Seeking Life in the Universe
Two interesting excerpts:
AN INHABITED UNIVERSE?
by Seth Shostak, reposted from the Stephen Hawking's Universe
Seth Shostak holds a degree in physics from Princeton University, and a Ph.D. in astronomy from the California Institute of Technology. He is the Public Programs Scientist at the SETI Institute, in Mountain View, California.
The soft lights from the stars on a summer night appear romantic, even enticing. But distance deceives us about the true nature of the universe. It is stupefyingly vast and depressingly empty. The cosmos is cold, silent, and brutally impersonal, a dark, three-dimensional canvas only occasionally punctuated by stars. From the surfaces of these glowing globes, scorching flames of gas lick the sky. Deep within the stars’ interiors, elementary particles, unseen and unheard, wildly collide in response to the ferocious heat of a billion-year-old nuclear reaction.
Extreme conditions are the norm. While the majority of the universe is a near-perfect vacuum, in some places matter overwhelms space. Where large stars have died or smashed together, the inexorable pull of gravity has crushed their raw materials into a volume that's smaller than a pinhead, smaller than an atom. In the vicinity of these so-called black holes, the very fabric of time and space is rent and twisted. These are truly the universe’s most bizarre neighborhoods, the intellectual stomping grounds of Stephen Hawking.
Space is host to the most inhospitable environments imaginable. Nonetheless, there are subtle properties of the universe that allow the delicate process of life to exist. Indeed, it appears as if the cosmos has been “fine tuned” to permit life. Had the Big Bang happened more quickly, the early condensations of matter that led to galaxies, stars, planets and us would never have taken place. Had it happened more slowly, the universe would have quickly collapsed and disappeared. If the physical constants that govern the pace at which stars age and die were slightly different, life would not have had the time to evolve to produce you, me, or Stephen Hawking.
The entire universe has been constructed with one blueprint. Physics is the same throughout. So if biology has appeared here, around an unremarkable star in the outskirts of a run-of-the-mill galaxy, won’t it have appeared manifold times elsewhere? After all, there are more stars visible to our telescopes than all the sand grains of Earth’s beaches. Shouldn’t we expect that life is a natural, frequent occurrence?
We don’t yet know, but there is enticing evidence that what has happened on Earth may be the norm, and not the exception. In the past three years, astronomers have succeeded in finding planets around other stars. They have done this by measuring the subtle dance made by these stars in response to orbiting worlds. While scientists have long suspected that planets are common throughout the cosmos, they now have observational proof. And planets may be sweet oases in a hostile universe.
We believe that it is only on these tiny, cool worlds that the complex chemistry necessary for life can exist. It now seems probable that there are many such worlds. In August, 1996, a team of NASA and university researchers announced evidence for fossilized microbes in a meteorite that had been torn loose from the surface of Mars. This evidence suggests that billions of years ago, when the red planet was warmer and wetter, primitive life floated in its long-vanished oceans and rivers. Although controversial, this research implies that life could spring up on any half-decent planet. If it’s true that Mars once sported biology, then life is a statistic, not a miracle.
Supposing that planets are common and life is easily begun, then perhaps the universe contains not only myriads of living creatures, but sophisticated societies as well. Perhaps the intelligent aliens that routinely appear in films and television have real counterparts in our galaxy.
How could we find such extraterrestrial beings? Rocketing off to other star systems is not feasible: Even with our fastest spacecraft, it would take more than 50,000 years to reach the nearest of these.
But nearly four decades ago, it was realized that while interstellar travel was expensive and time-consuming, interstellar communication might not be. Radio waves, particularly those at microwave frequencies, could easily penetrate the gas and dust between the stars. And even a modest signal, if properly beamed, would be sufficient to send a message from one star to another. Such signals would travel at the speed of light.
Scientists don’t broadcast deliberate signals into space, hoping to stir the interest of nearby aliens. But what some astronomers have done for many years is to listen. They use large antennas (radio telescopes) connected to sophisticated digital receivers in the hope of eavesdropping on radio traffic that may already suffuse the star fields of our galaxy. This enterprise is known as SETI, the Search for Extraterrestrial Intelligence.
