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Questions and answers with Peter Hoffmann

The author of Life's Ratchet answers a broad question about chaos in biology by focusing on the narrower issue of whether molecular machines violate the second law of thermodynamics.

Peter HoffmannPeter Manfred Hoffmann (image left) was born and raised in Germany in a small village near the French border. He studied physics and mathematics at Technical University of Clausthal in Clausthal-Zellerfeld. Then he moved to the US, where he completed his master's degree in physics at Southern Illinois University in Carbondale and his PhD in materials science and engineering at Johns Hopkins University in Baltimore, Maryland.

As a postdoc at the University of Oxford in the UK, Hoffmann conducted research on the properties of nanoconfined liquids. He continues that research as a professor of physics at Wayne State University in Detroit, Michigan. In his time at Wayne State, which commenced in 2001, Hoffmann has added single-molecule biophysics to his research portfolio. In 2008 he became founding director of Wayne State's biomedical physics undergraduate program, and in 2012 he was named associate dean for academic programs in the College of Liberal Arts and Sciences.

Growing up, Hoffmann says that biology was a mystery to him; unlike physics, it "seemed impossible in biology" to reduce nature to first principles. After he got into biophysics research, he discovered much about the physics of molecular machines in the primary literature—but very little about "their amazing story" in popular books. So, having always had an interest in writing, Hoffmann says he "decided to write the book that I could not find in the bookstore."

The result is Life's Ratchet: How Molecular Machines Extract Order from Chaos (Basic Books, 2012). Recently, Physics Today caught up with Hoffmann to discuss the book.

PT: How does physics contribute to the unanswered questions about molecular machines, and what will physicists outside this subfield learn from Life's Ratchet?

Hoffmann: The purpose of the book was to show that physics can answer one of the most perplexing questions of how life works: How do we create order out of chaos? Of course a physicist will translate that—and I have done that in the book—to, How is it possible that molecular machines do not violate the second law? As a physicist, I feel that a natural phenomenon is only truly explained if it can be modeled using known physical or mathematical relationships.

For me, learning about molecular machines was a profound experience, as it suddenly anchored an entire fascinating field of knowledge and research—molecular and cell biology—in physical reality. It seemed to me that when I learned biology, the connection between physics and biology was tenuous at best. It was acknowledged that biology was based on chemistry, which is ultimately based on physics, but this connection was rather indirect. What we can learn from molecular machines is that principles of physics can explain in exquisite detail how life fundamentally works. I think that's a revolution that people should know about. It makes both physics and biology more interesting.

PT: You say on your website that the book is aimed at all readers, including "science lovers as well as spiritual truth seekers." How so?

Hoffmann: I think there are roughly three types of scientists when it comes to the question of "spirituality." There are the ones who dismiss the very idea as nonsense, the ones who find a kind of rational spirituality in nature, and, of course, scientists who are actually religious. I see myself in the middle camp, along with some of my heroes [for example, Albert] Einstein and [Carl] Sagan. I am not religious, but I feel that science can give us profound answers to profound questions, such as the question, What is life? Moreover, these answers are awe-inspiring and happen to be based on facts. So, the book is for "spiritual truth seekers" in the sense that it addresses one of the deep questions and shows how a scientific answer to this question connects us to the deep structure of our universe.

PT: The reviewer raises concerns about an "imprecise" restatement of the second law of thermodynamics that appears on page 78 of your book: "There can be no process whose only result is to convert high-entropy (randomly distributed) energy into low-entropy (simply distributed, or concentrated) energy." What was your intent with this restatement?

Hoffmann: Discussions of the second law in popular science books have never satisfied me. I am completely in agreement with the reviewer on this. I also agree that the quote is not entirely correct as stated. However, this is why I spent a significant amount of time clarifying the second law in the book. There are few popular books [that] treat this subject with the same depth as my book. To understand something as profound as the second law, and explain it to the general public, you have to slowly build up your arguments.

Initially, I introduce the second law from a more macroscopic view, familiarizing the readers with the idea of entropy. That is where the quote is from. I go to great lengths to bring the concept of probability into it and make clear that entropy is not simply "disorder." Later, I talk about how the second law can be "violated" on the microscopic scale, pointing out that this is purely random and cannot be used to do work using any kind of cyclical process. Ultimately I point out [that] the second law is a statistical law. I introduce Jarzynski's equality and talk about the connections to information theory, leading to the realization that molecular machines use an energy-consuming "reset" step to repeatedly extract energy from the heat reservoir. All in all, I don't think that readers would go away thinking that I glossed over these issues.

PT: What's your general take on the depth and breadth to which popularizations should go in presenting such technical concepts as the second law?

Hoffmann: Explaining complex issues to a broad audience is always tricky. This is even true when we teach physics. I sometimes joke to students that what we teach them in introductory physics are really "lies," and that they have to take upper-level classes to find out the "truth." In writing, you have to find your own comfort level, which involves balancing rigor with readability. From the responses I have received about the book, I gather that some people felt I erred on the side of rigor, while others appreciate that the book provides more meat than most popular science books. I personally feel that the book gives a good balance. In the end, you should try to be as deep as you can without losing your audience. Science writers want to inform as well as excite. It is bad if you unintentionally mislead the public through oversimplification, but it is worse if you write the most profound and accurate book and nobody reads it.

PT: What books are you currently reading?

Hoffmann: I am currently reading some books to prepare for my next popular science book (I have to keep those secret). I am [also] reading Absolution Gap (Ace, 2004), a science fiction book by Alastair Reynolds; The Fellowship (Overlook, 2007), a book about the early history of the Royal Society by John Gribbin; and Caleb Carr's The Alienist (Random House, 1994), a mystery from 1890s New York.

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Scitation: Questions and answers with Peter Hoffmann
http://aip.metastore.ingenta.com/content/aip/magazine/physicstoday/news/10.1063/pt.5.3002
10.1063/PT.5.3002