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Life as No One Knows It: The Physics of Life's Emergence
What is life? This is among the most difficult open problems in science, right up there with the nature of consciousness and the existence of matter. All the definitions we have fall short. None help us understand how life originates or the full range of possibilities for what life on other planets might look like.
In Life as No One Knows It, physicist and astrobiologist Sara Imari Walker argues that solving the origin of life requires radical new thinking and an experimentally testable theory for what life is. This is an urgent issue for efforts to make life from scratch in laboratories here on Earth and missions searching for life on other planets.
Walker proposes a new paradigm for understanding what physics encompasses and what we recognize as life. She invites us into a world of maverick scientists working without a map, seeking not just answers but better ways to formulate the biggest questions we have about the universe. The book culminates with the bold proposal of a new theory for identifying and classifying life, one that applies not just to biological life on Earth but to any instance of life in the universe. Rigorous, accessible, and vital, Life as No One Knows It celebrates the mystery of life and the explanatory power of physics.
In Life as No One Knows It, physicist and astrobiologist Sara Imari Walker argues that solving the origin of life requires radical new thinking and an experimentally testable theory for what life is. This is an urgent issue for efforts to make life from scratch in laboratories here on Earth and missions searching for life on other planets.
Walker proposes a new paradigm for understanding what physics encompasses and what we recognize as life. She invites us into a world of maverick scientists working without a map, seeking not just answers but better ways to formulate the biggest questions we have about the universe. The book culminates with the bold proposal of a new theory for identifying and classifying life, one that applies not just to biological life on Earth but to any instance of life in the universe. Rigorous, accessible, and vital, Life as No One Knows It celebrates the mystery of life and the explanatory power of physics.
272 pages, Hardcover
First published August 6, 2024
407 people are currently reading
3761 people want to read
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Displaying 1 - 30 of 141 reviews
August 18, 2024
I have heard the author on multiple podcasts, and hoped this book would fully explain assembly theory. Although it was a worthwhile read, it was very repetitive- I did not feel that I learned much after the first few chapters. I actually had to read the Nature article (https://www.nature.com/articles/s4158...) to have a better understanding of the theory.
November 20, 2024
Listen, Douglas Adams is wrong: the answer to the great question, Life, the Universe and Everything, is not 42, but 15!
The difference between life and non-life is the construction steps (not to be confused with steps your builder takes to build your house), information plays a big role, and other related topics are what in Life as No One Knows It. It is called Assembly Theory, a scientific framework that explains the origin of life and evolution. It is yet to be proved, but what a fascinating theory, and potentially verifiable!
Sara Imari Walker is an American theoretical physicist, astrobiologist and a co-creator of Assembly Theory. The link is their paper published in Nature.
Life as No One Knows It is a longer version of the paper sans graphs and equations. For the theory itself, the paper is probably a better source. I find my mind wandering while reading the first two chapters, but I like Chapter Four: Aliens and Chapter Five: Origins very much. Using the theory as a guiding principle, if alien life is found on other planets or created on our planet, it would induce a paradigm shift indeed. Based on the theory, one thing is clear: RNA is a prerequisite for life on our planet, but not for all life; we probably won’t know it when we see an alien, and they are not like us. We, as RNA life, are most likely unique (meaning: alone) in the universe.
The difference between life and non-life is the construction steps (not to be confused with steps your builder takes to build your house), information plays a big role, and other related topics are what in Life as No One Knows It. It is called Assembly Theory, a scientific framework that explains the origin of life and evolution. It is yet to be proved, but what a fascinating theory, and potentially verifiable!
Sara Imari Walker is an American theoretical physicist, astrobiologist and a co-creator of Assembly Theory. The link is their paper published in Nature.
Life as No One Knows It is a longer version of the paper sans graphs and equations. For the theory itself, the paper is probably a better source. I find my mind wandering while reading the first two chapters, but I like Chapter Four: Aliens and Chapter Five: Origins very much. Using the theory as a guiding principle, if alien life is found on other planets or created on our planet, it would induce a paradigm shift indeed. Based on the theory, one thing is clear: RNA is a prerequisite for life on our planet, but not for all life; we probably won’t know it when we see an alien, and they are not like us. We, as RNA life, are most likely unique (meaning: alone) in the universe.
August 29, 2024
Brilliantly written and accessible, thoroughly enjoyed this one. audiobook read by the author is fab too. rtc later, maybe.
December 7, 2024
I was profoundly disappointed in this book; a result partly borne of my own personal excitement for the book after being introduced to assembly theory on the Santa Fe Institute’s podcast series. I finished this believing that podcast series is immensely better at explaining assembly theory, and also excited for someone else to write about it.
Aside from my own self-induced letdown, this book is objectively not a great read. It’s only 242 pages yet the first 90, a full third, comprise the introduction. That’s the page she first introduces the term “assembly theory.” For a book that underpins its entire thesis on a new theory, it’s weird that it’s introduced so late.
Her explanations drift quite a bit. She often says she’s going to explain something but spends several pages drifting into pontification rather than explanation.
The style of the book itself is weird as well. She refers to people by their first name. Far be it from me to enforce rules of formality on someone but I find it bizarre that after introducing someone of John von Neumann’s stature, she calls him Johnny thereafter, the same way she refers to a colleague she actively works with named “Mike.”