For nearly two decades, SETI was a NASA program, carried out by NASA centers in California. But in 1993, an amendment by Senator Richard Bryan of Nevada ended this effort. Since then, SETI has been a private endeavor, funded by individual donations.
The most ambitious search for cosmic company is known as Project Phoenix, and is conducted by the SETI Institute, in Mountain View, California. Phoenix scrutinizes the vicinities of about one thousand, nearby, sun-like stars for signals that are clearly of artificial origin. Since no one can be certain exactly where on the radio dial the aliens might be broadcasting, Phoenix carefully sifts through two billion narrow-band (1 Hz) channels between 1000 and 3000 MHz. It is in this spectral regime that the natural background noise from galaxies, quasars, and other celestial transmitters is minimal. It is a good band for a cosmic “hailing” signal.
So far, none of the SETI projects has booked success. Not a single, confirmed peep from the cosmos has been heard. But of course, that could change tomorrow, next week, or next year. If so, what would be the consequences?
To begin with, we would be confronted with one of the biggest news stories of all time. Unlike the daily reports of UFOs buzzing the countryside or of sex-starved aliens abducting citizens for salacious purposes, a signal detected by SETI researchers wouldn’t rely on anecdote or unsteady home videos. It could be quickly and repeatedly confirmed by scientists world-wide. The signal itself would come under intense scrutiny, and new receivers would be built to check it for “fine structure”—rapid variations that might convey a message.
But even if such variations are found, it’s unclear whether we would ever understand them. Humans have had radio technology for only a century, but any extraterrestrials we hear will more than likely have had it much longer. Their civilization will be far in advance of ours, perhaps by tens or hundreds of thousands of years. Only if they wish to educate us, to enlist us as members of some sort of “galactic club,” will they make it easy for us to decode their signal. In that event, we could experience a transcendent moment in human history. We would be brought into the fold of a society beyond our abilities to imagine, and might leapfrog millennia of history.
But even if none of this happens, even if we never understand the signal that we receive, we would still know that in the desolate vastness of a brutally hostile cosmos, other thinking beings exist and thrive. In Stephen Hawking’s universe, neither he nor we would be alone.
From Lee Smolin's
LIFE IN THE COSMOS
LIGHT and LIFE
Science is, above everything else, a search for an understanding of our relationship with the rest of the universe. We may begin it with the simplest, most basic fact about ourselves: Each of us is a living thing. As such, the most obvious and fundamental medium of our connection to the universe is light. For we, living things, live in a universe of light. We all see; even the simplest fungus or protozoa has receptors that respond to the presence of light. And is it not true that the most feared thing about imprisonment, or even death, is the loss of contact with the light? The dependence of life on light underlies so many metaphors and so much of the imagery of our culture (think of the fear of the dark) that to even quote examples is to risk cliche, but let me mention one, that to understand something is to attain an insight.
But, of course, light is the ultimate source of life. Without the light coming from the sun, there would be no life here on earth. Light is not only our medium of contact with the world; in a very real sense, it is the basis of our existence. If the difference between us and dead matter is organization, it is sunlight that provides the energy and the impetus for the self-organization of matter into life, on every scale, from the individual cell to the life of the whole planet and from my morning awakening to the whole history of evolution.
We will never know completely who we are until we understand why the universe is constructed in such a way that it contains living things. To comprehend that, the first thing we need to know is why we live in a universe filled with light. Thus, the problem of our relationship with the rest of the world rests partly on at least one question that science ought to be able to answer. Why is it that the universe is filled with stars?
But before we approach this question, there is another kind of relationship that I must comment on; that between author and reader. This is, as my literary friends have been telling me for some time, a rather problematic relationship. After all, the dominant literary theory taught by my colleagues these days is that books must be read as if, in a certain sense, the author does not exist. But, beyond my natural protest against such an assertion (in my present situation), there are special problems that arise when the author is a scientist and the reader is not. Anyone who sets out to teach ideas from physics to those who are not specialists, whether as a teacher in a lecture room or through a book such as this one, faces a curiously paradoxical situation. To begin with, there is no doubt that a great many people have a deep interest in physics and cosmology. Who has not looked up at the stars, or gazed at a tree or a kitten and wondered what the universe is and what our place in it might be? And, what culture has not had a story about how the universe was created?
