Q&A with Sönke Johnsen

Quinn Fusting, PUP’s editorial assistant in the life sciences, has conducted a Q&A with Sönke Johnsen, the author of The Optics of Life: A Biologist’s Guide to Light in Nature.

Q: When, how, and why did you become interested in light?

A: I grew up in a house where we made just about everything, including science toys. My dad was a physicist, and we would spend weekends building pinhole shoebox cameras, arc lamps from dismantled batteries, and once even a solar hot dog cooker made out of a sledding saucer covered in aluminum foil. He would also bring home surplus items from his lab, like head-sized Fresnel lenses and chunks of sapphire lasers. He also set up a black-and-white darkroom in the attic where I spent much of my childhood and adolescence. My mother was creative as well and introduced me to painting, drawing, tie-dying and such. There were no computers yet, and our TV only got two channels (three if my little brother stood in just the right spot), so I had plenty of time to fiddle around.

As for why…well, light is beautiful. What’s more wonderful than the light filtered through new leaves on a windy, Spring day? Or the green bioluminescence trailing your limbs as you swim on a moonless night?  The stars alone are worth having eyes for. I can’t imagine not studying light. 

Q: What drove you to write an optics guide for biologists?

A: I’m not entirely sure. I do enjoy writing, but this was a lot of work, so there must have been a reason. When I pitched the project to my editor, I told her that it would fill a niche, but I’ve never been one to lose sleep over unfilled holes. I also told her that optics was important to biology. It is, but so what? Steve Vogel told me once that writing books is wonderful because it transforms you from a competitor into an enabler. I do hope this book helps people use optics in their research, but honestly I still feel competitive. Maybe I just want people to stop me in the hall and say, “Nice book!” I’d be lying if I said this didn’t matter. I’m shallow, and flattery goes a long way with me.

There’s more though. While not religious, I am often overcome by this world — it’s like being given a prize over and over. The most remarkable part to me is that we are able to appreciate and at least partially understand it. Being a biologist, I can mumble about scientific curiosity being an epiphenomenon of natural selection for cooperative hunting, foraging, individual recognition, and so on, but that doesn’t make it any less incredible. As the physicist Isidor Rabi said when the muon was discovered, “Who ordered that?” However we acquired this ability to appreciate and understand the world, it would be rude to waste it. So I wrote this book to share this feeling, this amazement at what is all around us.

Q: What would you say is the most important thing for biologists to know about optics?


A: That it’s easier to learn than you think. The long history of the field and its connection with human vision has left us with a horrible mess of units and concepts. Only in optics do people still publish papers using units like stilbs, nits, candelas, trolands, and my personal favorite, foot-lamberts. However, the reality of optics itself is simple and elegant. With the right introduction, you can sidestep the mess and get right to the fun parts.

However, light is also harder to work with than many people appreciate. The main reason for this is that we don’t measure light in our daily lives. Since childhood, we develop an intuitive sense of weights, lengths, area, temperature, and so on. For example, we can guess someone’s height to within 5% and weight to within 10%-20%. However, even after a decade of measuring light, I can’t tell you how bright my office is on this overcast morning to within even an order of magnitude. This is like saying that I can’t decide whether I am six or sixty feet tall. So you need to be careful. It’s worth it though. The biological world is a funhouse of optical tricks and traits just waiting to be discovered. Just today, I read that jumping spiders use image defocus to judge distance and that bowerbirds play with visual perspective to impress their mates. How cool is that? 

Q: What is light anyway?

A: I have no idea. I have thought about light since I was five years old and am no closer to understanding its fundamental nature. I am in good company though. Even Richard Feynman, one of the creators of the theory of how light and matter interact and widely acknowledged as one of the best explainers of physics, said that light cannot be understood. We have equations that let us predict what light will do to a precision of more than twenty significant figures, but no one has come up with a description of light that makes sense. It is unlikely that anyone ever will. Read enough about the subject, and your head will start to itch.

However, while the non-intuitive nature of light can be unsatisfying, it doesn’t affect our ability to use it. In other words, as long as you do your measurements and math correctly, you can think of light as little purple buffaloes and it won’t matter. After all, we don’t really understand the fundamental nature of anything, but manage just fine.