12

THE COSMIC BIOSPHERE

The total number of minds in the universe is one.

—ERWIN SCHRÖDINGER

I have always wanted to know the answer to three questions: Why is the universe expanding? Is there life elsewhere in the universe? And if so, how did it originate? These might seem like distinct concerns, but I have come to the opinion that the questions about the expanding universe and life are linked. The last several chapters have focused on the first question. Now I want to deal with the second.

The thing is, I don’t think they are first and second questions. While we don’t have complete answers to these questions, I think origination and persistence of living systems are traced back to the expansion of the universe. You should be at least astonished by this claim, so let’s dive into it.

When we look at cosmic history, we see the chain of events that unfolded to generate the large-scale structure in the universe. Cosmic time unfolded with primordial quantum vibrations that blossomed into a hierarchy of stellar environments called galaxies and planets that are now part of an interwoven cosmic structure. When we look at the large-scale structure of galaxies, we assume that life and the universe that it inhabits, borrowing from the famed biologist Stephen Jay Gould, are “non-overlapping magisteria.” To most cosmologists, complex systems like life are of little consequence to the problems we are trying to solve, such as the big bang singularity and the parameters of the standard model. To my biologist friends, life is housed in a biosphere that is decoupled from the happenings of the universe out there. But what evidence do we have that life and the universe are truly decoupled? Conversely, what evidence do we have that life and the universe are coupled?

My dance with biology and physics started way back in college, when I considered majoring in biology. I have never been able to shake the biology bug, and my current research in cosmology has reawakened my biological questions, even though I put formal plans aside for a while. At my college, bio majors were required to have a year of organic chemistry, so laziness got the best of me. Still, my musings in biology persisted throughout my studies in physics. In the middle of my second year of graduate school I decided that I wanted a change, so I approached my field theory professor Gerry Guralnik, a codiscoverer of the Higgs boson, and confided to him that I was interested in biophysics and was considering leaving physics altogether. Then Guralnik said, “Let me call my former PhD adviser Wally now and get his advice.”

The Wally that Gerry was referring to is Walter Gilbert, a theoretical particle physicist who had also caught the biology bug and ended up winning the Nobel Prize for a key discovery in genetics—the nature of stretches of DNA known as introns and exons—which, among other things, led to the human genome project and gene therapy. Guralnik made the call and within minutes Gilbert invited me to visit his lab at Harvard. I spent three hours talking with Gilbert and he gave me an in-depth tour of his lab. He also made a recommendation for me to work in Harvard’s biophysics program. That summer, thanks to Gilbert’s recommendation, the renowned biophysicist Jim Hogle offered me a job in atomic resolution virus structure determination using X-ray crystallography. From that experience, I learned some new tools and gained a deep appreciation of the complexities involved in biology and the inapplicability of physical reductionism in attempting to comprehend life’s processes. It also comforted me to learn that I wasn’t alone: other physicists and mathematicians—including many of the greatest—had explored their own biological musings. People including John von Neumann, Eugene Wigner, Claude Shannon, Norbert Wiener, and Roger Penrose, to name a few. I especially think that we can take some lessons and inspiration from the story of Erwin Schrödinger, whose audacious speculations and predictions in biology have been hugely influential. Physics has undergone exponential growth since Schrödinger’s time, and in this “naive” spirit, I will playfully venture into ways in which biology may inform some mysteries in physics and vice versa. But first let’s learn from Schrödinger’s scientific audacity and ingenious contributions to biology.

Schrödinger moved to Ireland to escape the Nazis in 1938, and continued his work in Dublin. In 1943 he gave a series of lectures at Trinity College that would eventually revolutionize biology. In 1944 they were published in a tiny book called What Is Life? In it, Schrödinger speculated on how physics can synchronize with biology and chemistry to explain how life can emerge from inanimate matter. Schrödinger proposed his central question by asking, “How can the events in space and time which take place within the spatial boundary of a living organism be accounted for by physics and chemistry?”

In other words, how is it that the same laws of physics that describe a star account for the intricate processes of metabolism within the living cell? Schrödinger quickly admits that the physics of his time was insufficient to explain some of the ingenious experimental findings that his predecessors and contemporaries had made about the living cell. He even considered the possibility that physics as it was known then may not be enough, when he said, “One must be prepared to find a new physical law prevailing in it.” Despite this, Schrödinger marches ahead, using the physics of his time to make some auspicious predictions that inspired the discovery of the double helix structure and functioning of DNA.

