“It could be that whatever theory we uncover to explain life may similarly have a counterintuitive foundation and lead to even more revolutionary ideas about how our universe works—after all, life is far more complex than gravitation,” said astrobiologist and theoretical physicist, Sara Walker, Deputy Director of the Beyond Center for Fundamental Concepts in Science at Arizona State University. “But right now, we are without theory to guide our search for alien life. Without such a theory, even the 100-year time scale for the gravitational wave discovery may be sorely underestimating how far we are out from discovery of alien life, if it is indeed out there.”
Walker foreshadows Santa Fe Institute researchers Chris Kempes and David Krakauer who argue in a new paper that in order to recognize life’s full range of forms, we must develop a new theoretical frame.
What if life is better understood on the analogy of the eye, they ask, a convergent organ that evolved from independent origins? The history of life on Earth has often been likened to a four-billion-year-old torch relay. One flame, lit at the beginning of the chain, continues to pass on life in the same form all the way down. But what if life is better understood on the analogy of the eye, a convergent organ that evolved from independent origins? What if life evolved not just once, but multiple times independently?
Principles of Life Common in the Universe
In an email to The Daily Galaxy, Chris Kempes wrote: “Our perspective is that once you make the shift to identifying life as a set of principles, it may suddenly appear to be more common in the universe. This could be a shadow biosphere, but could also be much more familiar examples like the evolution of human culture, or complex computer simulations. The underlying materials of life, or the planetary conditions that give rise to it, might be quite diverse, but the shared properties of life at the principles level may be highly conserved across the universe. Life converges at the level of principles.”
In the same email Krakauer: added “We are not talking about shadows but clouds – fully illuminated visible objects that we have failed to see not because they are hidden but because we only look in one direction.”
Life May Have Started Many Times on Earth
Their research has echoes of the theory proposed by Arizona State University astrobiologist Paul Davies in The Demon in the Machine. “If life really does form readily in Earth-like conditions, it should have started many times right here on Earth, so we should look for a ‘shadow biosphere’ of life, but not as we know it, under our very noses.’”
“If life is a universal phenomenon,” wrote Sara Walker in an email to The Daily Galaxy, “explained by as-yet-unidentified physical laws, we should be seeking to understand these in as many contexts as possible. The idea of multiple origins of life becomes critical to this endeavor because it allows us to see more clearly the universal physics of life, in a way not possible if we just focus on its origins in chemistry.”
Both Krakauer and Kempes focus their research on the origins of life –how did life, in all of its complexity, arise from comparatively simple matter? The topic represents a major scientific challenge because of the requirement for synthetic knowledge from fields spanning basic physics and chemistry, geochemistry, planetary sciences, biochemistry, evolutionary theory, and paleobiology. They explore several of the most interesting questions facing the natural sciences and biology. These would include the following: (1) how do biotic mechanisms emerge from abiotic ones, (2) how can we be sure that we have found life if it is materially different from life on Earth, and by extension, how do we verify that an environment is truly lifeless, for example, in a sample of ice from Enceladus?, and (3) how do we in general understand the truly lifeless, for example, in a sample of ice from Enceladus?, and (3) how do we in general understand the range of possibilities for the origin and maintenance of life?
In their three-layered frame, Kempes and Krakauer call for researchers to consider, first, the full space of materials in which life could be possible; second, the constraints that limit the universe of possible life; and, third, the optimization processes that drive adaptation. In general, the framework considers life as adaptive information and adopts the analogy of computation to capture the processes central to life.
Several significant possibilities emerge when we consider life within the new framework. First, life originates multiple times—some apparent adaptations are actually “a new form of life, not just an adaptation,” explains Krakauer—and it takes a far broader range of forms than conventional definitions allow.
Culture, computation, and forests are all forms of life in this frame. As Kempes explains, “human culture lives on the material of minds, much like multicellular organisms live on the material of single-celled organisms.”
Life as a Continuum
When researchers focus on the life traits of single organisms, they often neglect the extent to which organisms’ lives depend upon entire ecosystems as their fundamental material, and also ignore the ways that a life system may be more or less living. Within the Kempes-Krakauer framework, by contrast, another implication appears: life becomes a continuum rather than a binary phenomenon. In this vein, the authors point to a variety of recent efforts that quantitatively place life on a spectrum.
By taking a broader view of life’s principles, Kempes and Krakauer hope to generate more fertile theories for studying life. With clearer principles for finding life forms, and a new range of possible life forms that emerges from new principles, we’ll not only clarify what life is, explains Krakauer, we’ll also be better equipped “to build devices to find life,” to create it in labs, and to recognize to what degree the life we see is living.
Avi Shporer, Research Scientist, MIT Kavli Institute for Astrophysics and Space Research via Sara Walker, Christopher Kempes, David Krakauer, Slate, and The Santa Fe Institute. Avi was formerly a NASA Sagan Fellow at the Jet Propulsion Laboratory (JPL).