Big History

From the Big Bang to the Present

Cynthia Stokes Brown

• Editore: The New Press
• Anno: 2012
• ISBN:
  9781595588456
• Argomento: History
• Categoria: World History

"This exciting saga crosses space and time to illustrate how humans, born of stardust, were shaped—and how they in turn shaped the world we know today." — Publishers Weekly This book offers "world history on a grand scale"—pulling back for a wider view and putting the relatively brief time span of human history in context. After all, our five thousand years of recorded civilization account for only about one millionth of the lifetime of our planet ( Kirkus Reviews ). Big History interweaves different disciplines of knowledge, drawing on both the natural sciences and the human sciences, to offer an all-encompassing account of history on Earth. This new edition is more relevant than ever before, as we increasingly grapple with accelerating rates of change and, ultimately, the legacy we will bequeath to future generations. Here is a path-breaking portrait of our world, from the birth of the universe from a single point the size of an atom to life on a twenty-first-century planet inhabited by seven billion people.

PART I

The Depths of Time and Space

1

Expanding into Universe

(13.7 Billion–4.6 Billion Years Ago)

We are all whirling about in space on a small planet, bathed for part of each day in the light and warmth of a nearby star we call the sun. We are traveling 12 million miles a day around the center of the Milky Way galaxy, which is whirling in a universe of more than 100 billion galaxies, each home to 100 billion stars (Fig. 1.1).

This universe in which we whirl began as a single point 13.7 billion years ago; it has been expanding ever since, with its temperature steadily decreasing. Our universe has at least four dimensions, three of space and one of time, meaning that time and space are interconnected. Just now the size of our observable universe is roughly 13.7 billion light-years on each of three dimensions by 13.7 billion years on the dimension of time, increasing as I write and you read.

Ever since human beings developed, they have been looking at points of light in the nighttime sky with awe and respect, learning what they could from direct observations and using this knowledge to make predictions, to travel on land, and to navigate by sea. Without specialized instruments, however, people could not detect much about the origin of our immense universe and the nature of matter, because the scale of the universe and of matter is so different from that of everyday life. By the late twentieth century, scientists had invented instruments that could begin to view the macroscopic heavens and the microscopic domain. Knowledge about these worlds has recently expanded exponentially. Now everyone can understand the amazing universe that is our home—if we use our imaginations and absorb the photographic images and diagrams that are currently available.¹

1.1 The Milky Way Galaxy

Fog and Transparency

It all began with an inconceivable event: the big bang. (This name was given by the British astrophysicist Fred Hoyle on a BBC radio broadcast in 1952.)² The universe erupted from a single point, perhaps the size of an atom, in which all known matter and energy and space and time were squeezed together in unimaginable density. Compressed space unfurled like a tidal wave, expanding in all directions and cooling, carrying along matter and energy to this very day. The power in this initial expansion was sufficient to fling a hundred billion galaxies for 13.7 billion years and counting. The billowing universe was under way.

Where did this eruption take place? Everywhere, including where each of us is right now. In the beginning all the locations that we see as separate were the same location.

Initially the universe was composed of “cosmic plasma,” a homogeneous substance so hot that it had no known structure at all. Matter and energy are interchangeable at temperatures of many trillion degrees; no one knows what energy is, but matter is energy at rest. As the universe cooled, the smallest constituents of matter that we know about, called quarks, began to clump together in groups of three, forming both protons and neutrons (Fig. 1.2). This took place at about one hundred thousandths of a second after the big bang, when the temperature had cooled to about a million times hotter than the sun’s interior. A hundredth of a second later, these protons and neutrons began hanging together to form what would later become the nuclei of the two lightest elements, hydrogen and helium.

1.2 The Constituents of Matter

Matter is composed of atoms, each of which is composed of electrons circling a nucleus containing protons and neutrons, both of which are made of quarks. Whether quarks are composed of something smaller is currently unknown.

