Jeremy England, a physicist at MIT, may have found the underlying physics driving the origin and evolution of life.
Physics is definitely not my strong suit. But the questions of how life arose on Earth, and how likely it is that life would arise on other planets, are intensely interesting to me. So in order to enhance my own understanding, and at the risk of getting things a bit wrong, I will attempt to put into my own words – with some paraphrasing from the original article in Quanta Magazine – an explanation of England’s theory.
England’s theory of life is based on the second law of thermodynamics, which is also known as the law of increasing entropy. Entropy is a measure of how dispersed the energy is among the particles in a system and how diffuse the particles are throughout space. Within any system, random motion tends to increase entropy over time as a matter of probability, because there are more ways for particles and energy to be spread out than for them to be concentrated. More ways for them to be disorganized than for them to be organized.
Systems tend to move toward maximum entropy, where energy is uniformly distributed. Think of a room where a hot cup of coffee sits on a table. The coffee dissipates its heat into the air around it, warming the air slightly as the coffee cools, until the coffee and the air are the same temperature. If we consider the room to be a system, we could say the system has reached maximum entropy.
Living things seem to violate this principle, somehow managing to maintain their own organization. How do they do this?
While entropy must increase over time in a “closed” system, an “open” system can keep its entropy low by increasing the entropy of its surroundings. Living things are open systems: they receive energy from an external source, and they dump heat into their environment. The law of increasing entropy is not violated because the dumped heat increases the overall entropy of the universe while the living organism maintains its orderly, low entropy structure.
From the standpoint of physics, the essential difference between living things and inanimate clumps of matter is that living things are much better at capturing energy from their environment and dissipating that energy back into the environment as heat. An example is photosynthesis, where plants absorb sunlight, use that energy to build sugars and support their life processes, and emit infrared light (heat), a much less concentrated form of energy.
Jeremy England derived a generalization of the 2nd law of thermodynamics that applies to any system that is driven by an external energy source and outputs heat into its environment. All living things are such systems. His formula shows that, in his words, “the more likely evolutionary outcomes are going to be the ones that absorbed and dissipated more energy from the environment’s external drives. This means clumps of atoms surrounded by a bath at some temperature, like the atmosphere or the ocean, should tend over time to arrange themselves to resonate better and better with the sources of mechanical, electromagnetic or chemical work in their environments.”
Self-replication is a mechanism by which a system can dissipate an increasing amount of energy over time. As England says, “A great way of dissipating more is to make more copies of yourself.” The self-replication of molecules of RNA, the nucleic acid believed to have been the precursor to DNA-based life, dissipates energy into the environment. England also showed that RNA is “a particularly cheap building material.” (I’m not exactly sure what this means.) He argues that once RNA arose, its “Darwinian takeover” was not surprising.
Besides self-replication, greater structural organization is another means by which systems can improve their ability to dissipate energy. A plant is better at capturing and using solar energy in an organized way than is a clump of carbon atoms. So England argues that under certain conditions matter will tend to spontaneously self-organize. And once you have self-organizing, self-replicating systems, evolution begins, leading to ever more complex self-replicating systems, which at some point we begin to consider living things.
While England’s theoretical results are generally considered valid, his conjecture that his formula represents the mechanism by which life arose from inanimate matter still remains unproven. But other scientists are excited about his theory, and are contemplating ways to test it experimentally.
We are still trying to answer the question of whether life exists anywhere besides our own planet. We’re actively searching for planets that are rather like Earth: not too big, not too small, not too close to their star and not too far away, planets where liquid water could exist. It makes sense for us to focus our search this way, because so far our single example of a planet that harbors life is our own.
But if Jeremy England is correct, it would seem that some form of life could originate under a wide variety of circumstances — perhaps on planets that are much hotter or much colder than ours. Perhaps on planets that have no solid surface, planets that have no water, planets that have very different chemical compositions.
Life could be much more common in the universe than we’ve been thinking.