It is a cliche to say that in the twentieth century science has replaced religion as the dominant cosmological authority. While this does not seem to have actually done much to decrease the popularity of religion, it is true that at the present time, for many of the cultures of the planet, we physicists are the official makers and keepers of the story of the cosmos. This, perhaps more than anything else, accounts for the peculiar combination of interest and distance that many people seem to bring to a meeting with a physicist. At the same time, it is unlikely that there is any subject in high school or university that is more disliked than physics. If a great many people want to know about what we think the universe is, almost no one seems much interested in the tools with which we acquire and construct this knowledge.
I have been teaching physics to non-science students for much of my career. While I am considered a good teacher, what has most impressed me is how unsuccessful, on the whole, I have been at imparting my love of physics. Thus, at some point during the last few years I began to ask my students directly why they don't like physics. Of course, a number found the sustained attention required to learn how to think in new ways disagreeable. Others are understandably put off by the unfortunate connection between physics and weapons of mass destruction. But from the most interesting students, the artists, the philosophers, the hot shot literary theory types who can sail through Derrida and Christeva but cannot penetrate textbooks developed and marketed at great expense especially for nonscientists, I began to hear another kind of answer. They find physics difficult because they don't like and don't believe the picture of nature embodied by the science they are being taught.
There is at least one good reason not to believe the physics that is taught in most courses for nonscientists. It isn't true. For a reason that after many years of university teaching remains opaque to me, physics is the only subject in the university curriculum in which the first year's study rarely gets beyond what was known in 1900. Now, Newtonian physics is a beautiful subject, as are the plays of Shakespeare. But no one tries to teach first year students to think about Shakespeare the way critics thought in the nineteenth century. A good literature teacher will teach the classic books in the context of the current debates about the nature of texts. Almost no one teaches Newtonian physics to beginning students in the context of the current debates about the nature of space and time.
Newtonian physics is useful, even if it is not true, as an approximation that helps us to understand many different phenomena. But it is completely discredited as an answer to any fundamental question about what the world is. It has a great deal of historical and philosophical interest, but this is rarely mentioned in beginning courses. Thus, it is not surprising if students find the subject uninspiring.
But, beyond the fact that they are given little reason to believe in it, I find that students simply are not drawn to the description of the world offered by Newtonian physics.
Once I suspected this I began to ask myself what exactly is it that they don't like about the Newtonian view of the cosmos?
I believe that the answer is that there is no place for life in the Newtonian universe. On the basis of the physics that was known in the nineteenth century, it is impossible to perceive a connection between ourselves as living things and the rest of the universe.
But physics must provide a way to understand what life is and why we are here. It is the "science of everything" whose task is to uncover those facts and laws that apply universally. Physics must underlie and explain biology because living creatures, like all things in the universe, are made out of atoms which obey the same laws as do every other atom in the world. An approach to physics that does not make the existence of life comprehensible must eventually give way to one that does.
One might have expected that before the twentieth century people would have been concerned about the fact that life did not fit easily into the Newtonian cosmos. If few scientists worried about this, it may in part be due to a philosophy called vitalism that was popular in the last century. According to it, there is no reason to expect that physics should illuminate the processes of life because living and non-living matter may obey different laws. Imagine how disappointing it would be were vitalism true, it would mean that there is no essential connection between us and what we see when we look around us. Still, there is no denying the attraction such a view holds for many people. The idea that life is not reducible to physics seems a remnant of the Greek and Christian cosmologies in which earth and sky are made from different essences. Behind it one can sense the ancient desire to escape nature and partake of heaven.
