Our quantum world has many odd and counter-intuitive features. One of these is “tunneling” — the ability of objects to pass through walls, escape from traps, and slip under mountains into the next valley. We don’t encounter this effect in daily life; objects we’re used to are so incredibly unlikely to tunnel from one place to another that we will never hear of one doing the apparently impossible. But in the atomic and subatomic realms, even in various types of modern technology, tunneling is an essential and commonplace feature of the quantum reality in which we live.
I’ve written a short article about this phenomenon, which you can read here, emphasizing the central role that tunneling plays in the world’s most powerful microscopes. It should be suitable for anyone who has read a little about atoms.
This article lays the groundwork for a discussion of how tunneling could someday, in the distant future, end the universe as we know it. It also prepares the way for a more advanced post about how a single physics theory (i.e., a set of equations designed to describe some aspect of nature) may have multiple `vacua’ (i.e. multiple solutions that each represent different ways that the universe could be configured — what empty space could be like, and what types of fields, forces and particles could be found in the universe — over long periods of time.) If that’s confusing, stay tuned for a few days; I’ll soon explain it.
I’ve been quite busy with some physics research this week, but I have nevertheless managed to finish a new article on electrons, part of my Structure of Matter series, which aims (among other things) to introduce a non-expert to particle physics, step-by-step. The completion of this article feels like a significant step for this website. After all, the electron was the first subatomic particle and the first of the apparently-elementary particles to be discovered, about 115 years ago, and its discovery really gave birth to the field of particle physics we know today. Moreover, it was the failure to describe the behavior of electrons within and outside of atoms that forced physicists to go beyond Newtonian views of physics processes, and introduce the theory of quantum mechanics. Electrons, tiny as they are, are enormous in human life; they play a key role in all chemical reactions, including those that sustain our bodies. Beyond that, they lie at the heart of much modern technology — electronics! And there’s more. So no particle physics website can be complete without an electron webpage.
Looking ahead, a question I sometimes get asked is whether I’m sure electrons (or any other elementary particles that physicists talk about) really exist. After all, it is true I’ve never seen a picture of one taken with any sort of microscope! Well, in answer to this question, I want to write an article on why we particle physicists are so confident that electrons (and atomic nuclei) exist… explaining the types of experiments and the types of logical reasoning that lead to this conclusion. I suspect a lot of readers will find such an article interesting; after all, why should one take expert knowledge for granted just because it appears in a textbook or on a website? Readers should demand to know where the knowledge came from — and a writer should be prepared to answer.
I’ve been adding to my series of layperson’s articles on The Structure of Matter, which eventually will serve as an introduction to particle physics for those coming to this site for the first time. You might recall that in early December I supplemented my older article on molecules with an article on atoms. I got some terrific reader feedback, in the form of incisive constructive criticism, which allowed me to greatly improve the latter article. Well, readers, you’ve got another chance to help me out if you would like to — or you can just enjoy the read. I have three new articles (two of them short) which were put up over the last few weeks. These are:
Incidentally, the next stage in this series will be to describe electrons, and then I will turn to atomic nuclei, to the neutrons and protons that they contain, and eventually to the quarks and gluons that make up the neutrons and protons.
It took me over six months, following my article on molecules, to write the sequel, on atoms. These are just two in a series, intended to introduce the structure of matter to novice readers who want to learn what particle physics is about. Atoms aren’t the main focus; future articles will focus on electrons, on protons and neutrons, on quarks, and on the forces that hold these objects together. But the essay on atoms might be the hardest of the set to write (at least I hope so). The long delay reflects the challenges involved, and as my readers’ wise and helpful criticisms of Friday’s first version confirmed, I didn’t meet them on my first try.
So after some thought, I’ve made another attempt. Critique still welcome from anyone who wants to make suggestions.
Aside from the fact that I fell into a couple of pedagogical traps that anyone who’d taught chemistry would have known about, I also struggled to describe atoms briefly, clearly and accurately because their features are determined by quantum mechanics — that weird but fundamental behavior of our world that we don’t encounter in daily life but is essential to the structure of matter. What’s profoundly confusing to the non-expert (and somewhat confusing even for experts) is that electrons are, on the one hand, best described in many circumstances as point-like particles (much smaller than atoms, and smaller even than atomic nuclei) yet around atoms they are in some way spread out in a very non-particle-like fashion. Well, indeed, thinking of elementary objects like electrons as “particles” will get you into trouble; for one thing, they are really “quanta” of quantum fields, and in most circumstances they behave much more like waves. And yet it is essential to explain that one can try to measure their size — essentially by forcing them, through an appropriate experiment, to reveal whether they, like baseballs, rocks and dumplings, have internal structure.
Ok, I can’t even figure out how to write this paragraph clearly. There needs to be a way to explain this issue, one that is both moderately intuitive and based on accurate and clear physical reasoning…
I have a number of loose ends to tie off on this site, and one of them is my set of articles for novice readers about the structure of matter, which when complete will introduce the basic particles out of which we and all of ordinary matter are made. A while ago I wrote an article about molecules; today I finished the next article, on atoms [Note added: A revised version is now ready; thanks to readers for helpful criticisms of the original]. Future articles will explore how atoms work in more detail, and the subatomic particles out of which they are made. As always, comments (especially on the clarity of the writing, as well as typos) are welcome.