But ultimately my criticism is that this book is confused as to whether it’s about her personal discovery and journey to understanding life, or whether it’s meant to explain the concepts. She provides uninteresting details about a lab in Glasgow, or pages referencing meta-analyses of paradigm shifts by introducing Thomas Kuhn. Overall she does this more than explaining her actual theories or attempted paradigm shift. It’s hard to tell what her goal is. The book ends abruptly with no synthesis, or conclusion as if she just decided to stop writing and move on to something else.
Aside from my own self-induced letdown, this book is objectively not a great read. It’s only 242 pages yet the first 90, a full third, comprise the introduction. That’s the page she first introduces the term “assembly theory.” For a book that underpins its entire thesis on a new theory, it’s weird that it’s introduced so late.
Her explanations drift quite a bit. She often says she’s going to explain something but spends several pages drifting into pontification rather than explanation.
The style of the book itself is weird as well. She refers to people by their first name. Far be it from me to enforce rules of formality on someone but I find it bizarre that after introducing someone of John von Neumann’s stature, she calls him Johnny thereafter, the same way she refers to a colleague she actively works with named “Mike.”
But ultimately my criticism is that this book is confused as to whether it’s about her personal discovery and journey to understanding life, or whether it’s meant to explain the concepts. She provides uninteresting details about a lab in Glasgow, or pages referencing meta-analyses of paradigm shifts by introducing Thomas Kuhn. Overall she does this more than explaining her actual theories or attempted paradigm shift. It’s hard to tell what her goal is. The book ends abruptly with no synthesis, or conclusion as if she just decided to stop writing and move on to something else.
Read
October 4, 2025A lot of the books I have read in the recent past have to do with trying to get a working definition of life and/or consciousness. I picked this one up to get more perspectives in that direction, but it gave me something else by shifting the frame. At exactly halfway through the book, there is a line that goes "what will really be alien are examples of life (biological or technological) that have traversed a completely different evolutionary trajectory than we have." And that's important because if we keep looking for markers based on life on earth, we may not find it anywhere else in the universe. It's thus important to find a framework that is agnostic of life as we know it, so that we have a measurable way of recognising and classifying signs of life/intelligence when we come across it.
Science has domains and subdomains and that has probably prevented it from looking at life in a more holistic way. Physicist and astrobiologist Sara Imari Walker is well placed to do that. Her approach to solving it is the Assembly Theory, a framework that tries to redefine our understanding of life through the complexity of objects and the informational processes that lead to their formation. The bias is thus more towards physics than biology, emphasising the former's role in the emergence of complex structures. Life is information - from molecules to minerals to RNA to the artefacts we build.
The theory, from what I understood, works around two concepts - assembly index, and copy number.
The assembly index is the minimum number of steps required to construct a specific object from basic building blocks, and copy number is the number of identical copies of that object exist within a system. The idea is that between these, we can determine the distinction between living and non-living entities. Objects with a high assembly index are associated with life since they are less likely to form spontaneously, and instead are more likely a result of information propagated across space and time, leading to the emergence of complex structures.
I preferred the first half of the book (why and what) over the second part (how) because the latter got a bit too technical for me. The former had all of the stuff that interested me. For instance, entropy and the concept of negative entropy, free will and how we have it but not always, the 'hard problems' of consciousness (how and why physical processes in the brain give rise to subjective experience), matter (things can be observed only in terms of interactions) and life (that abstractions i.e. information matter in determining what can exist).
"The origin of life is the unification point between biology and physics. It is where the universe described by the fixed laws of known physics - a universe without us - must yield to the seemingly endless forms of complexity generated in the evolution of our biosphere or any other. This unification must happen in what we call chemistry, because chemistry is the first thing the universe builds where not every object can exist. This leads to the possibility of an unfolding of different forms in different locations - what we might call different instances of "life". Not all chemical possibilities can exist all at once; the ones that do exist must therefore be selected. This is why chemistry also happens to be where life can first emerge."
As our explorations in AI and space accelerate, a means to identifying and classifying life, both on our planet and elsewhere in the universe is important. The book provides a view of what is happening on that front. I felt that the first half was quite accessible, but the second half went into thesis mode.
Science has domains and subdomains and that has probably prevented it from looking at life in a more holistic way. Physicist and astrobiologist Sara Imari Walker is well placed to do that. Her approach to solving it is the Assembly Theory, a framework that tries to redefine our understanding of life through the complexity of objects and the informational processes that lead to their formation. The bias is thus more towards physics than biology, emphasising the former's role in the emergence of complex structures. Life is information - from molecules to minerals to RNA to the artefacts we build.
The theory, from what I understood, works around two concepts - assembly index, and copy number.
The assembly index is the minimum number of steps required to construct a specific object from basic building blocks, and copy number is the number of identical copies of that object exist within a system. The idea is that between these, we can determine the distinction between living and non-living entities. Objects with a high assembly index are associated with life since they are less likely to form spontaneously, and instead are more likely a result of information propagated across space and time, leading to the emergence of complex structures.
I preferred the first half of the book (why and what) over the second part (how) because the latter got a bit too technical for me. The former had all of the stuff that interested me. For instance, entropy and the concept of negative entropy, free will and how we have it but not always, the 'hard problems' of consciousness (how and why physical processes in the brain give rise to subjective experience), matter (things can be observed only in terms of interactions) and life (that abstractions i.e. information matter in determining what can exist).
