The Problems of Physics, Reconsidered - A Conversation with Tony Leggett

Howard Burton

• Publisher: Ideas Roadshow
• Year: 2021
• eBook ISBN: 9781771700726
• Topic: Physical Sciences
• Subtopic: Astronomy & Astrophysics

This book is based on an in-depth conversation between Howard Burton and Physics Nobel Laureate Tony Leggett. The basis of this conversation is Tony Leggett's book The Problems of Physics and further explores the insightful plain-speaking itemization that he developed of the physics landscape according to four basic categories—the very small (particle physics), the very large (cosmology), the very complex (condensed matter physics) and the very unclear (foundations of quantum theory)—while providing a thoughtful follow-up analysis from a contemporary perspective to assess how much progress we've made and which mysteries remain or have come on the scene since the book was published.This carefully-edited book includes an introduction, The Gentleman Laureate, and questions for discussion at the end of each chapter: I. Back to the Future - Setting the StageII. The Very Small - Much the sameIII. The Very Large - CosmologyIV. A Glassy Digression - The perils of affirming the consequentV. The Very Complex - Condensed matter physics meets quantum informationVI. Understanding - What it actually meansVII. Different Regimes - Nature's ScalesVIII. Schrödinger's Cat - Different domains?IX. The Slings and Arrows of Time - Irreversible?X. The Anthropic Principle - Better left unsaid?XI. The Future of Physics - From Louis Armstrong to topological quantum computingAbout Ideas Roadshow Conversations Series: This book is part of a series of 100 Ideas Roadshow Conversations. Presented in an accessible, conversational format, Ideas Roadshow books not only explore frontline academic research featuring world-leading researchers, including 3 Nobel Laureates, but also reveal the inspirations and personal journeys behind the research.

The Conversation

I. Back to the Future

Setting the stage

HB: Do you remember what the general reaction was to your popular book, The Problems of Physics, when it was first published in 1987?

TL: I got a lot of interest from the sort of people I’d hoped to interest: people who are not professional physicists but have some interest in physics and moreover are prepared to do a certain amount of work on the subject. I got some quite favourable reactions.

Some of my colleagues liked it too. One or two, I think, took objection to one or two statements I had made in it but not many.

HB: But you were very careful. You had these phrases—I can’t recall them off the top of my head—to the effect of: “So far what I’ve done is orthodox, now I’m going to be much more speculative. If you have a problem with this, if you are a professional physicist, then you should be aware that I have written other things...”

TL: Yes. I tried to guard my back as best as I could. There were some who disagreed, but they didn’t take umbrage; they just wrote that they simply didn’t agree with what I had said.

HB: There wasn’t much in the way of popularization in 1987, was there?

TL: Actually, it was just at a time when a number of popular books, particularly on the foundations of quantum mechanics and its interpretational problems, were beginning to come out.

I think this was not necessarily the case for other areas like, say, cosmology, or problems relating to the arrow of time or anything like that. Even today I suspect that there are not many popular books in those areas. Nowadays, of course, one has a real flood of popular books on quantum mechanics.

HB: A veritable tsunami, as it were.

TL: Yes, indeed.

HB: I reread The Problems of Physics recently, the version that was reissued by Oxford University Press in 2006. I loved your categorizations: the very small, the very large, the very complex, and the very unclear.

I think it would be fun to go back and do a sort of follow-up analysis from our contemporary perspective using those same categories, assessing how much progress we’ve made and what mysteries remain or have come on the scene in the meantime.

TL: OK.

Questions for Discussion:

1. Why do you think that there are so many more popular books on the interpretation of quantum mechanics than other subjects in physics?
2. Is writing a popular science book more accepted today than it was 30 years ago? If so, why do you think that is? Are there any disadvantages associated with this change in attitude?

II. The Very Small

Much the same

TL: If one starts with the very small, then—and this is not an area that I’ve followed in great detail over the last 25 years since the book was written—I would say that the standard model of particle physics does seem to have worked rather well, by and large. As far as I know, there have been no huge pieces of evidence that have claimed that the whole thing is wrong. Of course, recently there have been these experiments that have discovered something that looks and smells pretty much like a Higgs boson, which is a nice, central piece of the jigsaw that does seem to be fitting in rather well.

HB: You say “looks and smells” but if I’m someone who doesn’t know anything about this I may think to myself: Well, Professor Leggett, you seem mostly convinced that this is really the Higgs boson, but are you really convinced, or are you waiting on mutual corroboration from enough people? Is there any lingering doubt in your mind? Or are you just saying that you don’t know enough about this area?

TL: I think I’m saying that I don’t know enough about this area. To really make a proper assessment of—and I’m not sure if you can rigorously define this concept—the degree of probability that the Higgs boson has been found, then you need to go into the nitty-gritty of both the theoretical predictions concerning it and the details of the experiment. And I certainly can’t. I’m basically basing my views on the opinions of my colleagues, and my impression is that it seems like a pretty good candidate.

HB: Sure. I should say that opening up The Problems of Physics was an interesting experience because I went into it thinking, Well, 1987 was a long time ago. That was before dark energy, string theory was a very different thing than it is now, and so forth. I suppose I was somehow naively expecting that I was going to look at this and find it to be completely out of date.

But it wasn’t that way at all, of course, which really brought home to me how little our understanding of this area has changed in the intervening time. You mentioned supersymmetry, for example, which was something that people were talking about in 1987. And they’re still talking about it now.

TL: Yes. By and large, at least in so far as I have any feeling for it, the picture of particle physics has not changed that much.

HB: I would think that there are probably more people who are talking about the idea of “physics beyond the standard model” now, than there were at that time. But perhaps not.

This is all speculative, of course, granted that this is not your area of expertise; but obviously you’re aware of many developments. Is there anything you have a gut feeling about—a speculative gut feeling about anything in particular related to particle physics?

TL: To be honest, not really. It seems to me, for example, that the problem of reconciling the existing structure of quantum field theory with what we believe about gravity is still, essentially, as severe as it was 25 years ago.

Questions for Discussion:

1. To what extent does the brief discussion of the Higgs boson in this chapter demonstrate the extent to which professional scientists need to trust the opinions and valuations of their colleagues?
2. Is the fact that our understanding of particle physics has changed so little in the past few decades evidence of the strength of our current knowledge or the lack of sufficiently probing experiments? Or, somehow, both?

III. The Very Large

Cosmology

HB: Cosmology, on the other hand, has changed enormously since 1987.

TL: It certainly has. Obviously, I think, the most spectacular development has been the apparent evidence that the expansion of the universe has actually accelerated, contrary to what had been expected.

My own personal feeling—again I’m speaking as a complete outsider who is just tr...

Table of contents

• A Note on the Text
• Introduction
• The Conversation
• Continuing the Conversation