is a formula of elements that make up the human body. We are a very select mix of atoms. Bodies are mostly hydrogen: for every atom of cobalt, for example, there are almost 400 million of hydrogen. By weight, we contain such a large amount of oxygen and carbon that we are virtually unique in the known universe.
One particular element missing from bodies tells a big story. Helium, the second-most abundant atom in the entire universe, has an internal structure that leaves it no room to trade electrons with others. Unable to make these exchanges, it cannot participate in the chemical reactions that define life—metabolism, reproduction, and growth. On the other hand, oxygen and carbon are about twenty times rarer than helium. But unlike helium, these atoms can easily interact with different elements to form the variety of chemical bonds that are essential in living matter. Reactivity is the order of the day for the common atoms of bodies. Loners need not apply.
The relative proportion of atoms is only a part of what defines our bodily structure. Bodies are organized like a set of Russian nesting dolls: tiny particles make atoms, groups of atoms make molecules, and molecules assemble and interact in different ways to compose our cells, tissues, and organs. Each level of organization brings new properties that are greater than the sum of its parts. You could know everything about each of the atoms inside your own liver, but that will not tell you how a liver works. Hierarchical architecture, smaller things making larger entities with new defining properties, is the basic way our world is organized and ultimately reveals our deepest connections to the universe, solar system, and planet.
Pick up a scientific journal in biology nowadays, and you stand a good chance of seeing a tree of relatedness. Every creature, from human to Thoroughbred to prize Hereford, has a pedigree—its family tree. These trees define how closely related living things are: first cousins are more closely related to one another than they are to second cousins. Knowing the pedigree becomes the basis for understanding how different creatures are connected to one another, how species came about, even why certain individuals may be more susceptible to disease than others. This is why doctors take family histories in medical exams.
A critical insight of modern biology is that our family history extends to all other living things. Unlocking this relationship means comparing different species with one another in a very precise way. An order to life is revealed in the features creatures have: closely related ones share more features with each other than do those more distantly related. A cow shares more organs and genes with people than it does with a fly: hair, warm-bloodedness, and mammary glands are shared by mammals and absent in insects. Until somebody finds a hairy fly with breasts, we would consider flies distant relatives to cows and people. Add a fish to this comparison, and we discover that fish are more closely related to cows and people than they are to flies. The reason is that fish, like people, have backbones, skulls, and appendages, all of which are lacking in flies. We can follow this logic to add species after species and find the family tree that relates people, fish, and flies to the millions of other species on the planet.
But why stop at living things?
The sun burns hydrogen. Other stars burn oxygen and carbon. The fundamental atoms that make our hands, feet, and brains serve as the fuel for stars. It isn’t merely the atoms in our bodies that extend across the far reaches of the universe: molecules that make our bodies are found in space. The building blocks for the proteins and larger molecules that make us—amino acids and nitrates—rain down to Earth in meteorites and lie on the rocky crust of Mars or on the moons of Jupiter. If our chemical cousins are in the stars, meteors, and other heavenly bodies, then clues to our deepest connections to the universe must lie in the sky above our heads.
Detecting patterns in the sky—the shapes of galaxies, the features on planets, or the components of a binary star—is no easy task. Eyes take some time to adjust to the dark, but so too does perception. You need to train the eye to perceive faint patterns in the night sky. When it comes to deciphering fuzzy patches of stars through a telescope or binoculars, imagination and expectation have a way of conjuring mirages in the void. Removing these and actually seeing dim objects in space means emphasizing peripheral vision, the most sensitive light-gathering part of our eyes, to pick up faint light and discriminate fuzzy patches from one another. As we learn to see the sky, color, depth, and shape emerge in the world above our heads much like when a fossil bone pops into view on a dusty desert floor beneath our feet.
Discriminating celestial objects is merely the first step in learning to see the sky. Like a painting that has graced a house for generations, the stellar landscape we encounter today is much the same as that witnessed by our parents, grandparents, even our apelike ancestors. Generations of humans have not only seen the sky but, over time, built new ways of perceiving our connection to it.
