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.
Just ask the Nobel Prize committee: is quantum physics some sort of speculative new science? (A smart educated woman asked me, just a week ago, `What do you think about that quantum physics stuff?’, as though it were in the same category as theories of consciousness, speculations about the origin of life, and string theory.) No way: it’s all over your computers and cell phones; it’s in many modern light bulbs; it’s the laser that reads the prices at the grocery store and your ticket at a concert; it’s the heart of the best timepieces and the eyes of the best microscopes; it’s what makes solids solid and liquids flow, and powers chemical reactions and radioactivity; it’s probably playing a big role in biology that we’re just starting to understand; and it’s sunshine and moonlight and the glowing auroras borealis and australis. It’s the foundation and fabric of your world.
And though it may be bizarre, it is by no means abstract. Maybe in the early 1930s one could still say it was abstract; but already for many decades particle physicists have passively observed individual particles, one at a time, behaving in quantum mechanical ways. Today scientists can control individual quantum objects, things whose behavior can only be predicted by accepting the odd rules and counter-intuitive implications of our quantum world. In particular, physicists have learned to capture and manipulate individual photons (particles of light), atoms, and ions (atoms with an electron removed or added, to make them electrically charged — see the Figure below.) It is for their work advancing these capabilities, making possible new classes of experiments and opening up the potential for new technologies, that Serge Haroche and David Wineland have won the Nobel Prize for 2012. Read about it here (brief press release or summary for non-technical readers)… using your preferred quantum-mechanical device.
Light emitted from three individual ions of Beryllium, trapped and held in place for an extended period of time. (National Institute of Standards and Technology image gallery.)