But in any case, before Einstein, people had little choice. Had Newtonian physics turned out to be correct, vitalism would have been necessary. It is only with the physics of the twentieth century that we have been able to understand how living things are constructed from the same ordinary atoms that make up rocks and stars. Thus, part of the movement from the Newtonian world to the modern one is a transition from a universe in which life is impossible to one in which life has a place. It is partly for this reason that the question of the existence of life becomes central to the twentieth century revolution in physics. Quantum physics, for all its intrinsic weirdness, gives us for the first time an opportunity to comprehend our relationship to the rest of the universe in a way that avoids both the Aristotelian fiction of our absolute centrality and the Newtonian fiction of our absolute alienation.
To appreciate the meaning of this change, we must first understand why it is that we would not expect to find anything like life in a universe governed by Newton's laws. Let us begin with an image that comes to mind when one asks the question of what our place is in the universe. This is the image of a warm, living earth, lost in the depth of an infinite, cold and dead cosmos. This image, which embodies one of those basic ideas that are so obvious as to seem almost beyond examination, hides, in my opinion, an absurdity. To see why, we may start by asking what must be true about the universe in order that it contain living things.
The first thing required for life is a variety of different atoms that can combine to form a very large number of molecules, which differ greatly in their sizes, shapes and chemical properties. It is often stressed that carbon is required because it is the only element that forms a sufficient variety of stable molecular structures. All of the living things on earth are made out of carbon compounds that are built with copious amounts of carbon, hydrogen, oxygen and nitrogen, as well as traces of many other atoms. But beyond the specifics of carbon chemistry, life would be impossible were there not a sufficient variety of atoms. A universe containing only one kind of atom would almost certainly be dead.
The problem with Newtonian physics is that it does not allow the existence of many distinct kinds of atoms. A Newtonian atom would be something like a solar system, but held together by the electrical attraction of the nuclei and electrons rather than by gravity. However, there is a problem with this, because when the electrons move in circles they radiate light waves, which carry energy away from the atom. The result is that the electrons lose energy and spiral into the nucleus.
If the world suddenly became Newtonian it would take only a fraction of a second for most of the electrons to fall into the nuclei. This was, in fact, the direct motivation for the introduction of the quantum mechanical picture of the atom. The fact that atoms are like solar systems, with most of the mass in the nuclei and most of the space taken up by the electrons, was discovered by Ernest Rutherford, in his laboratory in Cambridge in 1911. Within months his young protege, Niels Bohr, had invented the first quantum mechanical theory of the atom. Whatever else one may say about the quantum theory, its central success is that it explains the stability of atoms.
However, it is not enough that the laws of physics allow the existence of a variety of stable atoms. The universe must, during its history, produce these atoms in copious quantities so that they may be available for the development of living things.
Thus, we must ask what is required of a universe so that large amounts of carbon, oxygen and the other ingredients of life are plentifully produced. This question has a simple answer: the universe must contain stars. All but the lightest elements were forged in stars. Thus, it is not a coincidence that when we look up we see stars, just as it is not a coincidence that when we look around we see plants and trees Just as the plants produce the oxygen we breath, it is the stars that produced all the chemical elements out of which we, and the plants, are made.
This, at least in outline, settles the question of where the ingredients for life come from. But there is another, deeper question we must ask. Given the ingredients, what are the conditions that make the universe hospitable to life? What must be true about the world so that some of its atoms will spontaneously invent the astoundingly intricate dance which makes them living? That life arose from a simpler world seems the ultimate miracle. But, if we are to understand our place in the universe, we must come to understand it.
In its capacity to create organization and complexity where none existed before life seems to run contrary to the laws of physics. This was, in any case, what was thought by many in the nineteenth century, who worried that the law of increasing entropy (or, as it is also called, the second law of thermodynamics) contradicted the observed record of biological evolution.
Most people have an intuitive idea of the meaning of the law of increasing entropy. A hot cup of tea cools down until it is the same temperature as the air in the room. Snow melts on a warm day. These examples illustrate the tendency for differences between the temperatures in different parts of a system to be erased. The configuration in which all parts of a system have the same temperature, density and chemical composition is called thermodynamic equilibrium. The law of increasing entropy says that if I have a closed system, which is isolated from the rest of the universe, it is overwhelmingly probable that it will come to, and remain in, a state of thermodynamic equilibrium.
