Once upon a time, on finishing my undergraduate studies, I was forced to decide what sort of physics I might work on for my PhD. As it turns out, this decision affected not only the next few years, but the whole direction of my research career until now. I confess that my decision was not thought through in great detail, but arrived at on gut instinct: nevertheless, I don’t regret the decision I took then in the slightest.
At the time, I reckoned there were, broadly, three directions for a theoretical physicist to go. You might investigate the physics of really huge things: stars, galaxies, relativity, the Universe and all that. Or, you might go investigating physics on a really small scale: quantum mechanics, string theory, particle colliders and all that. I guess these two limits encapsulate the popular image of what physics is all about: the near-perfect, rolling spheres, both stellar and sub-atomic, as they fly around the universe or fleetingly appear and vanish in a quantum fluctuation. When physicists (rather pompously) speak of a “Theory of Everything” they are talking about a grand theory to unify these two extreme limits of physics; an overarching mathematical formalism from which might crystallise every known physical law of the rolling spheres, both big and small.
A theory of everything? Well, even a child might protest at such pomposity, for we know that there is very much to care about somewhere in between these scales of very big and very small. In fact, there is quite a lot of everything that might not appear at all in this Theory of Everything, if it were ever to be constructed. What about the world around us, the things we can touch and feel? What about life itself? Are these things beyond the interest of physics? Fortunately not (for me). I mentioned a third path that a theoretical physicist might travel. My twenty-year-old self had been lucky enough to secure a summer vacation job at a petrochemical company in Grangemouth, Scotland. There I learned that physicists might find gainful employment considering the properties of the materials around us: in this case the polymers and plastics we use in bags, bottles, cases, toys, games, upholstery, car parts, and so many other applications. I decided that I would like to do my PhD research into something I could hold in my hands and interact with, rather than the intangiably huge star, or tiny electron. I think I realised (like Goldilocks) that there was quite a lot of fun to be had in the middle, somewhere between big and small.
Cell walls are made from self-assembled phospholipid bilayers
My area of physics is called “soft condensed matter” – it is the physics of all the soft messy stuff around us: slime, jelly, rubber, food, foam, paste. It is also the physics which is involved in most of the processes of life itself. And this is, I think, because in the middle sizes, somewhere between big and small, some very important things happen. Firstly, these sizes are significantly bigger than the atomic scale, which means that many atoms are involved in any process which might occur. Wherever there are lots of things interacting, a seething chaotic dynamics usually ensues (imagine a huge crowd of people all running aimlessly in all directions, bumping and colliding into one another: such is the typical environment of an average molecule!). But (secondly) the middle sizes are small enough that sensible temperatures* can permanently sustain this constant, ceaseless, chaotic random motion. It is this constant random dance which allows life to happen. It allows (or even forces) ordered structures to emerge out of the atomic chaos (forming, for example, the walls of cells, or the assembly of proteins) – this is called self-assembly. The constant random motion also permits the diffusion of chemicals which power the little fluctuating molecular motors, which drive our muscles and the swimming of organisms (or the swimming of sperm, for that matter). And the random motion gives strength and elasticity to the soft materials in our bodies: without this motion, the molecules in these materials would fall limp; but the random motion makes them springy!
Two, very brief, conclusions:
- I am convinced that life is wholly impossible on any size scale other than our own. Too small, and there are just atoms. Too large, and temperature induced self-assembly is simply not possible. I do not believe in the pan-galactic hyper-intelligence of Star-Trek fame. So, when people talk about the Universe being so big, and us so small, I want to say: it couldn’t be any other way. I think the Universe needs to be this big to provide the conditions to support life, but living things cannot be enormous space monsters. It is in the middle, between the very large and the very small, where all the fun is to be had.
- We live on the boundary of chaos. In fact, life is impossible without the seething, chaotic motion of atoms and molecules – without the chaos, we are dead. So, we should perhaps not be surprised when chaos intrudes in our ordered life from time to time. We might complain, or ask what kind of God could permit this – these are big and painful questions, and we are right to ask them. But we should remember, the chaos gives us life too.
* By sensible temperatures, I mean not so low that everything freezes, not so high that everything chemically falls apart.
Occasional Read 
Akriti
/ November 27, 2014This is such a well thought & well written post.
I really liked it.
Best Wishes for all your future endeavours.
KEEP WRITING MORE 🙂