View 1. The Universe does not exist
This first philosophical view is familiar through the slogan “there is no spoon.” The only true reality, it says, is spiritual. Nothing physical actually exists. This view has been taught by some (though not all) schools of Hinduism. In Europe, it is associated with George Berkeley. The difficulty with this perspective is that the laws of science must, in some sense, be emergent from the spiritual reality. But how?
View 2a. The Universe exists, but has not always existed
This view implies a time t0 at which the Universe “began” – in the sense that nothing (not even time) existed before then. The immediate response is: why? Some kind of explanation for the existence of the Universe seems necessary (although Stephen Hawking argues not). Given that there could be no event before t0, a purely scientific explanation seems impossible, leaving religion or philosophy to supply one. The traditional explanation – from Plato, Christianity, and other religions – is some form of divine creation. Such an explanation is not everybody’s cup of tea, of course.
View 2b(i). The Universe has always existed, with a finite number of states
Alternatively, the Universe has always existed. If the number of possible states in the Universe is finite, this means that the present state of the Universe must have occurred infinitely often in the past (down to the position of every atom), and must occur infinitely often in the future. Previous analogues of me have blogged this comment infinitely often in the past, and infinitely many future analogues will do so again. This is true whether the Universe is deterministic or random. The Stoics were one group who believed in such a (rather depressing) cyclic Universe, but it seems difficult to swallow.
View 2b(ii). The Universe has always existed, with an infinite number of states
The prospect of “eternal recurrence” can be eliminated if the Universe has an infinite number of states, but this seems to require some kind of eternal expansion. The Steady State model was once proposed as a way of achieving this. A modern alternate suggestion is that new sub-Universes are constantly “popping into existence” as a result of quantum fluctuations in older sub-Universes, thus forming an infinite branching tree.
It is not quite clear how this branching would work, however, and Paul Davies points out that there are philosophical problems too: “For a start, how is the existence of the other universes to be tested? To be sure, all cosmologists accept that there are some regions of the universe that lie beyond the reach of our telescopes, but somewhere on the slippery slope between that and the idea that there are an infinite number of universes, credibility reaches a limit. As one slips down that slope, more and more must be accepted on faith, and less and less is open to scientific verification. Extreme multiverse explanations are therefore reminiscent of theological discussions. Indeed, invoking an infinity of unseen universes to explain the unusual features of the one we do see is just as ad hoc as invoking an unseen Creator. The multiverse theory may be dressed up in scientific language, but in essence it requires the same leap of faith.”
So there you have it. Four views, some of which have been around for millennia, and all of which have adherents and opponents. View 2a is the most commonly accepted. Which one do you think is correct?