"The origin of life is the unification point between biology and physics. It is where the universe described by the fixed laws of known physics - a universe without us - must yield to the seemingly endless forms of complexity generated in the evolution of our biosphere or any other. This unification must happen in what we call chemistry, because chemistry is the first thing the universe builds where not every object can exist. This leads to the possibility of an unfolding of different forms in different locations - what we might call different instances of "life". Not all chemical possibilities can exist all at once; the ones that do exist must therefore be selected. This is why chemistry also happens to be where life can first emerge."
As our explorations in AI and space accelerate, a means to identifying and classifying life, both on our planet and elsewhere in the universe is important. The book provides a view of what is happening on that front. I felt that the first half was quite accessible, but the second half went into thesis mode.
Read
July 23, 2024compelling new framework for an area of research i knew very little about before. she does an excellent job of situating the reader within the norms of the field while also critiquing it and charting a new path forward. very readable explanation of a highly abstract theory. will be curious to see whether assembly theory gets picked up by the field as a whole.
September 26, 2024
“We don’t want to conquer the cosmos, we simply want to extend the boundaries of Earth to the frontiers of the cosmos…. We are only seeking Man. We have no need of other worlds. We need mirrors.”
That’s Lem in Solaris. Couldn’t help but think of that once I got to the end of Life As No One Knows it – which is generally an astrobiologist’s attempt to explain and utilize assembly theory in order to solve one of the great scientific mysteries of Earth – how did life evolve from non-life? And what makes “life,” life? Walker does call herself an astrobiologist (or an exobiologist) – a still relatively new scientific focus that encompasses several branches of science: biology, physics, chemistry, geology, astronomy, math, quantum physics – pretty much all sciences. It’s similar to looking at the history of thought and going back to the Greek philosophers and seeing that philosophy and mathematics are being born out of the same petri dish of thought. Once you start going back billions of years of deep time to try to find that spark – something that might have happened on a subatomic level – that turned a rocky planet into a lush green planet capable of sustaining carbon-based life (as we know it!) – you’re looking for the building blocks of many different sciences that have been expounded upon for hundreds of years.
I’m fascinated by this mystery – I’ve read several different books that also try to find this moment, and use different approaches to try to find it. Walker presents assembly theory which to me (again, I was a film student, much of this is beyond me) feels like an attempt to create a new language with which to explore the mysteries of our planet billions of years ago. They’ve tried to re-create it in test tubes (Miller-Urey in the 50s), have plumbed the depths of the oceans to find forms of life on earth that are completely different from life on the surface. Walker is taking a theoretical approach, that even with these technological advances the language with which to describe the process of the formation of life is inadequate. Assembly theory tries to put the factors of the building blocks as universals – how things form that would work in any atmosphere and environment. By using this new physics, and hopefully by determining how we got here, we could start to posit if there are other life forms in the cosmos. I’m guessing by using assembly theory with the age of a planet, its rotation, orbit, chemical makeup, distance from its star – all of these factors, there’s a way to determine if life could be evolving on that planet.
Again – she lost me a bit in places in the earlier chapters of the book – her prose is a bit flowery which makes some of the early chapters feel a bit more philosophical than most of the pop science I read – it is describing a “theory” so that does make sense. She describes it as a “physics” but for some reason my instinct keeps wanting me to call it a “language” – I do see mathematics as a language so that might be why I keep doing it. I will say that the last chapter – Planetary Futures – I thought was fantastic and in some way might have worked as an introductory chapter. Walker addresses our technological present (the internet, AI, etc) and comes to a place I’m starting to see in other contemporary science books (post 2020 – specifically Journey of the Mind about the evolution of thought, and Where We Meet the World about perception) that technology has brought us to a place where we need to think about humanity on the planet as a oneness – that we are all connected now via technology, and we are seeing that our actions affect everyone else. I would love to see countries and languages dissolve – we can use translators through our phones that can translate foreign languages (and non-hearing people) in real time. So why cling on to old barriers? “That’s the way it’s always been.”
Again, I’m not equipped enough to tear apart a new physics, but I enjoyed reading about it and I hope that if anyone figures out how a “dead” rock managed to assemble subatomic particles in such a way that they were able to protect themselves, grow, replicate/reproduce, and communicate with each other in ways that they could build cities and make art, and thrive (as we know the meaning of the word thrive), what else could we assemble?
Also thought of Greg Egan’s Diaspora, which takes place in the far future and we finally find another life form on a distant planet – all of which resemble giant carpets of kelp floating on an ocean surface. The communication with this alien form was the process of analysis we undertake to determine what it is – applying the scientific process to the mysterious form. And in a way, Walker is attempting to do just that, to find a physics (or language or scientific process) to explore when we were the alien form on earth. I would also recommend that Walker watch the movie The Beach House. ;)
That’s Lem in Solaris. Couldn’t help but think of that once I got to the end of Life As No One Knows it – which is generally an astrobiologist’s attempt to explain and utilize assembly theory in order to solve one of the great scientific mysteries of Earth – how did life evolve from non-life? And what makes “life,” life? Walker does call herself an astrobiologist (or an exobiologist) – a still relatively new scientific focus that encompasses several branches of science: biology, physics, chemistry, geology, astronomy, math, quantum physics – pretty much all sciences. It’s similar to looking at the history of thought and going back to the Greek philosophers and seeing that philosophy and mathematics are being born out of the same petri dish of thought. Once you start going back billions of years of deep time to try to find that spark – something that might have happened on a subatomic level – that turned a rocky planet into a lush green planet capable of sustaining carbon-based life (as we know it!) – you’re looking for the building blocks of many different sciences that have been expounded upon for hundreds of years.
