Two men named Lee Cronin are probing the boundary between life and death. One, a chemist at the University of Glasgow, helped develop a framework called assembly theory that claims to measure what makes something alive. The other, an Irish horror director, recently released a film called “Lee Cronin’s The Mummy” that explores what happens when the dead refuse to stay buried. Their work converges on the same question: what distinguishes matter that persists from matter that decays?
What Assembly Theory Actually Claims
Lee Cronin the chemist proposes a deceptively simple idea. Take any complex object: a protein, a drug molecule, a piece of technology. Ask how many steps it would take to build that object from basic parts. This number, which Cronin calls the assembly index, reveals something profound about where the object came from.[s]
“The Assembly Index is literally a measure of the minimum amount of information required to make that molecule,” Cronin explains.[s] The higher the number, the more construction steps the object required. And here is the key insight: random chemistry cannot produce objects with very high assembly indices. Such complexity requires selection, a process that preserves useful intermediate structures and builds on them over time.
Assembly theory makes a testable prediction. Below a molecular assembly index around 15, relatively complex molecules can still appear in abiotic chemical settings such as meteorites, laboratory simulations, and environmental samples. Above that range, reported studies to date have found high-assembly molecules only in biological samples or in products ultimately made by living systems.[s][s]
Reported laboratory testing supports that boundary. Cronin’s team analyzed terrestrial, marine, laboratory, and extraterrestrial samples, and the Nature Communications study reported that molecular assembly measurements distinguished samples containing molecules produced by life from those that did not.[s]
Life as Copying and Existence
Traditional definitions of life tend toward the circular. NASA’s working definition describes life as “a self-sustaining chemical system capable of Darwinian evolution,” which defines life in terms of evolution, the thing we are trying to explain.[s] Metabolism-based definitions raise a different problem because thermodynamic disequilibrium alone is not unique to biology.
Assembly theory sidesteps this by focusing on products rather than processes. It asks not “what is life?” but “what does life do?” The answer, according to Cronin, involves two words: copying and existence.
“Life is extremely fragile chemistry that has found a way to copy itself to continue to exist,” Cronin states. “We, as living things, are the oldest artifacts on Earth, even older than some of the rocks, because we are able to copy ourselves and keep going.”[s]
For Cronin, existence itself is the core principle. “For an object to exist, it has to survive for a longer time than its natural life.”[s] This reframes the origin of life not as a singular miraculous event but as a gradual process: matter learning to persist, then to copy, then to complexify.
Why the Film “The Mummy” Matters Here
The other Lee Cronin, the Irish horror director behind Evil Dead Rise, which Variety described as giving that franchise its biggest box office to date, has recently turned from one famous horror property to another. His 2026 film “Lee Cronin’s The Mummy” reimagines a classic monster tale as a meditation on what happens when preservation goes wrong.
“What if a loved one was mummified?” the director asked in an interview with Variety. “What if it wasn’t a Pharaoh, king, queen or prince? What if it was the average person?”[s] From that premise, the horror emerged.
The film centers on a family whose missing daughter is found eight years later, sealed inside a tomb. She is alive but transformed, her return raising the question the chemist Cronin also asks: what exactly persists through time, and at what cost?[s]
“The past cannot return unless it mutates into something alien,” observes one review of the film.[s] This captures both the film’s horror and assembly theory’s scientific insight. Biological complexity requires memory: structures that persist across iterations, preserving information that random processes would destroy.
The Controversy
Assembly theory has provoked strong reactions from the scientific community. When Cronin and collaborator Sara Walker published their framework in Nature in 2023, evolutionary biologists struggled to understand what the paper was claiming.
