From: jimruttshow8596
Complexity and evolution are central themes explored by Sarah Walker and Lee Cronin, particularly through their proposed Assembly Theory. They argue for a re-evaluation of how complexity is measured and understood, especially in the context of life’s origins and its expansion throughout the universe [00:44:50].
Critiquing Existing Measures of Complexity
Traditional measures of complexity from computer science, such as Kolmogorov complexity, focus on program size or the minimal machine required to run something [01:28:00] [01:29:11]. Walker and Cronin assert that existing complexity theory is largely “incorrect” and suffers from a lack of a unified theory, often being a collection of examples rather than a cohesive understanding of behavior [02:20:00] [02:25:00]. Freeman Dyson, in an email to Lee Cronin, noted that the literature of complexity theory lacks a true “theory,” offering “interesting examples of complex objects and complex systems but no general understanding their behavior” [02:41:00] [02:49:00].
A key issue with traditional complexity measures is their inability to distinguish random from complex systems [01:56:00]. Random things often appear complex due to their unstructured nature [02:01:00]. Assembly Theory, in contrast, focuses on objects that exhibit reuse of parts, a hallmark of evolution [02:20:00].
Assembly Theory: A New Measure of Complexity
Assembly Theory proposes that complexity is an intrinsic physical feature of an object itself, not merely a computational measure [01:48:49] [01:51:00]. It seeks to define the minimal set of causal pathways required to create an object, with specific physical constraints [01:13:00].
Key concepts in Assembly Theory include:
- Number of Parts: The number of constituent parts an object has [01:48:49].
- Copy Number: The number of identical copies of an object that exist [01:50:00].
- Steps (Assembly Index): The shortest recursive path required to build an object from its constituent parts, allowing for component reuse [02:51:00] [02:53:00] [02:59:00]. The more steps an object has, the more improbable it is that it formed by chance [03:26:00] [03:42:00]. This is experimentally measurable using techniques like spectroscopy, magnetic resonance, and mass spectrometry [03:31:00] [03:40:00].
- Memory: Every object encodes its own memory of how its parts were built in the past [01:25:00]. For complex objects, memory—such as the deep memory in DNA and the local memory in cellular metabolism—is a prerequisite for their creation [03:22:00] [03:59:00]. As structures allowing deeper and more complicated memory increased in the universe’s evolution, the ability to take more assembly steps also increased [03:50:00].
- Selection: The theory posits that selection must predate biology as we know it, as it’s the mechanism by which complexity is built in steps [03:52:00] [03:56:00].
Implications for Evolution and Life’s Origin
The Biotic Threshold
Assembly Theory identifies a sharp phase transition in chemical complexity that distinguishes non-biotic (abiotic) from biotic chemistry [04:24:00] [04:28:00]. For molecules, an assembly index of 13 or 14 is considered the upper limit for non-biotic formation, while objects with 15 steps or more generally require a biotic (or equivalent) process [04:32:00] [04:40:00].
Life is seen as an “amplifier” of complexity, rapidly generating objects with high assembly numbers [04:09:00] [04:40:00]. While life can produce low-assembly objects, high-assembly objects are a definitive signature of living physics [04:30:00]. This threshold represents a physical constraint where a mechanism of selection (or “living physics”) must be present to observe high-assembly objects [04:48:00].
Life as a Stack of Objects
Assembly Theory conceptualizes life as a deep “stack of objects” that recursively assemble other objects over time [04:40:00]. This entire stack is necessary to produce high-assembly entities [04:46:00]. The theory addresses the origin of life not just as a chemical phenomenon, but as a continuous “recursive transformation” that began billions of years ago and continues as evolution [03:56:00] [04:00:00].
The Role of Information and Time
The theory suggests that information is not disembodied but is a “temporally embedded structure” that is accumulated over time [00:59:00] [01:00:00]. Complex objects are viewed as having “depth in time,” reflecting their long evolutionary lineage [01:05:00]. This perspective inherently clashes with the “block universe” concept of Einsteinian physics, which implies that all moments in time exist simultaneously and are unchanging [01:01:00]. Assembly Theory posits that novelty can exist, and that the universe intrinsically increases in complexity and options over time, which means that some things must happen before others [01:03:00] [01:09:00] [01:11:00].
Evolution of Technology and Intelligence
Beyond biological evolution, Assembly Theory may also predict a phase transition between life and technology, or even between life and intelligence [00:47:00]. Technology is seen as evolving itself [00:48:00]. Human intelligence, with its ability to synthesize highly complex molecules that biology cannot naturally produce (e.g., a chemist creating a molecule with an assembly index of 50 by combining 50 different elements), represents another level of complexity [00:48:00]. This suggests that the evolution of general intelligence may constitute a second major phase transition in the universe’s history, after the origin of life itself [00:49:00].
Implications for SETI and the Fermi Paradox
Assembly Theory offers new perspectives on the Fermi Paradox and the Search for Extraterrestrial Intelligence (SETI) [01:07:00].
- The Great Perceptual Filter: The challenge in finding alien life may stem from a “great perceptual filter” [01:35:00]. Humanity may not have yet developed the necessary “perceptual apparatus” or understanding of the physics of life to recognize alien technology or life itself [01:08:00] [01:09:00]. Just as gravitational waves permeated the universe for billions of years before humans developed the theory and instruments to detect them, alien life might exist in forms currently imperceptible to us [01:09:00].
- “Making Aliens from Scratch”: A profound way to advance SETI is by experimentally evolving alien life in the laboratory [01:10:00]. By understanding the fundamental physics of life’s origin and complexity on Earth, new “lenses” for observing the universe could be developed to detect life elsewhere [01:12:00].
- Techno-signatures: The theory suggests looking for “techno-signatures” in exoplanetary atmospheres—complex molecules with high assembly numbers that cannot be explained by non-biotic or typical biotic processes alone [01:07:00] [01:13:00].
- Probability of Life’s Evolution: Assembly Theory aims to make predictions about the likelihood of life emerging in specific chemical environments given certain constraints [01:19:00]. It emphasizes that the probability of life’s origin cannot be determined without understanding the fundamental physics of the transition from non-life to life [01:19:00]. The theory reframes the question from the historical “prebiotically plausible” to understanding how much selection is required for this transition to occur [01:21:00].
In essence, Assembly Theory provides a framework to quantify the depth of an object in time, reflecting its causal history and the evolutionary processes that brought it into existence. This allows for a unified descriptive language for both living and non-living systems, offering a novel approach to understanding complexity and evolution [01:12:00] [01:15:00].