Our relationship to the stars changed dramatically because of breakthroughs made by the Harvard Computers at the turn of the twentieth century. Edward Charles Pickering, then director of the Harvard College Observatory, had a problem that required serious computation and analysis. The observatory was collecting reams of pictures of constellations, stars, and nebulae—so many that just managing and plotting the images was a daunting task. Of course, digital computers as we know them didn’t exist at this time and the calculations had to be done by hand. Pickering was famously cheap and once declared in a fit of exasperation with his existing staff that he could hire his maid to do this work at half the cost. He fell in love with his new idea and ended up pressing his real maid, Williamina Fleming, into service at the observatory.
At age twenty-one and with a young son, Williamina Fleming was abandoned by her husband, leaving her penniless and without a trade. Pickering first hired her to clean house. Then, after his boast, he brought her to the observatory to manage his celestial images. Upon receipt of a large donation, Pickering was able to add a number of other women to the group. What Pickering could never have planned was that from this team grew some of the greatest astronomers of the time, or any time for that matter. These women collectively became known as the Harvard Computers: they sat with the raw data of astronomy, pictures of the heavens, and made sense of them.
Henrietta Leavitt, the daughter of a Congregational minister, came to the observatory in 1895, first volunteering and later earning a salary of thirty cents an hour. She developed a love for astronomy in school, a passion that served her well during the long years she had the mind-numbing task of cataloging photographic plate after plate of stars and nebulae.
As Leavitt knew, the different stars in the sky vary in color and magnitude of their light. Some stars are dim or small, others bright and big. Of course, there was no real way of knowing what magnitude meant for the real brilliance of a star, because an apparently dim star could be a big and bright one far away or a faint one relatively close.
Leavitt became fascinated by one type of star that changed regularly from bright to dim over the course of days or months. Mapping seventeen hundred stars, she charted every property she could measure: how bright they were, where they sat in the sky, and how rapidly these variable stars went from bright to dim. With all of these data, Leavitt uncovered an important regularity: there is a constant relationship between how fast some stars cycle from bright to dim and their real brightness.
Leavitt’s idea seems awfully esoteric, but it is profound. Starting with the principle that light travels at a constant speed, and knowing how bright the star actually was and how bright it appeared, meant that the distance of the star from Earth could be estimated. With this insight, Henrietta Leavitt gave us a ruler with which to measure distances in deep space.
We have to imagine astronomy in that era to appreciate the transformative power of Leavitt’s discovery. From the time of Galileo to Pickering, people observed the sky and saw the planets, nebulae, and fuzzy patches of light with ever-increasing clarity. But the central questions remained. How big is the universe? Is our own galaxy, the Milky Way, all there is?
No sooner had Leavitt proposed her idea in 1912 than other astronomers began to calibrate and apply it to the heavens. One Dutch scientist used Leavitt’s ruler to measure the distances between individual stars. It gave him a big number. The galaxy is vast almost beyond imagination. Then Edwin Hubble, armed with Leavitt’s idea, used the biggest telescope of the time to change our view of the universe almost overnight.
In 1918, Hubble, a Rhodes scholar and law student turned astronomer, deployed his enormous new Mount Wilson telescope to find one of the stars made famous by Leavitt. This star was special. It wasn’t alone in the sky; it sat inside a cloud of gas, known as the Andromeda Nebula. When Hubble applied Leavitt’s ruler to the star, he encountered a stunning fact: the star, in fact the whole nebula that contained it, was farther away from us than anything yet measured. The game changer came from the realization that this object was much more distant than any star in our own galaxy. This nebula was no cloud of gas; it was an entirely separate galaxy light-years from our own. With that observation, the Andromeda Nebula became the Andromeda Galaxy, and the world above our heads became vast and ancient almost beyond description.
Hubble, using the largest telescope of the day, mapped everything he could see with Leavitt’s variable stars inside. The Andromeda and Milky Way Galaxies were only the tip of the iceberg. The heavens were filled with other galaxies composed of billions of stars. Many of the fuzzy patches of gas seen by observers for a century or more were really star clusters that lie far beyond our own galaxy. In a scientific age when people were grappling with the age of Earth, then thought to be on the order of 10 million to 100 million years old, the age and size of the universe revealed our planet to be just a minuscule speck in a vast universe composed of innumerable galaxies. These insights emerged as people learned to look at the sky in a new way.
