The meeting “Why Trust a Theory? Reconsidering Scientific Methodology in Light of Modern Physics,” which took place at the Ludwig Maximilian University Munich, Dec. 7-9 2015, was for me a great opportunity to think in a broad way about where we stand in the search for a theory of fundamental physics. ...No, there is no scientific problem here, and there is nothing scientific about his approach.
As the only scientific representative of the multiverse at that meeting, a major goal for me was to explain why I believe with a fairly high degree of probability that this is the nature of our universe. But an equally important goal was to explain why, contrary to what many believe, string theory has been a tremendous success, and remains a great and inspiring hope for our ultimate success in understanding fundamental physics. ...
I am coming at this as an active scientist trying to solve a scientific problem, in my case the theory of quantum gravity. ... In the end, my estimate simply came down to combining four factors of two. This led to the probability 94% that the multiverse exists. If I had quoted this in binary, probability 0.1111, the scientific content would have been exactly the same but it would have led to much less merriment.
My estimate uses a kind of analysis known as Bayesian statistics.
He did not actually attend the meeting, as he was unable for unspecified health reasons.
His string theory is nutty enuf, but that is mainstream physics compared to his views about the multiverse, black hole firewalls, and the futility of experimental physics.
In effect we would be telling the experimentalists, who were spending billions of dollars and countless human-years of brilliant scientists, were essentially measuring random numbers, and I did not want to be the bearer of bad news. But for the most part Raphael’s point of view prevailed: we both agreed clearly on what the science was saying, and in the end one must be true to the science. I am not by nature a radical, but seem to have become one both with the multiverse and with the black hole firewall  just by following ideas to their logical conclusions. ...Okay, maybe I should not call him nutty if he has a genuine psychiatrist problem. But he is a respected theoretical physicist, and people take him seriously.
Still my anxiety grew, until eventually I needed serious help. So you can say quite literally that the multiverse drove me to the psychiatrist.2
[footnote 2] In truth, I should have gotten help for anxiety sooner, and for more general reasons. One should not be reluctant to seek help.
He claims to address the critics of string theory, but his main argument is to deny that it is a non-empirical theory. He says:
If I just make the same crude counting of a factor of 2 for each, I end up with probability 98.5 [%] for string theory to be correct.This is why Bayesians have a bad name.
He also attacks Peter Woit on the grounds that 10 years ago his blog had an anonymous comment that was rudely dismissive of a Steve Weinberg argument.
This must be a new low for ArXiv, the preprint server. I doubt that any real physics journal would publish such a complaint.
It is remarkable that the string theorists have done so little to rebut what Woit and other critics have said. You would think that big-shot professors would defend themselves, if everyone says that he is pursuing wrong and unscientific theories. Maybe they have no good defense.
Woit and Lubo have already posted their responses.
String theory could be described as something that was once a good idea that failed. The multiverse, black hole firewall, and Polchinsky's other ideas are unscientific nonsense from the start. And the philosophers at the German conference are clueless about what is scientific.
Update: Polchinski has moved his attack on Woit. He implies that Woit is not worthy of an attack on ArXiv. His attack on Woit is still online here.
Update: Separately, here is a Nature mag complaint that ArXiv has rejected some crappy papers that might be good enuf for a refereed journal.