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You're listening to the nocturnous conversations.

I'm Emily Silverman.

Today we're wrestling with one of the oldest questions in science.

What exactly is life?

For years, we've struggled to answer this question. We've said, maybe living things are defined by reproduction,

or compartments, or metabolism, or being a self-sustaining system.

But it seems like there's always an exception to the rule.

We either rule something in that clearly isn't life, like a car engine that metabolizes gasoline,

or we rule something out that clearly is alive, like a mule, which is sterile and can't reproduce.

It seems no matter what box we try to draw around life, it breaks free from our definitions. But our guest today, astrobiologist and theoretical physicist Sarah Walker,

wonders if maybe it's less important to define what life is and more important to define what life does.

This is at the heart of her work on assembly theory, which we talk about in this episode.

Sarah is the deputy director of the Beyond Center for Fundamental Concepts in Science and a professor

in the School of Earth and Space Exploration at Arizona State University.

She's a fellow at the Bergeren Institute and member of the external faculty at the Santa Fe Institute.

Her lab is internationally regarded as one of the leading labs building fundamental theories about life,

and she recently wrote a book called

Life as No One Knows It, The Physics of Life's Emergence.

...