Sara Walker: Physics of Life, Time, Complexity, and Aliens | Lex Fridman Podcast #433

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Sara Walker: Physics of Life, Time, Complexity, and Aliens | Lex Fridman Podcast #433

Introduction (00:00:00)

  • Sara Walker is an astrobiologist and theoretical physicist interested in the origin of life and discovering alien life.
  • Her new book, "Life as No One Knows It: The Physics of Life's Emergence," will be released on August 6th.
  • Life is a property that emerges from the evolution of technology.
  • The technosphere, or the collection of technologies, evolves over time and eventually develops life-like properties.
  • This process solves the origin of life and allows life to reproduce itself on other planets.
  • Complexity is a key feature of life.
  • Emergence is the process by which new properties and behaviors arise from the interactions of complex systems.
  • Life is an emergent property of complex systems.
  • The search for extraterrestrial life is a major scientific endeavor.
  • There are many different ways to search for aliens, including looking for technosignatures, or signs of technology, and searching for habitable planets.
  • The discovery of extraterrestrial life would have a profound impact on our understanding of the universe and our place in it.

Definition of life (00:01:07)

  • Vitalists believe that life has a non-physical aspect, while materialists believe it can be fully explained by physical matter.
  • The unknown aspects of the universe should be explored through scientific inquiry rather than dismissed as magic or boring.
  • Our understanding of matter may expand to incorporate life as a material property.
  • The laws of physics appear to be the same everywhere, but we lack a unified description of life because we don't know how to think about information materially.
  • Defining life is challenging due to counter-examples and the lack of a clear boundary between living and non-living entities.
  • The concept of an individual as a relevant unit in defining life is problematic because many organisms rely on societies and environments for survival.
  • Life emerges in chemistry but is not limited to chemical systems.
  • The universe's vastness and the combinatorial space of chemistry mean that not every possible molecule can be expressed.
  • Life emerges in chemistry because the universe selects what exists through historically contingent pathways.
  • Some things that have evolved on Earth, such as language, memes, and mathematics, may be considered alive or life-like.
  • Darwinian evolution is problematic as a definition of life because it happens at the population level, not the individual level.
  • Assembly theory offers a broader perspective on evolution as a constructive process.
  • A more expansive definition of life could encompass all things considered alive or life-like, such as the process of how information structures matter over time and space, leading to an open-ended cascade of generation of structure and increasing complexity.
  • Our current definitions of life, time, complexity, and aliens are not general, universal, deep, or abstract enough to capture the regularity of life on our planet.
  • We focus too much on individuals and short temporal moments instead of the larger causal structure of life.

Time and space (00:21:45)

  • Our perception of reality is limited by our evolved architecture, but technology allows us to see the world in new ways.
  • The universe is far larger in time than it is in space, and the more complex an object is, the bigger it is in time.
  • The modern technosphere, the global integration of life and technology on Earth, is the largest object in time in the universe that we know about.
  • Humans are closely connected in time and can understand each other because we diverged relatively recently in the history of the universe.
  • Life cannot be defined as an individual but rather as interconnected lineages that exchange parts.
  • Ayahuasca can induce a state where individuals can see the past selves of others, providing a glimpse into the temporal structure of consciousness.

Technosphere (00:32:26)

  • The technosphere, which encompasses our technology, can be considered a life form due to its creativity and lineage view of life.
  • Life should be viewed as a planetary-scale phenomenon, with life expanding into the possibilities of the universe.
  • Life exists at various scales, from cells to societies and global organizations, and understanding life requires integrating all these scales.
  • Solving the problem of life involves understanding everything on the planet that exhibits life-like characteristics and identifying the underlying structure.
  • Schrödinger suggested the existence of new laws of physics to explain life.
  • Schrödinger attempted to explain life using non-equilibrium physics and predicted the structure of DNA as an aperiodic crystal.
  • The question is why life can generate so much order, and current physics lacks a description for this.
  • Many physicists have tried to understand life, often later in their careers, and there's still a belief that non-equilibrium physics will explain life.
  • The author believes that non-equilibrium physics is not the right approach and that entropy alone cannot explain the emergence of complexity from randomness.

Theory of everything (00:36:51)

  • The universe is fundamentally random, and the current laws of physics are limited in describing reality at its most basic levels.
  • A Theory of Everything should explain everything, including itself, but this is challenging due to its recursive nature.
  • Physics can acknowledge the observer without creating paradoxes, and the definition of fundamental particles is limited by our technology and understanding.
  • The focus of modern physics lies in studying life, intelligence, and the existential impact of technology.
  • Humans are simultaneously fearful and fascinated by new technologies.
  • Studying physics humbles individuals and confronts them with their own insignificance, leading some physicists to feel a constant sense of uncertainty about their sanity.

