Before there ever could be biomolecules, or a genome, or living beings, there had to be carbon and the other chemical elements that are essential to life. The science of carbon is remarkable, and the more one knows about it, the more one can stand in awe of the amazing universe in which we live. My career in physics—in particular, the quantum physics of atoms and molecules and light at the interface of chemistry and physics—has taught me the depth and power of the natural sciences to understand the world. It is a pleasure to be able to contribute to the Biologos blog a few thoughts about carbon: how it came to be made in the fire of the stars of the early universe and how it enables the remarkable chemistry of life written out in the words of the genome. Putting it all together draws on connections between atomic and nuclear physics, cosmology, quantum theory, chemistry, biology, and what science is all about in the first place.
I tell the story based on all the positive knowledge we have from the sciences. Does it have anything to do with God and humanity? Tomorrow's post will help you decide. First, let us take a whirlwind tour of the picture science gives us of the early universe and of the origin of the chemical elements.
According to the best current measurements, our universe is approximately 13.8 billion years old, and had a long history before there was life on earth. After an initial “Big Bang,” the universe rapidly expanded and cooled so that after a few minutes the present abundance of most of the atomic nuclei in the universe had been established, about ¾ hydrogen and ¼ helium, plus a trace of lithium. The simplest atomic nucleus is hydrogen,1H, having a single positively charged proton, whereas the helium nucleus, 4He, known as an alpha particle, is comprised of two protons and two neutrons. In this early stage of the universe, there were no nuclei of species heavier than 7Li (lithium with 3 protons and 4 neutrons) such as carbon, oxygen, or iron.
After about 380,000 years of expansion and cooling, the positively charged hydrogen and helium nuclei recombined with negatively charged electrons to make ordinary electrically neutral hydrogen and helium atoms. The universe was still mostly uniform without clumping into galaxies and stars, but
once it was composed primarily of neutral atoms, it became transparent to light, that is, light could propagate freely throughout the universe. This light has continued to cool, and its afterglow is known as the
microwave cosmic microwave background radiation.
What about the heavier elements? Since stable nuclei heavier than lithium didn’t exist in the very early stages of the universe, where did they come from? How were they built up?
After the separation of light and matter in the early universe, the hydrogen and helium began to clump into large clouds of gas that under the influence of gravity condensed into galaxies and stars. The first stars and galaxies had already formed by the time the universe was one billion years old. It turns out that the heavier elements can be made in the hot interior of stars by fusing together lighter nuclei via sequences of nuclear reactions that can explain the observed abundance of these elements. It is only in the dying phase of certain types of stars that temperature and pressure is sufficiently high that these fusion processes occur to make the heavier elements. These elements are then expelled into the surrounding interstellar medium by the exploding star at the end of its life. The clouds of gas formed this way later condense into new stars, such as our sun, some of which have accompanying planetary systems. Consequently, before there could ever be carbon, there had to be a first generation of stars to be born and die. In other words, given what we understand about the laws of nature and star formation and evolution, the universe actually needs to be billions of years old before carbon-based life could be present.
How the heavier elements are made in stars was worked out in the 1940s and 1950s through discoveries about nuclear physics and nuclear reactions. A classic paper published in 1957, “Synthesis of the Elements in Stars,” by Margaret and Geoffery Burbidge, William Fowler, and Fred Hoyle, laid out the basic framework that remains with us today. Fowler received the 1983 Nobel Prize in Physics for his work on
nucleosynthesis, the two Burbidges received the Gold Medal of the Royal Astronomical Society in 2005, and Hoyle was later knighted for his work in astrophysics and was awarded the prestigious Crafoord Prize of the Swedish Academy of Sciences in 1997 for his work on the formation of the elements in stars.
Getting the heavier elements requires first making a carbon nucleus, which is very difficult. Making 12C requires that three alpha particles, 4He, fuse together. This is called the triple-alpha process, but it is impossible at the 15 million degree temperature inside a normal star like our sun, because the average velocity of the alpha particles is too low for them to overcome the very strong repulsive electric forces between the positively charged4He nuclei. Hans Bethe had already shown in 1939 that a temperature of 1 billion degrees would be required for such repulsion to be overcome. But such a high temperature does not occur even in stars.