I’m fascinated by this mystery – I’ve read several different books that also try to find this moment, and use different approaches to try to find it. Walker presents assembly theory which to me (again, I was a film student, much of this is beyond me) feels like an attempt to create a new language with which to explore the mysteries of our planet billions of years ago. They’ve tried to re-create it in test tubes (Miller-Urey in the 50s), have plumbed the depths of the oceans to find forms of life on earth that are completely different from life on the surface. Walker is taking a theoretical approach, that even with these technological advances the language with which to describe the process of the formation of life is inadequate. Assembly theory tries to put the factors of the building blocks as universals – how things form that would work in any atmosphere and environment. By using this new physics, and hopefully by determining how we got here, we could start to posit if there are other life forms in the cosmos. I’m guessing by using assembly theory with the age of a planet, its rotation, orbit, chemical makeup, distance from its star – all of these factors, there’s a way to determine if life could be evolving on that planet.
Again – she lost me a bit in places in the earlier chapters of the book – her prose is a bit flowery which makes some of the early chapters feel a bit more philosophical than most of the pop science I read – it is describing a “theory” so that does make sense. She describes it as a “physics” but for some reason my instinct keeps wanting me to call it a “language” – I do see mathematics as a language so that might be why I keep doing it. I will say that the last chapter – Planetary Futures – I thought was fantastic and in some way might have worked as an introductory chapter. Walker addresses our technological present (the internet, AI, etc) and comes to a place I’m starting to see in other contemporary science books (post 2020 – specifically Journey of the Mind about the evolution of thought, and Where We Meet the World about perception) that technology has brought us to a place where we need to think about humanity on the planet as a oneness – that we are all connected now via technology, and we are seeing that our actions affect everyone else. I would love to see countries and languages dissolve – we can use translators through our phones that can translate foreign languages (and non-hearing people) in real time. So why cling on to old barriers? “That’s the way it’s always been.”
Again, I’m not equipped enough to tear apart a new physics, but I enjoyed reading about it and I hope that if anyone figures out how a “dead” rock managed to assemble subatomic particles in such a way that they were able to protect themselves, grow, replicate/reproduce, and communicate with each other in ways that they could build cities and make art, and thrive (as we know the meaning of the word thrive), what else could we assemble?
Also thought of Greg Egan’s Diaspora, which takes place in the far future and we finally find another life form on a distant planet – all of which resemble giant carpets of kelp floating on an ocean surface. The communication with this alien form was the process of analysis we undertake to determine what it is – applying the scientific process to the mysterious form. And in a way, Walker is attempting to do just that, to find a physics (or language or scientific process) to explore when we were the alien form on earth. I would also recommend that Walker watch the movie The Beach House. ;)
August 13, 2025
I lasted until page 106, when I realized that besides the abominable style (perhaps because of the style?) that I wasn’t really interested.
Quoting from the abstract of her 2023 paper about Assembly Theory as a basis of life… “We introduce a measure called assembly (A), capturing the degree of causation required to produce a given ensemble of objects. This approach enables us to incorporate novelty generation and selection into the physics of complex objects. It explains how these objects can be characterized through a forward dynamical process considering their assembly.” (https://www.nature.com/articles/s4158...) With 391,000 accesses through the website, clearly a BIG paper. Though what assembly theory has to do with life was still not evident by nearly half the book – I admit this is probably on me because: DNF!
The author is a classically trained theoretical physicist (she reminds us too many times) who has many colleagues, co-authors and friends that - after a glancing introduction - she refers to by first names only (Michael, David, Lee,…). She also refers to “Albert” (Einstein) and “Charles” (Darwin). Too much: a) friendly name dropping, b) interjecting herself into the science, c) philosophizing – although maybe theory in this area demands it. BTW, she doesn’t get to assembly theory until page 95 – and then starts by assembling legos. At which time I was thoroughly disinterested in the entire question. Maybe I'm just not a lego person.
I want to love a woman working in theoretical physics – do I feel guilty? Yes. But I can’t read any more. Good on all you folks who gave it 5 stars.
Quoting from the abstract of her 2023 paper about Assembly Theory as a basis of life… “We introduce a measure called assembly (A), capturing the degree of causation required to produce a given ensemble of objects. This approach enables us to incorporate novelty generation and selection into the physics of complex objects. It explains how these objects can be characterized through a forward dynamical process considering their assembly.” (https://www.nature.com/articles/s4158...) With 391,000 accesses through the website, clearly a BIG paper. Though what assembly theory has to do with life was still not evident by nearly half the book – I admit this is probably on me because: DNF!
The author is a classically trained theoretical physicist (she reminds us too many times) who has many colleagues, co-authors and friends that - after a glancing introduction - she refers to by first names only (Michael, David, Lee,…). She also refers to “Albert” (Einstein) and “Charles” (Darwin). Too much: a) friendly name dropping, b) interjecting herself into the science, c) philosophizing – although maybe theory in this area demands it. BTW, she doesn’t get to assembly theory until page 95 – and then starts by assembling legos. At which time I was thoroughly disinterested in the entire question. Maybe I'm just not a lego person.
