By Jermey N. A. Matthews
Originally trained in mathematics and art, Duke University biologist Sönke Johnsen has been studying camouflage, eyes, tissue optics, and nonhuman visual modalities for more than 20 years. He has conducted research on coastal and terrestrial species, magnetoreception, and human cataracts, though his primary interest is in deep-sea animals. Johnsen is also interested in bridging the gaps between the fields of physics, biology, and is author of The Optics of Life: A Biologist's Guide to Light in Nature (Princeton University Press, 2012). Physics Today recently caught up with him to discuss the book.
PT : What motivated you to write this book?
Johnsen : I suppose the original inspiration was Steve Vogel's Life in Moving Fluids: The Physical Biology of Flow (PWS Kent Publishers, 1981). That book, which converted me to biology in 1987, explained fluid mechanics in a wonderfully intuitive way. The book was humorous and full of biological examples, but most importantly, it never took the easy way out. Conventional wisdom was always tossed aside, and all the subtleties and caveats were explored. So for the last 12 years I have wanted to write a similar book on optics. [Princeton University Press] must have had the same idea, because every year they sent a guy to my office who would ask me to write a book. I always answered, 'Let me get tenure first!' Then I got tenure and had no more excuses.
PT : Aside from its being a guide for biologists, can physicists also learn something from The Optics of Life?
Johnsen : I think so. First, while it only uses a moderate amount of math, the book is rigorous and delves more deeply into the central issues of optics than many textbooks do. Much of the book is the result of endless email conversations with [Pennsylvania State University atmospheric physicist] Craig Bohren, who, like Vogel, is never one to accept conventional wisdom. Physicists Laurie McNeil at the University of North Carolina at Chapel Hill and my father Rainer Johnsen at the University of Pittsburgh also played a big role in giving the book depth and accuracy. Second, many animals build optical structures that frankly make physical scientists and engineers drool, and this book describes many of these in detail.
PT : What is visual ecology and what got you interested in the field?
Johnsen : Visual ecologists study how eyes, signals, and camouflage have evolved in response to different optical environments. Typical questions include, What are the relative costs and benefits of compound versus camera eyes? How are eye designs in deep-sea animals affected by depth and turbidity? And does the birefringence of tissues in transparent animals make them vulnerable to detection by animals with polarization vision? It's not the best name for a field, since ecologists don't consider us to be in their camp, but it's the best we could come up with. As for why I study it, well who wouldn't want to? I get to dive with bioluminescent plankton and study invisible animals. How cool is that?
PT : What do you see as the promises and challenges of the broadening intersection of physics and biology?
Johnsen : The promises are enormous. Four billion years of evolution have given us millions of species that exploit nearly every known physical principle in diverse ways—with the interesting exception of radioactivity. Together, biologists and physicists can explore these adaptations with a level of sophistication that is far above what either can do alone. The central challenge is getting both groups to respect each other. Physicists often have scorn for most biologists' lack of mathematical skills, and biologists similarly feel that most physicists believe that there are only 10 different species of animal on earth. On a more fundamental level, I see this as a conflict about what is useful knowledge. Physicists can describe a system with high precision, but not one as complex as an animal, let alone millions of species of animals. Biologists can only hope for low precision, but in turn have a tremendous tolerance for ambiguity and diversity. It's not an easy gulf to bridge.
PT : What books are you reading at the moment?
Johnsen : Fundamentals of Atmospheric Radiation (Wiley, 2006) by Bohren and Eugene Clothiaux, which I think should be reissued as The Best Optics Text Ever; Haruki Marukami's 1Q84 (Knopf, 2011), which I didn't like as much as his earlier books; and The Hunger Games (by Suzanne Collins, Scholastic Press, 2010), so that I can keep up with my daughter. Who would have thought that a book about teenagers murdering each other would be so popular?
