Is it possible to study biological systems, including life forms as diverse as human embryos and plants, using the same theory that we apply to the physical properties of inanimate objects? This is the kind of question that interests American scientist William Bialek, a physics professor and member of the Lewis–Sigler Institute at Princeton University, USA. Bialek was in São Paulo at the end of January to give a mini-course on the use of physics in biological systems at the School on Physics Applications in Biology, an event promoted by the International Center for Theoretical Physics/South American Institute for Fundamental Research (ICTP/SAIFR) and the Institute of Theoretical Physics (IFT) at São Paulo State University (UNESP). In this interview, the researcher, who published the book Biophysics: Searching for Principles in 2012, talks about the difficulties of using quantitative experiments and the laws of physics to explain the functioning of complex biological systems.
Which areas of biophysics do you study?
The big issue for me has always been the tension that exists in trying to establish the general principles of biological systems while paying attention to the details of the particular cases that occur within biology. One of the lessons of physics is that qualitatively surprising phenomena are abundant in the living world and have deep theoretical explanations. But the biological systems in which these phenomena occur are complicated, and these complications run counter to physicists’ search for simplicity. We have detailed and quantitative models of many biological systems, but physics is more than a collection of these isolated stories: we have general principles from which we can derive the behavior of particular systems. Can we do this in the more complex context of living systems?
How and why can the physics used to describe inanimate matter also be used to characterize living systems?
The laws of physics apply equally to the atom and the moon. I think that is part of the answer. In physics, there is no motive force that causes superfluid helium to crawl up the sides of a container and escape, for example. This phenomenon emerges from the interactions between helium atoms, which in other contexts do much less surprising things. In the same way, there is something that distinguishes inanimate systems from living systems. But nowadays we no longer believe in a “life force” that animates inert things. Physicists who study the phenomena of life are not searching for a new force of nature. They want to understand how these surprising phenomena emerge from known forces.
In your opinion, what are the limitations of physics experiments on biological systems?
There used to be a strong belief that experiments on biological systems were messy and irreproducible and could never be quantifiable, meaning that using a quantitative approach would, at best, allow us to estimate probabilities and collect evidence against or in favor of particular hypotheses. But the phenomena we see in the living world are becoming increasingly susceptible to the quantitative experiments traditionally associated with physics. These experiments have led to the discovery that many biological phenomena are quite surprising, not just in qualitative terms, but also quantitatively. They have revealed that biological systems can exhibit very precise behaviors. These developments are occurring on every scale, from single molecules to large populations of organisms. This means we must demand more from our theories, we must look for the detailed and quantitative comparisons between theory and experiments that are characteristic of physics in general. The current landscape is very different from when I was younger, and it is very exciting.
In physics, we teach principles and derive predictions for particular examples. In biology, teaching is based on case studies
What are the main challenges faced by those studying the interface between physics and biological systems?
Academic disciplines are defined either by their objects of study or by their style of inquiry. A biologist is interested in what is alive; physicists are proud to “think like a physicist.” In physics, we try to teach principles and derive predictions for particular examples. In biology, teaching is based on case studies. Biophysics is not a mature field, and it is very hard to overcome the history of two disciplines at the same time. It is much harder to study physics and biology together than to study just one of them. How do you encourage students to have their own ideas and ask their own questions when they have to deal with the idiosyncrasies of two institutionalized disciplines?
How do you study quantum effects in living systems?
Sometimes we make mistakes by trying to use quantum mechanics to describe biological systems. Many years ago, I thought I had found evidence that the cells in our ears could take measurements limited by quantum physics, but in the end, I was wrong. I learned just how difficult this problem is. I still have hope that quantum effects will be more important in biological systems, but I am cautious. The observation of these quantum effects in a biological system always triggers excitement, but to see effects such as tunneling [in which a particle can cross barriers deemed insurmountable by classical physics], very low temperatures must be reached. This is not something that is observed in biological systems in everyday life. Quantum phenomena such as coherence [when the states of a system simultaneously overlap], however, may occur in the early moments of photosynthesis and when biological molecules interact with light, like in the first steps of vision. But there is no evidence that quantum coherence can occur on a macroscopic scale.
Are there any quantum phenomena that are observed in both macroscopic and microscopic biological systems?
The really deep and beautiful effects of quantum coherence are hard to see on a macro scale—the variables that we observe interact with so many other variables that we cannot follow them all at once. There are remnants of quantum behavior in the randomness of certain phenomena, such as radioactive decay. When matter absorbs light, the elementary steps are random, and this is so because of quantum mechanics.
Have you studied any other specific areas of biophysics?
There are physical limits to sensation and perception. The eyes, ears, and other senses send signals to the brain. I want to know the smallest signals that can be perceived by the brain, based on the physical limits of sensory measuring devices. How close do our sensory systems, which are measuring devices after all, come to the limits imposed by the laws of physics? The idea that the boundaries of perception are set by fundamental physical principles is very attractive. We use these same ideas to study how cells “sense” internal signals.
What are the cognitive implications of phenomena such as the internet?
We always seem to think that our particular moment is special. People have always worried that technological developments will change things in a way that creates losses and gains. The invention of the printing press certainly caused some loss of oral tradition: the local storyteller became obsolete. Now we can access the story without even printing the book, just by googling it. We no longer need to remember and pass along stories, although this is still a very human activity. We do not need to store information in our memory. Instead, we transfer part of our thought process and memories to our computers and cell phones. This is not actually a bad thing. Nowadays, more people have access to these things, to information that was once very exclusive. We cannot yet understand the cognitive implications of this, since the effects will only be observable in my grandchildren.