We Have No Idea

Most popular science books aim to explain ideas and answer questions. This is not the approach taken by Jorge Cham and Daniel Whiteson in their book, aptly titled We Have No Idea. Many questions are posed in their book, to which they answer (yes, you know it!) “we have no idea”. The point of the book is to explore the edge of our knowledge in physics (and cosmology, in particular). The authors tell us the many things they do know – but the edge, where knowledge and ignorance meet, is where things get interesting! The authors are enthusiastic about figuring out what we don’t know rather than throwing up our hands in despair – even though we have no idea what’s actually going on.

Readers might be familiar with Jorge Cham through PhD Comics – highly recommended reading for academics of any stripe. Daniel Whiteson is a physics professor at UC-Irvine. Their book is funny and engaging! Cham & Whiteson use both the text and the illustrations to great effect. It’s probably the most fun I’ve had learning about the edge of physics research. They also got me thinking about two familiar concepts – mass and charge – and what we know and don’t know about them. More on that in a moment.

Last week I read a lot of physics. Besides finishing Cham & Whiteson’s book, I also read Astrophysics for People in a Hurry by Neil DeGrasse Tyson, astrophysicist and go-to-guy for explaining astrophysics to the general public. Tyson is a good communicator both on video and in text, and if I hadn’t read Cham and Whiteson first, I would have enjoyed his book more. The first half of Tyson’s book has overlapping material with Cham and Whiteson, and the latter duo are more engaging on the topic – they’re hard to beat. I’m not sure why Tyson’s book has his name displayed more prominently than the book’s title. Maybe the publisher thought his name would be a bigger draw (in generating sales) than seeing the word “Astrophysics” in a title. Tyson’s book is much shorter and can be read in maybe two hours. A much longer book that I just started reading is Helge Kragh’s Niels Bohr and the Quantum Atom, a denser academic treatise very unlike the other two books written for a popular audience. (I will discuss Kragh’s book in a future blog post when I’ve made more progress.)

Let’s return to mass and charge. In chemistry, I take these quantities for granted, while Cham & Whiteson emphasized their strangeness. We don’t really know what these two ‘things’ are and yet my students and I use them ubiquitously in chemistry class. For example, today we talked about oxidation numbers and using them to identify redox reactions. A perceptive student asked me midway through class: “So what are oxidation numbers exactly? Are they charges?” The answer is no, they’re not charges. They’re just convenient book-keeping labels that we use. Cham & Whiteson go a step further: Fundamentally, charge is just a label, as far as we know. Why does the electron have a charge of –e (where e = 1.60 x 10^-19 Coulombs)? Where does that charge reside? Or is the whole electron just the charge? We haven’t successfully broken down any leptons (electrons are in the family of leptons) into further elementary particles. We have no idea what exactly they are, but we can balance redox chemical equations by making sure the appropriately labeled plusses and minuses balance out.

The last two weeks in my general chemistry course was on stoichiometry. Students balance chemical equations and then calculate amounts of reactants, products, and leftover reactants. There is a protocol. First, convert all amounts into number of moles. Then figure out everything in terms of moles and then convert the amounts back into whatever the problem asked for, usually in terms of mass. Why this convoluted scheme? Because it’s easy to measure mass. You weigh out reactants when designing a chemical reaction, and you weigh the products after the reaction is complete. But chemistry is about exchanging atoms through the making and breaking of chemical bonds. Unfortunately you can’t count the atoms directly. (You can weigh the substance as a whole and deduce the number of atoms if you know the chemical formula of the substance.) To avoid astronomically large numbers, chemists use the mole as the unit for atom-counting. The convoluted scheme is compounded by masses having non-integer values, and we have no idea (at the deepest level) why they have the exact numerical masses that they do.

If the previous two paragraphs sounded complicated, that’s because when we dig deep enough, we reach the point where… (wait for it…) we have no idea! Charges are just labels that tell us something about inter-particle interactions. Masses are what we can measure easily even though they are not the crucial underlying factor that organizes the world of chemistry. When the Periodic Table was being first formulated, mass was used as an organizing factor. Mendeleev used mass in his influential version of the periodic table, but it was an unknown Dutchman (Antonius van der Broek) forty years later, who influenced the giants in the field (Rutherford and Bohr) to adopt nuclear charge (rather than mass) as the organizing principle. This better approach was later confirmed by the X-ray work of Henry Moseley.

As messy as it is, this is what I find fascinating about chemistry – the elements are idiosyncratic. The periodic table at first glance looks like a wondrous organizing principle (and indeed it is) but it is full of idiosyncracies, exceptions and niggly details – to the dismay of my students when they start to realize this. The alchemists were secretive about their mysteries; today we are no longer as secretive but many mysteries remain.

I leave you with one photo I took from Cham & Whiteson, and if you want some old fun reading, here’s my blog post on Magicians, Mutants, Midichlorians.