In this research group, led by Jeremy England, we study the physics of how life-like behaviors emerge in matter that is stimulated by access to external sources of energy
Although biology and physics share common principles of scientific reasoning, they nonetheless assess the world in fundamentally different terms. Biology takes the existence of life for granted, and is specifically interested in how the qualities and behaviors of living things help them to flourish. In contrast, physics addresses itself to all matter, living or not, and aims to identify predictive mathematical relationships between measured quantities such as distance, time, and mass.
The most common way of combining these perspectives is to seek an explanation in physical terms for how a given piece of a living thing functions. From the folding of proteins to the firing of neurons, many fruitful lines of research have followed this path, including some pursued by England Group at MIT. In the last five years, however, our research has increasingly taken a different kind of inspiration from biology as we have set out to determine the sufficient physical conditions for life-like physical properties to emerge and persist in settings where they are initially absent.
When talking about living things in physical terms, there are some abilities that are more distinctively life-like than others. Cats fall in gravity, but so too do rocks; accordingly, we would not say the ability to fall is a life-like physical property. However, cats and other living things also copy themselves (through reproduction), harvest energy from their environment (by eating food), and use what they know about the past and present to act in ways that seem to anticipate their likely future. While any one of these abilities might not technically be unique to life, each nonetheless powerfully evokes what we find most impressive about living things, so we call them ‘distinctively life-like.’
In a range of projects that combine analytical derivation with numerical simulation, we have investigated the physical requirements of distinctively life-like behaviors. One detail that has been extremely useful in meeting this challenge is that life-likeness often appears to be very directional in time (for example: one bacterium self-replicates into two, but two bacteria never fuse and un-grow back into one). Any such apparent time-directionality of this sort in a collection of matter that changes its configuration over time at constant temperature is required by very general physical arguments to be powered by a directional flow of energy, such as occurs when heat flows from hot to cold.
Thus, our research program has progressed in part by deriving mathematical statements governing the thermodynamics of matter that changes configuration over time. For example, using a novel extension of the 2nd Law of Thermodynamics, we have shown that the growth rate and durability of self-replicators together set hard constraints on the minimum amount of chemical fuel required for growth. We have also achieved a proof of principle in simulation for a previously predicted ‘self-organization’ of a primitive metabolism, whereby a randomly-wired chemical network spontaneously discovers a finely-tuned, stable way extracting a rich source of chemical energy from its environment. The constraints that we have recently proven for the energetic costs of building precise molecular clocks and for maintaining self-healing structures should be of great potential interest to any nano-engineer who seeks to mimic the architecture of life. And in a forthcoming manuscript, we establish general conditions on a reacting mixture of particles that are sufficient to guarantee the spontaneous emergence of new self-replicating structures on a desired experimental time-scale. Thus, by combining general theoretical progress in statistical mechanics with creative simulations of toy models, we are gradually establishing the physics of how things get (and stay) life-like.
The most common way of combining these perspectives is to seek an explanation in physical terms for how a given piece of a living thing functions. From the folding of proteins to the firing of neurons, many fruitful lines of research have followed this path, including some pursued by England Group at MIT. In the last five years, however, our research has increasingly taken a different kind of inspiration from biology as we have set out to determine the sufficient physical conditions for life-like physical properties to emerge and persist in settings where they are initially absent.
When talking about living things in physical terms, there are some abilities that are more distinctively life-like than others. Cats fall in gravity, but so too do rocks; accordingly, we would not say the ability to fall is a life-like physical property. However, cats and other living things also copy themselves (through reproduction), harvest energy from their environment (by eating food), and use what they know about the past and present to act in ways that seem to anticipate their likely future. While any one of these abilities might not technically be unique to life, each nonetheless powerfully evokes what we find most impressive about living things, so we call them ‘distinctively life-like.’
In a range of projects that combine analytical derivation with numerical simulation, we have investigated the physical requirements of distinctively life-like behaviors. One detail that has been extremely useful in meeting this challenge is that life-likeness often appears to be very directional in time (for example: one bacterium self-replicates into two, but two bacteria never fuse and un-grow back into one). Any such apparent time-directionality of this sort in a collection of matter that changes its configuration over time at constant temperature is required by very general physical arguments to be powered by a directional flow of energy, such as occurs when heat flows from hot to cold.
Thus, our research program has progressed in part by deriving mathematical statements governing the thermodynamics of matter that changes configuration over time. For example, using a novel extension of the 2nd Law of Thermodynamics, we have shown that the growth rate and durability of self-replicators together set hard constraints on the minimum amount of chemical fuel required for growth. We have also achieved a proof of principle in simulation for a previously predicted ‘self-organization’ of a primitive metabolism, whereby a randomly-wired chemical network spontaneously discovers a finely-tuned, stable way extracting a rich source of chemical energy from its environment. The constraints that we have recently proven for the energetic costs of building precise molecular clocks and for maintaining self-healing structures should be of great potential interest to any nano-engineer who seeks to mimic the architecture of life. And in a forthcoming manuscript, we establish general conditions on a reacting mixture of particles that are sufficient to guarantee the spontaneous emergence of new self-replicating structures on a desired experimental time-scale. Thus, by combining general theoretical progress in statistical mechanics with creative simulations of toy models, we are gradually establishing the physics of how things get (and stay) life-like.