“After multiple reads I still have absolutely no idea what [this paper] is doing,” wrote one evolutionary biologist. Another said: “I think reading that paper has made me forget my own name.”[s]
Critics argue that assembly theory may be stating the obvious. “It’s obvious that if a molecule is complex and there are lots of copies of it, then it likely emerged from some process of evolution. And most chemists could spot such cases without the need for assembly theory.”[s]
Other critics, including computer scientist Hector Zenil, argue that the assembly index reduces to known compression algorithms, specifically the LZ77 compression used in file compression.[s]
Supporters counter that assembly theory provides something genuinely new: a measurable, substrate-independent framework for detecting life-like chemistry without first assuming Earth biochemistry.[s]
Why Detection Matters
The origin of life remains one of the most profound unresolved questions in science. Its investigation requires biology, chemistry, physics, astronomy, geology, information theory, and philosophy.[s] Physics and chemistry alone are necessary but not sufficient to explain biological complexity, which emerges from natural selection, genetic inheritance, and information processing.[s]
Assembly theory offers practical tools for astrobiology. Many biosignature searches look for specific molecules or chemical disequilibria, such as oxygen, methane, or phosphine. These depend on assumptions about alien biochemistry. Assembly theory offers an alternative: measure the assembly indices and abundance of whatever molecules you find. If high-assembly molecules appear in abundance, something may be selecting and preserving complex constructions.[s]
NASA has already engaged with this framework, using assembly theory as a potential universal marker for biology in the search for life beyond Earth.[s]
The Threshold as Boundary
In the reported molecular tests, the assembly index threshold around 15 functions as a dividing line between chemistry and biology, between dead matter and living processes. Below it, researchers found products consistent with abiotic chemistry. Above it, especially when high-copy-number molecules appear, assembly theory treats the pattern as evidence of selection.[s][s]
Both Lee Cronins are working on this boundary. The chemist quantifies it. The director dramatizes it. The mummy in the film and the molecule in the lab share a common feature: they are structures that persist when they should have decayed, carrying forward information that random processes would erase.
Whether assembly theory ultimately proves to be a revolutionary framework or a sophisticated restatement of existing ideas, it forces a confrontation with the question that has haunted both science and horror: what makes the difference between life and its absence?
Assembly Theory’s Formal Structure
Assembly theory formalizes the intuition that complex objects require construction histories. The assembly index (AI) quantifies the minimal number of recursive, compositional joining operations necessary to construct an object from its elementary parts.[s] Unlike Shannon entropy, which measures statistical patterns in data, the assembly index measures construction depth: how many distinct operations were performed, and whether earlier constructions were reused.[s]
Consider a string “ABCABC”. Its assembly index is 3: join A and B to make AB, join AB and C to make ABC, join ABC and ABC. The string “ABCDEFG” requires 6 operations. Despite having more unique characters, the first string has lower assembly because it reuses the ABC construction. This reuse signals that something other than pure randomness is at work.
The assembly equation formalizes how abundance and complexity combine:
A = Σi eai(ni − 1) / N
where ni is the copy number and ai the assembly index for the i-th distinguishable object, and N is the total number of objects in the system. Large values of A imply substantial selection must have occurred.[s]
Computational Complexity and the LZ77 Critique
Critics, particularly computer scientist Hector Zenil, have argued that assembly theory reduces to dictionary-based compression algorithms like LZ77.[s] Both identify repeated substructures and exploit reuse. The critique suggests assembly theory offers nothing that Kolmogorov complexity or Shannon entropy do not already provide.
Cronin and Walker’s rebuttal addresses this directly. Their 2025 paper in npj Complexity provides mathematical proofs that the assembly index belongs to a different computational complexity class than compression algorithms like Huffman encoding and LZW.[s] Computing the assembly index is NP-complete, placing it in a fundamentally different category than polynomial-time compression algorithms.
The proofs demonstrate formal non-equivalence through counterexamples: pairs of strings where assembly index matches but compression ratios differ, and vice versa. The authors present those cases as evidence that the metrics should not be treated as interchangeable.
Physical Measurability as Ontological Grounding
A key distinction between assembly theory and computational complexity metrics is measurability. The assembly index is defined as a physical observable: it can be measured using mass spectrometry, NMR, and infrared techniques.[s] You fragment the molecule, identify recurring substructures in the fragmentation pattern, and compute the minimal construction tree.