Quantum mechanics plays a key role in life, since it is the quantum that is necessary for the stability of atoms and the bonding rules to construct the plethora of molecules found in living matter. (As to whether the more “exotic” quantum properties, such as entanglement or quantum tunneling—where a wave function can actually pass through a barrier—may play a role in life, this remains an open research issue. We’ll get to that.) Schrödinger opens his argument by conjuring quantum mechanics as the starting point to understand the difference between nonliving and living matter. For example, the bulk properties of a piece of metal, such as its rigidity and ability to conduct electrons, require an emergent long-range order, as we saw when I first raised the emergence principle. These properties should be a result of the bonding mechanism and the collective effects of the quantum wavelike properties of electrons in the metal’s atoms. Schrödinger then describes how the atoms in inanimate matter can organize themselves spatially in a periodic crystal, before making a daring leap. Life clearly is more complicated and variable than a piece of metal, so periodicity isn’t going to cut it. So Schrödinger makes a bold proposal: that some key processes in living matter should be governed by aperiodic crystals. More astonishing, Schrödinger postulates this nonrepetitive molecular structure—which will turn out to be a great description of DNA—should house a “code-script” that would give rise to “the entire pattern of the individual’s future development and of its functioning in the mature state.”

Before Schrödinger’s time biologists had the idea of the gene, but it was a formless unit of inheritance, with much that was left unknown. When Schrödinger proposed his idea about how genetic material should work, it was completely unanticipated in anyone else’s work. Today, of course, the idea that genes are governed by a code, similar to a computer code, which could program the structures and mechanisms of the cell and determine the fate of living organisms, might just seem to be common sense. While I say this, exactly how this is accomplished at a molecular level is still a rich research enterprise in biology. What is remarkable is that Schrödinger used reasoning stemming from quantum mechanics to formulate his hypothesis. Schrödinger was an outsider to biology, and this naturally made him a hidden deviant and ripe for making a paradigm-shifting contribution. Whether quantum mechanics was operating in some subtle way for life’s processes was not central to Schrödinger’s argument, but his new line of reasoning provided a completely new set of concepts to explore novel mechanisms. It’s worth noting that no one took Schrödinger’s “code-script” seriously, even after biologist Oswald Avery’s 1944 publication of a paper that gave strong evidence for DNA as the carrier of genetic material. Of course, Avery’s work itself wasn’t immediately embraced: as described by science historian Matthew Cobb, part of the reason for this lack of excitement over Avery’s discovery was that DNA was thought to be a “boring” molecule with a repetitive structure—exactly what Schrödinger had said a gene could not be. Nevertheless, Schrödinger’s quantum reasoning led to a prediction that the aperiodic structure of DNA carried a code that could program life.

Schrödinger’s unappreciated insight came about from an auspicious set of events. In 1943 the US Scientific Research and Development Committee hired some scientists to study information from radar for antiaircraft purposes. Among the scientists were Claude Shannon, the pioneer of information theory, and Norbert Wiener, who found connections between control systems in machines and biological life and coined his findings cybernetics. Both fields have surged into prominence today, especially in the form of quantum information theory, as well as machine learning and artificial intelligence, but they were hugely influential in our understanding of the theoretical and computational underpinnings of life.

As important as Shannon and Wiener are, the game really changed when computer science pioneer John von Neumann argued that a gene was the carrier of information. Von Neumann imagined a gene as a tape that could program an organism. He made an analogy between self-replicating machines and cellular replications. In this case, in order for a machine to replicate itself, there must be an underlying mechanism present to copy the information that specifies the machine itself. In a 1951 conference proceeding, the godfather of developmental biology Sydney Brenner said “[Von Neumann] divided the machine—the automaton as he called it—into three components: the functional part of the automaton; a decoding section which actually takes a tape, reads the instructions and builds the automaton; and a device that takes a copy of this tape and inserts it into the new automaton.” It wasn’t immediately obvious what von Neumann was onto, at least not to Brenner: “I think that because of the cultural differences between most biologists on the one hand, and physicists and mathematicians on the other, it had absolutely no impact at all. Of course, I wasn’t smart enough to really see then that this is what DNA and the genetic code was all about.”1 Brenner’s observations about how cultural differences between biologists, physicists, and mathematicians were in part responsible for biologists missing von Neumann’s earth-shattering insight about information, genes, and replication remain relevant today. The silos of scientific disciplines and scientific social orders still limit how scientists work.