Hubble applied another technique to measure objects in the sky. This one relied on an essential property of light. Light radiating from a source that is traveling toward us looks more blue than light traveling away, which looks more red. This color shift happens because light shares some features with waves. Individual waves emanating from a source moving closer to you will look more compressed than ones moving away. In the world of color, more closely spaced waves are on the blue end of the spectrum, more separated ones on the red. If Leavitt’s technique was a ruler to measure distance in deep space, then the search for color shifts in light was a radar gun to measure speed.
With this tool, Hubble found a regularity: stars emit red-shifted light. This could mean only one thing. The objects in the heavens are moving away from us, and the universe itself is expanding. This expansion is not a pell-mell scatter; the heavens are scattering from a common center. Wind things back in time, and all the matter in the sky was at some distant time occupying a central point.
Not everybody liked this new idea; in fact, some experts hated it. Rival theories for the origin of the universe abounded. A proponent for one of them poked fun at Hubble’s by giving it the moniker “big bang.” Lacking in Hubble’s theory, or in any other for that matter, was direct evidence in the form of a smoking gun.
The major breakthrough was an incidental by-product of people’s need to communicate with one another. With technological innovations in wireless technology and expanding international commerce and collaboration in the late 1950s came a demand for transmission of radio, TV, and other signals across the oceans. NASA devised a special satellite, code-named Echo 1, for this purpose. Looking like a large shiny metal balloon, it was meant to bounce signals transmitted from one part of Earth to another. The problem with this system was that the signals returning to Earth were often far too weak to interpret.
Working for AT&T’s Bell Laboratories, at the time a utopia for scientists doing creative science, Arno Penzias and Robert Wilson were designing a radar dish to detect the extremely weak microwave signals reflected from NASA’s Echo 1 satellite. They spent a considerable amount of time, money, and expertise to develop a specialized radar dish for the task. Then, in 1962, NASA launched Telstar, a satellite that doesn’t passively bounce signals but relays them with a boost of its own. The bad news for Penzias and Wilson was that their dish was now useless for NASA.
The good news was that, now free of anyone else’s priorities, Penzias and Wilson were able to turn the dish to their real goal—observing the radio waves that hit Earth from space. But their wonderful contraption was not up to the new job. The sensitivity, so essential for their gig with NASA, made the dish a nightmare to work with. It picked up all kinds of faint signals and noise, almost like persistent static on a TV.
Their efforts to remove the noise read today like an attempt to find and remove a fine needle from a shag rug. First they tried to filter out the signals produced by radios. No luck; interference remained. Then they cooled the detector to -270 degrees centigrade, a temperature at which molecules come close to stopping their movement. Still interference. They climbed inside the detector and found that birds had sullied the interior via their digestive processes. Wiping away the evidence of those encounters helped a bit, but the interference remained. This background noise was constant through day and night and was about one hundred times more than they would have expected.
Unknown to Penzias and Wilson, a set of Princeton scientists used computer models to make a conjecture. If there was a big bang, some of the energy should be remaining in the heavens, drifting like smoke from an explosion. With 13.7 billion years of cooling and expansion since the event, this radiation should be found everywhere and be of a particular wavelength. This was quite a specific quantitative prediction, and it offered no room for waffling. A friend showed Penzias and Wilson these papers, and immediately they saw the real meaning of their static interference. The background interference was not noise; it was a signal. And it was of the exact type predicted by theory. Penzias and Wilson had discovered the remnants of the big bang, a discovery that won them the Nobel Prize in 1978.
Being a fossil hunter, I dig in the ground to uncover relics. But every astronomer is a paleontologist of sorts. As Carl Sagan famously said, the light of the stars we see was formed in chemical reactions from a long time ago. The vastness of space means that starlight hitting our eyes is no artifact; it is the real deal—a visitor from a time before the birth of our species, even in some cases our planet itself. With such time travelers coming down to us each night, the trick to reconstructing our past comes from learning to see the light and radiation of stars in new ways.
