Introduction

Abstract

Abstract The infinite has to be a relative concept. Go any distance: an infinite space means that there is more to explore. The end is never reached. Could the universe be like that? The notion that the universe could be infinite has excited extreme views. To some, the concept of an infinite universe is horrifying. The chances of creating intelligent life may be infinitesimal, but they are finite. It happened at least once! In an infinite universe replicas of us are inevitable. There would be identical copies of ourselves replicating every action, every word, somewhere. This seems hard to accept. But this is hardly a good scientific reason for abandoning an infinite universe. Indeed, modern astronomy tells us that the infinite universe may be more than just a metaphysical concept. Physics may even require the universe to be infinite. And if it were actually infinite, would we ever know? I shall argue that there are means of exploring both a very large but finite and conceivably even an infinite universe. If the universe is topologically small – that is, very large but finite in volume – there may be clues to be unlocked in such observables as the fossil radiation left over from the Big Bang. In contrast, exploration and verification of an infinite universe is not far from the voyages of science fiction, but arguably lies in the realm of physics.