The Universe Within (5 page)

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 =
mc
²
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 =
mc
²
, 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.