Origins: Fourteen Billion Years of Cosmic Evolution Read Free

arm) of an undistinguished galaxy (the Milky Way) in an undistinguished part of the universe (the outskirts of the Virgo supercluster). The gas cloud from which the Sun formed contained a sufficient supply of heavy elements to spawn a few planets, thousands of asteroids, and billions of comets. During the formation of this star system, matter condensed and accreted out of the parent cloud of gas while circling the Sun. For several hundred million years, the persistent impacts of high-velocity comets and other leftover debris rendered molten the surfaces of the rocky planets, preventing the formation of complex molecules. As less and less accretable matter remained in the solar system, the planets’ surfaces began to cool. The planet we call Earth formed in an orbit where its atmosphere can sustain oceans, largely in liquid form. Had Earth formed much closer to the Sun, the oceans would have vaporized. Had Earth formed much farther, the oceans would have frozen. In either case, life as we know it would not have evolved.
    Within the chemically rich liquid oceans, by a mechanism unknown, simple anaerobic bacteria emerged that unwittingly transformed Earth’s carbon dioxide–rich atmosphere into one with sufficient oxygen to allow aerobic organisms to form, evolve, and dominate the oceans and land. These same oxygen atoms, normally found in pairs (O 2 ), also combined in threes to form ozone (O 3 ) in the upper atmosphere, which shields Earth’s surface from most of the Sun’s molecule-hostile ultraviolet photons.
    The remarkable diversity of life on Earth, and (we may presume) elsewhere in the universe, arises from the cosmic abundance of carbon and the countless number of molecules (simple and complex) made from it; more varieties of carbon-based molecules exist than of all other molecules combined. But life is fragile. Earth’s encounters with large objects, left over from the formation of the solar system, which were once common events, still wreak intermittent havoc upon our ecosystem. A mere 65 million years ago (less than 2 percent of Earth’s past), a 10-trillion-ton asteroid struck what is now the Yucatán Peninsula and obliterated over 70 percent of Earth’s land-based flora and fauna-including all the dinosaurs, the dominant land animals of that epoch. This ecological tragedy opened an opportunity for small, surviving mammals to fill freshly vacant niches. A big-brained branch of these mammals, one we call primates, evolved a genus and species— Homo sapiens —to a level of intelligence that enabled them to invent methods and tools of science; to invent astrophysics; and to deduce the origin and evolution of the universe.
    Yes, the universe had a beginning. Yes, the universe continues to evolve. And yes, every one of our body’s atoms is traceable to the big bang and to the thermonuclear furnaces within high-mass stars. We are not simply in the universe, we are part of it. We are born from it. One might even say that the universe has empowered us, here in our small corner of the cosmos, to figure itself out. And we have only just begun.

Part I
    The Origin of
the Universe

CHAPTER 1
    In the Beginning
    I n the beginning, there was physics. “Physics” describes how matter, energy, space, and time behave and interact with one another. The interplay of these characters in our cosmic drama underlies all biological and chemical phenomena. Hence everything fundamental and familiar to us earthlings begins with, and rests upon, the laws of physics. When we apply these laws to astronomical settings, we deal with physics writ large, which we call astrophysics.
    In almost any area of scientific inquiry, but especially in physics, the frontier of discovery lives at the extremes of our ability to measure events and situations. In an extreme of matter, such as the neighborhood of a black hole, gravity strongly warps the surrounding space-time continuum. At an extreme of energy, thermonuclear fusion sustains itself within