Before one second had elapsed the four fundamental forces that govern matter had come into being: gravitational force, electromagnetic force, the strong nuclear force, and the weak nuclear force. Gravitational force, or gravity, is the weakest of the four forces. It was described by Newton’s theory of gravity and by Einstein’s general theory of relativity, but it still cannot be defined. Electromagnetic force is a union of the electric and the magnetic forces. The strong nuclear force, the strongest of the four, is responsible for keeping quarks locked inside of protons and neutrons and for keeping protons and neutrons crammed inside of atomic nuclei. The weak nuclear force mediates the decay (or disintegration of the atomic nuclei) of radioactive elements. Scientists believe that all four forces must be aspects of one force, but they have not yet been able to create a unifying theory.

These four forces work in perfect balance to allow the universe to exist and expand at a sustainable rate. If the gravitational force were a tiny bit stronger, all matter would likely implode in on itself. If gravity were slightly weaker, stars could not form. If the temperature of the universe had dropped more slowly, the protons and neutrons might not have stopped at helium and lithium but continued to bond until they formed iron, too heavy to form galaxies and stars. The exquisite balance provided by the four forces seems to be the only way in which the universe can maintain itself. Scientists wonder if perhaps many other universes came into existence but vanished before this one survived. The newborn universe evolved with phenomenal speed, setting in place in a tiny fraction of a second the fundamental properties that have remained stable since.

During about 300,000 years of expanding and cooling, the wildly streaming electrons, negatively charged, slowed down. The atomic nuclei, protons and neutrons, were positively charged. When the electrons had slowed down sufficiently, the nuclei could attract them by their electric charge and form the first electrically neutral atoms: hydrogen (H) and helium (He), the lightest elements, the first matter. Hydrogen consists of one proton and one electron; helium consists of two protons and two electrons.

This became a pivotal moment in the story of the universe. Before the formation of stable atoms, the universe was filled with so many zigzagging particles, some negative, some positive, that light (consisting of subatomic particles called photons) could not move through the bath of charged particles. This was so because photons interact with electrically charged particles and are either deflected or absorbed. If anyone had been there to see it, the universe would have appeared as a dense fog or a blinding snowstorm.

As soon as atoms formed, binding the negative electrons and positive protons together, the photons of light could travel freely. The dense fog of radiation lifted. Matter had formed, and the universe became transparent. Its full expanse came into view—if anyone had been there to see it—consisting mostly of vast empty space filled with huge clouds of hydrogen and helium with immense amounts of energy pouring through them.

Today we can see some of the photons left from the big bang—as “snow” on our television screens. To do so we must disconnect the cable feed and tune to a channel the set does not receive. About 1 percent of the “snow” we see is residual light/heat left from the big bang that forms a cosmic sea of background microwave radiation.³ If our eyes were sensitive to microwaves, which they are not, we would see a diffuse glow in the world around us.

By using radio equipment, scientists have documented the background microwave radiation. By the 1950s and 1960s physicists realized, from what they already knew about the universe, that the present universe should be filled with primordial photons, cooled over 13.5 billion years to a few degrees above absolute zero. In the spring of 1965 two radio astronomers, Arno A. Penzias and Robert W. Wilson, working for Bell Laboratories in New Jersey, accidentally detected this afterglow as a background hissing noise while they were testing a new microwave antenna to be used with communication satellites. In 1989 NASA sent up the Cosmic Background Explorer (COBE) satellite, which collected information that confirmed with high precision that there are about 400 million photons in every cubic meter of the universe—an invisible cosmic sea of microwave radiation, at 3 degrees above absolute, just as predicted by the theory of the big bang.

In 2002 NASA sent a sixteen-foot probe called the Wilkinson Microwave Anisotropy Probe, or WMAP, a million miles out from Earth. For a year WMAP took time exposures of the entire sky, showing in high resolution the map of the cosmic background radiation (CBR) from 380,000 years after the big bang and confirming again the big bang account of the universe.

