Introduction and Overview

Physics is about things that we can hold in our hands, but also about the history of the universe as a whole. The discipline is defined not by the objects being studied, which have changed over time, but rather by the kinds of questions being asked and the kinds of answers being sought. The physics community takes seriously the Galilean dictum that “the book of Nature is written in the language of mathematics,” and searches for an understanding that is expressible in a compact and compelling mathematical structure. This understanding emerges through an intricate dialogue between theory and experiment. Physicists build new instruments, extending humanity’s ability to observe the world; these instruments test the predictions of our theories and enable discovery in places where our theories are silent. Physicists explore new theories, both as explanations of puzzling observations and as worlds unto themselves, sometimes connecting back to the world of our experience only after decades of work. Victory is declared when theory and experiment agree in quantitative detail, but the community also prizes approximate reasoning, allowing for less precise predictions with proportionally less effort. The history of physics teaches us that particular numerical facts about the world are explained by reference to more general principles, and that the most striking phenomena will connect to the deepest concepts. Biological physics, or the physics of living systems, brings this physicist’s style of inquiry to bear on the beautiful and complex phenomena of life.

READER’S GUIDE

This report addresses three broad questions, in the three major parts of the report:

1. What is biological physics? (Part I)
2. How is biological physics connected to other parts of physics, to biology, and to applications of direct relevance to society? (Part II)
3. What challenges do we face in realizing the promise of the field? (Part III)

As will become clear, the intellectual agenda of biological physics is extremely broad, touching phenomena on scales ranging from molecules to ecosystems. The committee has organized the exploration of this agenda, in Part I, around four major conceptual questions, each of which is illustrated by multiple examples. Each major question is the subject of a separate chapter, each of these chapters begins with a general introduction that defines the question, and each example concludes with a perspective about the new physics that has been discovered. This organization is not intended to be canonical, but rather to give a feeling for the breadth and depth of the field as a branch of physics, and for its unifying themes, in the physics tradition.

Where Part I emphasized the internal coherence of biological physics, Part II emphasizes its strong connection to other fields of science and technology. There are deep and sometimes surprising connections to other areas of physics (Chapter 5), as well as interactions with disparate parts of biology, chemistry, and even psychology, sometimes extending over a century (Chapter 6). As with all areas of physics, progress in biological physics has practical consequences, and we see these consequences in contexts ranging from the doctor’s office and the diagnostic lab to robots and artificial intelligence, with many stops in between (Chapter 7).

Realizing the ambitious agenda of biological physics will require addressing many challenges, as explained in Part III. New science is fueled by new young people entering the field, and it matters how they are educated. Integration of biological physics into the physics curriculum, at all levels, can be synergistic with a broader modernization of physics teaching and the nurturing of a more quantitative biology (Chapter 8). Progress also is fueled by funding, and here the major challenge is to align the funding mechanisms to the structure of the field, rather than fragmenting the field along the lines defined by different grant programs (Chapter 9). Finally, as with all areas of physics and science more generally, biological physics faces challenges in welcoming talent from all segments of our society, including those who have been the targets of historic and continuing injustice (Chapter 10). The bulk of the report’s recommendations are found in Part III, addressing these challenges.

The present chapter is meant both as an introduction to the report and as a self-contained overview. In that spirit, we recapitulate the major “parts” of the report in the following sections. Because this is the first time that biological physics is being surveyed as a part of physics, the committee has taken the liberty of providing more than the usual historical background for the field, followed by a brief description of how this report fits into the larger context of the decadal surveys of physics. Finally, the introduction concludes with a summary of the committee’s findings, conclusions, and recommendations.

DEFINING THE FIELD

The phenomena of life are startling. A single cell can make an almost exact copy of itself, with just a handful of errors along the millions or even billions of bases of DNA sequence that define its identity. In some species it takes just 24 hours for a single cell to develop into a multicellular organism that crawls away from its discarded eggshell and engages in a wide range of behaviors. The swimming of bacteria is driven by a rotary engine comparable in size to a single transistor on a modern computer chip. When we humans sit quietly on a dark night, we can see when just a few quanta of light arrive at our retina, and we remember these sensory experiences years or even decades later, when most of the molecules in our brain have been replaced. Physicists have been fascinated by all of these phenomena, and much more.

In defining a scientific field, it is important to remember that phenomena in nature do not come labeled as belonging to particular disciplines. Thus, the behavior of electrons in solids is of interest to chemists, engineers, and materials scientists, while at the same time being a core topic in condensed matter physics. Similarly, the phenomena of life have attracted the attention of biologists, chemists, engineers, and psychologists, as well as the growing community of physicists whose work is explored in this report. Faced with the same phenomena, scientists from different disciplines ask different questions and search for different kinds of answers. Answers to questions coming from one discipline often lead to new questions or even whole research programs in other disciplines, and this has been especially true at the borders of physics, chemistry, and biology. These rich interactions among scientific cultures are a source of excitement, but complicate any effort to define the boundaries of different fields.

In this first attempt to survey biological physics as a part of physics, the committee has taken a broad view: Biological physics is the effort to understand the phenomena of life in ways that parallel the physicists’ understanding of the inanimate world, prizing the search for new physics that does not have an obvious analog outside the living world. Even though physicists ask different questions, the biological physics community often builds on foundations laid by generations of biologists. Similarly, the answers to questions posed by the biological physics

community, and the tools developed in answering these questions, often have substantial impact on the mainstream of biology. Beyond the traditional confines of biology, the construction of analogs to living systems is an important way of connecting biological physics to the rest of physics and to engineering. This flow of ideas and methods across disciplinary boundaries speaks to the centrality of biological physics in the current scientific landscape.

A Brief History

For centuries, the phenomena of life were seen as fundamental challenges to human understanding of the physical world. In the 17th century, some of the first objects to be discovered with the light microscope were living cells. In the 18th century, modern ideas about charge and voltage emerged in part from explorations of “animal electricity.” In the 19th century, the laws of thermodynamics were not fully established until one could balance the energy budget of animal movements, and the emerging understanding of light and sound was contiguous with the study of vision and hearing, including the nature of the inferences that the brain could draw from data collected by our eyes and ears. In the 20th century, both physics and biology were revolutionized, and there was an extraordinarily productive interaction between the disciplines. From the double helical structure of DNA to magnetic resonance images of our brain in action, the results of this collaboration between physics and biology are central to the modern view of life. But these great successes were codified as parts of biology, not physics. As the 20th century drew to a close, this began to change. Today, the phenomena of life are seen once again as challenges to physics itself.

What is it that changed, making it possible for the study of living systems to be part of physics, rather than being seen only as the application of physics to biology, or some interdisciplinary amalgam? The changes seem to have been gradual, with no obvious single “eureka” moment. Components of these changes were internal to separate communities of physicists and biologists.

From a biological perspective, the sequencing of DNA for whole organisms—studying genomes rather than individual genes—meant that the project of enumerating the molecular building blocks of life was approaching completion. At the same time, cell biologists and physiologists who had focused on how large assemblies of molecules come to life began to exploit new methods adapted from molecular biology, and classical tools of microscopy were revolutionized, in part with ideas from physics. Independently, neurobiologists appreciated that progress in understanding the brain would require making quantitative connections between the dynamics of neural circuits and the macroscopic phenomena of behavior, from perception and decision-making to learning, memory, and motor control. By focusing on microorganisms that reproduce quickly, evolution was being turned

into a subject for laboratory experiments rather than being restricted to field observations. This list is illustrative but far from complete; by the start of the 21st century, almost every subfield of biology was being transformed, dramatically, when compared to the state of the field just one decade before.

From the physicist’s perspective, the last decades of the 20th century brought new views of the interplay between simplicity and complexity. Some of the most beautiful and compelling macroscopic phenomena in real materials, such as critical behavior near the transitions between phases of matter, proved to be universal, quantitatively independent of microscopic detail, and a theoretical framework—the renormalization group—was developed within which these behaviors could be explained and predicted. Strikingly, these same theoretical ideas proved central to the development of the standard model of elementary particle interactions, uniting macroscopic and microscopic physics. In parallel, physicists explored more complex systems, including polymers and liquid crystals, that traditionally had been the domain of chemists and engineers. Where impurities and disorder had once been viewed as distractions from the idealized behavior of perfect crystals, it became clear that disordered materials had their own beautiful and profound regularities. The striking patterns that form in a variety of dynamical systems, from the layering of fluid flows to the branching of snowflakes, were brought into focus as physics problems. Even chaos itself could be tamed. These successes certainly emboldened the physics community, providing examples where it was possible to “find the physics” in ever more complex systems. Rekindling old dreams, many physicists began to wonder if the marvelous phenomena of life itself might be within reach. Looking back, it seems clear that the parallel revolutions in physics and biology encouraged physicists to start asking fundamental questions about some of the most complex systems on Earth, living organisms.

