Bernard Carr, the Professor of Astronomy and Mathematics at Queen Mary, University of London has written a very short piece in the independent in which he says:
‘is the "multiverse" a proper scientific proposal or just philosophy? Despite the growing popularity of the proposal, the idea is speculative and currently untestable – and it may always remain so. Astronomers may never be able to observe the other universes with their telescopes and particle physicists may never be able to detect the extra dimensions with their accelerators. So, although some physicists favour the multiverse because it may do away with the need for a creator, others regard the idea as equally metaphysical. What is really at stake is the nature of science itself’
Support for the idea of the multiverse is growing rapidly in many circles, particularly among String Theorists whose theory of everything predicts a vast array of universes, but also among more conservative cosmologists like Sir Martin Rees who argue that the eerie fine tuning of the physical constants mean the universe cannot be seen as purely self explanatory. This will inevitably mean that an array of scientific observations will be interpreted as evidence for a multiverse even if such a conclusion is highly speculative. Looking at the current wave of multiverse hype, I can’t help but agree with Peter Woit’s conclusion that:
‘It seems that selling pseudo-science with the argument “it’s either this or religion” works.’
Is there a way to test the proposition that we live in a multiverse. Roger Penrose of Oxford University in his book The Road to Reality, pp. 762-5) has argued that if our universe is but one member of an infinite world ensemble of randomly varying universes, then it is overwhelmingly more probable that we should be observing a much different universe than that which we in fact observe.
Penrose calculates that the odds of our universe’s low entropy condition obtaining by chance alone are on the order of 1:1010(123) (this is under the Weyl Curvature hypothesis). The odds of our solar system’s being formed instantly by random collisions of particles is, on the other hand, about 1:1010(60), a vast number, but inconceivably smaller than 1010(123). If our universe were but one member of a collection of randomly ordered worlds, then it is vastly more probable that we should be observing a much smaller universe. Observable universes like that are much more plenteous in the ensemble of universes than worlds like ours and, therefore, ought to be observed by us if the universe were but one random member of an ensemble.
If our universe is but one random member of a multiverse, then we ought to be observing highly extraordinary events, like horses and unicorns popping into and out of existence by random collisions since these are vastly more probable than all of nature’s constants and quantities falling by chance into the virtually infinitesimal life-permitting range. Penrose concludes that multiple universe explanations are so “impotent” that it is actually “misconceived” to appeal to them to explain the special features of the universe. I wouldn’t take as cynical a view as that; I find it conceivable that the cosmos could be much larger than this one universe. But such a view is metaphysics; it is not scientific and it is important to know the difference.
Another set of theories that have been making a bit of a comeback are the cyclic universe or ‘big bounce’ models. One would think these would have disappeared with the recent finding that our universes’ rate of expansion is increasing due to dark energy. They still seem to be hanging in there in the hope that dark energy will mysteriously change into a repulsive force. If this is the case then our universe might keep expanding and contracting ad infintum. I must confess I rather like this idea because, as well as failing to explain why there should be a lawlike bouncing universe for no reason, it vindicates Nietzsche’s idea of eternal recurrence. This was a slightly off the wall Idea Nietzsche picked up from Heinrich Heine, who wrote
‘[T]ime is infinite, but the things in time, the concrete bodies, are finite. They may indeed disperse into the smallest particles; but these particles, the atoms, have their determinate numbers, and the numbers of the configurations which, all of themselves, are formed out of them is also determinate. Now, however long a time may pass, according to the eternal laws governing the combinations of this eternal play of repetition, all configurations which have previously existed on this earth must yet meet, attract, repulse, kiss, and corrupt each other again...’
Nietzsche called this idea "horrifying and paralyzing" remarking that:
What, if some day or night a demon were to steal after you into your loneliest loneliness and say to you: 'This life as you now live it and have lived it, you will have to live once more and innumerable times more' ... Would you not throw yourself down and gnash your teeth and curse the demon who spoke thus? Or have you once experienced a tremendous moment when you would have answered him: 'You are a god and never have I heard anything more divine.' [The Gay Science, §34]
I would agree. Horrifying, paralyzing and mind bogglingly silly; such is the state of play in 21st century cosmology.
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