From cosmologist George Ellis at Inference Review:
THEORETICAL PHYSICS AND cosmology find themselves in a strange place. Scientific theories have since the seventeenth century been held tight by an experimental leash. In the last twenty years or so, both string theory and theories of the multiverse have slipped the leash. Their owners argue that this is no time to bring these subjects to heel.
It is this that is strange.
If the multiverse is scientifically problematic, it is always open to philosophers to rescue the multiverse by expanding the margins of science. A theory, so the argument runs, need not be confirmed by empirical evidence. Richard Dawid has argued as much in a paper entitled “The Significance of Non-Empirical Confirmation in Fundamental Physics.” “In the absence of empirical confirmation,” he writes, “scientists may judge a theory’s chances of being viable based on a wide range of arguments.”
Nothing, Dawid argues, succeeds like success. Theories that satisfy a certain set of conditions have worked well in the past. This increases the probability that a new theory satisfying the same conditions is apt to work well in the future. This argument embodies the triumph of hope over experience. In 1974, Howard Georgi and Sheldon Lee Glashow proposed an exquisite grand unified theory, one that was supposed to unite the strong and electroweak forces. It predicted that, as the result of spontaneous symmetry breaking, protons would decay. Such was the hope. So far as experiments can determine, protons do not decay. Such is the experience. More.
But the multiverse is essentially a post-modern concept. It soars past evidence.
After all, the notion of evidence is an evolutionarily adapted user illusion. It was useful in the past. Now Cool rules. The serfs will soon be brought into line.
See also: How naturalism rots science from the head down
Nature: Stuck with a battle it dare not fight, even for the soul of science. Excuse me guys but, as in so many looming strategic disasters, the guns are facing the wrong way.
String theory as the ultimate Cool: Escaping the need for evidence