3) The multiverse, if real, would reduce our own world to a Matrix-like simulation. This objection, voiced by Davies, is surely the most bizarre of the lot. If there really were myriad universes, Davies argues, then some would contain advanced technological civilizations that could use computers to simulate consciousness and create endless virtual worlds. So, he continues, taking the multiverse theory at face value means "there is no reason to expect our world—the one in which you are reading this right now—to be real as opposed to a simulation." This is a terrible argument for at least two reasons. If it were valid, it would rule out technologically advanced civilizations in this universe since they, too, would presumably create such simulations. And the hypothesis that we are living in a simulation itself has no empirical content. We cannot even talk about it coherently, as Hilary Putnam has pointed out, since our words could refer only to things "inside" the alleged simulation.
How seriously should you take multiple universes? That depends on how scrupulous you are about your ontological commitments. I know people who still regard atoms as theoretical fictions. I have friends who claim to doubt the reality of the past, of the future, of other minds. I have heard of academics—though I cannot believe they actually exist—who think that the cosmos is a social construction. But I am a robust scientific realist. If an empirically sound theory entails that unobservable entities exist, then I take them at face value. After all, reality has over and over again turned out to be much more inclusive than we've given it credit for being. Just a century ago, our puny Milky Way was thought to comprise the entire cosmos.
If the choices we make in our everyday lives seem a little absurd from the viewpoint of a single vast and eternal universe, then, from the viewpoint of an infinite ensemble of universes containing infinite copies of ourselves, all making every possible choice, they are absolutely absurd. Thankfully, in our own little world, those choices remain terribly meaningful and important.