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.
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…