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| Fred Hoyle |
In 1953 the young astrophysicist Fred Hoyle realized that accounting for the relative abundances of carbon and oxygen in the universe required that there be a special quantum state of the 12C nucleus that would allow it to form in stars at temperatures around only 100 million degrees. The postulated quantum state, which may or may not exist, had to have just the right properties to allow fast enough production of 12C nuclei but to prevent their destruction by rapid conversion to 16O upon fusing with another alpha particle. While visiting the Kellogg Radiation Laboratory at Caltech, Hoyle told William Fowler and his colleagues and students there about his prediction, and it was verified through laboratory experiments that the needed state existed at close to the predicted value. With this knowledge in hand, Hoyle and others could then understand how the heavier elements could be made through sequences of nuclear reactions starting with 12C and 16O, and the foundation was laid for understanding how all the heavier elements came to be.
All the elements needed for life are synthesized in the late stages of the life cycle of certain stars. Without the Hoyle state in the triple alpha process, we would not be here as living beings who can understand such things. In an article entitled “The Universe: Past and Present Reflections,” published in the Annual Reviews of Astronomy and Astrophysics in 1983, Hoyle wrote the following (Vol. 20, p. 16):
From 1953 onward, Willy Fowler and I have always been intrigued by the remarkable relation of the 7.65 Mev energy level in the nucleus of 12C to the 7.12 Mev level in 16O. If you wanted to produce carbon and oxygen in roughly equal quantities in stellar nucleosynthesis, these are the two levels you would have to fix, and your fixing would have to be just where these levels are actually found to be. Another put up job? Following the above argument, I am inclined to think so. A common sense interpretation of the facts suggests that a superintellect has monkeyed with physics, as well as with chemistry and biology, and that there are no blind forces worth speaking of in nature.
Hoyle was known for making controversial claims. While few scientists would claim that the science would establish that “a superintellect has monkeyed with physics,” the Hoyle state does provide another example where the laws of physics of our actual universe are fine tuned such that carbon-based life is possible.
Be sure to check out tomorrow’s post to learn more about the intersection of science, carbon, and life.
Paul S. Julienne recently retired from his career as a physicist at the National Institute of Standards and Technology and the Joint Quantum Institute of NIST and the University of Maryland. He has published over 200 scientific papers on the theory of quantum processes in atomic, molecular, and optical physics.
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Word and Fire: The Amazing Story of Carbon, Part 2: Word
http://biologos.org/blog/word-and-fire-the-amazing-story-of-carbon-part-2-word
Today's entry was written by Paul Julienne. Please note the views expressed here are those of the author, not necessarily of The BioLogos Foundation. You can read more about what we believe here.
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Part 1 of this article told us how a special quantum state in the compound state of three alpha particles plays a critical role in the production of carbon and the rest of the heavier chemical elements in the hot interior of a dying star. Carbon made this way became part of the gas cloud that eventually condensed into our sun and its planetary system, and became part of our earth where we live. Let us now skip to today and reflect a bit on science and life—life as we know it as ordinary human beings and life as made possible by the unique chemistry of carbon. Among other things, this chemistry makes possible the molecules of life, including the remarkable DNA molecule that is the basis of molecular genetics and the human genome.
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Dying Red Giant carbon-rich star U Camelopardalis, 1500 light years from the
earth, blowing off a shell of hot gas. From the Hubble Space Telescope. |
I had the pleasure of knowing Francis Collins even before he founded BioLogos. We both shared the concern that too many people in our churches, in the general public, and in the sciences were being influenced by the widespread misconception that science and Christian faith must be in conflict with one another. The reality of the situation is much more interesting and subtle than can be captured by such a generalization. We also shared the concern that young people going into the sciences need not have to face a dilemma of choosing between science and their faith, as if one excluded the other. I count among my friends a number of scientists who, like Francis and myself, see no conflict between their science and their belief in God.
The word “science” comes from the Latin scientia, knowledge. Scientists seek understanding of the world. What it is really like? How does it work? Nobel laureate physicist Richard Feynman said that a really important aspect of science “is its contents, the things that have been found out. This is the yield. This is the gold. This is the excitement, the pay you get for all the disciplined thinking and hard work.” Most scientists I know will share Feynman’s passionate enthusiasm about understanding the world.
Scientific knowledge is derived from the scientific method of observing the world as it is. Science has been enormously fruitful and successful. Knowledge about the way the world works has enabled the marvels of modern communication, transportation, and medicine. Yet science is concerned with the world on scales of time and distance that extend well beyond those encountered in everyday human life. Much of what science discovers about the world is very counterintuitive—it surprises us. This is certainly true of the quantum theory, which is one of the most successful theories of contemporary science in its highly quantitative characterization of the atomic and subatomic world. Yet, the quantum world has dramatically different properties than our everyday world, so much so that Richard Feynman said about it: “Nobody knows how it can be like that.” Even now, over 50 years after the discovery of the theory, in spite of agreement on its mathematical formulation and the accuracy and power of its predictions, physicists do not yet agree on how the theory should be interpreted.