There were two more insights that Schrödinger posited between life and physics. I will leave it for you to read his landmark book What Is Life? about his reasoning that living things have to negate the second law of thermodynamics, which describes the fact that closed systems evolve to maximize disorder, or entropy. Schrödinger called this negentropy: “What an organism feeds upon is negative entropy. Or, to put it less paradoxically, the essential thing in metabolism is that the organism succeeds in freeing itself from all the entropy it cannot help producing while alive.” Living entities have to stabilize their structure and function over their lifetime against the fundamental tendency for disorder, since entropy always increases. Other biologists, mathematicians, and physicists have further developed Schrödinger’s idea into rigorous mathematical statements about how this works.

His third insight has to do with consciousness, and we’ll come back to that in the conclusion of the book. First I want to ask, how would Schrödinger revise What Is Life? with the new developments in modern biology and cosmology?

Over the years I have developed a pattern: I have chosen to make friends with biologists. Having those friendships means that I’m always asking about what they think is cool in biology. In the past several years I’ve had frequent conversations with my friend Salvador Almagro-Moreno, a molecular biologist. Sometimes meeting over a drink, we exchange ideas: I tell him my latest musings in cosmology research and he tells me about his musings in biology. It probably won’t surprise you to learn that Salvador is a proud owner of a first edition of Schrödinger’s What Is Life? He and I share a vision that I think many of our fellow biologists and physicists would find too deviant, and even repugnant. We don’t let that stop us, and there have been many times that we stayed up late talking about this fascination. There was definitely some strategy here: in part our conversations were an exercise in deliberately generating an outsider perspective, hopefully to benefit each other’s research insights. But it wasn’t all so calculating: it was a lot of fun, and just one of the things that make our jobs as scientists so rewarding. What is interesting to me about our discussions is not just the ideas themselves, but how our conversations generated new questions in both our zones of inquiry.

In 2014, I held the E. E. Just chair in natural sciences at Dartmouth College. Ernest Everett Just was a pioneering Black developmental biologist who cemented the early field of epigenetics. His remarkable life story, scientific contributions, and legacy are majestically described in Black Apollo of Science by Kenneth Manning. As the E. E. Just professor, I had the responsibility of running a university-wide science program for promising students from underrepresented groups interested in science. Salvador was awarded the E. E. Just postdoctoral fellowship and helped me with the program by leading its mentoring and teaching component. Nowadays, Salvador is a biology professor at the University of Central Florida, one of the largest Hispanic-serving institutes in the United States, and is leading similar efforts as the E. E. Just program. One day we were discussing some program business when the conversation, as usual for us, evolved. I started telling my friend about a research idea I had in cosmology. The idea was a new mechanism to understand what is called the fine-tuning problem: as with the value of the cosmological constant, there are other constants of nature that have values that are just the way they need to be so that life could happen. A hugely important set of constants, known as coupling constants, that determine the strength of the force—such as electromagnetism or the weak force—are involved in interaction between particles. The idea I told Salvador about was that, if the universe went through a large number of cycles of collapse and expansion, the big bang phase would provide an opportunity to reset the values of the coupling constants. Most cycles of expansion might not host life, but eventually the universe would hit the jackpot. Salvador asked me very precise questions about my project, and the next day, in a state of elation, he told me that he was able to implement the cyclic-universe idea into the development of a theory based on some experiments he completed involving genetic evolution in biology.

One of Salvador’s concerns was understanding what it took for bacteria to become pathogenic—capable of causing disease in a host like us. According to him, various combinations of genes, like a slot machine, can hit the jackpot in giving the bacteria the ability to become harmful. Salvador made a brilliant analogy between the coupling constants in my cosmological model and the various forms of a gene, known as alleles of the gene. He likened the bacterium’s population cycles and environmental factors to a cyclic universe as a mechanism to change the different combination of genes. The different replicating populations represented the many cycles in the model, each with its own alleles or variations. This led him to propose the theory of virulence adaptive polymorphisms (VAPs).2 The work was published in the top journal in microbiology. The idea worked and has made a big mark on his field.