Kolmogorov complexity, by contrast, is uncomputable in the general case. Shannon entropy requires labeled data and a chosen encoding scheme. Assembly theory grounds complexity in physics, not computation.
The theory was explicitly developed in the context of laboratory capabilities, “with its initial development as a rigorous method for laboratory studies aiming to identify molecules as biosignatures.”[s]
The AI > 15 Threshold
Experimental studies reported to date indicate a threshold at assembly index 15. Molecules with AI > 15 have been found only in living samples in those studies.[s] This threshold corresponds to the point where random assembly becomes astronomically improbable: the combinatorial space expands super-exponentially with each joining operation, making high-AI structures vanishingly unlikely without selection.
Cronin’s lab tested this prediction against terrestrial, marine, laboratory, and extraterrestrial samples. In those tests, biological samples showed high-MA molecules, while the abiotic and extraterrestrial samples did not.[s] The separation was sharp in the reported dataset.
This operational definition of life is substrate-independent. It does not require knowledge of specific biochemistry: carbon versus silicon, DNA versus alternative genetic systems. “A molecule that has no symmetry, has lots of parts that can’t be duplicated, is unique, and has a high copy number equals biology,” Cronin states.[s]
The Director’s Parallel Inquiry
Horror director Lee Cronin’s 2026 film “Lee Cronin’s The Mummy” explores preservation and transformation through a different lens. Following his success with Evil Dead Rise, which grossed $147 million off a sub-$20 million budget, the Irish filmmaker has established himself as a distinctive voice in genre cinema.[s]
The film asks what happens when a preserved body returns changed. A family’s missing daughter is found eight years later, sealed in a tomb: alive but transformed, her persistence across time rendering her alien rather than familiar.[s]
“Time sits at the centre, not as nostalgia, but as something irretrievable.”[s] The film’s treatment of temporal persistence mirrors assembly theory’s focus on objects that survive longer than their “natural life,” carrying forward structure that entropy should have dissolved.
Criticism and Open Questions
Assembly theory faces legitimate scientific skepticism. Evolutionary biologists have criticized its use of terms like “selection” in ways that differ from established biological usage.[s] The 2023 Nature paper’s framing, with claims about “reconciling biological evolution with the immutable laws of the Universe,” struck some readers as echoing creationist arguments.[s]
Others question whether assembly theory addresses a real problem. “As assembly theory itself, it seems to have been developed in the course of Cronin and Walker’s efforts to find a general way to recognise signs of life on alien planets, and even create artificial life.”[s] Critics suggest the framework may prove useful in astrobiology while offering little new insight into terrestrial evolution.
The theory also faces the challenge that detecting selection does not explain the selector. “The best that Assembly Theory can do is detect that high-level selection has happened, but the very existence of life does not explain the mechanism of how life came to be.”[s]
Supporters, including chemist Timothy Cook of the University at Buffalo, take a more measured view: “My view is that assembly theory is interesting as one approach of several to analyze a system that introduces a set of rules that may not be immediately obvious using other methods.”[s]
Implications for Life Detection
Regardless of whether assembly theory revolutionizes evolutionary biology, its application to astrobiology appears more straightforward. The framework offers a protocol: collect molecular samples, measure assembly indices via mass spectrometry, and look for a distribution skewed toward high-AI molecules in abundance.
NASA has engaged with this approach, treating assembly theory as a potential universal biosignature.[s] Unlike searches for specific molecules that assume alien biochemistry resembles Earth’s, assembly-based detection asks only whether something is selecting and preserving complex structures.
Both Lee Cronins work at the interface between persistence and decay. The chemist measures the threshold. The director dramatizes what happens when that threshold is crossed in monstrous ways. Their shared insight: what persists against entropy carries forward a history, and that history is what separates life from dead matter.