I want to love a woman working in theoretical physics – do I feel guilty? Yes. But I can’t read any more. Good on all you folks who gave it 5 stars.
October 10, 2024
What is life? This book explores some cool new ideas. Fast, succinct, enjoyable, thought-provoking.
Thanks for the rec DP!
Thanks for the rec DP!
August 7, 2025
Great read. I was able to understand the use of assembly theory (sometimes with the help of chatGPT) to open new doors in understanding and maybe discovering the origin of life.
Read
May 21, 2025A fascinating look at the intersection of philosophy, biology, and physics in regards to emergent life. The first I've heard of 'assembly theory' but I like it. My only gripe would be it sometimes gets a bit too technical and academic for the layperson (me) that sometimes left me lost, but never too an egregious degree.
July 17, 2024
Walker attempts to apply assembly theory to better understand what life is, how it may have originated, and what it might look like on other planets. What is assembly theory? To grossly simplify (I am not at all an expert), it is a relatively new (and in my understanding somewhat controversial, though Walker does not dwell on that) approach to physics that defines objects in part by how many steps are required to put them together. So, a small simple molecule is “low assembly,” you just throw a couple atoms together. But a human, a genome, or a rocket ship are high assembly, with a lot more parts that are a lot more complex to put together. In fact, Walker argues, such objects *can’t* be put together without some mechanism for memory or information storage—random chance won’t cut it.
All that is a bit of a mouthful; Walker explains it mostly clearly but it’s definitely not light reading. It’s interesting stuff, though. My biggest critique is that (by her own admission) when she talks about life she typically is thinking about humans and our technology, or else very early unicellular life. Plants, fungi, and nonhuman animals make very few appearances, when I think more varied examples could have helped clear things up. I am reminded of the Ted Chiang story “The Great Silence,” narrated by a parrot who laments that humans are more interested in making contact with alien civilizations than in actually listening to the species with whom we share Earth.
All that is a bit of a mouthful; Walker explains it mostly clearly but it’s definitely not light reading. It’s interesting stuff, though. My biggest critique is that (by her own admission) when she talks about life she typically is thinking about humans and our technology, or else very early unicellular life. Plants, fungi, and nonhuman animals make very few appearances, when I think more varied examples could have helped clear things up. I am reminded of the Ted Chiang story “The Great Silence,” narrated by a parrot who laments that humans are more interested in making contact with alien civilizations than in actually listening to the species with whom we share Earth.
October 5, 2024
Quite a ride, but that's theoretical physics and astrobiology for you. While being an interesting introduction to assemblage theory in this book enthusiasm and hype seem do more of the heavy lifting than plausibility. The praise of Lee Cronin's work gets a bit tired as does the constant name-dropping of other scientists as "friends". I really wish there was more actual underpinning of their ideas but especially the last part slips toward blind "tech/AI as next step of evolution" hype without arguments. Still, I'm glad I read it because it was a nice challenge for thoughts.
November 15, 2024
Sara Walker very quickly rose to the top of my life-science/physics scientist list after listening to her on the Lex Friedman podcast. I was elated to find out she just published this book and it was worth every page of reading. She dives much deeper into assembly theory than in surface-level interviews she's done on the topic. Fwiw, I'm sold and now believe her work on the origins of life with her partner, Lee Cronin, is an extremely viable foundational theory and major contribution to the sciences. I could read this book seven times and not lose interest. Thank you Sara for this gift.
October 1, 2024
Quantum physics explains the small. General relativity explains the large. But what about all the stuff in between? What about, say, us? LIFE AS NO ONE KNOWS IT introduces you to assembly theory, which treats all matter as information and all creations as stacked lineages of causal information, subject to natural selection. Could such a radical theory explain the origins of life? Or outline how we might identify the existence of extraterrestrial beings? Fuck yeah it could. And so much more.
November 7, 2024
"You know, I can understand nine words in that book now." - Billy Madison
This was the October pick for The Planetary Society Book Club. Let me start off by saying that it is clear the Sara Imari Walker is extremely intelligent. I'm certainly not as smart as her, but I, and I write this with the utmost humility, am a pretty smart guy. Lastly, I've never felt more like a dum-dum than while reading this book.
From what I could understand about the concepts of assembly theory, which wasn't much, it seems like an interesting theory about how life came to be from the standpoint of physics. In other words, how did life form from nothingness? But not in the "oh, God created man" faith sort of thing, but in the "what are the physics behind life emerging and what would that look like elsewhere?" Would we even know life if we found it? A lot of scientists searching for life on other worlds go by "we'll know it when we see it;" but Sara posits that we may not know it when we see it without first understanding what we're even looking for. What is life? When does something become alive? When I'm alone, am I actually dead until someone interacts with me?
And... that's about how much I understood. I didn't understand exactly what assembly theory is enough to be able to describe it here. I know she used a LEGO example, which kind of made it easier to understand, but also not really.
At any rate, I'm not going to sit here and debate anyone on how life came to be. If you want to leave it at God, that's fine. If you want more than that, I'm probably in that boat too. If you're a scientist, but you totally disagree with assembly theory, who am I to judge?
So at this point I'll shift to the basic readability of this book. And really, there's nothing basic about it. Sara can write - that much is clear. But I wouldn't put her in the Carl Sagan, Bill Nye, or Neil deGrasse Tyson world of making science reachable to the lay person. Carl, Bill, and Neil have all popularized science for the general public. They made it so that dum-dums like me could get a grasp and even feel the awe of the cosmos. Unfortunately, Sara wasn't quite as captivating in her writing.
