Throughout much of the 20th century, quantum mechanics seemed to kill the idea that human beings could develop an “intelligible, mechanical model of the world.” But today, the search for a “simple” model of the physical world is alive and well.
Question: Can science give us a precise image of the universe?
David Albert: Oh, I see what you're saying. Look, that is -- throughout most of the 20th century, what was widely considered to be the lesson of quantum mechanics, what was widely considered to be the upshot, the deep upshot of our scientific investigations of subatomic particles, was precisely that: the thought that science was going to ultimately give us a picture of the world all the way to the bottom, which we were going to be able to carry around in our heads -- okay? -- which we were going to be able to understand in the way we understand billiard balls colliding with one another or something like that. It's widely been thought to be the upshot of quantum mechanics that those expectations of science have now been exposed as quaint and naïve and old-fashioned, and moreover as presumptuous, okay? Who were we to think, with these brains evolved for very different purposes of hunting and gathering and so forth, that there was going to be this kind of intelligible, mechanical model of the world that we were going to be able to get our heads around, okay?
And indeed, the response to this measurement problem throughout most of the 20th century was precisely that: look, this is where our scientific imagination gives out in its attempt to penetrate the world. We have encountered for the first time ever the ultimate limits of the capacity of the scientific project to penetrate into the foundations of the world. We're not going to get farther than this; we should be thankful enough that we have a good mechanism for predicting the behaviors of these particles, and so on and so forth. That was very much the consensus throughout most of the 20th century. And if students were to raise their hands and say, gee, how can you be so sure of this? I mean, have people tried to make these modifications, blah blah blah? -- those students would be referred to a number of famous so-called no-go theorems or no hidden variable theorems, the most famous of which for most of the century was one due to the mathematician John von Neumann.
And it wasn't until rather late in the century that attention began to be focused on the fact that these theorems and these arguments that we couldn't do better than this were hasty, were premature; that the theorems, especially the von Neumann theorem, was just a very flawed theorem. The mathematics was completely correct, but the presumptions that he started with were much too restrictive. There was no reason to be persuaded that those assumptions were true. And since then, mostly over the past 25 years, enormous progress has been made, okay, in actually proposing ways to tinker with these fundamental equations in such a way as to solve this problem, in such a way as indeed to provide us with precisely the sort of thoroughly intelligible mechanical picture of what was going on that was said for most of the 20th century to be quaint and outmoded and immature and so on and so forth.
So yeah, you're right: throughout most of the 20th century the reaction was, the lesson to take from this is that there are limits to the capacity of the human scientific imagination to penetrate the mysteries of nature; and the mature thing to do, the grownup thing to do, is to accept these limits. It isn't until recently that it's become clear that these pronouncements were enormously premature. Who knows if we're going to finish the scientific project or not? Who knows if we're every going to get to the bottom of it? But there is this really interesting episode in the 20th century where it was thought that we had. And it's now becoming clearer and clearer that the announcements of the death of this project, after Mark Twain, were greatly exaggerated.