Four states of matter are recognized in physics: solid, liquid, gas, and plasma. But, University of Rochester astrophysicist Adam Frank tells us at Big Think,

Over the past few decades, physicists have increasingly begun to view life as a unique “state of matter” that requires special consideration. It began 70 years ago when Edwin Schrödinger wrote his seminal work, What Is Life? In that small book, he asked whether living systems might require the development of new laws of physics. Although that remains a contentious question, many scientists who study life as a “complex system” have come to believe that living systems are unique in at least one remarkable way: they use information.

Adam Frank, “A new model for defining life across the Universe,” Big Think, July 4, 2024

Every life form, from the most simple to the most complex, constantly uses information to keep itself in existence by finding food and avoiding predators. Rocks, as Frank points out, just sit there, slowly eroding into sand, dust, minerals…

Life forms as “information-driven systems”

Frank, along with University of Rochester physicist Gourab Ghoshal and information theory researcher Artemy Kolchinsky, is hosting a three-day Templeton-funded workshop there next week to explore the significance of life forms as information-driven systems.

Not only are cells adept at using information, but they also depend on it. In this sense they are information-driven: They need to continually gain and use information from their environments to stay alive. It’s also worth noting that some physicists used the term “active matter” to describe living systems, but the active part is really about information.

Frank, “Life across the Universe”

Two speakers will be NASA’s Caleb Scharf, and Florida Institute of Technology’s Manasvi Lingam. They’re interested in questions such as, which regions of the universe enable the information-processing that life requires and what adaptations are needed.

But life needs meaningful information, not just information

Another speaker, Damian Sowinski, will look at the importance to life forms of semantic information, that is, meaningful information.

For example, a zoology textbook might offer reams of information about mice that is bound to be useful to somebody. But none of it means anything to a starving cat. For the cat, meaningful information is the scent trails that mice leave — trails that cats as well as mice follow.

Sowinski, Frank, and Ghoshal, along with colleagues, published an open-access paper last year on that topic.

They define semantic information as “The subset of information that is meaningful, and perhaps necessary for being alive.” They constructed a mathematical model of a “foraging agent” moving in an environment and collecting information about the resources. From the university’s media release:

Imagine a bird in its forest. It knows where to find the food it has stored to nourish itself. Say you move that bird 100 feet to a different part of the forest. “By doing so, you’ve cut some of the bird’s correlations or connections with its environment, but there are still enough correlations that it doesn’t affect viability, or the ability of the bird to survive,” explains Damian Sowinski, the lead author of the paper and a postdoctoral associate in the Department of Physics and Astronomy at Rochester.

Now, move the bird 1,000 feet away—or, more drastically, 1,000 miles away.

“Eventually, the bird is not going to know anything about its environment—all of the connections are cut. The viability of the bird goes from not really being affected to all of a sudden starting to plummet,” says Sowinski.

By contrast, moving a non-living thing like a pebble 100 feet, 1,000 feet, or even 1,000 miles away doesn’t fundamentally change the connections between the environment and the pebble. That’s because the pebble isn’t harnessing any information—relevant or irrelevant—about its surroundings to maintain or reproduce itself.

Sofia Tokar, “How do living things use meaningful information to survive?,” University of Rochester News Center, November 28, 2023

The researchers’ simulations enabled them to identify a semantic threshold: “the critical point where information matters for the agent’s survival. Above this threshold, removing some information doesn’t affect survival, but below it, every bit of information is crucial.”

Seen from this perspective, the information in the zoology textbook is far above the cat’s threshold but the mice’s scent trails are crucially below it.

But now the philosophical questions start

Life — including the cat stalking mice — shows agency. That is, life forms act in order to continue their own survival. How did agency come to exist in life forms? The Rochester group is not backing away from the philosophical questions that raises:

“That’s a deep philosophical question,” says coauthor Adam Frank, the Helen F. and Fred H. Gowen Professor in the Department of Physics and Astronomy. “The whole point of advances in science is to take questions that used to be the domain of philosophical speculation and find a way to talk about them quantitatively. This paper does that in a mathematically rigorous way.”…

“By using this language of information theory, we’re creating a bridge between the mechanistic narratives in the physical sciences and the more informational or behavioral narratives used in the life sciences,” says Sowinski.

He, like his colleagues, is energized to continue the team’s line of inquiry into the fundamental mystery of life. As Sowinski puts it, “Our work is a promising first step to answering a bigger question: What in the world causes a lifeless rock full of pebbles to eventually be covered with purposeful entities that are interacting meaningfully with one another and their environment?”

Tokar, “Meaningful information”

One question they will eventually need to tackle is, can agency come into existence without an Agent? Another question: How can meaning exist in an officially mindless universe?