Nikta Fakhri explores the profound physics behind life through the lens of non-equilibrium systems, using examples like starling murmurations and cellular processes to illustrate how energy, symmetry breaking, and time shape living organisms.
Imagine a crisp fall evening, where the sky transforms into a canvas of amber and violet. Suddenly, thousands of starlings appear, performing a breathtaking aerial ballet known as murmuration. This stunning natural phenomenon holds the secret to the very essence of life. As a physicist, I see profound principles in the flight of these starlings that govern not just birds but all forms of life, from the tiniest cells to vast ecosystems. Join me on a journey to discover the physics of non-equilibrium systems that account for the phenomena of life.
To understand the world around us, we must grasp two fundamental concepts: equilibrium and non-equilibrium.
Equilibrium is a state of balance and stability. To illustrate this, consider a simple bar magnet. If we zoom in, we see that the magnet is composed of countless tiny domains, each resembling a compass needle. In an ordinary piece of iron, these domains point in random directions. However, when an external magnetic field is applied, these domains begin to align. This alignment process exemplifies symmetry breaking in physics. Initially, there is no preferred direction for the domains, representing symmetry. When the external magnetic field is applied, this symmetry breaks, and the system chooses a specific direction by aligning the domains. Once aligned, these domains reach a state of equilibrium—stable, predictable, and unchanging.
In this state, time loses its direction; if we were to play a film of these domains backward, it would look almost identical to the forward version. This is a hallmark of equilibrium. However, this state is not where life thrives; in fact, it is the antithesis of life.
Life, in all its messy, complex, and beautiful glory, exists far from equilibrium. Let’s return to our starlings, a more complex and dynamic example. Each bird in this aerial ballet can be thought of as a flying living compass needle. Just as the alignment of magnetic domains led to the emergence of a macroscopic magnetic field, these birds align their velocities with their neighbors. However, this alignment is ever-changing, responding moment by moment to the movements of neighboring birds.
The result is a mesmerizing display of collective behavior that seems to defy explanation. Some observers see a thrashing serpent, others a billowing cloud, or even a pulsing heart in their formation. The flock moves as one, yet it is composed of thousands of individual decision-makers. This dynamic living system never settles into the quiet equilibrium of our bar magnet; instead, it remains in constant motion, perpetually consuming energy to maintain its intricate dance. This perpetual motion and ceaseless consumption of energy define non-equilibrium.
In this state of non-equilibrium, we find the seeds of life's beauty and complexity. With this understanding, let’s revisit the idea of symmetry breaking. In non-equilibrium systems like our starling flock, symmetry breaking is not a one-time event leading to a stable state. Instead, it is an ongoing process driven by the constant flow of energy and matter.
We observe a cascade of symmetry-breaking events, where each break creates new possibilities, patterns, and structures. It resembles a never-ending game of dominoes, where each fallen piece triggers new and unexpected arrangements. This continuous symmetry breaking in non-equilibrium systems allows for the incredible diversity and adaptability of life. It explains why living systems can respond to their environment, evolve, and create increasingly complex structures.
Combining the ideas of non-equilibrium and symmetry breaking, we can revisit the starling murmuration. This phenomenon exemplifies emergence in a non-equilibrium system. Just as the alignment of microscopic domains in our bar magnet led to the emergence of a macroscopic magnetic field, the coordination among individual starlings leads to the emergence of the flock's complex and fluid-like behavior.
However, unlike the magnet, where emergence leads to a stable equilibrium state, the flock's emergence is dynamic and ongoing. The behavior of the flock continuously emerges from the interactions of individual birds, creating a feedback loop that maintains the system far from equilibrium. This dynamic emergence is a feature of living systems, allowing collections of cells to become thinking, feeling human beings or groups of humans to form complex societies.
The principles of non-equilibrium are not confined to the macroscopic scale of murmurations; they manifest across all scales of life. Let’s zoom in from our murmuration to something much smaller yet equally wondrous: a single living cell.
In my lab, using advanced microscopes, we can observe proteins—the building blocks of life—organizing into waves and spirals of activity that ripple across the surface of a dividing cell. Just as each starling responds to its neighbors to create the sweeping patterns of murmuration, these proteins interact with their molecular neighbors to create patterns that guide the development of life itself. Remarkably, we can use the same principles of non-equilibrium physics to describe these intricate biological processes.
For instance, we have discovered that these protein spirals behave like charged particles, with the core of each spiral corresponding to either a positive or negative charge depending on their rotation. Just like electric charges organize electric fields, these focal points of protein activity orchestrate developmental processes across an entire organism.
As we observe these protein patterns dance across the surface of a dividing cell, we witness something even more fundamental: another symmetry that life breaks—the symmetry of time itself. In the equilibrium state of our bar magnet, time loses its direction. We could play the movie of the magnet forward and backward, and it would look almost identical. However, in the non-equilibrium world of living systems, time is an arrow with a clear irreversible direction.
Consider our murmuration; if we played the video in reverse, it would immediately appear wrong and unnatural. Every wingbeat of a starling, every cell division in a developing embryo, and every heartbeat in your chest represents a step forward in time that cannot be undone.
The most remarkable aspect is that this arrow of time is mathematically related to the flow of energy in living systems. In other words, the direction of time arises from energy dissipation, or how far from equilibrium your system is. We can quantify this using a thermodynamic concept called entropy, which is a measure of disorder. In living systems that continuously exchange energy and matter with their environment, higher energy flows lead to higher entropy production and more irreversible processes. My group's experiments with these protein patterns have confirmed this.
Understanding these fundamental principles of non-equilibrium from cells to starlings raises important questions about our view of the world. Embracing this dynamic perspective of life encourages us to explore new possibilities. For instance, can we use the principles of non-equilibrium physics to design smarter, more adaptable materials? Could studying energy flows in ecosystems help us discover more sustainable ways to produce and use energy? If life is indeed a phenomenon of non-equilibrium physics, should we search for the origins of life in places where energy fluxes create the potential for complexity?
By thinking this way, we open ourselves to discovering new forms of life or lifelike processes that we have yet to imagine. The most amazing part is that we don’t have to look far to see these fundamental processes in action. Our planet is rich with diversity arising from these principles. Consider a coral reef, a delicate balance where countless species thrive within the flow of energy and matter. Or think about the human brain, where billions of neurons fire in coordinated patterns to create what we call consciousness. Even our societies, with their complex economic and social structures, can be understood through the lens of non-equilibrium physics.
As our journey comes to an end, let’s return once more to our starlings, now seen through new eyes. As the last light fades, they bring their ballet to a graceful conclusion, settling into their roosts. Through them, we witness how energy drives matter to self-organize, how breaking symmetries creates diversity, and how time's arrow arises from the processes that drive life.
I will never forget that moment in my lab, watching through the microscope as the protein patterns ripple across the surface of a dividing cell, with energy flowing and conducting this ballet through time. That moment fundamentally shifted my perspective. I realized that life isn't about reaching equilibrium; it's about maintaining this dance far from it. In this constant flux, this journey of becoming, lies the true wonder of existence—a dance we are all part of every moment.
