Brian's book is about the multiverse, a hot topic these days in cosmology circles. I haven't had a chance to read it yet, but he is one of the clearest and most level-headed people we have writing about modern physics, so I'm sure it's worth checking out. We've certainly touched on the multiverse idea on this very blog, for example here and here. It's a controversial topic, as you may have heard. People worry that talking about unobservable things is a repudiation of what it means to do science, a symptom of the decadence of modern society, etc. Click the links to rehash the usual debates. But a new rhetorical strategy has appeared among the anti-multiverse crowd -- not that the idea is wrong (which would be very interesting, if there were a good argument for it), or even that it's nonscientific (the usual complaint), but that it's immoral. We are actually violating the Categorical Imperative by talking about universes beyond our own. Points for novelty! Or not. The immorality argument was recently advanced by John Horgan and Peter Woit. But if you read the posts, it's the usual curmudgeonly sniping, with the shrillness knob turned up a click or two. The actual argument is the same as it ever was: talking about unobservable things is not science. [Update: Peter explains his objection here.] However, a truly novel version of the immorality charge was leveled by Clay Naff at the Huffington Post. Naff introduces a "moral principle," which informs us to "resist accepting any proposition that tends to disable moral reasoning, unless and until the scientifically interpreted evidence compels us." That is, instead of judging ideas by our conventional criteria of whether they are likely to be "right" or "wrong," we should include an additional new factor that weights against ideas that would disable morality. Hopefully the problem with this idea is immediately evident: ideas about how the universe works can't possibly "disable moral reasoning." The world does whatever it does, quite independently of our moral judgments. The job of morality is to figure out what we think we human beings should be doing, which, as we've been discussing, does not reduce to looking at what actually happens in the universe. Of course, what counts as a moral action certainly depends on what actually happens in the universe. (Saving lives would be less urgent if everyone who dies goes to Paradise in the afterlife.) But Naff's worry is a little funny. What he seems to be concerned about -- although he never quite comes out and says it, so a bit of interpretation is required, and I could always be misreading -- is the possibility that our moral intuitions could be undermined by the idea that there are an infinite number of copies of ourselves out there in the multiverse, some of them exactly like us and many of them slightly different, e.g. worlds where Hitler was victorious, etc. In such a setup, should we be concerned that morality is pointless, because every good thing and every bad thing eventually occurs elsewhere in the cosmos? I don't think we should be concerned about that (even if it's true, which it may very well be). An idea like this doesn't "disable our moral reasoning" -- in fact, it might be extremely helpful to our moral reasoning. If your version of morality depends on the assumption that what happens here on Earth is unique in the universe, then it's time to update your morality, not to put your hands over your ears when people start talking about the multiverse. The real problem with Naff's position is its fundamentally paternalistic tone -- even if, to his credit, he seems to include himself among those who need protection from these scary ideas.
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The danger lies in how they take root in popular culture. If we come to believe that choices do not matter, that any action is matched by its opposite somewhere, we risk losing our capacity for moral reasoning. History shows that, inbuilt though that capacity may be, ideas can short-circuit it. In short, what I am saying is that those of us who are NOT so brilliant as to be able to follow the math need to resist being seduced by visions of parallel bubbles in a multiverse.
I have this old-fashioned notion that if an idea about the universe is very possibly correct, there is no moral or scientific advantage to pretending otherwise, even among those who can't follow the math. Our capacity for moral reasoning shouldn't depend on what's happening many googols of parsecs away in an unobservable part of the universe. If it does, our moral reasoning needs an upgrade. And if reading popular books about the multiverse help nudge people along that path, I'm all for it.