Doing Physics in a Biological Context

The previous paragraphs outline an optimistic view of history, with parallel developments in physics and biology leading toward the emergence of biological physics as a branch of physics. In fact, this was once a minority point of view. Some biologists saw the physicist’s search for simplicity and universality as poorly matched to the complexity and diversity of life on Earth; theory, a crucial part of the physics culture, was openly derided in many, though not all, areas of biology. From the other side, some physicists worried that the phenomena of life might best be described as an accumulation of mechanistic details, with no hint of the unifying principles that are characteristic of physics more broadly. In this view, the complexity and diversity of life are evidence that biology and physics are separate subjects, and will remain separate forever. If this view were correct, then there are useful applications of physics to the problems of biology, but there is no hope for

a physics of life. Establishing the physics of living systems as a field of physics has required a systematic response to this skepticism.

A first step is to turn qualitative impressions into quantitative measurements, taming the complexity and organizing the diversity of life. This proved to be a decades-long project. Many physicists began by searching for the microscopic building blocks of life. This approach is most famously connected to the emergence of molecular biology (see below), but it was repeated many times—the reaction center that allows photosynthetic organisms to capture the energy of sunlight, the ion channels that provide the basis for all electrical activity in the brain, and more. It is an extraordinary discovery that these molecular components are universal and often interchangeable, even across eons of evolutionary change. In many cases, it became possible to make precise measurements on the behavior of these basic molecules, one at a time, giving us a remarkably precise view of life’s mechanisms. These single-molecule experiments have, unambiguously, the “look and feel” of physics experiments.

But much of what fascinates us about life is not visible in the behavior of its isolated parts. To capture these phenomena requires doing physics experiments on intact biological systems, in all their complexity, and this is where there has been dramatic progress in recent years. Thus, beyond observing single molecules of messenger RNA (mRNA) being transcribed, it now is possible to see and count essentially every one of these mRNA molecules, representing information being read out from thousands of genes, across many single cells. Beyond the electrical currents flowing through single ion channels, or the voltages generated by single cells, new methods make it possible to monitor, simultaneously, the electrical activity of hundreds or even thousands of individual neurons in the brain as an animal executes complex behaviors. Beyond the classic experiments of tracking the behavior of a single bacterium, experiments now monitor thousands of individual cells in a growing bacterial community, or thousands of individual birds in a flock, as they engage in collective behaviors. This list is illustrative rather than exhaustive. Importantly, this progress has emerged from a rich interplay between the intellectual traditions of physics and biology, and has touched phenomena across a wide range of spatial and temporal scales.

The last decades thus have seen enormous progress in our ability to “do physics” on intact, functioning biological systems in all of their richness. This involves uncovering precise and reproducible quantitative features of functional behavior in particular systems, and connecting these experimental observations to theoretical ideas grounded in more general principles. This approach has made inroads into the exploration of life on all scales, from single molecules to vast groups of diverse organisms. Ideas about information flow and collective behavior cut across these scales, holding out hope for a more unified understanding. Interaction between theory and experiment now happens, frequently, at the level of detail that we expect in physics, but which not so long ago seemed impossible in a biological context.

What emerges from all of this excitement is a new subfield of physics—biological physics, or the physics of living systems—which takes its place alongside established subfields such as astrophysics, atomic physics, condensed matter physics, elementary particle physics, nuclear physics, and plasma physics. Biological physics, as with the rest of physics, is both a theoretical and an experimental subject, and necessarily engages with the details of particular living systems; searching for simplicity does not mean ignoring complexity, but taming it. The physics of living systems is focused not only on what is interesting for physicists but on what matters in the lives of organisms.

Physics has made progress in part by going to extremes. Elementary particle physics strives to observe matter on the very smallest scales of length and time, while astrophysics and cosmology probe the very largest scales. One theme of modern atomic physics is the study of matter at extraordinarily low temperatures, while plasma physicists are interested in temperatures comparable to those inside the sun. Condensed matter physics studies the unexpected behaviors that emerge when very many particles interact with one another. In this catalogue of extremes, biological physics is concerned with matter that is extremely organized, and organized in ways that make possible the remarkable functions that are the everyday business of life. Biological physics, or the physics of living systems, aims to characterize this organization, to understand how it happens, or even how it is possible.

Reductionism, Emergence, and What Is Special About Life

Perhaps the defining problem of biological physics is to discern what distinguishes living systems from inanimate matter: What are the essential physical principles that enable the remarkable phenomena of life? As in physics more broadly, one can identify two very different approaches to the physics of living systems, reductionism and emergence. The reductionist approach searches for the fundamental building blocks of life and characterizes their interactions, in the spirit of elementary particle physics. In focusing on emergence, the goal is to classify and understand behaviors that arise when many of the building blocks interact, in the spirit of condensed matter physics. Each of these approaches to the physics of life has a substantial history, starting well before biological physics was accepted as a part of physics. Since this is the first decadal survey of the field, it seems appropriate to provide a coherent view of the current state and its historical context.

Reductionism

In the 1950s and 1960s, X-ray diffraction made it possible, for the first time, to visualize the events of life as being embodied in the structure and dynamics of particular molecules. While X-ray diffraction had been discovered and under-

stood in the early years of the 20th century, new physics and chemistry would be needed to determine the structure of such large and complex molecules from their diffraction patterns. The fact that DNA is a helix was evident from the famous photograph 51 (see Figure I.1A), but only because the theory of diffraction from a helix had been developed not long before, in an effort to understand the structure of proteins. The double helix (see Figure I.1B) immediately suggested a theory for how genetic information is encoded in DNA and transmitted from one generation to the next. These experimental and theoretical developments, emerging in large part from physics departments, provided the foundations for modern molecular biology. There was a long path from these early structures to revealing the positions of many thousands of atoms in a protein, going far beyond anything that had been done in the established methods of physics and chemistry. The revolution in our view of biological molecules made possible by X-ray diffraction would be extended by new synchrotron light sources; by developments in nuclear magnetic resonance (NMR) which made it possible to infer the structure of molecules free in solution rather than confined in crystals; and most recently by the addition of new detectors to cryogenic electron microscopes, which have made cryo-EM a widely used tool for determining the structure of proteins at atomic resolution.

Beyond visualizing these building blocks of life, a new generation of single-molecule experiments made it possible to observe and manipulate individual molecules as they carry out their functions—controlling the electrical currents flowing in neurons and muscles, generating forces, reading the information encoded in DNA, and more. This reductionist program continues to generate a stream of exciting results, characterizing the structures and dynamics of ever more complex molecular machines that carry out remarkable functions in living cells. These results are driven by new experimental methods, including a whole family of imaging methods that circumvent the diffraction limit to the spatial resolution of microscopes, allowing us literally to see the mechanisms of life in unprecedented detail (see Figure I.2). These methods required new mastery over the physics of light, connecting to core problems in atomic, molecular, and optical physics. In parallel, these experiments sharpen new theoretical questions about the physical principles that govern these nanoscale systems, connecting to a renaissance in non-equilibrium statistical physics and the thermodynamics of small systems.

Emergence

Life is more than the sum of its parts. This is evident on very large scales, as with the ordered yet fluid behavior of birds in a flock, but also on very small scales, as protein structures emerge from interactions among many amino acids. It is an old dream of the physics community that such emergent phenomena in living systems could be described in the language of statistical mechanics. In the 1980s, concrete statistical mechanics approaches to neural networks led to deeper understanding of memory, perception, and learning, and eventually to today’s revolutionary developments in artificial intelligence. In the 1990s, flocks of birds, swarms of insects, and populations of bacteria inspired genuinely new statistical mechanics problems, which launched the field of active matter. Neural networks and active matter have been the source of new and profound problems in statistical physics, emphasizing how the effort to understand or even describe the phenomena of life leads to new physics.