That the universe is intelligible is an utterly remarkable fact. It is understandable to our human minds even if it still holds mysteries for us. Perhaps one of the most profound things that Albert Einstein said is: “The most incomprehensible thing about the universe is that it is comprehensible.” Why is it that we human beings can actually understand the universe so well? Why are we so passionately driven to try to grasp the truth about it, and are satisfied when we do, however incompletely? Could it be that we are meant to be this way?
The eminent French physicist and philosopher Roland Omnes writes in Quantum Philosophy: Understanding and Interpreting Contemporary Science (1999) about how science, quantum physics in particular, is formal and abstract in its formulation, yet incredibly fruitful in its precise and quantitative characterization of Reality. Omnes asks:
How can science exist? Or: How is science possible? The obviousness of this question and the silence surrounding it echo Aristotle’s beautiful words: ‘Like night birds blinded by the glare of the sun, such is the behavior of the eyes of our mind when they stare at the most luminous facts.’ … The answer is perhaps as obvious as the question: science is possible because there is order in Reality. …The whole of science suggests such an answer, but science alone cannot establish or even formulate it, for this assertion is beyond science’s own representations.
There are some questions that science cannot answer. Even understanding why science is possible requires, as Omnes puts it, “leaving science and entering metaphysics.” When we do the latter, we must make critical judgments about the nature of the world based on considerations that lie beyond science per se. It takes wisdom to do that. Elsewhere in the book, Omnes does not hesitate to use an ancient philosophical term to characterize the order behind Reality, namely, its Logos, that is to say, its fundamental “logic,” “principle,” or ”ground.”
This subtle term Logos is also used in the familiar opening verse of the Gospel of John: “In the beginning was the Word [Logos], and the Word was with God, and the Word was God…. All things were made through him…” The term “Word” used here to translate the Greek λόγος has a significance that is clearly more than literal, situating the Logos at the ground of all there is, at the root of all intelligibility and order in the totality of Reality. John’s verse is also an echo of the opening words of Genesis, where God creates by speaking. The wonderfully spare and austere language in the first chapter of Genesis also tells us that human beings are made in the image of God. John goes on to tell us something even more remarkable: “And the Word became flesh and dwelt among us.”
John identifies the Word-made-flesh with Jesus of Nazareth, the one who shows us—uncovers for us—the very character of God. Here is the heart, the logic, the Logos, of the whole gospel: the paradoxical story of Jesus and his self-giving, self-sacrificial love communicates to us the key to the essential nature of Reality, about the cosmos and humanity. It is the Logos-become-flesh who shows us how to bear the image of God rightly and flourish as human beings. I have yet to find anything from what I have learned from the natural sciences—physical, chemical, biological, or bio-medical—that necessarily conflicts with a robust Christian theology centered on the person Jesus of Nazareth understood as being fully God and fully human.
Words are an essential part of our humanity. Perhaps like science itself we take our words too lightly. How are words possible? Words are the basis for language by which we communicate to one another. Words tumble and cascade one after the other, yet they convey a whole. They make sense, at least if we speak the language. They communicate information. The scientific knowledge by which the universe is intelligible is communicated by words. Words can also communicate emotions, love and anger, and express poetry. They describe. They convey a tone, a mood. Words can be written or spoken. Yet words can be hopelessly inadequate to the task of conveying what we would like to express. Can we even put into words the aroma of a cup of coffee, if we wanted to express what it is like to another person who had never experienced it?
Now is a good time to re-enter the story of carbon. The incredibly rich life of a cell, and by extension an entire living organism, is based on the special chemistry made possible by the specific molecular bonding properties that a carbon atom has with another carbon atom or with different atoms like hydrogen, oxygen, nitrogen, and many others. There is a large subfield of the chemical sciences known as “organic chemistry” that studies the structure, properties, and reactions of such carbon-containing molecules. There is an enormous variety of such molecules, since carbon can bond with other carbon atoms to form long chains with branching substructures. Different kinds of molecules make proteins, fats, carbohydrates, hemoglobin, insulin, DNA, and all the other kinds of molecules involved in life. The field of “molecular biology” studies these molecules in their biological context.
