What was it like at the origin of the Universe? Exactly what happened at the instant of time's beginning? Can anything concrete be said about the precise start of the Universe itself, or about the prevailing conditions during its first few moments? And how have those conditions changed to give rise to the Universe we see around us today?

These are surely fundamental questions. They are also hard questions. Yet they are among the most basic wonders that perhaps every thinking human being who has ever lived has contemplated in one way or another, at one time or another. Now, after more than 10,000 years of organized civilization, 21st-century science seems poised to provide some testable ideas regarding the ultimate origin of all things.

Explanations that scientists offer about the "origin of origins" should be considered qualified and provisional. Times long past are times long gone. It's difficult to be precise about events we cannot observe directly. To be sure, the early Universe was a decidedly unearthly domain, quite unlike anything encountered today. Neither stars nor planets, indeed not even atoms then existed; all was pure energy, the cosmic currency that makes change happen. Nonetheless, Universe models can be constructed—mathematical sketches based on theoretical insights and lodes of data constraining the size, shape, and structure of the cosmos. These models grant us some inkling of what the Universe was like well more than 10 billion years ago, indeed surprisingly close to its very origin.

Exploring the entire Universe requires big thinking. And there are hardly bigger ideas than cosmological ones. Cosmology is the study of the structure, evolution, and destiny of the Universe—the totality of all known or supposed objects and phenomena, formerly existing, now present, or to come, taken as a whole. Here we strive to gain an appreciation for the properties of the Universe in bulk: its matter and energy, its size and scale, perhaps something about its origin and fate.

Cosmic issues elicit grand perspective, and rightly so. Compared to the whole Universe truly writ large, its smaller contents such as planets and stars—even galaxies, to a certain extent—become nearly inconsequential. To the cosmologist, planets are hardly relevant, stars only point sources of hydrogen consumption, and galaxies mere details in the much broader context of all space.

Time also shrinks in significance when compared to eternity. Reckoning change on human scales pales in comparison to all change on the cosmological stage. Durations of a thousand years seem like nothing, a million years a mere wink of an eye in the cosmic scheme of things. Even a billion years comprise a rather short interval in the context of all time.

To appreciate cosmology, we must broaden our view and expand our minds to include all of space and all of time. If we have ever wanted to think big, now is the time!

The learning goals for this epoch are:

• to understand various cosmologies of the Universe, including particle evolution that underlies them
• to know of the extremely hot and dense conditions present just after the origin of the Universe
• to understand how matter naturally emerged from the primeval fireball of radiation
• to appreciate some of the efforts now underway to unify the known forces of the Universe
• to gain an inkling about current scientific models of creation itself
• to begin building a chronology of events based on the ages of Nature’s many varied objects
• to realize that ordered structures observed in the Universe obey known principles of modern science.