Explanatory usefulness and existence

We have seen that there are major problems in confirming any ensemble proposal in the usual scientific manner. We can also ask whether the idea is useful. It does provide a plausible kind of explanation of anthropic coincidences (e.g. in the context of the cosmological constant), but ultimately its usefulness as a scientific proposal is dubious. Also any ensemble proposal is not a final explanation; it just pushes the ultimate question back one stage further. For if one assumes the existence of a multiverse, the deeper issue then becomes: Why this multiverse rather than another one? Why an ensemble that allows life rather than one that does not [14]? The only multiverse proposal that necessarily admits life is Tegmark's extreme version of 'all that can happen does happen' [8]. But then why should this be the one that exists, with its extraordinary profligacy of infinities? The crucial existential questions recur and the multiverse proposal per se cannot answer them.

Given its essentially philosophical nature, a useful question is whether there is a philosophically preferable version of the multiverse proposal. In my view, Smolin's idea of a Darwinian evolutionary process in cosmology [9] is the most radical and satisfactory one, because it introduces the crucial idea of natural selection - the one process that can produce apparent design out of mechanistic interactions - into cosmology. Thus it extends fundamental physics to include central biological principles, making it a much more inclusive view than any of the other proposals, which are all based purely on theoretical physics. However, this proposal is incomplete in several ways [50], so it would be helpful to have its physical basis investigated in more detail.

So finally the question is: Does a multiverse in fact exist? The considerations of this article suggest that, in scientific terms, we simply do not know and probably never will. In the end, belief in a multiverse will always be a matter of faith that the logical arguments proposed give the correct answer in a situation where direct observational proof is unattainable and the supposed underlying physics is untestable.

This situation would change if we were able to point to compelling reasons, based on scientific evidence, for a particular specifiable ensemble, or at least a narrowly defined class of ensembles. One way in which this could be accomplished would be by accumulating evidence that an inflaton potential, capable of generating a particular ensemble of domains, was dominant in the very early universe. Otherwise, there will be no way of ever knowing which (if any) particular ensemble is realized. We can always claim whatever we wish about an ensemble, provided it includes at least one universe that admits life. It may contain only one universe or a vast number of them (but not an infinite number if the above arguments are correct) and the evidence will not allow us to choose. Gardner [51] puts it this way:

There is not the slightest shred of reliable evidence that there is any universe other than the one we are in. No multiverse theory has so far provided a prediction that can be tested. As far as we can tell, universes are not even as plentiful as two blackberries.

The existence of multiverses is neither established nor scientifically estab-lishable. The concept is justified by philosophy rather than science. They have explanatory power, but the philosophical nature of their justification must be appreciated.

Was this article helpful?

0 0

Post a comment