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! It’s 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.
= you are alive
= all the shards of metal from the explosion followed paths that were “you-friendly”.
= 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 .
Now, the fact that you are alive means that all the shards missed you.
Also, the probability that all the shards missed your body, given that they travelled in straight lines from the explosion, is very small:. But, according to IJ, we must condition on L. Thus, we find:
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 , 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.)
B. Make your own universe
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.