Living things, of course, do not behave like this. My body stays at about the same temperature, no matter what the temperature of my environment might be, at least as long as I am healthy. My cat also maintains a constant body temperature, which is different from mine. If I sleep with my clothes on, then when I wake up they have the same temperature as me. If I sleep with my cat, he wakes up (for the few minutes he condescends to enter that state) with his own unique temperature.
Another, related meaning of entropy is that it is a measure of disorganization. The atoms in a gas are disordered to the extent that there is no way to tell one from another. In equilibrium there is maximal disorder, because every atom moves randomly, with the same average energy as any other atom. A living system, on the contrary, continually creates an enormous number of different kind of molecules, each of which generally perform a unique function. The entropy of a living thing is consequently much lower, atom for atom, than anything else in the world.
It is an interesting historical fact that the laws of thermodynamics were put in their modern form during the second half of the nineteenth century, more or less at the same time that the theory of natural selection was introduced by Darwin and Wallace. Since that time, many people, both inside and outside of science, have made a great deal of the apparent contradiction between these two developments. The fossil record tells us that the biosphere has become more organized and more varied over time. The laws of thermodynamics say that there is a tendency for systems to become less organized and less varied over time. Thus, one argument that was often made for vitalism during the last century is that the matter living things are made of must be excluded from the strictures of the laws of thermodynamics.
In fact, the case of thermodynamics is different from that of Newtonian physics. The laws of thermodynamics are not in contradiction with the existence or the evolution of life. Not only is the existence of life compatible with thermodynamics, the two subjects are actually so intimately related that the clearest characterization of life I know of is one given in thermodynamic terms. This is because once we understand what it means for a system to be in thermodynamic equilibrium, we can understand its opposite: what is required for a system to be out of equilibrium, as all living things are, for arbitrarily long periods of time.
Nothing can live in an environment in thermal equilibrium. If life is to exist there must then be regions of the universe that are kept far from thermodynamic equilibrium for the billions of years it takes for life to evolve. We then want to ask, What is required of the universe so that it contains such regions? The answer to this question is easy. There must be things in the universe that are much hotter than the rest of it, and are able to maintain themselves as constant sources of light and heat for enormous periods of time.
What kinds of things can do this? The answer to this question is the same as the answer to the other questions we raised in this chapter: There must be stars.
We can thus begin to see what is wrong with the picture of a warm living earth inside a cold dead cosmos. If the universe really were cold and dead, if it contained no stars, there would be no living planets. The existence of stars is thus the key to the problem of why the cosmos is hospitable to life.
I would like to inject one note of caution before proceeding. If we were interested only in feeling better about ourselves, we might be happy to jump from vitalism to a kind of pantheism according to which life exists because the universe itself is alive. But our goal should be more than inventing a story that explains what we are doing in the universe. In the end what is wrong with the Newtonian theory of the universe is its essential irrationality, as it leaves unexplained too many aspects of the world that we may hope to comprehend. What is needed is a deeper understanding of what both life and the universe are that allows us to comprehend why it is natural to find one inhabited by the other.
The scientific revolution did not take off when Copernicus simply switched the places of the earth and sun in the Aristotelian cosmos. To put the earth on one of the crystal spheres was logically absurd, as it contradicted the basic assumptions behind the Aristotelian cosmos such as the immutability of the heavens. Any intelligent sixteenth-century person could explain why what Copernicus had done didn't really make sense. The revolution began in earnest when Kepler abolished the crystal spheres and cast the planets adrift in empty space. Then he had to ask a new question: How does a planet in the midst of empty space know where to move? It was this and other new questions that drove the revolution.
Similarly, to assert simply that the universe is alive is absurd. Instead, I would like to suggest that the time has come for us to knock our understanding of what the laws of physics represent off a kind of philosophical mooring that has become as outdated as Aristotle's crystal spheres were in the seventeenth century. Set adrift, we have now to ask new questions about how the regularities we refer to as the laws of physics came to be and whether, and how, they can change. The search for answers to these questions may then lead us to reconsider our familiar understandings about the relationships between the fundamental and the emergent and between physics and biology. To put it another way, one of the questions we will be seeking to answer in the following chapters is whether it is purely an accident, or whether it is to some extent necessary, that this, or any, cosmos is a universe of light and life.