Today, observations on real flocks and swarms in their natural environments are revealing surprising collective behaviors, beyond the predictions of existing theories of active matter (see Figure I.3), showing that we have not exhausted the new physics to be discovered in these systems. Theories of neural networks, grounded in statistical physics, are having greater impact on thinking about the brain itself as new experimental methods make it possible to monitor, simultaneously, the electrical activity in thousands of individual neurons. On a smaller scale, collective behaviors of molecules are manifest in the discovery that some of the organelles inside cells, and inside the nuclei of cells, are condensed droplets of proteins and nucleic acids (see Figure I.4), an idea that has swept through the cell biology and biological physics communities in less than a decade. There are new statistical phys-

ics approaches to the evolution of protein families and the persistence of ecological diversity, to the dynamics of chromosomes and the mechanics and movement of cells in tissues, and more. Abstract theoretical formulations are being connected to experiments on particular living systems, in unprecedented quantitative detail. Statistical physics provides a unifying language, connecting phenomena across the full range of scales, identifying new kinds of order, and locating living systems in the phase diagram of possible systems.

Searching for What Is Special About Living Systems

Biological physics encourages us to view living systems as examples drawn from a much larger class of possible systems. This view makes clear that what we see in

real organisms is not typical of random choices from this larger space of possibilities. Random sequences of amino acids do not fold into well-defined structures, unlike real proteins; networks of neurons with random connections are chaotic rather than functional. Specifying functions, and performance at these functions, points to limited regions in the space of possible systems. In this way, natural selection can stabilize behaviors that are inaccessible or unstable in the world of inanimate matter, revealing new physics.

A modest example from the 1950s is the idea that the size of lenses in insect eyes is chosen to maximize the quality of images subject to the constraints set by diffraction. This example connects otherwise arbitrary facts about the living world to basic physical principles, quantitatively, and is based on the idea that evolution can select for structures and mechanisms that come close to the physical limits on their performance at tasks crucial in the life of the organism. Ideas in this spirit now appear more widely, both in the abstract and in detailed partnership with experiment: Amino acid sequences could be selected to minimize the competing interactions that would frustrate protein folding; gene expression levels in bacteria could be tuned to maximize the conversion of nutrients into growth; the dynamics

of immunological memory could be selected to optimize the response to the likely time course of antigenic challenges; neural codes could provide efficient representation of information in patterns of electrical activity, or efficient storage of memories in patterns of connections between neurons. Even if real organisms do not reach true optima, these theories provide useful idealizations and more precise ideas about what physics problems organisms need to solve in order to survive. Related work has explored the full functional landscape, constructing models for maximally diverse populations of organisms that reach some criterion level of performance, on average. There is a separate notion of optimizing the volume that this population occupies in parameter space, creating the largest possible target for evolution to find. Theories of evolutionary dynamics explain how organisms can find these targets, and when they cannot. These and other approaches to defining what is special about living systems generate controversy, but also exciting new experiments and theory.

Exploring Big Questions

To emphasize the uniqueness and coherence of biological physics, this report is organized not around particular biological systems but around larger conceptual questions, in the intellectual tradition of physics. These four questions echo the themes above, but are not quite the same. This choice of questions is not exhaustive, nor is it meant to be canonical.¹ Rather, the goal is to capture the spirit of the field at an exciting moment in its development, reviewing successes and pointing to exciting open problems. The committee hopes that the questions are broad enough to encompass the breadth of the field, but specific enough that we will see crisp answers over the next decade. Full exploration of these questions appears in Part I.

What are the physics problems that organisms need to solve? In order to survive in the world, organisms have to accomplish various tasks. They must move toward sources of food, sometimes over long distances, guided only by weak cues about the location of the source. They have to sense useful signals in the environment, and internal signals that guide the control of their own state. They often need to generate dynamics on time scales, which are not the natural scales given by the underlying mechanisms. All of these tasks consume energy, and hence require the organism to extract this energy from the environment. We refer to these various tasks of the organism as “functions,” and this notion of function is an essential part of what sets living matter apart from non-living matter. One of the central problems in biological physics is to turn qualitative notions of biological function into new and precise physical concepts, as described in Chapter 1.

How do living systems represent and process information? A traditional introduction to physics emphasizes that the subject is about forces and energies. This might lead us to think that the physics of living systems is about the forces and energies relevant for life, and certainly this is an important part of the subject. But life depends not only on energy; it also depends on information. Organisms and even individual cells need information about what is happening in their environment, and they need information about their own internal states. Many crucial functions operate in a limit where information is scarce, creating pressure to represent and process this information efficiently; new physics emerges as mechanisms are selected to extract the maximum information from limited physical resources. Understanding the physics of living systems requires us to understand how information flows across many scales, from single molecules to groups of organisms, as described in Chapter 2.

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¹ In particular, the committee chose to resist the language of “grand challenges.” The committee hopes that its account of the many exciting things happening in the search for a physics of life conveys a sense of grandeur for the enterprise as a whole. The grouping of topics into conceptual questions is meant to aid, rather than constrain, the readers’ imagination.

How do macroscopic functions of life emerge from interactions among many microscopic constituents? One of the great triumphs of science in the 20th century was the enumeration and characterization of the molecular components of life. But much of what strikes us as most interesting about living systems emerges from interactions among many of these molecular components. For us as humans, much of what we do happens on the scale of centimeters or even meters. For a single cell this behavioral scale is on the order of microns, something we can only see through a microscope but still a thousand times larger than the nanometer scale of individual molecules. Efforts to bridge these scales, from microscopic to macroscopic, have led to discovery of new physics in novel kinds of ordering, in phenomena ranging from protein folding to flocks and swarms. Many of the central questions in biological physics are aimed at understanding these emergent phenomena, as described in Chapter 3.

How do living systems navigate parameter space? Any attempt at a “realistic” description of biological systems leads immediately to a forest of details. If we want to make quantitative predictions about the behavior of a system, it seems we need to know many, many numerical facts: how many kinds of each relevant molecule we find inside a cell; how strongly these molecules interact with one another; how cells interact with one another, whether through synapses in the brain or mechanical contacts in a tissue; and more. The enormous number of these parameters that we encounter in describing living systems is quite unlike what happens in the rest of physics. It is not only that as scientists we find the enormous number of parameters frustrating, but the organism itself must “set” these numbers in order to function effectively. These many parameters are not fundamental constants; instead, they are themselves subject to change over time, and in different contexts these processes of parameter adjustment are called adaptation, learning, and evolution. Many different problems in the physics of living systems, from bacteria to brains, revolve around how organisms navigate parameter space, leading to physics problems that have no analog in the inanimate world, as described in Chapter 4.

Answers to these abstract questions will have concrete consequences. Physics provides not only compelling explanations for what we see in the world around us, but also precise predictions about what we will see when we look in new places, or engineer new devices and environments. As examples:

• Understanding the physics problems that organisms must solve will identify principles that can be emulated in technology, and constraints that must be obeyed as we try to harness life’s mechanisms for applications.
• Understanding the representation and processing of information in living systems will continue to have impact on artificial intelligence, but also on our ability to control the decisions that cells make in determining health and disease.

• Understanding how macroscopic functions emerge from interactions among microscopic constituents will provide a framework for engineering on many scales, from designing new proteins to coordinating swarms of robots.
• Understanding how living systems navigate parameter space already is having an impact on our ability to predict the evolution of viruses, including those that cause the flu and the current COVID-19 pandemic, and will define the landscape within which medical treatments can be personalized.

More deeply, biological physics holds the promise of unifying ideas, seeing new and common physical principles at work in disparate biological systems. There is the hope of understanding not only particular mechanisms at work in living systems but the principles that stand behind the selection of these mechanisms. Along the way to realizing this promise, the biological physics community will develop new experimental methods that expand our ability to explore the living world, and new theories that expand the conceptual framework of physics. Success will lead to a redrawing of the intellectual landscape, likely in ways that will surprise us. Ultimately, a mature physics of life will change our view of ourselves as humans.

