“Life is matter with meaning”: the new physics of life and the search for aliens through information

When scientists say that life is not just chemistry but “matter with meaning,” it sounds like poetry, but it stands on very pragmatic grounds. Stuart Bartlett’s team at Caltech, along with colleagues at the SETI Institute, are proposing a physical, not just a biological, framework to explain life—from the first cells on Earth to potential organisms in the bowels of Titan. Their thesis is radical and simple: what we call living is distinguished not by the shape of its molecules, but by the way that matter processes information for one basic purpose—not to die. And this is precisely what could become a tool for searching for aliens, even if they don’t look at all like terrestrial organisms.

From “what is life?” to “what makes life special?”

In a new article in the journal PRX Life, Bartlett and co-authors propose viewing life as a physical process that combines energy, chemistry, and information into a single system.¹. They do not attempt to create a “perfect definition” of life—instead, they highlight its distinguishing feature: the ability to use information to maintain viability. Unlike a rock or a hurricane, which may be complex but “indifferent to their death,” living systems have an intrinsic goal—to continue to exist.

This approach expands on Bartlett's previously proposed Lyfe Framework, which describes "universal life" through four pillars: dissipation, autocatalysis (the ability to grow), homeostasis (stabilization of the internal state), and learning (information processing).^{1 2}The new work delves into the fourth pillar—“learning”—and attempts to formally describe what information living systems consider important.

Semantic vs. syntactic information: what really matters in life

The authors distinguish between two types of information: “syntactic” (SINT) — that is, raw data without any connection to meaning; and “semantic” (SI — Semantic Information) — that is, information that actually affects the viability of the system.¹For example, the signal “red berry is poisonous” for an organism is semantic information, because survival depends on it; the color of the sand under your feet is syntactic, because an error in reading it is not life-threatening.

From a physics perspective, living systems are constantly sampling SI from the chaotic stream of SINT, spending energy on measurement, processing, and reaction. In this framework, life is matter that “learns” from data, but only where it increases its chances of survival. Everything else is noise that can be ignored without drastic consequences.

Lyfe Framework: Four Pillars of the Physics of Life

The Lyfe Framework highlights four necessary conditions that together create a physical space for living^{1 2 3}:

• Dissipation: the system has a source of free energy (sunlight, chemical gradients) and transforms it, increasing the entropy of the environment, but at the same time maintaining its own order.
• Autocatalysis: components of the system promote their own reproduction and growth (like enzymes that speed up reactions to create new copies of themselves).
• Homeostasis: maintaining a relatively stable internal state despite changing environments — from pH to temperature.
• Learning: the ability to change behavior and structure by absorbing SI, which increases vitality.

None of the pillars alone guarantees “life”: fire dissipates energy and grows; crystals self-assemble; machine regulatory systems maintain stability; AI algorithms learn from data. But only their combination with a survival orientation gives what the authors propose to call “life as a physical phenomenon.”

Information Transition: When Chemistry Becomes Life

In the debate about the origin of life, this framework suggests shifting the focus from “when did DNA appear?” to the question “when did matter start using information to survive?”¹The authors speak of an “information transition”: the moment when a system that previously simply responded to local chemistry begins to process SI in a coherent manner, accumulating it and changing its architecture.

This brings the various theories of abiogenesis closer to a common denominator: it doesn’t matter whether RNA, lipid vesicles, or metabolic networks came first—what matters is when they began to read their environment in a way that enhanced their own viability. This approach, unlike many “origin hypotheses,” offers specific experiments for testing.

“Chemical Garden” and epsilon automata: how to test whether a stone can “think”

One such experiment involves so-called "chemical gardens" - structures that self-assemble when metal salts are put into solution and grow fantastic columns that look like miniature geysers.¹The idea is to connect to this process a generator of complex electrical signals, controlled by an epsilon machine - an algorithm that creates hidden patterns.

If these electrical “patterns” begin to be reflected in the growth, geometry, or internal structure of the chemical garden, it would be a hint that even “mere” minerals are capable of not only passively responding, but also adapting to a hidden pattern of information.¹Comparing the state of the epsilon machine and the microstructure of the garden will allow us to verify whether this is already the germ of “information processing.”