You must become an ignorant man again
And see the sun again with an ignorant eye
And see it clearly in the idea of it.
"Notes Toward a Supreme Fiction"
THE LOGIC of ATOMISM
"We are stardust" Joni Mitchell sings, and it rings so true that we have to pinch ourselves to remember that it is less than seventy years since we learned that everything we are made of, except hydrogen, was fused in stars. What is, on the other hand, very old is the idea that the world is made of atoms. The philosophy of atomism goes back at least to the Greek philosophers Democritus and Leucippus in the 6th century BC. According to them, the universe consists of a large number of fundamental particles, moving in empty space. As obvious as this idea may seem to us now, it was rejected by Aristotle, and was only revived many centuries later at the start of the scientific revolution. But atomism triumphed only in this century, as quantum physics opened up the atom to our understanding. In quick succession we descended through several levels of structure, so that we now study the quarks: the things within the things within the atom.
The triumph of atomism is by now so complete that any challenge to it seems at first to point outside of the boundaries of science. The Greeks could only dream of a science in which the properties of anything in the world could be explained by decomposing it into its atoms. We have this science, it is the foundation of everything we understand from immunology to transistors to nuclear physics. And if the atoms and the nuclei turned out to be divisible, we have now reasonable candidates for truly elementary particles in the electrons, neutrinos and quarks.
But if it is hard to conceive of it being wrong, there are still questions that the atomistic philosophy cannot help us answer. Some of these have to do with the elementary particles themselves: The electron is lighter than the proton, but not as light as the neutrino. Why? Why is the neutron just a bit heavier than the proton? Why doesn't the neutrino have any electric charge?
We cannot understand the elementary particles, as we do everything else, by breaking them into parts. First of all, there is no evidence that they are made of still smaller things. But even if there were, eventually the game must stop, we must at some point arrive at some truly elementary particles. In a whimsical mood we may entertain the idea that there is an infinite regress, but this seems unlikely. For one thing, there is good reason to believe there really is a smallest ultimate size to things, which I will explain later, in Part Five. Whatever the elementary particles are, we are going to have to understand them, and we are going to have to do this in terms different than those we use to understand everything made from them.
According to the Greek philosophers, the elementary particles are eternal, never created or destroyed. This seemed to them the only alternative, for if they were created they would have to be put together out of some parts. Then they would no longer be the smallest things. Making the elementary particles eternal puts the questions as to their properties in the realm of the absolute: They are like that because they always were and always will be. As a consequence, each of the elementary particles exist independently of all of the others. Neither the history of the universe nor its present configuration can have any effect on the properties of any single elementary particle. It is completely conceivable that the universe might have but one neutron in it. And, according to this philosophy, that neutron would be exactly the same as one found in an atom of my cat's whisker.
Modern elementary particle physics does allow the elementary particles to be created and destroyed. But their properties are determined by laws, which endow each particle, when created, with certain properties, completely independent of whatever else may exist in the universe. These laws are presumed to be absolute and to hold for all time. Thus, the idea of the absolute plays an essential role for us, as it did for the Greeks. It has just been abstracted, from eternal atoms to eternal laws. That the laws of physics might be created or modified seems to us as nonsensical as it would have seemed to Democritus to build a machine that creates elementary particles.
The idea that there is an absolute law of nature, which fixes once and for all the properties of the elementary particles, has been so successful it is difficult to imagine a scientific approach to understanding nature that does not begin there. But, in fact, there are very good reasons to believe that in the end this idea cannot be right. Some of these reasons come from the logic of atomism itself. I will argue as we go along that the reductionist philosophy that underlies atomism is necessarily incomplete. A philosophy that tells us to explain things by breaking them into parts will not help us when we confront the question of understanding the things that have no parts. At that point we must turn to some different strategies if science is to progress.
