Gfrom it a very first moment? Or has this world of space, time and matter always existed? Philosophy has notoriously disagreed on this since Aristotle contradicted his teacher Plato. In his dialogue “Timaeus” he wrote that there was no such thing as a period of time “before heaven came into being”, meaning that the world and time were “put into action at the same time”. Aristotle, however, pleaded for the eternity of the world. Finally, Immanuel Kant declared the question unsolvable. In his main epistemological work, he presented it in 1781 as an “antinomy of pure reason”: Both for a beginning of time and a finiteness of the universe as well as against each logically watertight proofs could be provided – but both could not be true. Kant wanted to show how easy it is to shipwreck with pure, i.e. non-empirical, thinking.
The question arises whether and, if so, to what extent empirical natural science can answer the question. In fact, this one went a good deal further than Kant would have thought possible. Modern astrophysics can claim, on the best empirical grounds, that 13.8 billion years ago the observable universe was a hot and dense ball—say, about the size of a grapefruit—that thereafter expanded to its current size. That’s the big bang theory. Today it is universally accepted, even if there was resistance, including at first from Albert Einstein.