at the start: I wouldn’t call these counterexamples. There’s every chance that they are just puzzles to be solved by clear thinking.

1. Incidentally, if this scenario is true of our universe, I may have just won the competition for our creator. The downside is that, with the competition over, our creator has no motivation to continue sustaining our universe. My sincerest apologies if I have consigned our universe to some transcendent trash bin.

More of my posts on fine-tuning are here.

7 Responses

1. lukebarnes,
your grandfather thought experiment reminds me of a paper by V. Palonen entitled Bayesian considerations on the Multiverse explanation of cosmic fine-tuning (see the link below).
In short he argues that Multiverse hypotheses don’t explain fine-tuning. He also provides a version of the firing squad thought experiment to make (part of) his point.
I am curious to read your thoughts on this. If you find the time to read it that is.

http://thewarfareismental.files.wordpress.com/2011/01/cornell-palonen-v.pdf

Cheers

2. […] More technical response to Ikeda and Jeffreys’ Bayesian probability critique: 1, 2. (DM, kindly take notice. This critique, by reasonable extension,  also applies to Sobers’ […]

3. […] I would like to add that Dr. Barnes has also written an incisive online critique of Mike Ikeda and Bill Jeffery’s widely cited paper, The Anthropic Principle Does Not Support Supernaturalism, which is cited by Professor Stenger in his book, in order to show that even if some observation were to establish that the universe is fine-tuned, it could only count as evidence against God’s existence. Part 1 of Dr. Barnes’ reply is here; Part 2 is here. […]

4. […] Dr. Barnes’ ARXIV paper, The Fine-Tuning of the Universe for Intelligent Life (Version 1, December 21, 2011), is available online. Readers who dislike technical jargon can find a non-technical overview of key excerpts from Barnes’ paper in my blog post, Is fine-tuning a fallacy? (January 5, 2012). I would like to add that Dr. Barnes has also written an incisive online critique of Mike Ikeda and Bill Jeffery’s widely cited paper, The Anthropic Principle Does Not Support Supernaturalism, which is cited by Professor Stenger in his book, in order to show that even if some observation were to establish that the universe is fine-tuned, it could only count as evidence against God’s existence. Part 1 of Dr. Barnes’ reply is here; Part 2 is here. […]

5. […] I understand that Loftus is a big fan of Professor Victor Stenger, an American particle physicist and a noted atheist, who is also the author of the recent best-seller, The Fallacy of Fine-Tuning: How the Universe is Not Designed for Humanity (Prometheus Books, 2011). Stenger’s latest book has been received with great acclaim by atheists: “Stenger has demolished the fine-tuning proponents,” in the words of one gushing Amazon reviewer. Unfortunately for Loftus, however, the claims made in Stenger’s book have been completely demolished in a critical review by Dr. Luke A. Barnes, a post-doctoral researcher at the Institute for Astronomy, ETH Zurich, Switzerland. In his review, Dr. Barnes takes great care to avoid drawing any metaphysical conclusions from the fact of fine-tuning. His main concern is simply to establish that the fine-tuning of the universe is real, contrary to the claims of Professor Stenger, who asserts that all of the alleged examples of fine-tuning in our universe can be explained without the need for a multiverse. Readers who are daunted by the technical jargon in Dr. Barnes’ online ARXIV paper, The Fine-Tuning of the Universe for Intelligent Life (Version 1, December 21, 2011), may prefer to peruse a non-technical overview containing key excerpts from Barnes’ paper in my blog post, Is fine-tuning a fallacy? (January 5, 2012). I would like to add that Dr. Barnes has written an incisive online critique of Mike Ikeda and Bill Jeffery’s widely cited paper, The Anthropic Principle Does Not Support Supernaturalism, which is cited by Professor Stenger in his book, in order to show that even if some observation were to establish that the universe is fine-tuned, it could only count as evidence against God’s existence. Part 1 of Dr. Barnes’ reply to Ikeda and Jeffery is here; Part 2 is here. […]

6. Thank you for your post. However, I believe there is a minor error in reasoning in the scenario you present.

The assumption is made that P(F|NL) = 1. However, this assumption is poorly motivated in your scenario. To see this, consider more deeply the justification given: “the fact that you are alive means that all the shards missed you.” This is incorrect since one can imagine many counterexamples where you are hit by shards to various degrees but are left with a marginal amount of life. For example, your body could be so filled with metal shrapnel that you have only 9 seconds of conscious life remaining. Or you could have 9.9 seconds remaining. Or 9.99 seconds. Etc. In any of those scenarios, both N & L would be true, yet F is not. There are countless similar scenarios, and they are more probable than the “friendly” alternatives (given N). Therefore, P(F|NL) << 1.

In other words, it would indeed be ridiculous to observe "every inch of your Grandpa’s house has shards of metal sticking out of it, except for two perfect silhouettes" without concluding that something unnatural occurred. If you did see such "perfect silhouettes," concluding something unnatural happened *would* be justified using Bayesian reasoning. You would realize how unlikely two perfect silhouettes were — you certainly wouldn't assume P(two perfect silhouettes|NL) = 1.

7. […] responded to Ikeda and Jeffrey’s article here and here. Their reasoning is valid, but is not about fine-tuning. I show how the fine-tuning argument, […]