For most of the last century, elementary particle physics moved at a rapid pace, with a new discovery appearing at least once a decade. During this time we have come to see it as the route to answering all the most fundamental questions about nature. When I was trained as an elementary particle theorist, I believed myself to be joining the exalted ranks of those whose task is to discover the fundamental reality behind our perceptions of nature. I always felt a bit sorry for scientists who were not elementary particle theorists, for I could never understand how they could find complete satisfaction in investigating nature at any other than its most fundamental level. Nor was I terribly interested in the "higher order sciences", such as biology or astronomy, because nothing that they could learn could have any bearing on the fundamental questions, which were about the elementary particles.
Unfortunately, for the last twenty years elementary particle physics has not moved at the pace it once did. In the middle-1970's, there was a great triumph, in which the theory that we call the standard model of elementary particle physics was constructed. This theory puts us in the position to predict the results of virtually any experiment that could be done with present technology, with one significant exception, which encompasses anything having to do with gravity. But it leaves open a large number of questions, and these past twenty years have been a very frustrating period because almost none of these questions have been answered.
The most important of these questions is how to include gravity, and this cannot be done until we know how to unify general relativity with quantum theory. But there are also other questions that the standard model does not answer, which have remained mysteries. Many of these have to do with the properties of the elementary particles, such as: Why do they have particular masses and charges?
The persistence of these problems does not imply that important work has not been done. On the theoretical side especially, new ideas have been invented that are likely to help explain some of the questions left over by the standard model. But on the experimental side, nothing has been discovered that could not be explained in terms of the standard model. At the same time, not one of the theoretical ideas intended as answers to the questions left open by the standard model has been confirmed experimentally. Perhaps if elementary particle physics had not been so successful, this situation would not be so worrying. But one has to look back more than a century to find a comparable twenty-year period without definitive progress in our understanding of the basic laws of nature.
There are several reasons for this, one of which is certainly the great difficulty and expense of making new experiments that probe layers of structure smaller than those described by the standard model. But I believe that part of the present crisis is inevitable, and is due to our having reached the limits of what we can learn solely by breaking things into their parts. The very success of the reductionist philosophy may have brought us to the moment when we have in our hands at least some of the truly elementary particles. If so, it should not surprise us if methods that have been so successful up to this point seem to be failing.
In science, detective movies, love or any other area of life, when one is confronted with a situation in which the old assumptions are no longer working as they used to, it is perhaps time to look for new questions to ask. But how does one search, not for new answers, but for new questions? Perhaps the first thing to do is to try to look around us with fresh eyes and examine the evidence that is close at hand. Sometimes a crucial piece of evidence lies right in front of us that has up till now lacked any significance. Looked at in a new way, our familiar world can all of a sudden reveal new meanings.
It is exactly such a new look that I would like to propose we take to the problems of elementary particle physics. The important question, if we are to try to begin again, is which assumptions we should keep and which we should throw away. To begin with, there can be nothing wrong with atomism, as long as we take that to mean only the simple idea that most things in the world are made of elementary particles, which are not themselves composed of anything smaller. But we may question the more radical assumption that the properties of these elementary particles themselves are fixed eternally in terms of absolute laws. To distinguish this idea from commonsense notions of atomism and reductionism, I will give it a name. I will call it radical atomism. Similarly, there is no need to question the idea that there are laws of nature. But we can question the idea that if we knew only those laws, and nothing else about the history or organization of the universe, we could deduce the properties of a quark or electron.
One reason to question radical atomism is that it must eventually lead either to infinite regress or to a brick wall. If the elementary particles have no parts, then no explanation of any of their properties can be found by looking inside them. The only alternative may be to look outside them. This means we must try to determine if the properties of the elementary particles might be somehow influenced by their relationships with the things that are around them. If elementary particles are so influenced, then perhaps those properties are not absolute and eternal. Instead, to understand a quark or an electron, we may have to know something about the history or organization of the universe.
I must confess that it is still not completely easy, even after the years I have spent thinking about it, to write these last sentences. The weight of all the philosophy that lay behind my training as a physicist tells me that this is the wrong thing to try to do. There is, of course, absolutely no evidence that the elementary particles are affected by the environments in which we find them. Observations of the light from distant stars affirms that the protons they are made of are exactly the same as those I am breathing now. But this does not mean that there can be no effect by which an elementary particle is influenced by its environment. It only means that to find such effects, we probably have no alternative but to look at scales much larger than stars and galaxies.
