Multiverse A brief overview
The multiverse concept is founded upon the idea that what we have hitherto considered to be the universe is but a small component of a vast assemblage of universes. According to the multiverse thesis, each universe may differ with regards to their physical laws, in such a way that all conceivable constants and laws are represented in a universe somewhere. The hypothesis is intimately associated with the so-called Anthropic Principle, which states that our own existence acts as a selection principle determining which properties of the universe we can observe. That is to say, any observed properties of the universe which may at first seem to be astonishingly improbable can only be seen in their true perspective after we realize that other properties couldnt be observed by us, since we can only observe properties of the universe which are conducive to our own existence. The Anthropic Principle is thus used by many people, often in conjunction with the Multiverse principle, to show why we shouldnt be surprised at the astonishingly improbable fine-tuning of the universe for intelligent life.
Multiverse The problems
The multiverse explanation is highly problematic. Perhaps the biggest difficulty is that the existence of such parallel universes can be neither verified nor falsified. The model is thus ad hoc and contrived. Second, given that the biofriendliness of the universe is in no way conducive to cosmic sustainability, no form of selection process or cosmic evolution can be invoked. Third, if the multiverse thesis is to commend itself as a plausible hypothesis, then a mechanism for generating such universes needs to be advanced. The concept of a bubble of universes, each with their own fundamental constants and values, only throws the paradox back one step -- as one could easily ask who built the generator to give rise to this cosmic lottery.
Roger Penrose of Oxford University has calculated that the odds of our universes low entropy condition obtaining by chance alone are on the order of 1:10123, an inconceivable number. If our cosmos were indeed but one member of a much vaster multiverse of randomly ordered worlds, then it is vastly more probable that we should be observing a much smaller universe. The probability of our solar system forming randomly is about 1:1060, a vast number but inconceivably smaller than 10123.
Science is founded on the notion of the rationality and uniformity of nature. The universe is ordered in a rational way, and scientists seek reasons for why things are the way they are. If the universe as a whole is without transcendency or purpose, then it exists without reason. It is therefore ultimately arbitrary and absurd. We are subsequently invited to contemplate a state of affairs in which all scientific chains of reasoning are ultimately grounded in absurdity. The concept of a cosmic order would then have no foundation. Thus, the multiverse theory undercuts the very premise upon which the scientific method is founded.
All this has been said, of course, without asking whether the multiverse itself must not exhibit some degree of cosmic fine-tuning in order to exist. If it does, as some have argued, then it is a non-starter as an alternative to design.
Without a scientifically rigorous means by which such a multiverse concept can be tested, verified and falsified, the idea remains as but a conjecture -- a fudge factor invoked merely to evade the apparent design of our cosmos. In addition, the idea suffers from a number of scientific difficulties and problems -- but a handful of which are discussed herein.
Whereas one knows that one universe exists, one does not -- nor can -- know whether more than one universe exists. Once observers exist in universe A, the theory of general relativity indicates that the space-time envelope of that universe can never overlap the space-time envelope of any other possibly existing universe. In other words, even if God made ten universes, we would forever lack the scientific means to detect any universe besides our own. The sample size of universes therefore is limited to one. Thus, the only rational option is that there exists only one universe and that God exquisitely designed the universe for the benefit of mankind.