I found this Evolution News post about it, thanks to a J. Warner Wallace tweet. The article they linked is by two well-known cosmologists.
Here’s what George Ellis and Joe Silk say in Nature (“Scientific Method: Defend the Integrity of Physics”):
This year, debates in physics circles took a worrying turn. Faced with difficulties in applying fundamental theories to the observed Universe, some researchers called for a change in how theoretical physics is done. They began to argue — explicitly — that if a theory is sufficiently elegant and explanatory, it need not be tested experimentally, breaking with centuries of philosophical tradition of defining scientific knowledge as empirical. We disagree. As the philosopher of science Karl Popper argued: a theory must be falsifiable to be scientific. (Emphasis added.)
In particular, they chide the string theorists, multiverse advocates, inflation theorists, and purveyors of the “many worlds” interpretation of quantum mechanics.
Their concern is that the requirement for testability is being relaxed for junky theories.
Whether Ellis and Silk’s definitions of science and the scientific method are adequate is beside the point (the definition of science is a vexed question, testability is vague, and falsifiability has its flaws). What worries them is something else:
The issue of testability has been lurking for a decade. String theory and multiverse theory have been criticized in popular books and articles, including some by one of us (G.E.). In March, theorist Paul Steinhardt wrote in this journal that the theory of inflationary cosmology is no longer scientific because it is so flexible that it can accommodate any observational result. Theorist and philosopher Richard Dawid and cosmologist Sean Carroll have countered those criticisms with a philosophical case to weaken the testability requirement for fundamental physics.
Interesting that Sean Carroll, a naturalist who proposes naturalistic alternatives to the standard (theism-friendly) cosmology model (creation out of nothing), wants to weaken the testability requirement. Why do you think that is? Well, if we go by which model is testable, rather than which model is acceptable to that old-time naturalistic religion, then then the standard model (creation out of nothing) wins. That’s because we have experimental evidence for the standard model, (light element abundances, cosmic microwave background radiation, second law of thermodynamics, etc.) Carroll’s model is falsified by observations (e.g. – humans exist, not Boltzmann brains), and that’s why why he weakens the criterion of testability. If testability is what makes science, then he’s really just engaged in creative writing.
And about the multiverse in particular:
Look what they say about multiverse theory:
The multiverse is motivated by a puzzle: why fundamental constants of nature, such as the fine-structure constant that characterizes the strength of electromagnetic interactions between particles and the cosmological constant associated with the acceleration of the expansion of the Universe, have values that lie in the small range that allows life to exist. Multiverse theory claims that there are billions of unobservable sister universes out there in which all possible values of these constants can occur. So somewhere there will be a bio-friendly universe like ours, however improbable that is.
That sounds like a lead-up to The Privileged Planet, or to Privileged Species. Ellis and Silk go on to describe how one of the constants, the cosmological constant, is 120 orders of magnitude off from the predicted theoretical value. So are they ready to consider scientific theories that embrace this evidence, like intelligent design? No, but one thing they do know: multiverse theory is not scientific.
Billions of universes — and of galaxies and copies of each of us — accumulate with no possibility of communication between them or of testing their reality. But if a duplicate self exists in every multiverse domain and there are infinitely many, which is the real ‘me’ that I experience now? Is any version of oneself preferred over any other? How could ‘I’ ever know what the ‘true’ nature of reality is if one self favours the multiverse and another does not?
That’s a logical statement, not an observational one. By this, we see that they are not against using logical inference to eliminate unworthy theories. Isn’t that what Meyer does in his books, using “inference to the best explanation”? Isn’t that what Dembski does to eliminate the chance hypothesis?
In the end, Ellis and Silk never explain cosmic fine-tuning. They just preach that science needs to stick to the old-time religion: respect for observable, testable evidence.
The article by Ellis and Silk takes a lot of shots at fundamentalist religion, but at least we fundamentalists are OK with following testable science wherever it goes. Unlike naturalists.