For thousands of years, mankind considered itself the pinnacle of life’s creation on a planet sitting in the center of the universe. Science changed that perception. Leavitt, Hubble, and others helped us see that we live near the margin of a vast galaxy, in a universe of galaxies, with our planet one of many worlds. Darwin and the biologists had their say too. Our entire species is but one little twig on an enormous tree of life filled with all life on Earth. But each discovery that moves us from the center of creation to some obscure corner brings an entirely new relation between us, other species, and the entire universe. All the galaxies in the cosmos, like every creature on the planet, and every atom, molecule, and body on Earth are deeply connected. That connection begins at a single point 13.7 billion years ago.
As a species whose history has been in oceans, streams, and savanna plains, we humans have had our senses tuned to the chemical and physical world of land and water—to predators, prey, and mates we can see or hear. Nowhere in our history has there been a premium on the ability to perceive extra dimensions, times on the order of billions of years, or distances in a virtual infinity of light-years. To achieve these insights, we repurpose tools that served us so well in our terrestrial existence to new ends. Logic, creativity, and invention project our senses and ideas to the far reaches of time and space.
The physics of the point that existed 13.7 billion years ago is mostly beyond our imaginations, not to mention our conceptual tools. Gravity, electromagnetism—all the forces at work around us did not have an independent existence. Matter as we know it didn’t exist either. With everything that would become the universe packed so tightly in one spot, there was an enormous amount of energy. In such a universe, the physics of small particles, quantum mechanics, and that of large bodies, general relativity, were somehow part of a single, overarching, and still unknown theory. Just what that theory is awaits the next Einstein.
By about .000000000000000000000000000000000000000001 second the universe was roughly 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 degrees Fahrenheit, and the state of things starts to come more clearly into focus. This time begins the period of very rapid expansion of the universe. The big bang is not like an explosion where objects are projected from each other; space itself expands. With this expansion comes cooling over time. As the universe cooled and expanded, the forces and particles that make our world today emerged.
Einstein’s relation E = mc2 holds a key to the early events of the universe. The equation reveals the relationship between energy (E) and mass (m). Since the speed of light (c) is a huge number, it takes an enormous amount of energy to make an ounce of mass. The converse is also true: an infinitesimal amount of mass can be converted into a vast amount of energy.
One-trillionth of a second after the big bang, the universe was the size of a baseball. The energy contained in the universe at these early moments was the raw material for the production of a gargantuan amount of mass. As space expanded, energy, following Einstein’s equation, converted into mass, in this case ephemeral particles. In such a hot and small universe, everything was unstable: particles formed, collided, and disintegrated only to repeat the process trillions upon trillions of times.
The particles at this moment of history were of two opposing kinds, matter and antimatter. Matter and antimatter are opposites and annihilate each other on contact. As energy converted to mass, no sooner were matter and antimatter particles produced than they collided. Most of these collisions led to the particles being completely extinguished. If this were the complete state of affairs, we—people, Earth, even the Milky Way—would never be. Particles would have been destroyed almost as soon as they formed. A slight—and by that we mean about one-billionth of 1 percent—excess of matter over antimatter was enough for matter to take hold in the universe. Because of that tiny imbalance, we are, as the physicist Lawrence Krauss once described, every bit the direct descendants of that one-billionth of 1 percent surplus of matter over antimatter as we are of our own grandparents.
At one second, our universe started to form entities we would recognize, if only very briefly. These are the collection of subatomic particles that make momentary appearances in some of the largest atom smashers today—leptons, bosons, quarks, and their kin.
A little over three minutes after the birth of the universe began the stirrings of one of the deepest patterns in the world, captured by the chart that is the source of either awe or angst for young science students—the periodic table. The periodic table catalogs all known elements by the weight of their nuclei. The chart drawn for this moment of time would be a huge relief to our students. There would be only three boxes on it: hydrogen, helium, and lithium.