Now it was time for my friend to return the favor and inspire some ideas for cosmology. Over the years we had mischievously developed a conviction and intuition that there is a hidden interdependence between living systems and cosmology. I came at the question from cosmology. Salvador came at it from a biological direction. And to our delight this question led us to a few issues that the big bang and living systems (such as ecosystems) have in common.

A major concern for both of us has to do with the flow of entropy in the universe, whether at biological or cosmological scales. In the epoch in the early universe before there were stars and planets, the universe was mostly filled with an equal amount of radiation and matter, where the photons and electrons were in thermal equilibrium. If a collection of gas molecules occupy a closed system, say a room, they are going to tend to thermal equilibrium—the temperature, essentially, will become the same throughout the room. As they approach equilibrium, their entropy will increase. Entropy is a measure of disorder, and so of ignorance about what the gas molecules are doing. The entropy will increase when there are more particles and more space for the particles to potentially occupy—it becomes increasingly difficult to specify what they are all doing. Entropy also negatively affects the ability of any system to do work. Physics, biology, and chemistry rely on an important concept called free energy, which is a measure of how much energy in a system (such as a living cell) is able to be used for work. Mathematically we can express free energy as ΔF=ΔE−TΔS. The equation states that a system can do work with a positive change in free energy (ΔF), where a positive contribution comes from a change in energy (ΔE) and a negative contribution from the change in entropy (ΔS). The entropy contribution to free energy reduces the amount of energy that can be used to do work. For example, sunlight shining on Earth generates free energy, which we calculate by adding the contribution of the potential energy stored in the wavelength of the photons and subtracting the entropy from the array of photons.

But there are some important caveats having to do with gravity. The gravitational expansion of the universe keeps the matter and photons in the cosmic microwave background homogeneously distributed. Situations of extremely high gravitational entropy are contained when matter collapses into localized objects like black holes, which did not exist in the era when the CMB formed. So, when the universe expands, gravity acts to distribute matter in a homogenous, ordered fashion, and this lowers the entropy of the universe. When gravity acts to coalesce matter into supermassive black holes, entropy goes up: the heavier the black holes the larger the entropy.3

And there is an important problem. The photons and matter in our universe were in equilibrium during the CMB epoch, so the entropy then was high. But as the universe continued to evolve, the entropy would continue to increase. This implies that the entropy of the very early universe, before the CMB epoch, must have been very low.

At the largest observable distances, we see a connected pattern of large-scale structure of galaxies distributed across the universe. As the universe continued to expand and cool, out-of-equilibrium structures with varying complexity like stars, clusters of galaxies, and life formed. The structures will contain lower entropy than the rest of the universe. By starting off with low entropy, the universe is able to arrest the growth of entropy against the trend of the second law, by concentrating regions of lower entropy within cosmic structures. These cosmic structures, such as stars, store potential energy; in the case of stars, it’s from the rest mass of hydrogen, which will release highly energetic photons from nuclear fusion. This entropy-lowering network of structures becomes the main currency for the biosphere and life on planets. Even the father of thermodynamics, Ludwig Boltzmann, said, “The general struggle for existence of animate beings is therefore not a struggle for raw materials… nor for energy which exists in plenty in any body in the form of heat, but a struggle for entropy, which becomes available through the transition of energy from the hot sun to the cold earth.”4 Nevertheless, even as the universe deviated from homogeneity, by seeding and forming lower entropy structure, entropy elsewhere in the universe continued to grow. And entropy also has a tendency to grow within those structures. This makes entropy, or its absence, a key player in sustaining cosmic structure, such as stars and life; therefore, an early lifeless universe with low entropy is necessary for life here on Earth. Stars like our sun radiate free energy to the earth. This free energy is absorbed by electrons in plants and used for the necessary chemical work for its living function. The plant will release this energy in the form of heat and give off to the universe more entropy than it took in.

