If there was no birth-time of earth and heaven and they have been from everlasting, why before the Theban war and the destruction of Troy have not other poets as well sung other themes? -- Lucretius, De rerum natura ----- Ever since our distant ancestors began to contemplate the world around them, the question of its beginning has been on humankind's mind. The above quotation, from Lucretius's first-century-BCE work De rerum natura, can be found in the treatise The Birth-Time of the World, published in 1914 by John Joly, a professor of geology at Trinity College Dublin. True to his profession, Joly moves the realm of first events from cultural achievements and mischief to the impersonal planet Earth. He writes: "Notwithstanding our limitations, the date of the birth-time of our geological era is the most important date in Science." Interest in the question of how it all began has persisted throughout the millennia, but our understanding of what "all" sums up has evolved. Scientific discoveries have led us to push the beginning back to earlier and earlier times, and nowadays, following the advent and great success of modern cosmology, we tend to disagree with Joly and shift the beginning to grander cosmic events. Physicists have developed theories about the formation of galaxies and the stars they contain, the nucleosynthesis of elements, the genesis of protons and neutrons from quarks, and more speculatively, the creation of matter excitations during cosmic inflation from nothing but quantum fluctuations. Exciting matter out of the vacuum seems to violate energy conservation, and indeed, conservation laws are the strictest keepers of the gates of time: If some quantities must remain constant, they cannot begin to acquire nonzero values. At whatever time we choose to mark "the beginning," conserved quantities must remain zero, exactly balanced. In theory, inflation can produce matter energy, but only by taking it from some other source -- spacetime. According to general relativity, the energy-balance law includes not only the usual matter terms but also a negative contribution from spacetime. The sum always remains zero, and matter can arise. If matter forms under gravity's sponsorship, it cannot be part of the absolute beginning. Yet again, we have to push the beginning backwards. Matter emerges from spacetime, but how did space and time begin? How can it even be possible that time had an absolute beginning, with no time "before"?