Hydrogen and helium today remain the most common elements in the universe. Hydrogen makes up about 90 percent of all matter, helium about 5 percent. All of the others that compose us and run through the lives of people and stars are but a rounding error.
After 300,000 years the universe had cooled and expanded enough so that true atoms could exist. Nuclei were able to pull electrons into their orbits. This new combination of electrons with atomic nuclei set the stage for reactions that underpin every moment of our lives today.
We live in a daily marketplace of electrons, with trades measured in millionths of seconds. I write this book and you read it based on the energy released from these exchanges. The molecules in our bodies exchange these tiny charged particles as part of the daily business of their interactions. Some electron movements release energy; reactions involving oxygen tend toward this outcome. Other reactions serve to bind atoms into molecules or molecules with one another. These daily trades define the reactions between the planet’s atmosphere, its climate, and the metabolisms of every creature on Earth. When you eat an apple, electrons from that material course through your cells to drive the metabolism to power your body. The electrons inside the apple to begin with were derived from the minerals in the ground and the water that fell from the sky. The electrons in both have cycled through our world for eons. And all of these came about well before the formation of the planet, the solar system, or even the stars.
With expansion and cooling, the stage was set: particles came together to make nuclei, nuclei came together with electrons to make atoms, and different atoms could now make the trades that are so essential for assembling ever-larger entities. One important thing had yet to take hold: gravity.
About 1 million years after the big bang, the universe cooled and expanded to the point where matter could get big enough for the force of gravity to have a meaningful impact on the shape of things. Order and pattern in the heavens emerge via a balance of forces: gravity serves to attract objects, while other forces, such as heat, and more mysterious ones, such as dark energy, serve to repel them. These relationships define the origin of the patterns we see in the universe, from the shape of gas clouds and stars to galaxies and planets. More fundamentally, they explain how chemistry itself evolved from a periodic table with only three elements to the one with over one hundred we live with today.
How did the world of atoms that make our planet and our bodies come about from the three that existed 13.69 billion years ago?
The march up the periodic table, from lighter elements like hydrogen and helium to heavier ones like oxygen and carbon, happens by the manufacture of ever-bigger nuclei. Under the right conditions two small nuclei can come together and make a larger one. The arithmetic of this combination depends on the physics of the nuclei themselves. In most cases, 1 + 1 does not equal 2: nuclei do not come together to make a new nucleus that is their simple sum. Often the new nucleus is lighter than that sum, and matter has been lost. But we know from Einstein’s E = mc2 that matter is not really lost; it is converted to energy. These fusion reactions, then, can release enormous amounts of energy.
Humankind has tried to marshal the energies of fusion, but under normal circumstances atomic nuclei don’t fuse spontaneously. The reaction takes a lot of energy to jump-start. Using this principle, Edward Teller, the father of the hydrogen bomb, made the first fusion device by attaching an atom bomb to another machine that allowed for the combination of nuclei. Atom bombs release energy by fission, a reaction that doesn’t require much energy at the start. Teller, with his colleague Stanislaw Ulam, designed a system, code-named Ivy Mike, that was about the size of a small factory on the Pacific island of Enewetak. When it exploded in November 1952, the energy from the atom bomb forced the hydrogen atoms in the reactor to fuse, and a massive explosion ensued. Teller witnessed it from the seismograph in the basement of the geology building at the University of California at Berkeley. Enewetak was totally denuded, with a hole a mile wide in its center. Fragments from the island’s lush coral reefs were ejected fifteen miles away. In analyzing the detritus left from the conflagration, the scientific teams discovered that the energy caused a number of large nuclei in the neighborhood to fuse, thereby producing entirely new elements never before seen on the planet. They were given the names einsteinium and fermium, after the scientists whose breakthroughs told us of the energy inside the atom.
Fusion reactions are the atomic engine that fuels the heat of stars. There is an essential difference between the Teller-Ulam device and celestial objects: Teller used an atom bomb to jump-start his fusion reactions, while the reactions inside stars depend on the force of gravity.