Another problem with the philosophy of radical atomism is that it gives us little ground to understand why the universe is as organized as it seems to be. If the universe is nothing but atoms moving in a void, then it is hard to understand why it isn't far simpler than it is. From a fundamental point of view, a universe filled with a gas of atoms in thermal equilibrium is as plausible as a world full of a variety of structures. Indeed, it is much more than plausible, for according to the law of increasing entropy, it is much more probable that the world be disorganized, be merely a gas in thermal equilibrium.
Why is the universe so dynamical? Why is it not closer to thermal equilibrium, as nineteenth century cosmologists expected? As I suggested in the last chapter, the answer to these questions is that there are stars. For they are the primary sites for transformations of energy and matter in the universe. In each star, as the elements are forged, gravitational and nuclear energy are converted into light and radiation and sent out into the universe. Indeed, just as our life is embedded in the ecological cycles of the biosphere, our whole planet exists as a part of a much older cycle of material and energy that forms the galaxy.
Another thing that must strike us when we look around at the universe is that it seems to be structured hierarchically. Imagine that we have stepped for the first time, not into a universe, but into a library. To use it we need to know how it is organized. We find first that the library is divided into sections, each of which is divided into a large number of books. Most of the books are further divided. For example, this book is divided into parts, each of which is further divided into chapters. The meaning of the chapters is conveyed in paragraphs, which are composed of sentences. A sentence is made of words, in certain orders, each of which is made out of letters. Finally, each letter is a combination of a small number of basic shapes, lines, circles, and arcs.
Our universe has at least as many levels of organization as a library. The elementary particles, small in number, are something like the basic shapes; the atoms something like the letters. In each case there are several dozen of each. The atoms are organized into an enormous number of different molecules, just as the letters spell out an enormous number of words. As the order of the letters on the page is relevant for the meaning of the word, the arrangement of the atoms in three dimensional space is crucial for the properties of the molecule. Molecules can be organized many different ways, as solids, crystals, liquids, gases, just as there are many kinds of texts. The arrangement of the elementary particles in the world is much more interesting than the ancient atomists pictured it to be, for the atoms are not just dancing about. Instead their organization is structural, containing a great complexity, on which depend the enormously diverse chemical and physical properties of the molecules.
But when we raise our eyes from the molecules, and look at the universe on a large scale, we also see a hierarchical structure. One of the great discoveries of the present period is that the galaxies are not distributed randomly in space. Instead, we find structure in the arrangements of the galaxies on every scale up to the largest that has so far been surveyed. The largest structures that have so far been mapped are great systems of galaxies, each of which contains many clusters, each of which contains dozens to thousands of galaxies. An example of such a great system is the "Great Wall," which is a sheet of clusters of galaxies spread over a large part of our sky, at a distance of about thirty million light years from us.
Seen from the largest scales, the galaxies are the basic structural units of the organization of the universe. And what then are the galaxies? We will later devote a whole chapter to this question, but the simple answer is that galaxies are great systems for making stars.
The hierarchies of structures that we see in the sky are not random, they are created and maintained by processes that go on in stars and galaxies. To comprehend them requires more than just knowing how to break everything into its parts; we must understand how it is that such a complex hierarchy of structures and processes arose as the universe evolved. The question of the origin of the structure in the universe is then not unlike the question of the origin of life. We need to know if, given the laws of physics, it was probable that such structures and processes spontaneously form.
As long as we do not comprehend why it was probable that living things formed spontaneously as soon as conditions in the earth's oceans allowed, our understanding of biology must be considered incomplete. Similarly, any philosophy according to which the existence of stars and galaxies appears to be very unlikely, or rests on unexplained coincidence, cannot be satisfactory. In the next chapter, I will explain that the radical atomist philosophy is in great danger in this regard. We shall see that, in spite of all that we have learned, given the basic principles and laws of nature as we understand them now, it is extraordinarily improbable that the universe be full of stars.
--Read the book Life in the Cosmos (1997), as well as his other latest ones.