Origin of life (00:45:32)

  • The origin of life involves the emergence of self-reinforcing structures that maintain their existence against randomness, forming closed, self-reinforcing structures that persist over time.
  • Stuart Kaufman proposed the theory of autocatalytic sets, but it requires ad hoc assumptions and is brittle as a theory.
  • Sara Walker suggests a more general approach by considering the structure of histories that make objects, where causal structures loop back on themselves to generate higher-level structures.
  • Lee's discovery of the self-reproducing malonamide ring demonstrates how the system collapses onto a single structure from random events, reinforcing its own production.
  • The origin of life involves a combinatorial explosion of possible structures, but it collapses onto a small space of mutually reinforcing possibilities, which is the essence of autocatalytic feedback.
  • Chirality, the property of having a mirror image, is a perplexing feature of life's chemistry and breaks time symmetry, contributing to the vastness of chemical space.
  • The transition from non-chiral to chiral molecules requires life and marks a fundamental boundary in chemical space.
  • Sight is a crucial invention that has transformed life's ability to perceive and comprehend the world.
  • The process of germline cells and development is an incredible invention that all living things go through at some point in their life cycle.
  • Embryogenesis, the development of an organism from a single cell, involves complex gene expression and interactions with other cells.

Assembly theory (01:07:10)

  • Assembly Theory proposes that the universe constructs itself through historically contingent paths and causal chains of events, resulting in the emergence of complexity unique to life on Earth.
  • Complexity, measured by copy number and minimal recursive steps, is observed to have a boundary beyond which it is unlikely to occur outside of an evolutionary chain of events.
  • The assembly universe is ordered in time and causation, with the number of steps to produce an object defining its assembly index.
  • The transition from non-life to life is abrupt, involving a rapid collapse of the possibility space onto a self-reinforcing structure.
  • Existence excludes numerous possibilities due to historical accidents and the exponential growth of the space of objects.
  • Meaning emerges from causation, recurrence, and relationships between objects, with language serving as a highly regular structure that enables the emergence of meaning through combinations of words.
  • Sara Walker suggests using Twitter as an experimental platform to observe interpretations of written content and proposes filtering responses based on user sentiment.
  • Walker emphasizes the complexity of human nature and suggests that there are more personality categories than can be expressed through a limited number of colors.

Aliens (01:23:24)

  • Sara Walker discusses the physics of life, time, complexity, and the possibility of alien civilizations.
  • She proposes that advanced civilizations may become increasingly virtualized and exist in a temporal rather than spatial dimension, making them difficult to detect.
  • Walker also mentions the concept of "Quint intelligence," where advanced beings may transform themselves into quantum computers operating in the vacuum of space.
  • Extinction events are like pinching off entire causal structures, similar to black holes that might be imperceptible to us.
  • The problem of discovering alien life and solving the origin of life are deeply coupled and are essentially the same problem.
  • Solving the origin of life on Earth is essential for understanding ourselves, getting off-planet, and recognizing other alien intelligence.
  • Walker emphasizes the importance of exploring ideas that one may not necessarily agree with in order to gain a deeper understanding of the world.

Great Perceptual Filter (01:35:14)

  • Sara Walker discusses the concept of the "great perceptual filter," which suggests that there may be a point in the development of complex objects where they become too difficult to perceive.
  • She uses the example of microbial life, which humans were unable to perceive until the invention of microscopes.
  • Walker also mentions the idea of "flickering lights" in the universe, representing potential intelligent civilizations, and the challenges of distinguishing these signals from natural phenomena.
  • Walker describes her research on non-human communication, inspired by fireflies.
  • She explains how fireflies evolve their signaling patterns to differentiate themselves from other fireflies in the same environment.
  • Walker's lab is building a model of alien communication based on firefly behavior, using a pulsar background to simulate the universe.
  • She discusses the challenges of distinguishing alien signals from natural pulsars and suggests potential methods for identifying anomalous signals.

Fashion (01:39:12)

  • Sara Walker discusses the complexity of human aesthetics using the example of her closet.
  • She describes her closet as a "temporal time crystal" that visualizes the history of her personality.
  • Walker emphasizes the importance of self-expression through clothing and the bravery and confidence required to experiment with style.
  • She explains that she deliberately thinks about her outfit every morning and considers various options before making a decision.
  • Walker mentions that yellow is her daughter's favorite color and she has been experimenting with wearing different shades of yellow lately.
  • Sara Walker shares her thoughts on beauty.