Most molecules have a well-prescribed structure and shape, conforming to solution of the quantum mechanical equation that describes the ensemble of atoms that comprise the molecule. Molecules will normally have a definite structure that corresponds to the solution of the equation that has the lowest energy for the sequence of atoms in the molecule. Quantum chemists routinely do large-scale computer calculations of such structures on moderately sized molecules. The DNA molecule that bears the genetic information in the genome of an organism is quite different from most biomolecules. While the DNA has a definite double helix structure, the genetic code is carried by the sequence of “base pairs” of 4 possible base molecules, with any three pairs in the sequence coding for one of 20 possible amino acid molecules. These base pairs that make up the genome are strung out along the sugar-phosphate backbone of the double helix structure in a sequence that is energy-neutral, that is, not determined by energetic or chemical bonding requirements. Consequently, any sequence is possible, and the actual sequence serves as the letters of a genetic alphabet that the cellular machinery reads to fabricate the particular sequence of amino acid components to make specific proteins needed by the cell. The sequence is thus neither predetermined by chemical forces nor random, but carries information of great complexity that enables the cell to grow and function and replicate accurately. The same basic genetic alphabet is universal for all life forms on earth, whether animals like human beings, plants, bacteria, or viruses.
One of the most far-reaching revolutions in thinking in the contemporary sciences is to view the world in terms of information and its transformations. Loosely speaking, information concerns how the world is organized into complex, meaningful patterns instead of randomness. In the biological sciences, this view hinges around the realization that information is at the center of life. Whole new university departments and scientific journals are being set up in the new field of bioinformatics. One accomplishment of the human genome project is to lay out the details in our DNA like a vast encyclopedia of words. Geneticists talk of genes “expressing themselves” through the natural processes in our cells, depending both on the genome and epigenetic factors beyond the DNA sequence.
In the view of contemporary biology, we are, in a sense more literal than figurative, embodied words. The words in the genome take flesh and make a living being. They become alive in a unique confluence of atoms, molecules, cells, and organs that make a coherent whole, a living person who can understand, speak, and love. The chemistry of carbon-bearing molecules makes this possible. In the case of the remarkable human animal, we find a being with the capacity to comprehend the whole universe that makes his being possible, who can comprehend the triple alpha process in ancient stars that enabled him to be here.
If we have the eyes to see, is it too much a stretch of the poetic imagination to think of each one of us, as it were, as being a unique utterance of God, a “word” spoken with an invitation to respond? Perhaps this helps us gain new insight on what it means for humankind to be created in the image and likeness of God. Perhaps the ancient Psalmist said more than he intended when he penned (Ps. 19:1-4a):
The heavens declare the glory of God;
the skies proclaim the work of his hands.
Day after day they pour forth speech;
night after night they reveal knowledge.
They have no speech, they use no words;
no sound is heard from them.
Yet their voice goes out into all the earth,
their words to the ends of the world. [NIV]
Word and fire: The fire in ancient stars has forged the material in which the words in the genome are written. We know this from science. This is possible because there is order in Reality, a Logos, a ground, that lies behind all that is and gives it coherence. The story of Jesus identifies the Logos and enables us to see that Reality is intelligible because the Word comes before the fire. This is not science, but represents wisdom beyond science to enable us to see why science is possible in the first place. Word begets words. It is really just as simple and deep as that.
Additional Reading:
Endnote:
A word is in order about what a quantum state is. Ordinary everyday objects can have any energy content. By contrast, a collection of quantum particles bound together in a small volume like an atomic nucleus will have a set of specific quantum states, each having a discrete quantized energy and a distinct set of “quantum number” labels. The Hoyle state is actually what physicists call a resonance state, namely, a state of a compound system that has the same energy as the individual particles that come together in a collision to form it. In this case the 12C Hoyle resonance state made from three alpha particles is an excited state that emits a gamma ray photon and decays to a stable, lower-energy form of 12C. Since the spread of energy in the hot alpha particles is actually quite small compared to the typical spread in energy between different quantum states, there is no guarantee that such a resonance would exist. That such a resonance occurs is a feature of the actual laws of physics being what they are. The actual rate of 12C production is extremely sensitive to the subtle details of the resonance, and the detailed dependence on temperature is still being worked out in papers being published in the scientific literature. Only recently has a fully first-principles mathematical calculation with powerful computers been possible to calculate the energy of the Hoyle resonance. This is explained in detail here.
Paul S. Julienne recently retired from his career as a physicist at the National Institute of Standards and Technology and the Joint Quantum Institute of NIST and the University of Maryland. He has published over 200 scientific papers on the theory of quantum processes in atomic, molecular, and optical physics.