An Emerging Community

The emergence of biological physics is visible not only in its intellectual development but also in the changing sociology of the scientific community. As noted above, some of the first major steps in the modern reductionist approach to the physics of life emerged in the 1950s, especially in the United Kingdom. While housed in physics departments, many of these efforts were supported by the UK Medical Research Council; what grew out of this were institutions such as the Laboratory of Molecular Biology that hosted a new style of biological research, but outside of physics. In this same period, physics departments in the Netherlands had small biophysics groups with efforts on vision, hearing, and photosynthesis, and the descendants of these groups are active today, still in physics departments. The first major U.S. physics department to invest in biological physics was at the University of California, San Diego, which started building a group in the late 1960s. By the late 1970s, there was a substantial effort in biological physics at Bell Laboratories. Today, there is at least some representation of the field on the faculty of almost every one of the top 100 physics doctoral programs in the United States; parallel developments have occurred around the world. There is increasing representation of biological physics at annual conferences of the American Physical Society (see Figure I.5) and at other gatherings of physicists around the world.

A growing number of physics PhD students do their thesis work in biological physics. The National Center for Science and Engineering Statistics (NCSES) tracks

the awarding of PhDs in the United States by field and subfield; since 2004 NCSES has tracked biological physics as a subfield of physics, as discussed in Chapter 8. Although many people have the sense that biological physics is a nascent or minor activity in the physics community, in fact the number of students receiving physics PhDs with a specialization in biological physics has grown, in just 15 years, to a volume comparable to that of well-established subfields (see Figure 8.1 in Chapter 8). Biological physics today is producing the same number of new PhDs annually as did elementary particle physics in the years 2000–2005, and is continuing to grow.

Biology continues to be a much larger enterprise, producing, for example, nearly five times as many PhDs per year as in physics, spread across many more distinct subfields. Many of these subfields—molecular biology, structural biology, cell biology, systems biology, neurobiology, and more—have had, and continue to have, important input from the ideas and methods of physics. Many of these activities are categorized as “biophysics,” and some of the practitioners identify themselves as biophysicists. There is thus a biophysics that is a field within the biological or biomedical sciences, and a biological physics that is a field within physics. Although it might be more accurate to view all of this activity as a continuum, the NCSES

tracks the number of PhDs given in “biophysics (biological sciences)” as well as in “biophysics (physics).” Over the past decade the number of PhDs in biophysics (biological sciences) has declined slowly, while the number in biophysics (physics) has increased, with the total staying relatively constant (see Figure 8.2 in Chapter 8). Physics students who become fascinated by the phenomena of life now have more opportunities to pursue their interests either as physicists or as biologists.

CONNECTIONS

No healthy scientific field exists in isolation. This is especially true for biological physics, which by definition connects both to other parts of physics and to the enormously diverse enterprise of biology. Connections reach even further, to chemistry and engineering, and to medicine and technology, ultimately having deep implications for society. The field has been both a generous provider and an eager recipient of new concepts and principles, new instruments and tools. Part II of this report explores how biological physics has contributed to and benefited from its relationships with other scientific fields, and then describes the relationship of the field to human health, industry, and society more broadly.

Part of the beauty of physics is its interconnectedness, and biological physics is no exception (Chapter 5). Experimentalists studying the molecules of life use X-ray detectors that grew out of elementary particle physics, and particle physicists process their data with machine learning methods that grew out of theories for networks of neurons in the brain. Experiments from the biological physics community provide the most compelling measurements of the entropic elasticity of polymers, a problem that appears in almost all statistical physics textbooks. Polymers, membranes, and other materials inspired by biological molecules were at the origins of soft matter physics, while attempts to describe the collective behavior of flocks and swarms provided a foundation for the field of active matter; soft and active matter now are burgeoning fields of physics, independent of their connection to the phenomena of life. Neurons, the heart, and even slime molds have been a source of problems for the nonlinear dynamics community. Soft matter, nonlinear dynamics, and biological physics come together as these communities try to understand how organisms move, and control their movements, through granular media such as soils and sands. Efforts to observe living systems at ever-higher resolution were one of the primary drivers of a revolution in microscopy, making it possible to see beyond the diffraction limit, routinely (see Figure I.2).

Theories of neural networks are a rich source of problems in statistical physics, so much so that one of the categories for papers on the electronic archive of physics papers, arXiv.org, is “neural networks and disordered systems.” Living systems provided crucial inspiration for early ideas in the thermodynamics of computation, and more recently for developments in non-equilibrium statistical mechanics. As

with the elasticity of polymers, some of the most decisive tests of these ideas have come in single molecule experiments on biological molecules, adapting methods developed in the biological physics community.

All of these examples, and more, emphasize that the physics of living systems is not only a recipient of ideas and methods from other fields of physics, but also a source. The physics problems that arise in thinking about the phenomena of life not only contribute to shaping biological physics, but can take on a life of their own and contribute to the rest of physics.

Biological physics forms a nexus between physics and the many different subfields of biology and chemistry (Chapter 6). In some cases, the flux of ideas and results is from biology to physics: The biological physics community is able to ask new questions about the phenomena of life because of the foundations laid in the mainstream of biology. In return, biological physicists have given the broader biology community new tools for discovery (Chapter 6), and new ideas. The result is a continuum of activity, with different components acquiring different labels at different times (see Box I.1). As emphasized above, the committee takes a broad view of “biological physics” or the “physics of living systems,” terms that we use interchangeably. We intend these terms to describe the exploration of problems that can be seen as part of physics more broadly, even if they can also be seen as parts of other disciplines.

In describing the relationship between biological physics and biology, Chapter 6 focuses on examples where ideas, methods, and results from the physics community have enabled new developments in a broader community of biologists. Increasingly this involves both experimental tools and theoretical structures (see Box I.2). The classic example is how X-ray diffraction, nuclear magnetic resonance, and cryogenic electron microscopy have made it possible to determine the structure of crucial biological molecules down to the positions of individual atoms; these methods have been exported to create structural biology, enabling exploration of a wide range of biology problems (Chapter 6). Thinking about the dynamics of these biomolecules has been driven by the theoretical ideas about energy landscapes which emerged from the biological physics community. The methods of single molecule manipulation and visualization, as well as microfluidics, are at the heart of modern, genome-wide surveys of gene expression in single cells, which are reshaping ideas about the identity of cells and cell types in complex organisms (Chapter 6). The realization that cellular organelles such as the nucleolus, known for a century, really are condensed droplets of proteins and nucleic acids has revolutionized cell biology (Chapter 6). The discovery by biological physicists that cells can sense and respond to the rigidity of their environment has had profound impacts both on developmental biology and on the biology of tumors.

The connections between biological physics and biology have led to numerous applications in public health, which have been particularly highlighted in the past

year by the community’s contributions to the response to the COVID-19 pandemic. As described in Chapter 7, the biological physics community has contributed to epidemiological models that have helped guide public health decisions, and to our understanding of the physics of aerosol droplets and their role in disease transmission. Individual researchers have been central to many local university efforts to expand testing and establish safe campus reopening plans, and to the analysis of the evolutionary dynamics by which variants of concern continue to arise. Work in biological physics also has been critical to our understanding of the SARS-CoV-2 spike protein structure, its interactions with host receptors, with neutralizing anti-

bodies, and with potential drugs. It was also fortunate that fundamental research in structural biology, supported by decades of developments in X-ray crystallography and cryo-EM methods, provided a running start to the development of vaccines for COVID-19 (see Figure I.6). Many of the novel vaccine strategies that were used to deliver vaccines in record time were informed by very detailed knowledge of the structure and dynamics of the spike protein.

Beyond the scale of molecules and cells, physicists have been fascinated by the brain, and in trying to answer their own questions have created methods that have swept through neuroscience more generally, even reaching to psychology (Chapter 6). This has involved a mix of theory and experiment, observing the dynamics of single channels but also building mathematical models that explain how these dynamics shape the computations done by neurons; making it possible to record, simultaneously, the electrical activity of thousands of neurons but also providing theoretical frameworks within which to search for meaningful collective dynamics in these large data sets. Functional magnetic resonance imaging (fMRI) provides a unique ability to observe the activity of the human brain during sensory perception, diverse modes of cognition and decision-making, language processing, social interactions, and motor control tasks. These developments completely reshaped modern discussions of the brain and mind.

