Review of LIFE AS NO ONE KNOWS IT

A radical new definition of life

We all have an intuition of what life is. Even young kids know the difference between things that are alive and things that are not. But when asked to define what life is, we fumble. And so do scientists. Life, despite its ubiquity, has no single definition. And the “definitions” that do exist are more like lists of features that life is thought to have, but not all life has all features.

This is a big challenge in science. One that caught the attention of Sara Imari Walker early in her career. Now, she has published a book, Life As No One Knows it: The Physics of Life’s Emergence, that lays out the philosophical and physical theory of life – opening up a whole new arena of research.

The problem with the current “definition” of life is that it’s not actionable in science. It’s not measurable. It doesn’t allow one to apply it across forms. And it doesn’t help in our search for alien life. So, it’s a bad definition.

But Walker sees things differently. Her training in theoretical physics allows her to see the problem of life in a new way from biologists, one with solid theoretical foundations that can allow for rigorous scientific testing.

Life As No One Knows It is organized into four parts: the problem of defining life, which focuses on the philosophy of the problem; the new physics of life, which is the ground work of her theory; how her work allows for better searching and creating of alien life; and finally what it means for life’s origins.

The first two chapters dealing with the philosophy of life were my least favorite because most philosophy writing I find less interesting than the rest of it. But she makes a strong case that the problem of life is maybe the “hardest” problem – even more than the problem of consciousness! Spicy.

But the star of the book is assembly theory – her and her colleague Lee Cronin’s theory. Assembly theory “is a framework developed to quantify the complexity of molecules and objects by assessing the minimal number of steps required to assemble them from fundamental building blocks.” The details are a bit beyond my limited formal physics education but it essentially marries physics and selection (including time) to explain biology and other complex things.

The big implications, though, are that assembly theory provides a measurable “assembly index”. According to Walker, life seems defined by objects with an assembly index over 15, and is “the only mechanism by which high assembly object can be produced in abundance in our universe. This is because we expect high assembly objects to form only via the process of evolution and selection.”

Those two paragraphs are trying to do a lot of work which is why Walker wrote a book and not a blog. Beyond the two core chapters about assembly theory and what life is, her work allows a “robustly-falsifiable” hypothesis for searching for alien life. How can we reasonably search for extraterrestrial life if we don’t know what we’re looking for?

The book is really cool. The theory is really cool. This kind of book is why I love reading science books. Am I explaining it well? Not really, I don’t think. Which is why you should read it for yourself.

---

Reader poll

---

Published: August 2024

Publisher: Riverhead Books

Format: Hardcover

---

If you think this sounds interesting, bookmark these other great reads:

• Life's Edge: The Search for What It Means to Be Alive (2021) by Carl Zimmer

• What Is Life?: Understand Biology in Five Steps (2020) by Paul Nurse

---

You may also like…