We can see evidence of these kinds of reactions today. Stare long enough at the constellation Orion using your peripheral vision, concentrating on the three stars that make the dagger on its belt, and if weather permits, you will see the fuzzy patch known as the Orion Nebula. When seen through a telescope, the nebula gains texture and complexity, appearing as a broad cloud with a number of smaller stars inside. The nebula itself is a huge field of gas, which, not entirely unlike that of the primordial universe, is giving birth to stars—about seven hundred of them. Of course, given the distance of the nebula from us, we are looking at baby pictures of starry infants from thousands of years ago.
During the formation of stars, fields of gas get so massive that the more particles they pull in, the stronger the force of gravitational attraction grows inside the cloud. At some point the mass of the gas cloud crosses a critical transition, and the gravitational attraction becomes a runaway process in which all the gas begins to collapse into a central point. Gravity pulls all the nuclei of the elements together, merging them. This union forces the nucleus to make a new combination; instead of one proton, it now forms a heavier nucleus with two. But this new nucleus is lighter than the sum of its parts. The lost mass, following E = mc2, is converted to an enormous amount of energy released into space.
The size and life of any given star are defined by the push and pull that goes on inside the star: the force of gravity pulls elements in, and the heat of the fusion reactions works to separate things.
Stars are like an engine that first consumes one fuel, then, as this fuel is depleted, begins consuming a new one. The most basic star is one that fuses the smallest atom, hydrogen, to make helium. The sun is one of these ordinary stars. Over time, as hydrogen is consumed and the conditions become right, the star shifts to fusing the helium it made. For a while, it chugs along consuming the nuclei of helium to make even heavier elements. Once the helium is depleted, fusion reactions consume those heavier elements. And so on. This process leads to the production of oxygen, carbon, and heavier atoms. Through the fusion reactions inside stars, the periodic table went from having only three elements to having scores of them.
Stars can consume ever-heavier atomic fuels until they hit a stopping point defined by the laws of physics and chemistry. That point—the element iron—holds a very special place in the periodic table. Elements smaller than iron can fuse and concomitantly release enormous amounts of energy. Elements larger than iron can also fuse but, because of the structure of their atomic nuclei, not as much energy is released. More energy needs to be put into fusing these larger nuclei than can be gained from the fusion reaction itself. If, for example, iron formed the basis for a power company’s nuclear reactor, less energy would be gained from the reactor than was put into it.
This equation is losing math for a star, but a huge gain for us. As a star consumes all of the lighter elements, and marches ever higher in the periodic table in the fuels it consumes, iron accumulates in the center. As more and more iron accumulates, the fuel for fusion is consumed, nuclear fusion reactions cease, and the star begins to emit less heat. Iron nuclei, under the right conditions, can absorb energy, almost like a nuclear explosion in reverse. With so much energy released only to be absorbed, these conditions can set off a massive chain reaction that ends as a vast and catastrophic explosion. In seconds, these explosions release more energy than stars like our sun emit in their entire lifetime.
This blast is one kind of supernova (another kind can be triggered by collisions of stars). Supernovae work something like Teller and Ulam’s crude device. The energy of one explosion brings new kinds of fusion reactions. Recall those fusion reactions for elements heavier than iron? Supernovae release so much energy that these expensive reactions happen. All the elements heavier than iron, such as the cobalt and cesium in our bodies, derive from supernovae.
Here comes the important part, at least for us. The blast of the supernova spreads atoms of the dead star across the galaxies. Supernovae are one engine that powers the movement of atoms from one star system to another.
The smallest parts of our bodies have a history as big as the universe itself. Beginning as energy that converted to matter, the hydrogen atoms originated soon after the big bang and later recombined to form ever-larger atoms in stars and supernovae.
The sky, like a thriving forest, continually recycles matter. With the heavens so full of stars manufacturing elements, then occasionally exploding and releasing them, only to recombine them again as a new star forms, the atoms that reach our planet have been the denizens of innumerable other suns. Each galaxy, star, or person is the temporary owner of particles that have passed through the births and deaths of entities across vast reaches of time and space. The particles that make us have traveled billions of years across the universe; long after we and our planet are gone, they will be a part of other worlds.