There were too many big words that slowed down the reading. The science, when she tried to explain it, still went over my head. The LEGO example I've already mentioned was probably the closest I could get to even a minute understanding of what she was trying to get across, but even that was a lot to conceptualize. I assume someone with some training in physics probably got through this quite easily. But this didn't really feel like a science popularization book to me. It just wasn't super accessible to me.
Something that Sara did throughout the book, which I saw another Goodreads review note, was the constant name-dropping of other famous scientists, many of whom she referred to as friends, or colleagues, or fellow whatevers. I get it. She's in a cohort of some of the most intelligent people on the planet. But it seemed a little self-aggrandizing at times. Not all of her references were that way, though. She'd refer to Albert Einstein or Erwin Schrodinger from time to time, referencing Albert's general theory of relativity or Erwin's work in quantum mechanics.
At this point you may be feeling a little uncomfortable that I refer to everyone so casually by their first names. Well, guess what - I was pretty uncomfortable with it too. Referring to historical figures by their first names feels too casual and kind of diminishes their gravitas. Basically, the tone of familiarity throughout this text doesn't match the weight of the subject. Perhaps the author was trying to make the subject matter feel more casual or informal by doing this. But it was simply too jarring. It felt like she was overreaching in an attempt to make these figures feel relatable. I'm sure there was a sense of consistency that she (or her editors) wanted to keep when referring to individuals that she does know personally. But in a science book especially I expect everyone to be referred to by their last name. Even if it's Doctor or Professor So-and-so.
A lot of people don't rate non-fiction books because it can be taken the wrong way. By this I mean that if you give a non-fiction book five stars, what is that saying? That the book was well-written? That you agree with the subject matter? What about memoirs, autobiographies, or biographies?
My rating of non-fiction books is simply in relation to the readability and understandability of the book in question. If I don't agree or like the subject matter, I probably just won't finish the book. With that in mind, I'm giving this book 2.5 out of 5 stars. What Sara was able to do here was get me interested in learning more about this theory of how life emerges from non-life. It is something I wouldn't shy away from if I encounter it elsewhere. Her examples throughout were good, but not always reachable or conceptualizable to me. I'm not making an overall judgment of the author as I could imagine picking up another one of her books. But I might go into it a little more cautiously and aware that it may be a slow burn for me.
This was the October pick for The Planetary Society Book Club. Let me start off by saying that it is clear the Sara Imari Walker is extremely intelligent. I'm certainly not as smart as her, but I, and I write this with the utmost humility, am a pretty smart guy. Lastly, I've never felt more like a dum-dum than while reading this book.
From what I could understand about the concepts of assembly theory, which wasn't much, it seems like an interesting theory about how life came to be from the standpoint of physics. In other words, how did life form from nothingness? But not in the "oh, God created man" faith sort of thing, but in the "what are the physics behind life emerging and what would that look like elsewhere?" Would we even know life if we found it? A lot of scientists searching for life on other worlds go by "we'll know it when we see it;" but Sara posits that we may not know it when we see it without first understanding what we're even looking for. What is life? When does something become alive? When I'm alone, am I actually dead until someone interacts with me?
And... that's about how much I understood. I didn't understand exactly what assembly theory is enough to be able to describe it here. I know she used a LEGO example, which kind of made it easier to understand, but also not really.
At any rate, I'm not going to sit here and debate anyone on how life came to be. If you want to leave it at God, that's fine. If you want more than that, I'm probably in that boat too. If you're a scientist, but you totally disagree with assembly theory, who am I to judge?
So at this point I'll shift to the basic readability of this book. And really, there's nothing basic about it. Sara can write - that much is clear. But I wouldn't put her in the Carl Sagan, Bill Nye, or Neil deGrasse Tyson world of making science reachable to the lay person. Carl, Bill, and Neil have all popularized science for the general public. They made it so that dum-dums like me could get a grasp and even feel the awe of the cosmos. Unfortunately, Sara wasn't quite as captivating in her writing.
There were too many big words that slowed down the reading. The science, when she tried to explain it, still went over my head. The LEGO example I've already mentioned was probably the closest I could get to even a minute understanding of what she was trying to get across, but even that was a lot to conceptualize. I assume someone with some training in physics probably got through this quite easily. But this didn't really feel like a science popularization book to me. It just wasn't super accessible to me.
Something that Sara did throughout the book, which I saw another Goodreads review note, was the constant name-dropping of other famous scientists, many of whom she referred to as friends, or colleagues, or fellow whatevers. I get it. She's in a cohort of some of the most intelligent people on the planet. But it seemed a little self-aggrandizing at times. Not all of her references were that way, though. She'd refer to Albert Einstein or Erwin Schrodinger from time to time, referencing Albert's general theory of relativity or Erwin's work in quantum mechanics.
At this point you may be feeling a little uncomfortable that I refer to everyone so casually by their first names. Well, guess what - I was pretty uncomfortable with it too. Referring to historical figures by their first names feels too casual and kind of diminishes their gravitas. Basically, the tone of familiarity throughout this text doesn't match the weight of the subject. Perhaps the author was trying to make the subject matter feel more casual or informal by doing this. But it was simply too jarring. It felt like she was overreaching in an attempt to make these figures feel relatable. I'm sure there was a sense of consistency that she (or her editors) wanted to keep when referring to individuals that she does know personally. But in a science book especially I expect everyone to be referred to by their last name. Even if it's Doctor or Professor So-and-so.