Unfortunately, it is difficult to explain with our current understanding of physics why the entropy was so low in the early universe. In fact, this problem of the low entropy we demand of the big bang is one of the major problems with the theory. It was first identified by Roger Penrose. Its solution remains a mystery.5 I remember discussing this problem with Penrose on a nice summer walk, and we both agreed that if we wanted to understand how gravity could have helped set up this unlikely scenario, we were going to need the real connection between entropy and gravity, which is currently lacking, to reveal its nature. One hint is that at the earliest moments of the universe, close to the big bang, the curvature of space-time approached infinity. Whatever new physics tamed this infinity should tell us why the entropy of the universe was so low. We will get to this.

The biology side of the story stems from Salvador Almagro-Moreno’s research into the genetic and ecological drivers that lead populations of harmless bacteria to evolve and emerge as pathogens. Crucial to the story is that it isn’t just a question of the genetic code of the bacteria. One of Salvador’s mantras is that life is an adaptive phenomena responding to constant and unexpected changes in pressures from the environment. If life can have more channels and resources for being adaptative, it will find a way to use them. Central to his research is understanding evolution from the genetic code in a population of organisms, and the epigenetic influences from the ecosystem. Epigenetic factors are called that because they sit on top of genetic factors, and they are one of those other channels for adapting beyond changes to the genetic code. For example, an environmental factor, such as a pattern of electrical current hitting the cell membrane during replication, can enhance or suppress certain genetic factors, leading to completely different features in the phenotype of the offspring.

FIGURE 25: A simulation of the large-scale structure of the universe. Each dot represents a galactic system.

This makes an organism an emergent phenomenon, where the final shape of it is not contained in the individual pieces and influences that make it up. Recall that in emergent phenomenon in general, it is the interactions of the building blocks that collectively exhibit the emergence. This also implies that a population is emergent, too. Living things comprise a network of interactions that is mediated through the environment. A living system is able to regulate billions of cells to maintain its overall functioning. Beyond that, collections of organisms belong to a network called an ecosystem, which also maintains a dynamical equilibrium.

This extends all the way to networks at life’s largest scales. The idea of the earth being a self-regulating ecosystem was codiscovered by James Lovelock and Lynn Margulis in the 1970s, and it became known as the Gaia theory. The name Gaia came from the goddess who personified Earth in Greek mythology. In response to the name, Lovelock, a chemist, observed that “biologists scorned it… it gradually became known as Earth Systems Science, but it is the same thing.” Whatever you call it, the takeaway for me is that the flow of negative entropy exists not only for individual living things but for the entire earth. The sun sends free energy to the earth, and through a chain of complex interactions, the energy gets distributed through a network of interactions to living things, each relying on it to maintain its complexity in the face of increasing disorder. But there’s no free lunch: when living things release this energy back into the environment, they mostly do so in a form that has higher entropy than what they received. Salvador and I noticed the uncanny parallels between living systems and the evolution of the universe through the lens of entropy.

This could seem like a coincidence in the behavior of the universe and of life, but we decided to treat the parallel as though it were not. Instead, we proposed that Schrödinger’s idea of negentropy is one of the central organizing principles of the evolution of the cosmos and the existence of life. Salvador elected to call this the entropocentric principle, a wink at the anthropic principle that first emerged from string theory and caused such a controversy when I was first working on the vacuum-energy problem. The anthropic principle, in its strong form, states that the universe is fine-tuned for life. The laws of nature and values of coupling constants of their interactions have the values that are consistent with life on Earth. For example, if the strength of the nuclear interactions differed by a few percent then stars would not be able to produce carbon and there would be no carbon-based life. The fine-tuning problem may not be as severe as it seems. In research I conducted with my colleagues Fred Adams, Evan Grohs, and Laura Mersini-Houghton, we showed that the universe can be fit for life even when we let the constants of nature like gravity, vacuum, and electromagnetism vary, so long as they vary simultaneously.6 Maybe we don’t need the anthropic principle after all. The entropocentric principle, on the other hand, is harder to shake. If the universe was unable to provide pathways that enabled it to transfer regions of lower entropy, then life as we know it would not exist. We call this biological dependence on the entropic relationship of the cosmic structure the entropocentric universe. Living systems situate themselves to reduce their entropy by expelling it out into the environment, while consuming energy from their environment. Did the universe play the same game near the big bang?