Ideas and results from the biological physics community have had extensive impact on health, medicine, and technology more generally (Chapter 7). Walking into a doctor’s office or a hospital, one encounters a myriad of instruments that have grown out of the biological physics community. From Doppler sonography to detect the heartbeat of an infant in utero to surgeries that are guided by sophisticated optical and X-ray imaging, medicine has been revolutionized by the physics-based ability to see inside the human body. The same imaging methods that make it possible to observe live cells at unprecedented resolution have applications in pathology and other diagnosis methods. Prosthetic devices, from cochlear implants for the deaf to brain-computer interfaces for quadriplegics, depend on recording/stimulation methods that grow out of techniques developed in the biological physics community, and theoretical ideas about how information is represented in the brain.

Tools and ideas developed in studying the physics of living systems provide a foundation for the design of new molecules with useful functions, and there is a particularly close connection between theoretical ideas about protein folding and the design of new proteins. Experimental methods for structure determination lead to structure-based drug design, which has become central to the pharmaceutical

industry. Understanding of dynamics and information flow in genetic networks provides tools for synthetic biology, with applications ranging from biofuels to personalized medicine. As noted above, statistical physics approaches to evolution have advanced to the point of predicting the evolution of viruses, feeding into vaccine design.

Ideas and results from biological physics reach beyond health and medicine to technology more broadly. The ease with which we walk or run through complex environments belies the enormously challenging physics problems that complicate efforts to build robots. There are clear paths from ideas in the biological physics community about the mechanics and neural control of movement to robots that implement a broad range of locomotion strategies, from insect-like hexapods to snake-like limbless robots. Similarly, there is a path from physics-based models of neural networks in the brain to the artificial networks that are driving the deep learning revolution, changing forever how humans interact with machines. The circle is closing, as these deep networks become tools in the biological physics laboratory.

Every piece of technology in the modern world has at its foundation remarkable developments in basic science. The path from science to useful technology can be long, and requires its own unique innovations, but without the scientific foundation none of this is possible. While it is not so difficult to trace back in time from useful technology to foundational scientific discoveries, it is much harder to predict which discoveries or even which areas of research will lead to useful technology. More subtly, the more sophisticated the technology the more different threads that need to be woven together. One should thus be careful of the claim that the results of any single scientific field are uniquely responsible for a technological advance. Nonetheless, biological physics has been one essential component of many revolutionary developments.

CHALLENGES

Biological physics is healthy, growing, and exciting. Realizing the promise of the field, however, requires addressing fundamental challenges in how the community is organized, how it is funded, how students are taught, and more generally how aspiring scientists and welcomed and nurtured. These challenges are addressed in Part III of this report.

Building a new scientific field is a multigenerational project. Success in communicating the enticing intellectual opportunities of biological physics, and thus attracting talented young scientists to the field, depends on effective integration of biological physics into physics education, and into education more generally. The importance of this challenge is reflected in the fact that the majority of input that the committee received from the community was about education. This input came

from colleagues at all career stages—from senior faculty to beginning students—and from a wide range of institutions, including community colleges, primarily undergraduate institutions, and major research universities.

There is no unique model for biological physics education that would fit the enormous variety of educational institutions, but there is a foundation on which to build these efforts. Although teaching physics of course involves teaching particular things, there is a unique physics culture at the core of our teaching. This culture emphasizes general principles, and the use of these principles, to predict the behavior of specific systems; the importance of numerical facts about the world, and how these facts are related to one another through the general principles; the value of idealization and simplification, sometimes even to the point of over-simplification; and the deep connections between distant subfields of physics. It is vital that this unifying culture is transmitted to students in biological physics.

Chapter 8 emphasizes that what is needed is not added specialization, but integration: Biological physics needs to be integrated into the core physics curriculum, at all levels. Ideas and results from the physics of living systems convey central ideas in physics: Flying, swimming, and walking provide an engaging universe of examples in classical mechanics; the dynamics of neurons provide examples of electric circuits and current flow; optical trapping and super-resolution microscopy illustrate deep principles of electromagnetism and optics; and the broad optical absorption bands of biological molecules, which literally provide color to much of our world, provide opportunities to build quantum mechanical intuition beyond the energy levels of isolated atoms. The concepts and methods of statistical physics, in particular, are illustrated by numerous phenomena from the living world, on all scales from protein folding to flocking and swarming. In an important counter to the impression that experiments on biological systems are messy, some of the most quantitative tests of simple polymer physics models, and the notion of entropic elasticity, have been done with DNA.

The emergence of a new field also provides the opportunity to rethink the physics curriculum more broadly. In statistical mechanics and optics—two topics that are central to biological physics—there have been revolutionary developments that are hardly reflected in current undergraduate teaching. Modernizing the teaching of these subjects would be good not only for the progress of biological physics but for physics more generally. It is important to emphasize that all of this curricular innovation will require institutional support.

While many of the educational challenges and opportunities created by the emergence of biological physics are internal to physics departments, there also are clear connections to the larger project of nurturing a more quantitative biology. Building on ideas articulated nearly 20 years ago, there continue to be important opportunities for physicists and biologists to collaborate, especially on introductory courses, and this collaboration needs to be supported by college and university

administrators, above the level of departments. These opportunities cannot be realized by making longer lists of courses from multiple departments, but again require an integrated approach, weaving biological physics into the fabric of science education in ways that truly add value for students from all backgrounds.

Realizing the promise of biological physics obviously depends on having sufficient financial support. As explained in Chapter 9, research on the physics of living systems is supported by a surprisingly wide array of federal agencies and private foundations. While this diversity of funding sources has advantages, and speaks to the impact of the field on many different agency missions, it also creates problems. Only one program—the Physics of Living Systems program within the Physics Division of the National Science Foundation (NSF)—sees the field in the broad and coherent form outlined above and described more fully in Part I. But this program represents only a small fraction of the total funding for the field. Other existing funding structures fragment the field in various ways, obscuring its coherence and perhaps even slowing the emergence of unifying ideas and methods. Chapter 9 addresses various ways in which this problem can be overcome, within the overall structures provided by the federal agencies, and touches on important roles of funding agencies like the National Institutes of Health (NIH) and the Department of Energy (DOE) for specific sections of biological physics, even if they do not have a comprehensive and broad-reaching program like NSF.

There also are issues about how support is distributed across the different dimensions of the scientific enterprise. While there is widespread agreement that engagement of undergraduates in research is good for the students and good for the scientific enterprise, there is less appreciation that this engagement builds on high-quality coursework, especially at the introductory level. The committee finds that there remains too sharp a boundary between support for “scientific workforce development” and support for education. At the graduate level, different agencies have different approaches, and there are opportunities to combine best practices. As in many fields, there is a challenge in maintaining a portfolio of mechanisms to fund the spontaneity of individual investigators, the supportive mentoring environments of research centers, and the ambitious projects requiring larger collaborations. As biological physics matures, theory plays a more central role, not just as a tool for data analysis but as an independent activity, and there is an opportunity to develop programs that support this independence, as in other subfields of physics.

Much of the justification for the support of science rests on its impact in technology, medicine, and the economy more broadly, and biological physics has been a major contributor in these areas. As noted above and described more fully in Chapter 7, these contributions range from ultrasound imaging to robotics, from the design of vaccines to artificial intelligence, and more. To maintain the flow of ideas, methods, and results into these more practical domains may require new structures, but certainly will require maintaining robust support for the basic science.

Finally, scientific fields are defined as much by their community as by the list of questions they address. It is important to build a community that is not only productive, but welcoming—welcoming of aspiring scientists from all over the world, and from all the different segments of global society, including those who have been the victims of historical and ongoing injustices. These human dimensions of the scientific enterprise are explored in Chapter 10.

A DECADAL SURVEY IN CONTEXT

This volume stands in a long history of efforts to grapple with the astonishing breadth and depth of physics. The first such survey was released by the National Research Council in 1966.² Twenty years later,³ Physics Through the 1990s divided physics into six subdisciplines, each described in a separate volume: elementary particle physics; nuclear physics; condensed matter physics; atomic, molecular, and optical physics; plasmas and fluids; and gravitation, cosmology, and cosmic-ray physics. There was, in addition, a volume devoted to “scientific interfaces and technological applications,” and that volume contained a section about biophysics. This organization enshrined the view that physicists who became engaged with the phenomena of life became applied physicists, using the tools of the discipline to answer questions outside its boundaries. Such applications could be profound, and they could have enormous impact on society, but they were not seen as being in the intellectual core of physics.