A lot of people don't rate non-fiction books because it can be taken the wrong way. By this I mean that if you give a non-fiction book five stars, what is that saying? That the book was well-written? That you agree with the subject matter? What about memoirs, autobiographies, or biographies?
My rating of non-fiction books is simply in relation to the readability and understandability of the book in question. If I don't agree or like the subject matter, I probably just won't finish the book. With that in mind, I'm giving this book 2.5 out of 5 stars. What Sara was able to do here was get me interested in learning more about this theory of how life emerges from non-life. It is something I wouldn't shy away from if I encounter it elsewhere. Her examples throughout were good, but not always reachable or conceptualizable to me. I'm not making an overall judgment of the author as I could imagine picking up another one of her books. But I might go into it a little more cautiously and aware that it may be a slow burn for me.
October 6, 2024
Sara Imari Walker introduces an amazing concept in her book: Assembly number - how many "steps" are needed to "assemble" that thing. Assembly numbers over 15 can't arise spontaneously and, therefore, must be created by an intelligent being. As simple as that, but ofc there are tonnes of math and physics behind this. (See the nature article if you want to dig deeper.)
The book touches on many other interesting aspects of intelligence, life, astrobiology, and philosophy, but I found it slightly to repetitive to thoroughly enjoy it.
There is one amazing quote I want to highlight:
The book touches on many other interesting aspects of intelligence, life, astrobiology, and philosophy, but I found it slightly to repetitive to thoroughly enjoy it.
There is one amazing quote I want to highlight:
Features of reality appear 'material' or 'physical' to us if they smaller in time than we are. Examples includes elementary particles, atoms, and biological cells. By contrast, objects that are larger than us in time, look 'abstract' and 'informational.' An example is human culture, as mediated by our languages, which does not look like a tangible physical structure to us as individuals yet nevertheless binds us together as a collective object that undergoes selection and evolution. Artificial intelligences like ChatGPT are alienating to us because they take structures that are large in time, things like language distributed over over many human minds and compress them to an object as size and timescale we can interact with; the large language model.
June 10, 2025
There were some truly interesting and, at least to me, novel ideas in here. I just wish the text spent more time on outlining those new ideas, rather than analyzing why competing ideas are fallacious.
Assembly theory seems both compelling and intuitive, and according to the author, there is a high potential for experimental proofs, which would have foundation shaking consequences for the so called "hard problem of life." I thought that the philosophical ramifications of this were explained quite logically, while being sufficiently thought provoking to make me pause and reflect at several instances, which I love. Again though, I wanted to spend more time on this, and feel I was promised more time spent on this, assembly theory being the supposed core tenet of the text.
Another criticism I had was with the writing style. There seemed to be no real direction for the text. It seemed more like the meandering thoughts of a subject matter expert than an intentional, directed explanation.
Overall, very intellectually stirring, and I hope to read more about assembly theory in the future, the writing itself just didn't jive with me at times.
Assembly theory seems both compelling and intuitive, and according to the author, there is a high potential for experimental proofs, which would have foundation shaking consequences for the so called "hard problem of life." I thought that the philosophical ramifications of this were explained quite logically, while being sufficiently thought provoking to make me pause and reflect at several instances, which I love. Again though, I wanted to spend more time on this, and feel I was promised more time spent on this, assembly theory being the supposed core tenet of the text.
Another criticism I had was with the writing style. There seemed to be no real direction for the text. It seemed more like the meandering thoughts of a subject matter expert than an intentional, directed explanation.
Overall, very intellectually stirring, and I hope to read more about assembly theory in the future, the writing itself just didn't jive with me at times.
March 16, 2025
This book’s pretty mind-blowing. It explores the idea that scientists don’t really agree on a definition of what life is. Walker and her colleagues’ interdisciplinary research seems like a creative way to finally get some answers. I audibly gasped when I read about an experiment they’re working on. I won’t spoil that here.
Walker tries hard to make the book concepts accessible: She recaps information often, and she uses everyday metaphors - mixing cream into coffee, building with legos, etc. - to explain abstract ideas in assembly theory. Despite all that, I only grasped maybe ~70% of the book’s ideas. Not sure if that’s because her efforts to make it accessible weren’t enough, or I just don’t have the brain for this topic, or there’s really no way to make these ideas fully accessible, or some/all of the above. (For context, I’m a liberal arts-educated person who doesn’t have a science degree or job in a scientific field but reads a fair bit about science.) So, maybe if you’re like me, it’s a book to read more than once, discuss with others to help you grasp its ideas better, etc.
Walker tries hard to make the book concepts accessible: She recaps information often, and she uses everyday metaphors - mixing cream into coffee, building with legos, etc. - to explain abstract ideas in assembly theory. Despite all that, I only grasped maybe ~70% of the book’s ideas. Not sure if that’s because her efforts to make it accessible weren’t enough, or I just don’t have the brain for this topic, or there’s really no way to make these ideas fully accessible, or some/all of the above. (For context, I’m a liberal arts-educated person who doesn’t have a science degree or job in a scientific field but reads a fair bit about science.) So, maybe if you’re like me, it’s a book to read more than once, discuss with others to help you grasp its ideas better, etc.
