What is life? Scientists still can’t agree on an answer. Many suggest that life requires metabolism, genetic material, and the ability to self-replicate, but there the possibility of broad agreement ends. Are viruses alive? What about a storm or a flame? Worse still, the driving force that leads to the emergence of life still eludes us.
Since the time of Darwin, scientists have struggled to reconcile the evolution of biological forms in a universe determined by fixed laws. These laws underlie the origin of life, evolution, human culture and technology, as defined by the boundary conditions of the universe. However, these laws cannot predict the emergence of these things.
The theory of evolution works in the opposite direction, showing how selection can explain why some things exist and other things don’t. To understand how open shapes can emerge in an advanced process of physics that does not include their design, a new approach to understanding the transition from non-biological to biological is needed.
A unique property of living systems is the existence of complex architectures that cannot form by chance. These architectures can exist for billions of years, resisting environmental degradation. How is this achieved? Selection is the answer: it is the force that creates life in the universe through the emergence of evolutionary systems. Selection preceded evolution.
Imagine you are a rock climber scaling a vertical rock face with a ladder, building it up one rung at a time. The raw material for the ladder parts is randomly “produced” and thrown at you. If the materials come too fast, you can’t catch them and you’ll end up dying. If the materials come in too slowly, you won’t be able to reach the top, and again you will die. If the materials arrive at the right rate, however, the “production” time and the “discovery” time of the parts will be balanced so that the selection can take place.
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The formation of these scales must occur at the molecular level for selection to occur, but causation is not accepted by physics as a fundamentally occurring process. On the contrary, causality emerges in complex systems. But where do these complex systems come from to help the emergence of causality?
The “assembly theory” and the mark of life
A few years ago we realized that it was possible to tell the difference between complex molecules and simple molecules by the number of steps required to build the molecule from a line of parts. The greater the number of parts required, the more complex the molecule. We call the shortest way to assemble a molecule its “assembly index”. The Assembly Index literally tells us the minimum amount of memory the universe needs to have to remember how to create this object as quickly and simply as possible.
We then realized that this observation led to a much deeper framework that we call ‘assembly theory’, which, in simple terms, helps explain why something exists. Indeed, the assembly index makes it possible to order in time, which explains why certain objects exist before others: it is due to constraints in the path which leads to the object in question. In other words, if A is simpler than B and B is simpler than C, A and B must exist before C exists.
How does this translate into a clear idea of how to find life? Assembly theory allows us to identify objects that are both complex (i.e. with a high assembly index) and that form in such abundance that they cannot be formed than by life. The greater the abundance of objects with a high assembly index, the more unlikely it is that the objects could be produced without a highly directed process requiring evolution. Therefore, assemblage theory explains the underlying mechanism or framework from which selection results in the emergence of life itself.
Universal Life Detector
The quest to discover the precise origin of life on Earth has been a great challenge for several reasons. The first is that it is not possible to map the exact processes that gave rise to life at the level of atoms and molecules. Another is that the emergence of the specific life we find on Earth appears to be entirely dependent on Earth’s history, which cannot be fully replicated in the laboratory.
However, that doesn’t mean the pursuit will forever elude science. I am optimistic that we will be able to detect the origin of life in laboratory experiments on Earth, as well as find life elsewhere in the universe. We’re hoping the plethora of exoplanets out there means that life is still going to emerge somewhere in the universe – the same way stars are constantly dying and being born.
If we can shift our thinking to look for selection-producing collections of objects (like ladder-building climber-like molecules) with high assembly indices as a clear precursor to life, then our approach to finding the life in the universe is expanding dramatically. The goal now is to find complex objects with a common causal history. We call this a “shared assembly space”, and it will help map interactions throughout the universe.
Another way to search for life in the universe is to design experiments that allow us to search for the emergence of life in the laboratory. How could we do this? If life emerged over 100 million years using the entire planet as a test tube or a small hot pond, then how could we recreate such a massive experiment, and how would we know if we were successful? You have to start with the Universal Life Detector (ULD). The ULD will detect objects, systems and trajectories that have high assembly indices and, therefore, are the products of selection.
“Chemputation” and search for chemical space
To answer the big scientific questions, you have to ask the right questions. I have long thought that the question of the origin of life should be framed as a research problem in “chemical space”. This means that a large number of chemical reactions, from a set of single input chemicals, must be explored over many cycles and reaction environments for the process of selection and causation to emerge over time. .
For example, if a molecule is generated in a random soup and that molecule can catalyze or cause its own formation, then the soup will be transformed from a collection of random molecules into a highly specific collection of molecules with multiple copies of each molecule. At the molecular level, the emergence of the self-replicating molecule can be seen as the simplest example of the emergence of “causal power” and is one of the mechanisms that allows selection to occur in the universe.
How can we explore chemical space in a way that goes far beyond what computer simulations can accomplish? To do this, we need to build a series of modular robots that understand and can perform chemistry. (A major challenge is that the physical architecture to do this does not yet exist, and most chemists believe that programmable control of chemical synthesis and reactions is impossible. However, I believe it is possible. But to suggest this idea is to suggest the Internet before computers existed.)
About ten years ago, we asked if it was possible to build a universal chemical robot capable of manufacturing any molecule. This seemed like an insurmountable problem, because the chemistry is very messy and complex, and the instructions used to make molecules are often ambiguous or incomplete. By analogy, compare this to the generalized abstraction of computation, in which the Turing machine can be used to run any computer program. Could a universal abstraction for chemistry be constructed – a type of chemical Turing machine?
To achieve this, we need to consider the minimal chemputing architecture required to make any molecule. This is the key abstraction that allowed the concept of chemputation – the process of making any molecule from code in a chemputer – to come into being. And the first working programmable chimputer was built in 2018. Initially, chimputers were used to publicize molecules, develop better synthetic routes, and discover new molecules.
We aim to design and build networks of chemputers, or a “chemputer-mesh”, dedicated to the search for the origin of life in my laboratory and throughout the world. All chimputers in the mesh will use the same universal chemical programming language and aim to search the chemical space for evidence of selection from very simple molecules. By designing an “assembly detector”, according to the same principles as for the ULD but adapted to the laboratory, we aim to capture the engine responsible for the origin of life in the act.
Compare that to the large detectors at the Large Hadron Collider built to find the high-energy Higgs boson. Our assembly detector will look for complex molecules that have a high assembly index and are produced in large numbers from a soup of simple molecules. The next step will be to set up the chemputer-mesh to explore the chemical universe to find the conditions from which life can emerge. If this is successful and we can demonstrate how simply these conditions can emerge on Earth, we will be able to follow how evolution can start from the inorganic world – not just on our planet, but on all exoplanets in the universe.