The next cycle of decadal surveys culminated in the report Physics in a New Era, released in 2001.⁴ Strikingly, the physics of biological systems had moved from the chapters on physics and society into the lead section on physics frontiers. By the next cycle, the survey volume on condensed matter and materials physics identified the physics of life as one of six scientific challenges to the field. That discussion concluded:⁵

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² National Research Council (NRC), 1966, Physics: Survey and Outlook—A Report on the Present State of U.S. Physics and Its Requirements for Future Growth, National Academy Press, Washington, DC.

³ NRC, 1986, An Overview: Physics Through the 1990s, National Academy Press, Washington, DC.

⁴ NRC, 2001, Physics in a New Era: An Overview, National Academy Press, Washington, DC.

⁵ NRC, 2007, Condensed-Matter and Materials Physics: The Science of the World Around Us, The National Academies Press, Washington, DC.

Finally, the present volume marks the first time that the National Academies of Sciences, Engineering, and Medicine are surveying biological physics, or the physics of living systems, as a distinct branch of physics, standing alongside other subfields in the decadal survey of physics as a whole. This completes a process that has taken a generation.

As with all decadal surveys, this report is responding to specific questions, and the outline follows this statement of task (Appendix A). As part of the process, the committee gathered community input through written submissions and at two town hall meetings, one at the Biophysical Society Meeting (February 16, 2020) and one held online through the Division of Biological Physics of the American Physical Society after the pandemic resulted in cancellation of the American Physical Society March Meeting (April 16, 2020). The clarity and consistency of community input, on several themes, was striking.

The community admonished the committee to view the field in the broadest possible terms, to articulate the rich connections to other fields while clarifying what makes this field distinct, to emphasize the special role of theory, and to point forward to exciting opportunities. There were clear hopes that the report would highlight the extraordinary contribution that the tools and methods of physics have made to the exploration of life, but not characterize the field merely as the application of physics to biology. Instead, the committee was advised to emphasize the many places where physicists have asked new questions about the living world, introducing new concepts and searching for more general principles that connect myriad particular systems.

The largest component of community input drew attention to the challenges connected to education, with clearly articulated concerns and suggestions coming from young students and from senior faculty, from colleagues at research universities, at primarily undergraduate institutions, and at community colleges. Thoughts about federal support for research rose above the usual concerns about the amount of funding, pinpointing the mismatches between narrowly defined funding structures and the broad scope of the field. Finally, many community members spoke to the unique appeal of the field. Where the physicist’s intellectual style can seem demanding and inaccessible, taking inspiration from the phenomena of life connects these scientific ambitions to the imagination of a wider audience. Many members of the biological physics community see this as a special path to exciting the public about science more generally, to recruiting and retaining a more diverse community of students, and ultimately to shaping how we think of ourselves as humans.

All of these ideas found resonance with the experiences of the committee. We hope that we have done justice to the breadth and depth of the community’s views.

FINDINGS, CONCLUSIONS, AND RECOMMENDATIONS

This introduction and overview concludes with a collection of the committee’s findings, conclusions, and recommendations. Complete discussions of these issues can be found at appropriate places in the main text, as indicated. A compact summary of the recommendations alone can be found in Appendix B.

Transparency

Summarizing the results of the committee’s deliberations provides an opportunity to reflect on the process that led to this report. The National Academies have established a framework for these efforts that is designed to minimize the risks of conflict and bias, and this process has been honed over the long history of the National Academies’ role in advising the nation.⁶ Nominations to the committee are solicited from a broad cross-section of the community, the membership is vetted by the National Academies’ staff and ultimately approved by the President of the National Academy of Sciences in her role as Chair of the National Research Council. The goal is to assemble a group that is balanced along relevant axes, and an important part of the committee’s initial meeting is a full disclosure to one another about individual affiliations and commitments that may bias its views. These disclosures are updated over the course of the committee’s work, and the final editing of the report provided a chance to revisit these issues, which can be subtle. As an example, not only have all committee members been supported by one or more of the federal agencies and private foundations whose funding programs are described in Chapter 9, several committee members have provided advice to these agencies and foundations. In accord with National Academies’ policies, all of these potential problems have been disclosed, and the character of the committee’s discussion was such that no single member’s views were taken as authoritative on any issue. This is a consensus report, and as such, all findings, conclusions, and recommendations have been agreed to by all members.

Emergence of a New Field

The enormous range of phenomena encountered in living systems—phenomena that often have no analog or precedent in the inanimate world—means that the intellectual agenda of biological physics is exceptionally broad, even by the

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⁶ For a brief summary, see National Academies of Sciences, Engineering, and Medicine, “Our Study Process,” https://www.nationalacademies.org/about/our-study-process.

ambitious standards of physics. Part I of this report surveys these exciting developments, organized around the four conceptual questions outlined above, which serve to define biological physics as a field of physics. The seemingly disparate examples encountered in Part I—from the first femtoseconds of photosynthesis to evolution over thousands of generations—are united by their intellectual style. Rekindling century-old dreams, the search for a broad and unifying physics of life now is a realistic agenda. This leads to the committee’s first, overarching conclusion:

Conclusion: Biological physics, or the physics of living systems, now has emerged fully as a field of physics, alongside more traditional fields of astrophysics and cosmology; atomic, molecular, and optical physics; condensed matter physics; nuclear physics; particle physics; and plasma physics.

At the same time that this report marks the emergence of biological physics as a distinct enterprise, it is essential to remember that all fields of physics have extensive connections to one another, and to other disciplines:

Conclusion: Explorations in the physics of living systems have produced results, ideas, and methods that have had enormous impact on neighboring fields within physics, many fields of biology, on the sciences more generally, and on society through medicine and industry.

These observations about the field lead to the first general recommendations:

General Recommendation: Realizing the promise of biological physics requires recognition that is distinct from, but synergistic with, related fields, both in physics and in biology. In colleges and universities it should have a home in physics departments, even as its intellectual agenda connects profoundly to efforts in many other departments across schools of science, engineering, and medicine.

General Recommendation: Physics departments at research universities should have identifiable efforts in the physics of living systems, alongside groups in more traditional subfields of physics.

While biological physicists find homes in a wide range of academic departments, research institutes, and laboratories, representation in physics departments is important for the development of the field. This representation will take different forms in different institutions, but positioning biological physics as a core component of the physics community reinforces an approach to the beautiful and complex

phenomena of the living world through the “physics mindset” that prizes not just simplification but unification—the search for analogies and deeper commonalities among diverse systems. At the same time, this is not enough to ensure the health of the biological physics community.

Specific Recommendation: The biological physics community should support exploration of the full range of questions being addressed in the field, and assert its identity as a distinct and coherent subfield embedded in the larger physics community.

Educating the Next Generation

Establishing a new field and stretching the boundaries of well-established disciplines are multigenerational projects. As emphasized above, the largest components of community input to the committee focused on these educational issues, which are the topic of Chapter 8. The survey of the current educational landscape reveals both striking progress and startling gaps. Some issues are specific to realizing the promise of the field, and some are more general. The analysis begins with issues that are internal to physics departments, and then turns to challenges that can be addressed only by collaboration among faculty across multiple departments. There are special concerns and opportunities in the integration of education and research, and about the trajectories of young scientists after earning their PhD.

Finding: There has been considerable growth in the number of PhD students working in biological physics, so that the field now is comparable in size to well-established subfields of physics. This growth has occurred in less than a generation, and is continuing.

Finding: Biological physics remains poorly represented in the core undergraduate physics curriculum, and few students have opportunities for specialized courses that convey the full breadth and depth of the field.

Conclusion: The current physics curriculum misses opportunities to convey both the coherence of biological physics as a part of physics and its impact on biology.

The lack of coherence in the presentation of biological physics to students is impeding the progress of the field. It is possible for students to receive an undergraduate degree in physics and not even realize that there is a physics of living systems. To address these issues requires rethinking of the core physics curriculum.

General Recommendation: All universities and colleges should integrate biological physics into the mainstream physics curriculum, at all levels.

