Science & Nature

Starfish Whisperer Develops a Physical Language of Life

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In a sunny lab at the Massachusetts Institute of Technology, two starfish fought over their prey. Overlapping arms pinned a hunk of thawing cocktail shrimp against the side of the tank. Thousands of suction cups rippled furiously against the glass as each echinoderm struggled to inch the prize toward its own maw.

The physicist Nikta Fakhri looked on with a grin. Not many physicists keep ocean life in their labs, but Fakhri has learned to care for starfish nearly as well as a marine biologist would. And now she’s expanding her menagerie; when a reporter visited recently, a couple of tanks awaited the imminent arrival of sea urchins.

Fakhri has turned to echinoderms in the hope of answering an age-old question: What is life? Or, in one modern formulation: How do the microscopic operations of proteins and cells add up to a clash between hungry starfish?

In the quest to understand how the turning of biological gears produces the unspeakably complex business of living, Fakhri found it natural to turn to physics — a field that’s adept at linking microscopic and macroscopic phenomena. Physicists have learned that temperature emerges from the motions of molecules, magnetism from the orientations of atoms, and superconductivity from the pairing up of electrons. Perhaps life, too, can be elegantly described as a property that can emerge under the right circumstances.

But which circumstances?

By scrutinizing starfish embryos, Fakhri has made strides toward accounting for those circumstances using concepts from physics. She notes that, like other states of matter, life “breaks symmetry” — the growth of an embryo distinguishes its past from its future, for instance. Fakhri has extended the language of symmetry-breaking to describe how proteins and other tiny biological components conspire to enable movement, reproduction and other hallmarks of life. Along the way, she has observed a bizarre new state of matter that may help life influence its surroundings.

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Fakhri grew up in Tehran, Iran. Despite the oppressive environment for women, her parents supported her education, and she eventually made her way to leading institutions abroad. Last year, the American Physical Society recognized her with its Early Career Award for Soft Matter Research, for “groundbreaking and inspiring developments.” Quanta’s recent conversation with Fakhri in her lab on the MIT campus has been condensed and edited for clarity.

What’s the problem with biology, and how might physics help?

Biology is a field that’s really defined by its molecules. It has been very successful at identifying the components and microscopic mechanisms of life. Of course, knowing the details is important, but there’s still a big gap between understanding how, say, a protein consumes energy and understanding how putting all these parts together adds up to lifelike behavior.

Physics takes a somewhat different view. We want to understand the principles that explain things across various scales, from the very small to the very large, using a sort of universal language. For example, we once thought of heat as a fluid. But with thermodynamics, we were able to account for temperature as the movement of molecules.

In the case of life, we would like to know: How do you go from energy dissipation at a single-particle level all the way up to a flock of birds?

That seems like a lofty target, given that a bird is vastly more complicated than a molecule. Could ideas as simple as those that have defined temperature really be usefully applied to living organisms?

Life is undoubtedly complex beyond what we’re used to in physics, but I think that’s an exciting challenge. In the past, physics has shown that this approach of trying to understand a unit as more than the sum of its parts is at the heart of many complex phenomena. I would like to be optimistic that physical rules may allow us to understand what might be the ultimate complexity in the world.

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What’s the primary challenge in developing a physical framework for life?

In physics, we need a system to be at equilibrium to define just about anything. Equilibrium is what lets us understand the pressure of a gas just by knowing the number of molecules in a box, without worrying what kind of molecules they are or what the box is made of. It’s an incredible achievement that we often take for granted. But life is not in equilibrium. There’s a famous saying that when a living system reaches equilibrium, it’s dead. With life, there’s a constant shifting between different types of stability — like how you go from awake to asleep and back to awake again. We need to develop ways of understanding how a living system changes from one such steady state to another.

This accounting can also enrich physics. Physics has been very successful, but it isn’t really equipped to handle the nonequilibrium nature of living systems.

What sort of framework might be able to handle life’s constant changes?

The key to understanding transitions from one state of a system to another is symmetry-breaking. The classic example is a metal becoming magnetized. Initially, you have particles pointing every which way — the metal has “rotational symmetry” because every direction looks the same from the point of view of a particle. Then you switch on a magnetic field and suddenly all the particles orient in one special direction, breaking the symmetry.

You can then define what’s called an order parameter, which is an important way of going from one particle to a description of many particles. In a magnet, the order parameter is the arrow at each point telling you in what direction a bunch of nearby particles are pointing on average. The order parameter allows you to understand what the broken symmetry is and what happens during a transition. But finding the right order parameter is an art.

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That’s a big part of what we’re trying to do with our model system, starfish egg cells. We describe the ways they change in terms of order parameters and broken symmetries.

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