To make this vast expanse of time even remotely comprehensible, some scholars have depicted the history of the cosmos as if it were a single calendar year (see Snapshot). On that cosmic calendar, most of the action took place in the first few milliseconds of January 1. As astronomers, physicists, and chemists tell it, the universe that we know began in an eruption of inconceivable power and heat. Out of that explosion of creation emerged matter, energy, gravity, electromagnetism, and the “strong” and “weak” forces that govern the behavior of atomic nuclei. As gravity pulled the rapidly expanding cosmic gases into increasingly dense masses, stars formed, with the first ones lighting up around 1 to 2 billion years after the big bang, or the end of January to mid-February on the cosmic calendar.

Hundreds of billions of stars followed, each with its own history, though following common patterns. They emerge, flourish for a time, and then collapse and die. In their final stages, they sometimes generate supernovae, black holes, and pulsars—phenomena at least as fantastic as the most exotic of earlier creation stories. Within the stars, enormous nuclear reactions gave rise to the elements that are reflected in the periodic table known to all students of chemistry. Over eons, these stars came together in galaxies, such as our own Milky Way, which probably emerged in March or early April, and in even larger structures called groups, clusters, and superclusters. Adding to the strangeness of our picture of the cosmos is the recent and controversial notion that perhaps 90 percent or more of the total mass of the universe is invisible to us, consisting of a mysterious and mathematically predicted substance known to scholars only as “dark matter.”

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The contemplation of cosmic history has prompted profound religious or philosophical questions about the meaning of human life. For some, it has engendered a sense of great insignificance in the face of cosmic vastness. In disputing the earth and human-centered view of the cosmos, long held by the Catholic Church, the eighteenth-century French thinker Voltaire wrote: “This little globe, nothing more than a point, rolls in space like so many other globes; we are lost in this immensity.”3 Nonetheless, human consciousness and our awareness of the mystery of this immeasurable universe render us unique and generate for many people feelings of awe, gratitude, and humility that are almost religious. As tiny but knowing observers of this majestic cosmos, we have found ourselves living in a grander home than ever we knew before.