From: jimruttshow8596
Assembly Theory, proposed by Sarah Walker and Lee Cronin, offers a new conceptualization of complexity and time, particularly relevant to chemistry and the origin of life [02:07:10]. It stems from the observation that certain objects are highly improbable to form by chance [00:09:58] [01:13:54].
Core Concepts of Assembly Theory
Assembly Theory quantifies an object’s complexity based on two main components [01:46:46]:
- Number of Parts: The number of constituent parts an object has [01:48:48].
- Number of Copies: The number of identical copies in which the object occurs [01:50:00].
The theory suggests that an object with a large number of parts that is also present in a large number of identical copies is highly unlikely to have formed by chance [01:10:00] [01:37:00]. For example, finding ten identical iPhone 14s on Mars would strongly indicate they did not form randomly [01:36:33].
Assembly Steps and Causal Pathways
A key concept is the “steps” required to form an object [02:04:59]. This refers to the shortest possible route to re-form a molecule by reusing components [02:34:00] [02:53:07]. The larger the number of steps, the more improbable it is that the object formed by random chance [02:37:00] [02:42:00].
Assembly Theory distinguishes itself from traditional complexity measures, such as Komodorov complexity, by focusing on the “minimal set of causal pathways” for making an object, rather than program size or computational complexity [01:51:13] [01:56:06]. This approach considers the universe as the “computer” bringing the object into existence, and it strictly adheres to the laws of physics [01:54:00].
Measurable Complexity in Chemistry
A profound aspect of Assembly Theory is its experimental measurability [02:55:00]. It was developed starting from what could be measured in a lab, particularly regarding molecules [02:56:00].
The “assembly index” – a measure of the number of parts – can be determined through various analytical techniques [03:26:00]:
- Spectroscopy: By shining light on a molecule and observing how many different wavelengths it absorbs, the number of distinct parts can be inferred [03:22:00].
- Magnetic Resonance: Similar to spectroscopy, the number of different radio frequencies absorbed indicates the number of distinct parts [03:28:00].
- Mass Spectrometry (Mass Spec): By weighing a molecule and fragmenting it, the number of distinct bits produced is proportional to the assembly index [03:29:00].
This experimental validation means that each molecule has a minimum assembly index associated with it [03:37:00].
Memory and the Emergence of Life
Assembly Theory introduces the concept that for highly complex objects, systems need “memory” [03:06:00]. In biological systems, this memory is instantiated in physical objects, such as DNA’s deep memory and the local memory in the cytoplasm and metabolism of a cell [03:22:00]. This allows for the creation of complex organic molecules [03:39:00].
The theory posits that a critical event in the origin of life was the establishment of selection processes that predated biology [03:52:00] [03:56:00]. Without pre-biological selection, the emergence of complex life would necessitate a “miracle” [03:59:00]. Assembly Theory provides a mechanism for this, where random steps initially build systems, and then mechanisms of memory become established through selection and evolution [03:59:00].
The Biotic Threshold
Assembly Theory reveals a sharp phase transition between non-biotic and biotic chemistry [04:27:00] [04:56:00]. On Earth, molecules with an assembly index of 15 steps or above are typically biotic (produced by life) [04:37:00]. While life can produce low-assembly objects, high-assembly objects require the physics governing life (selection mechanisms) to be in place [04:39:00].
This threshold exists because the “possibility space” of molecules grows exponentially with each step, making random formation of complex objects highly improbable [04:44:00]. Life, through its ability to reuse parts and maintain a memory of past structures, can explore and build within this exponentially growing space, acting as a “selection amplifier” [04:09:00] [04:20:00] [04:42:00].
Assembly Theory as a Theory of Time and Information
Assembly Theory proposes that objects encode their own memory, meaning every object is extended in time as a recursive, hierarchical, modular structure [01:52:00]. This perspective views time not as an external fluid, but as an intrinsic, physical property of objects themselves [00:42:00] [03:36:00].
According to Sarah Walker, the theory allows information to be treated as a material entity, accumulated over time and embedded in the object’s structure [04:59:00] [04:00:00]. Just as mass is a relevant physical quantity for gravity, Assembly Theory posits that a concept of “information” or “causation” (measured by shortest path and copy number) is relevant for describing the physics of evolution and the coming into existence of objects [05:01:00]. This implies a rejection of Einstein’s block universe, as Assembly Theory suggests that novelty and causality are fundamental, requiring some things to happen before others [05:02:00] [05:06:00].
Future Applications and Implications
Distinguishing Life, Non-Life, and Technology
Assembly Theory aims to unify the non-living and living universe under a common descriptive language [04:54:00]. It may provide a way to distinguish between dead matter, life, and even technology by identifying different phase transitions in complexity [05:32:00]. For example, human-designed molecules, such as complex synthetic compounds, could achieve very high assembly indices, which biology might not typically produce [04:46:00].
Search for Extraterrestrial Intelligence (SETI)
Assembly Theory has implications for SETI and the Fermi Paradox [06:09:00]. The theory suggests that the “great filter” might be a “great perceptual filter,” meaning humanity hasn’t developed the necessary apparatus to perceive alien life or technology [06:33:00]. Just as gravitational waves were imperceptible until Einstein’s theory predicted them and detectors were built, alien life might operate on a different causal or “assembly” chain that requires a new understanding of physics to detect [06:36:00].
One future direction is to use Assembly Theory to remotely sense complex molecules in exoplanetary atmospheres using technologies like the James Webb Space Telescope [07:11:00]. This would involve modeling planetary evolution in terms of assembly theoretic principles to detect how much “memory” a planet holds of past states [07:18:00].
Probability of Life’s Emergence
Assembly Theory suggests that statements about the probability of life emerging on an otherwise suitable planet are currently flawed [07:51:00]. The entire causal chain of life on Earth is a unique, interconnected structure, not a series of isolated rare events [07:55:00]. The theory aims to make predictions about the likelihood of life emerging in certain chemical environments by understanding the physics of the transition from non-life to life, moving beyond the “prebiotically plausible” arguments [08:11:00] [08:24:00]. Lee Cronin suggests that selection is a fundamental process occurring throughout the universe, and the key question is how much selection is required to make the transition to life [09:19:00]. This reframing moves away from assuming life is an inevitability and instead focuses on the conditions and processes required for its emergence [09:05:00].