This integration necessarily will take different forms at different institutions, although there are guiding principles. Chapter 8 explores several places in the physics curriculum where the phenomena of life, and the progress of biological physics, can be used to convey core physics principles, not just in the introductory courses but continuing into more advanced undergraduate material on classical mechanics, electricity and magnetism, quantum mechanics, and statistical mechanics.

Conclusion: There is a need to develop, collect, and disseminate resources showing how examples from biological physics can be used to teach core physics principles.

Specific Recommendation: Physics courses and textbooks should illustrate major principles with examples from biological physics, in all courses from introductory to advanced levels.

Finding: Current undergraduate courses in statistical mechanics often do not reflect our modern understanding of the subject, or even its full historical role in the development of physics. Among other neglected topics, Brownian motion, Monte Carlo simulation, and the renormalization group all belong in the undergraduate curriculum.

Finding: Statistical mechanics courses typically come late in the undergraduate curriculum, limiting the window in which students can explore biological physics with an adequate foundation.

Specific Recommendation: Physics faculty should modernize the presentation of statistical physics to undergraduates, find ways of moving at least parts of the subject earlier in the curriculum, and highlight connections to biological physics.

Finding: Current treatment of optics in the undergraduate physics curriculum does not reflect modern developments, many of which have strong connections to biological physics. Among other neglected topics, optical traps and tweezers, laser scanning, nonlinear optical imaging modalities, and imaging beyond the diffraction limit all belong in the undergraduate curriculum.

Specific Recommendation: Physics faculty should modernize undergraduate laboratory courses to include modules on light microscopy that emphasize recent developments, and highlight connections to biological physics.

Physics departments offer advanced courses that introduce both undergraduate and graduate students to the distinct fields of physics, bridging some of the gap between the core curriculum and the frontiers of modern research. Biological physics courses now stand alongside more traditional courses on astrophysics and cosmology, condensed matter, elementary particles, and so forth.

Conclusion: The great breadth of the field poses a challenge in teaching an introduction to biological physics for advanced undergraduates or beginning graduate students.

General Recommendation: Physics faculty should organize biological physics coursework around general principles, and ensure that students specializing in biological physics receive a broad and deep general physics education.

Almost all fields of science are being revolutionized by the opportunity to gather “big data.” While this often is presented as a recent development, experimental high energy physics and cosmological surveys entered the big data era before it had a name. Today, biological physics is following a similar path, with even modest experiments generating terabytes of data in an afternoon and many experiments reaching the petabyte scale.

Conclusion: Biological physics, and physics more generally, faces a challenge in embracing the excitement that surrounds big data, while maintaining the unique physics culture of interaction between experiment and theory.

Parallel with the emergence of biological physics, biology itself has experienced dramatic changes, with new experimental methods making it possible to explore the living world on an unprecedented scale. Twenty years ago, the BIO 2010 report brought attention to the educational challenges that follow from these developments, emphasizing that quantitative measurements and mathematical analyses would play a central role in the future of the biomedical sciences.⁷ The intervening decades have seen even more rapid progress, in directions that have strong overlap with the interests of the biological physics community. These developments underscore the continued relevance of the message in BIO 2010. As detailed in Chapter 8, there is an opportunity for biology and physics faculty to work together, especially in the design of introductory courses.

Conclusion: There still is room to improve the integration of quantitative methods and theoretical ideas into the core biology curriculum, continuing the spirit of BIO 2010. This remains crucial in preparing students for the bio-

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⁷ NRC, 2003, BIO 2010: Transforming Undergraduate Education for Future Research Biologists, The National Academies Press, Washington, DC.

medical sciences as they are practiced today, and as they are likely to evolve over the coming generation.

In reaching outside the physics department, it is crucial to present not just the application of physicist’s tools to biological problems, but the physicist’s approach to asking questions. While mathematical models and computational analyses have become more widespread in biology and in biology education, there remains a significant challenge in communicating the physics community’s view of the interactions among quantitative experiment, data analysis, and theory. All of these initiatives will need support.

Conclusion: The biological physics community has a central role to play in initiatives for multidisciplinary education in quantitative biology, bioengineering, and related directions.

General Recommendation: University and college administrators should allocate resources to physics departments as part of their growing educational and research initiatives in quantitative biology and biological engineering, acknowledging the central role of biological physics in these fields.

One of the most important products of the research enterprise is educated people. Research and education are intertwined, and this connection has deep implications for our society.

Finding: Meaningful engagement with research plays a crucial role in awakening and maintaining undergraduate student interest in the sciences.

Conclusion: Biological physics presents unique opportunities for the involvement of undergraduates in research at the frontier of our understanding, offering more intimate communities through smaller research groups and providing opportunities for students to enter with varying levels of background knowledge and from a range of undergraduate majors.

Conclusion: Equality of opportunity for students to engage with physics, including biological physics, depends on high-quality introductory courses, emphasizing the interconnectedness of education and research.

Finding: Current models for support of undergraduate research perpetuate a sharp distinction between the core curriculum (education) and the development of the scientific workforce (research). This extends to the fact that science and education are overseen by different standing committees in Congress.

Conclusion: Support for the development of the scientific workforce will require direct federal investment in the core of undergraduate education, especially at an introductory level.

Specific Recommendation: Universities should provide and fund opportunities for undergraduate students to engage in biological physics research, as an integral part of their education, starting as soon as their first year.

Specific Recommendation: Funding agencies, such as the National Institutes of Health, the National Science Foundation, the Department of Energy, the Department of Defense, as well as private foundations, should develop and expand programs to support integrated efforts in education and research at all levels, from beginning undergraduates to more senior scientists migrating across disciplinary boundaries.

Supporting the Field

The health of a scientific field depends on financial support, which needs to match not just the scale of the opportunities but also their character. With the relatively recent emergence of biological physics as an identifiable field, it perhaps is not surprising that existing funding structures are not ideal. This report’s survey of funding, collaboration, and coordination in Chapter 9 begins, however, with some of the many positive features of the current funding environment. In the first instance, this survey is organized agency by agency; note that larger facilities are the subject of a separate discussion:

Finding: The Physics of Living Systems program in the Physics Division of the National Science Foundation is the only federal program that aims to match the breadth of the field as a subfield of physics.

Finding: The United States has had a long-standing role as a leader in the area of biological physics at the molecular scale. Crucial support for this effort comes from Department of Energy investment in programs and user facilities.

Finding: The National Institutes of Health provide strong support for many individual investigators in biological physics, through multiple institutes and funding mechanisms.

Finding: Department of Defense agencies have highlighted multiple areas where the interests of the biological physics community intersect their missions.

Finding: Private foundations have supported programs that engage the biological physics community, often before such programs become mainstream in federal agencies, and have explored different funding models.

Finding: Biological physics has benefited from funding programs that are shared across divisions within individual federal funding agencies, between agencies, and between federal agencies and private foundations.

At the same time, there are features of the funding environment that work against realizing the full promise of the field:

Finding: National Science Foundation award sizes for individual investigators in biological physics have reached dangerously low levels, both in contrast to the National Institutes of Health and in absolute terms.

Finding: Support for the physics of living systems is scattered widely across the National Institutes of Health, making it difficult for investigators to find their way and obscuring the coherence of the field.

Finding: The Department of Energy (DOE) has become a major sponsor of research in biological physics, especially through facilities, without acknowledging the field’s supporting contribution to the DOE mission.

As an alternative to looking at individual agencies, it also is useful to look at how funding is distributed across other dimensions of the scientific enterprise:

Conclusion: As in many areas of science, there is a challenge in maintaining a portfolio of mechanisms to fund the spontaneity of individual investigators, the supportive mentoring environments of research centers, and the ambitious projects requiring larger collaborations.

Finding: Physics programs do not have the stable, programmatic support for PhD students that is the norm in the biomedical sciences.

Conclusion: Accelerating young researchers to independence is critical to empowering the next generation of biological physicists. As in other fields of physics, independent, individual fellowships are an effective mechanism.

Finding: Physics has a unique view of the relationship between theory and experiment, and in many fields of physics this is supported by separate pro-

grams funding theorists and experimentalists. This structure does not exist in biological physics.

Finding: Large-scale physical tools, particularly those for imaging and advanced computing and data, are an important part of the infrastructure supporting thousands of researchers exploring the living world.