Minimum size of life: why a cell smaller than 0,4 micrometers is non-viable

Another consequence is the physical limit on the minimum size of a cell capable of operating with SI. Bartlett and colleagues estimate that the lower limit is about 0,4 micrometers (0,4 μm).¹The reason is Brownian motion and limitations for sensors:

• a cell that is too small “shakes” so much from thermal motion that it loses orientation in space and cannot stably compare signals with its own position;
• The fluctuations of the surrounding molecules become so chaotic that the “measurement” of the environment turns into noise that is more likely to harm than help viability.

If this limit is correct, then the “smallest possible cells” in the universe—from Earth to Titan—should be roughly the same size. This provides a concrete guideline for both biophysicists and astrobiologists modeling potential life forms in exotic environments.

How to “poke” into extraterrestrial life: information interaction as a test

The authors propose another approach to searching for aliens: not just passively listening, but also “knocking” on their possible systems and watching for a response. If, for example, we send a signal to a certain region of space, and the planet or system responds with an increase in information richness (complex, structured patterns), this can be interpreted as a sign of the presence of systems that process SI.¹.

Of course, this overlaps with the old SETI and METI debates - whether we have the right to make contact and "announce" ourselves without understanding who will hear us. But the information criterion makes the discussion more concrete: it is not only important whether someone responds, but whether this response contains signs of conscious use of information.

Assembly Theory: How Molecules Can “Sell” the Presence of Evolution

Another tool that fits well with Bartlett's approach is Assembly Theory, which estimates the "assembly index" of a molecule.^{1 4}If certain structures are chemically too complex to have arisen by chance, their presence hints at a process that used information—such as evolution.

Combined with SI physics, this gives a double filter: we look for systems where:

• chemistry contains “unhealthily complex” molecules;
• The behavior of the environment (atmosphere, surface, energy flows) demonstrates the use of information for stabilization or growth.

Such a combination could take astrobiology beyond the banal search for “oxygen in the atmosphere” or methane and provide a more general, physical language for describing life anywhere.

Why it matters not just for space: medicine, AI and synthetic biology

Although the work is presented in the context of astrobiology, its implications extend far beyond astronomy. In medicine, this approach could help to more clearly separate “living” activity (cancer cells, pathogens) from simply complex chemistry by analyzing how systems gather SI about their microenvironment.¹In synthetic biology, the question arises: when does a “smart material” or self-assembling system cross the threshold beyond which we should consider it as living in an ethical sense?

For AI, this framework sets a provocative vector: if a system learns and changes its own structure to maximize “survival” under resource constraints, how far is this from the physical definition of life? The authors are cautious in their analogies, but acknowledge that information optics allows us to see common features between the evolution of cells, neural networks, and algorithms.

Criticism and open questions: where is the line between “living” and “overly complex inanimate”?

The most obvious criticism of the new approach is: does it not make the concept of “life” so broad that it begins to include complex artificial systems or even entire economies? In response, Bartlett and colleagues insist on three points:^{1 3}:

• viability as a goal: the system has a local goal of preserving its own structure and boundaries;
• information must have a physical medium and a direct impact on the flows of energy and matter;
• The criteria are subject to testing in experiments (such as chemical gardens) and do not remain at the level of metaphors.

Despite this, the line between complex “survival” systems (quasi-organisms, global networks, climate as a dynamic system) and life itself remains blurred — and perhaps this is where the space for further work lies.

Conclusion: “matter with meaning” as a language for talking about the life of the Universe

The concept of life as matter that operates on semantic information offers not a new poetic metaphor but a physical framework for understanding how chaotic chemistry grows into something that can fear death, learn, change, and respond to signals. If this framework holds up experimentally, we will have universal tools to answer two major questions: when life “turned on” on our planet—and how to recognize that it is already burning somewhere many light years away.

Sources

1. Phys.org / Universe Today: Life is just matter with meaning, 2025
2. PRX Life: Stuart Bartlett et al., Physics of Life: Exploring Information as a Distinctive Feature of Living Systems, 2025
3. Phys.org: Defining life with constants from physics, 2025
4. Phys.org: Theory linking evolution and physics (Assembly Theory), 2023