Quantum Physics

"Again, bear in mind what I’ve just said, that when you start to embark on a career as a scientist it’s about digging a hole for yourself. You effectively want to create a reputation, you want to create a name for yourself, publish papers, and that means devoting all your energy and time to becoming an expert in the area in which you’re doing research. I did my first degree, I did a PhD at Oxford, I’d done a couple of years of postdoctoral research, and then I became a university lecturer at the University of Reading. So, I’m teaching as well as doing research and trying to write research papers. Your time really is squeezed. But there was still that bit of me that didn’t want to let go. I happened to pick up a book when I was doing some work at the University of Madison, Wisconsin in 1987, and it gave me an introduction to something that I had completely missed and that is the famous Einstein–Podolsky–Rosen experiment. In the culmination of Einstein’s big debate with Bohr in 1935, he devised this devious, what he called ‘gedankenexperiment’ or thought experiment—that arguably undermined Bohr’s defensive position. It’s a bit like a game of chess between these two grandmasters. Bohr’s response was quite weak, in many ways, but also opened the door to a really quite bizarre interpretation of quantum mechanics which says that nothing is anything until it’s seen or measured. This kind of thing gives rise to all of those great questions like, ‘If a tree falls in the forest, and there’s no one around to hear, does it still make a sound?’ ‘Is the moon there when nobody looks?’ You’re kind of in that bizarre mode of thinking. But what had happened was that, having been nothing other than a thought experiment, by the time you got to the 1970s and early 1980s, there were guys doing experiments to find out whether this thought experiment actually did open up quantum mechanics to the cry that it was somehow incomplete or inconsistent. These experiments proved very clearly that quantum mechanics is complete for all practical purposes, it is consistent—it’s just mad. Understanding the nature of these experiments, understanding the nature of the Einstein–Podolsky–Rosen challenge, became a mission. “Quantum mechanics is complete for all practical purposes, it is consistent—it’s just mad” I learned about it, I bought some other books, but Alastair Rae’s little volume is a wonderful introduction. There’s a little bit of maths in it, for the initiated who are comfortable with a bit of algebra. But there’s nothing particularly difficult about what Alistair Rae says. I just felt that this made it all clear. I finally understood what the hell was going on with this challenge and the nature of the experiments that were being performed. Nature is what nature is. It’s us that then looks it at and says ‘Oh, that’s really difficult’ or ‘That doesn’t make any sense.’ What these experiments and quantum theory are telling us is that objects like electrons don’t exist in the way that we understand them—with mass, with spin, with charge—until we look. That sounds like a piece of childish, kindergarten philosophy. But it’s true. It’s amazing to me, I’ve called these experiments ‘experimental philosophy.’ You have to go back to Immanuel Kant. What you take as the things-in-themselves, reality-in-itself, we can have no knowledge of that reality because, by definition, we only know of the things that we look at: the things that we measure. So what we see is not the thing-in-themselves but only the things as they appear. But there is nature. I am a realist so I believe that the universe really does exist when nobody looks. What quantum theory is telling you is that everything that you understand about the nature of that reality depends on you looking. And don’t be surprised when what you get when you look is not necessarily entirely representative of what the thing is in-itself. Yes. Arguably, what you have is the sense that sound is a relational thing. You have to have something with an auditory sensory apparatus or, at least, a recording instrument of some description. You have to have something; you have to have a measurement. Without a measurement, there is a sense in which it makes no sound at all. Now, does it produce an acoustic disturbance in the air? For sure, I would argue. But you can’t call that a sound unless you’ve got something on the other end to detect it."

"This is a completely popular book about quantum physics: there is not a single equation in there, I think. What he does is to go through all the major ways in which we try to understand quantum physics, all the major interpretations. It’s extremely good in that he writes in a very objective way and it’s very difficult to tell which one he supports. It’s very passionately argued as well, and it’s a beautiful exposition, very philosophical. I think it’s the best, probably my favourite, popular account of all the things we argue about on the fundamental side of quantum physics. Right. There are connections with religion, then there are extremes saying it’s all in the mind: basically that nothing becomes real until we measure it and look at it and consciously record it. On the other side there is a point of view that it’s as real as anything else, out there independently of us and so on. He talks about these two extreme views and what quantum physics tells us about this very old question: whether the world is ideal or real. He really leaves it open because, to be completely honest about these issues, I don’t think we have something that’s universally accepted as the view: each has lots of positive points but also something that makes it a not completely plausible view to hold. That’s a really nice book."