Conclusion: There is an opportunity for Department of Defense agencies to use the Multidisciplinary University Research Initiatives Program to support biological physics, and for the National Science Foundation and the National Institutes of Health to expand their support of these mid-sized collaborations.

Stepping back once more to survey the funding landscape as whole:

Finding: Total support for biological physics is barely consistent with the minimum needed to maintain a steady flow of young people into the field. This approximate balance of needs and support leaves significant gaps, and provides little room for new initiatives.

Conclusion: Biological physics is supported by multiple agencies and foundations, but this support is fragmented, obscuring the breadth and coherence of the field. It is dangerously close to the minimum needed for the health of the field.

These observations lead to the committee’s recommendations about financial support for the field (Chapter 9), starting with an overarching response to the concerns outlined above:

General Recommendation: Funding agencies, including the National Institutes of Health, the National Science Foundation, the Department of Energy, and the Department of Defense, as well as private foundations, should develop and expand programs that match the breadth of biological physics as a coherent field.

This recommendation is embodied differently in relation to different agencies:

Specific Recommendation: The federal government should provide the National Science Foundation with substantially more resources to fulfill its mission, allowing a much needed increase in the size of individual grant awards without compromising the breadth of its activities.

Specific Recommendation: The National Institutes of Health should form study sections devoted to biological physics, in its full breadth.

Specific Recommendation: Congress should expand the Department of Energy mission to partner with the National Institutes of Health and the National Science Foundation to construct and manage user facilities and infrastructure in order to advance the field of biological physics more broadly.

Specific Recommendation: The Department of Defense should support research in biological physics that aims to discover broad principles that can be emulated in engineered systems of relevance to its mission.

Specific Recommendation: Industrial research laboratories should reinvest in biological physics, embracing their historic role in nurturing the field.

Supporting the full range of activities in biological physics also involves issues that potentially cut across the agencies:

Specific Recommendation: Federal funding agencies should establish grant program(s) for the direct, institutional support of graduate education in biological physics.

Specific Recommendation: Federal agencies and private foundations should establish programs for the support of international students in U.S. PhD programs, in biological physics and more generally.

Specific Recommendation: Federal agencies and private foundations should develop funding programs that recognize and support theory as an independent activity in biological physics, as in other fields of physics.

Finally, an essential part of the justification for federal support of science is that it generates useful products. The modern vision of the connections among science, technology, and society was articulated 75 years ago, in what can be seen as the founding document for our current system of federal science funding, Science—The Endless Frontier.⁸ Today, a large fraction of the nation’s economy is driven by and depends on technology, and with the benefit of hindsight each of these many technological advances can be traced back to foundational advances in the basic

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⁸ V. Bush, 1945, Science—The Endless Frontier. A Report to the President on a Program for Postwar Scientific Research, U.S. Government Printing Office, Washington, DC.

sciences. But it would have been difficult if not impossible to plan these trajectories from science to technology, to health care, and to economic growth.

General Recommendation: To maintain the flow of concepts and methods from biological physics into medicine and technology, the federal government should recommit to the vigorous support of basic science, including theory and the development of new technologies for experiments.

Human Dimensions of Science

Science is a human activity. Progress depends on recruiting, welcoming, and nurturing a continuous flux of new talent. At the same time, the scientific community has stewardship of precious resources—access to high-quality science education and the opportunity for individuals to pursue their intellectual passions as professional scientists. It is crucial both to maximize the progress of science and to exercise stewardship with justice. These goals are not in conflict. Chapter 10 explores the human dimensions of science, focusing on international engagement and equality of opportunity. Many of the issues are immediately relevant to biological physics, but also much more general, and need to be addressed across science as a whole.

Policies regarding the nation’s engagement with the international scientific community should be grounded in historical facts:

Finding: Science in the United States has long benefited from the influx of talented students and scientists from elsewhere in the world.

Finding: International students have made substantial contributions to the economy of the United States.

Indeed, across the second half of the 20th century in particular, the United States held a privileged position on the world’s scientific stage. This position is at risk:

Finding: Applications to U.S. physics graduate programs from international students have decreased since 2016.

Finding: Many international students find the United States unwelcoming and feel that they have better opportunities outside the United States.

These changes are not coincidental. They have occurred against a backdrop of dramatic changes in U.S. immigration policy, even more dramatic changes in rhetoric, and the prosecution of scientists under the Department of Justice “China Initia-

tive.” While there are specific incidents that need to be addressed, there is a danger that normal components of academic interaction and scientific collaboration are being criminalized.

Finding: Discussions of U.S. policy toward international students and scientists are being driven by concerns about national and economic security.

Conclusion: The open exchange of people and ideas is critical to the health of biological physics, physics, and the scientific enterprise generally. This exchange has enormous economic and security benefits.

General Recommendation: All branches of the U.S. government should support the open exchange of people and ideas. The scientific community should support this openness by maintaining the highest ethical standards.

Concrete steps to implement this recommendation are discussed in Chapter 10. The committee’s suggestions echo and extend those articulated in the recent decadal survey of atomic, molecular, and optical physics.⁹

In principle, issues surrounding international engagement are quite general. In practice, as noted above, current attention is focused on relations with China. As this report is being written, the United States is experiencing a dramatic increase in anti-Asian violence on American streets, even in cities that are home to well-established Asian American communities. This suggests that movement toward more productive policies concerning academic exchange and international collaboration will require reckoning with larger issues about race in our society.

Discrimination based on race has a long history, and this history will not be overcome by actions of the scientific community alone. The challenge for our community is to do everything possible to welcome, support, and nurture talented young people from around the world and from U.S. citizens of all ethnic groups. The structure of physics education creates special circumstances:

Finding: Physics education is layered, with one layer building strongly on the one below. Inequality of access or resources is compounded.

The compounding effect of inequality creates burdens that fall with greater weight on those already subject to systemic discrimination.

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⁹ National Academies of Sciences, Engineering, and Medicine, 2020, Manipulating Quantum Systems: An Assessment of Atomic, Molecular, and Optical Physics in the United States, The National Academies Press, Washington, DC.

Finding: Recent data indicate that while the number of Black students earning physics bachelor’s degrees is growing, the percentage has not increased.

Finding: Historically Black Colleges and Universities have played a crucial role in the scientific and professional education of Black Americans.

Finding: The total number of physics bachelor’s degrees awarded by Historically Black Colleges and Universities has shrunk.

Conclusion: Inequalities of educational opportunity continue to limit the accessibility of physics education for Black students.

Although the experience of each group is unique, one can find related problems for all of the underrepresented groups in the biological physics community. Parallel to the role of Historically Black Colleges and Universities (HBCUs) for Black students are the broader collection of Minority Serving Institutions (MSIs) and Tribal Colleges and Universities (TCUs). There is also a strong connection between the committee’s specific concerns about the education of underrepresented groups and its general concerns about the lack of proper support for core undergraduate education as part of scientific workforce development, as described above.

General Recommendation: Federal agencies should make new resources available to support core undergraduate physics education for underrepresented and historically excluded groups, and the integration of research into their education.

Specific Recommendation: Recognizing the historical impact of Historically Black Colleges and Universities, Minority Serving Institutions, and Tribal Colleges and Universities, faculty from these institutions should play a central role in shaping and implementing new federal programs aimed at recruiting and retaining students from underrepresented and historically excluded groups.

In addition to underrepresentation of ethnic minority groups, it is well known that women continue to be underrepresented in the sciences, and that this gap is particularly large in physics.

Finding: The fraction of women who take a high school physics course is almost equal to the fraction of men, but women comprise only ∼25 percent of students in the most advanced high school courses.

Finding: After steady growth for a generation, the fraction of bachelor’s degrees in physics earned by women plateaued in 2007 at ∼20 percent. The fraction of PhDs in physics earned by women has continued to grow, now matching the fraction of bachelor’s degrees.

Specific Recommendation: In implementing this report’s recommendations on introductory undergraduate education and its integration with research, special attention should be paid to the experience of women students.

Finally, the committee notes that these findings, conclusions, and recommendations regarding the human dimensions of science apply in large part to all areas of physics, and in many cases to the scientific community more generally. There is a sense, however, that biological physics has a special role to play in welcoming a broader community.

Conclusion: The biological physics community has a special opportunity to reach broader audiences, leveraging human fascination with the living world to create entrance points to physics for a more diverse population of students and for the general public.