Fortunately for astronomers, on the scale of the universe, distance is a time machine. The farther away something is, the younger we see it; this is because the more distant something is, the longer its radiation takes to reach us. We can never see the universe as it is today, only as it once was, because it takes millions and billions of years for the light of distant galaxies and stars, traveling at nearly 6 trillion miles a year, to reach us. Hence, we can see far back into the past. By picking up microwave radiation, we can “see” back nearly to the beginning of the universe (Fig. 1.3).

Think of it this way. The light from our nearest star, the sun, takes eight minutes and twenty seconds to reach us. Light from Jupiter takes about thirty-five minutes when it is closest to us, about an hour when it is farthest away in its orbit. The light of the brightest star in the night sky, Sirius, takes 8.6 years to reach us. (The distance the light travels is 8.6 light-years, or 50.5 trillion miles). The light from stars we can see without optical aid takes from four years to 4,000 years to reach us. If we should see a star exploding 3,000 light-years away, then that explosion occurred 3,000 years ago—the time it takes for the light to reach us.

Twinkling Galaxies

As described earlier, the universe became transparent some 300,000 years after the big bang. Immense clouds of hydrogen and helium drifted until these clouds broke into about a trillion separate clouds, each with its own dynamics, each escaping from the universe’s expansion in that the diameter of each cloud remained the same while the space between the clouds increased.

1.3 Our View of the Universe

From our position in the Milky Way galaxy—one of the galaxies in the Local Group—we see the universe in the distant past, because the light from remote galaxies takes billions of years to reach us. In this distant past the universe was smaller, and galaxies collided more often. Quasars are very distant objects thought to be the nuclei of younger galaxies, possibly in collision.

As the universe cooled and calmed down, each separate cloud of hydrogen and helium became a separate galaxy of stars joined by gravity. This happened as the atoms of hydrogen and helium collided with each other. As they collided, the friction created temperatures so high that the atoms were stripped of their electrons. The hydrogen nuclei started to fuse, forming helium ions. These fusion reactions released a huge amount of heat/energy, according to Einstein’s equation E = mc², in which the loss of a tiny bit of mass results in energy multiplied by the speed of light squared. As the hydrogen begins to burn, millions of tons of matter are transformed into energy each second, and a star is born. The earliest stars formed only about 200,000 years after the big bang.

The universe is filled with an enormous range of objects as measured by their mass. The largest objects are stars, which produce their own energy. The largest stars are up to twenty times more massive than the star that is our sun. The smallest objects in the universe are dust particles visible only under a microscope and which rain down into the Earth’s atmosphere at the rate of a hundred tons a day. The silt in the eaves of any house probably contains a minute amount of interstellar material. Planets are middle-range objects; their mass is not sufficient to produce their own energy through hydrogen-fusion reactions.

Stars come in a vast range of sizes and densities, and they evolve over time from one type to another. Most of the stars nearest us are red stars, but the one we know best, the sun, is a stable yellow star burning hydrogen, called hydrogen fusion as described earlier. When its hydrogen is used up, in about 5 billion years, our sun will switch to burning helium, called helium fusion. Since helium fusion is a hotter process with a greater energy output, the pressure from the extra energy will expand the sun until it becomes what is called a red giant. When the helium fuel is used up, the red giant will collapse to a white dwarf. Then it will slowly cool until it becomes a cinder called a black dwarf, about the size of Earth and 200,000 times its mass. No black dwarf has yet been found because the universe is not old enough for any to have completed the slow process of cooling down.

Some yellow stars, the ones that are larger than our sun at their inception, become larger red giants than our sun will. When their red-giant stage is over, they do not shrink into white dwarfs. In them heavier elements are created and burned: carbon, nitrogen, oxygen, magnesium, and finally iron. But iron cannot be used as a stellar fuel. Energy production stops and gravity takes over. The star’s core implodes and triggers an immense explosion of the outer layers that blasts most of the star to smithereens. Only the core survives as a white dwarf, a neutron star (tiny and incredibly dense), or a black hole, which is an...