Beauty (01:43:14)

  • Sara Walker finds playing with aesthetics intellectually stimulating and enjoys bridging the gap between the natural sciences and fashion.
  • She appreciates the dynamic nature of fashion and sees it as a way to express herself and push boundaries.
  • Walker admires Alexander McQueen's ability to blend horror and beauty in his fashion designs, sparking controversy and challenging societal norms.
  • She believes that beauty lacks a clear function but exerts significant influence and can serve as a signal of health or other adaptive traits.
  • Walker emphasizes that the perception of beauty is subjective and shaped by individual experiences and interactions with the world.
  • She argues that beauty is not just an adaptive trait for sexual selection but also plays a role in social hierarchy, social mobility, and social dynamics.

Language (01:49:35)

  • Language is a complex living entity with its own structure and mechanisms, distinct from the things it describes.
  • Words have their own ontology and can create meaning and causation, making the life of the mind richer than physical reality.
  • Large language models have shown the limitations of language as the sole means of understanding and expressing ideas.
  • The magic of words lies in their ability to be played with unconventionally to create new perspectives and insights.
  • Sara Walker discusses the difficulty of describing complex ideas accurately and accessibly, citing her paper "Assembly Theory" as an example of a work that challenged conventional thinking.
  • Walker emphasizes the importance of creative and precise language when discussing abstract concepts.
  • Her collaboration with Lee Smolin highlights the complementary nature of their work, with Smolin's thinking operating at a deeper level of abstraction than language can easily express.

Computation (01:56:16)

  • Computation is a powerful language that allows us to describe things in any other language, but it is not the fundamental basis of reality.
  • Cellular automata provide an intuition of how complexity can emerge from simple beginnings, but they are embedded slices in a much larger causal structure that is not dynamical.
  • Sara Walker criticizes Stephen Wolfram's theory that suggests computation is the fundamental basis of reality, arguing that computation itself is not a fundamental property and that it is unclear what question Wolfram's theory is trying to answer.
  • Walker emphasizes the importance of having a clear question to address when building a theory of reality and suggests that the question of what life is could be a starting point.
  • She proposes that demonstrating that physics can solve the "original life" problem, which involves understanding the origin and nature of life, could provide a more meaningful approach to understanding reality.

Consciousness (02:06:03)

  • Assembly theory aims to answer the question, "What is life?" and is considered the easiest of the hard problems.
  • Intelligence and consciousness may be different aspects of the same thing, emerging at different stages of assembly.
  • Consciousness is seen as a manifestation of our temporally extended existence and is not shared because each individual occupies a separate thread in time.
  • Consciousness may exist before life, but there's a horizon where the structure becomes so large that it accesses a non-physical space.
  • Intelligence arises from objects selected to exist by constraining the possible space of objects, and high-density configurations of matter with a lot of selection embody the physics of selection and can select on possible futures.

Artificial life (02:14:55)

  • Large language models (LLMs) represent a crystallization of human language and embody societal-level technology, raising questions about their potential power and the need for accurate language when describing them.
  • Sara Walker emphasizes the importance of using precise language when discussing AI technologies, warns against over-fearing them, and suggests that a formal test for consciousness is necessary to move beyond the current ambiguity.
  • The technosphere, a global-scale process that integrates technology with the social organism, is transforming our planet and may eventually expand to other planets.
  • The Kardashev scale, which measures energy consumption, is not a useful way to understand alien life as it overlooks the creative and exploratory aspects of life.
  • Life on Earth is built on predator-prey dynamics, and it is uncertain if we can escape this dynamic. Death is a necessary part of the universe as it makes way for new things.
  • The frontier of knowledge is vast and may not have a limit, but it can be seen as a receding horizon due to the expanding universe. The book of knowledge is finite but growing as our understanding of the universe increases.
  • New questions, such as intelligence and artificial general intelligence, have emerged as the universe evolved, and we may develop better languages to ask more profound questions in the future.

Free will (02:38:48)

  • The universe may be infinite, but there is likely a finite explanation for every aspect of it, including consciousness and life.
  • Quantum mechanics suggests that the future is larger than the past, with constant branching but no clear directionality.
  • Our deterministic structures exist within a random background, allowing us to select possible futures and exercise free will.
  • Randomness generates novelty and flexibility, while a common tutorial history provides structure and coherence.
  • Time should be viewed as combinatorial, with the future being a combination of existing structures.
  • Free will operates within a temporal horizon and is not instantaneous.

Why anything exists (02:45:32)

  • Sara Walker believes that understanding the nature of life may help us understand existence, but it's a complex and challenging task.
  • She views mathematical concepts as emerging within our biosphere and proposes studying math itself as an object of study for physicists.
  • Walker finds beauty in exploring the physics of life, particularly in generating novel ideas and communicating them to others.
  • She enjoys challenging people's conventional thinking and appreciates the sense of mystery and wonder that comes from exploring the boundaries of our understanding.
  • Sara Walker's greatest wish is to contribute to an idea that transforms the way we think and gain a deeper understanding of the world and life.

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