February 16, 2025
4.75 ⭐️
This book serves as a fantastic introduction on assembly theory. This book is best read if you have a solid handle on a lot of basics around Physics and want to engage more... unfortunately for me, I did not (although my background in biochemistry did come in handy!)
If you're like me, I feel like there are two ways to go about this book. Either glaze through some of the details when she covers unfamiliar subjects, and you'll get most of what assembly theory entails anyway.... or you can do what I did and spend three weeks reading 10 pages, then looking up every scientist/project she plugged and try to teach yourself any gaps of understanding (which I 100% recommend)
Her genuine enthusiasm for the subject is contagious, and her playful way of explaining concepts turned what could've been an unindating read into something that kept my attention and made me want to fully understand what she was talking about.
This book serves as a fantastic introduction on assembly theory. This book is best read if you have a solid handle on a lot of basics around Physics and want to engage more... unfortunately for me, I did not (although my background in biochemistry did come in handy!)
If you're like me, I feel like there are two ways to go about this book. Either glaze through some of the details when she covers unfamiliar subjects, and you'll get most of what assembly theory entails anyway.... or you can do what I did and spend three weeks reading 10 pages, then looking up every scientist/project she plugged and try to teach yourself any gaps of understanding (which I 100% recommend)
Her genuine enthusiasm for the subject is contagious, and her playful way of explaining concepts turned what could've been an unindating read into something that kept my attention and made me want to fully understand what she was talking about.
October 14, 2024
Thought-provoking
I thought this book was an informative and through-provoking read. It laid out the groundwork for “assembly theory” a new framework for understanding what life is and how we can define and detect it. The book nicely explained the theory and often on interesting side quests that provided the theory context. I felt that at times the explanations and discussion of assembly theory were redundant though they were certainly reinforcing. I especially like the final two chapters were the author expands assembly theory to discuss the moment we find ourselves now in with the advent of AI and whether this technology qualifies as life.
If you’re interested in questions of origin of life - I highly recommend this book to read.
I thought this book was an informative and through-provoking read. It laid out the groundwork for “assembly theory” a new framework for understanding what life is and how we can define and detect it. The book nicely explained the theory and often on interesting side quests that provided the theory context. I felt that at times the explanations and discussion of assembly theory were redundant though they were certainly reinforcing. I especially like the final two chapters were the author expands assembly theory to discuss the moment we find ourselves now in with the advent of AI and whether this technology qualifies as life.
If you’re interested in questions of origin of life - I highly recommend this book to read.
July 27, 2025
Sara Imari Walker held a talk at The Long Now Foundation on this topic, which is available here: https://youtu.be/zhzxQraB2m0
“What is life?”
In her Long Now Talk, astrobiologist and theoretical physicist Sara Imari Walker explores the many dimensions of that seemingly simple question.
Starting from the simplest precursors, Walker assembled a grand cathedral of meaning, tracing an arc across existence that linked the fundamentals of organic chemistry, the possibility space of lego bricks, and the materialist philosophy of Madonna.
January 24, 2025
This is an overview of a new scientific framework called assembly theory that wants to ask the questions such as the origin of life. It's a fascinating idea and I knew nothing about it so this was informative as well as exciting in giving a glimpse of some different approaches in theoretical physics. I did want it to be more in depth and have more technical details, but I suppose I can read the actual literature to learn more.
December 11, 2024
Assembly theory is definitely an innovative way to think about the origin of life problem more generally. The author points out why it is cool and how to think through the ideas in this theory. However, I feel that that the book could be much shorter and/or incorporate more broader talking points connected to this research (other than their own theory/close collaborators).
December 14, 2024
I picked this up as soon as it was available, after listening to Sara Imari Walker on a couple different podcasts and reading some technical papers. I really think she and her colleagues are onto something. I really enjoyed her insights, especially the idea that we are objects in time that stretch back 3.8 billion years, and that if you look at it that way, objects that are bigger than us in time - like our technosphere - seem virtual to us. And it a just a fascinating look into someone's mind, richly indexed and footnoted to facilitate a deeper dive.
I'll be returning to this one and working it's ideas into my own writing.
I'll be returning to this one and working it's ideas into my own writing.
Want to read
August 4, 20248/4/24 Found it from a link in the NYTs weekly Flashback History quiz posted by an entry for Darwin. Assembly Theory apparently states that evolution isn't purely random as there must be a me hanism for 'memory' at the biological level.
A Test for Life Versus Non-Life https://www.nytimes.com/2024/07/31/sc...
A Test for Life Versus Non-Life https://www.nytimes.com/2024/07/31/sc...
August 3, 2025
Interesting and engaging introduction to assembly theory - a multidisciplinary theory that aims to formalize and quantify learning and evolution so that we may be better positioned to create a harmonized theory of life.
September 20, 2025
I loved the cross-disciplinary thinking and scale, but felt there was too much motivational windup before getting to the nuts and bolts of assembly theory (the core idea), then transitioned too quickly to selling a big science agenda to search over chemical space for possible origins of life. Interesting ideas, would love a book going deeper into assembly theory on its own merits without trying to convince me it may be the One True Theory of everything.
November 21, 2024
Sarah walker is fun to listen to because she thinks about stuff aliens, machine learning, and physics. Normally I’m a big note taker but this I just enjoyed the vibes.
Read
January 18, 2025Dry theoretical physics featuring LEGOs.
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