John Horgan has an interesting interview with Steven Weinberg here. Weinberg isn’t very optimistic about possible progress these days:
Horgan: In 1995 you told me that it’s a “terrible time for particle physics.” Are you feeling any better about your field now? Are there any particular advances that give you hope?
Weinberg: I’m not much more cheerful.
Horgan: Do you still believe in the attainability of a “final theory” of physics, one that ends what you called “the ancient search for those principles that cannot be explained in terms of deeper principles”?
Weinberg: I still expect there to be a final theory, but I’m less confident that humans will discover it in this century.
When asked about when string theory should be abandoned as a dead end he ignores that part of the question:
Horgan: In your new book, To Explain the World, you write that “scientific theories cannot be deduced by purely mathematical reasoning.” Doesn’t that principle apply to string theory? At what point, if ever, should string theory be abandoned as a dead end?
Weinberg: String theory may be inspired by mathematical reasoning, but not deduced, and certainly not confirmed.
He defends the multiverse with
Further, if we find some future theory that does make successful predictions about a lot of things, which turn out to be true rather than false, and if that theory also predicts the existence of a multiverse, then we should take that prediction seriously even though it can’t be tested directly.
which is true enough, but doesn’t address the fact that there is no such theory. The string theory landscape “prediction” of a multiverse is exactly the opposite sort of thing, not a corollary of successful predictions, but something being invoked as an excuse for failure to make predictions about anything at all.
For something more substantive, I recommend Alessandro Strumia’s theory summary for Moriond 2015. It has a lot of interesting commentary about a range of phenomenological topics. On the multiverse and anthropics he takes a quite different point of view than Weinberg:
Nobody talked about anthropics at Moriond 2015. This has an anthropic interpretation: Moriond is not in California. Clearly, social factors are playing a role, as always when experiments cannot set the issue. On one side, `having discovered the multiverse’ is physically indistinguishable from `having pursued a failed unification program’, but sounds much better. On the other side, future physicists could consider us as crazy for not having immediately accepted anthropic arguments.
He discusses “naturalness” extensively, including explaining why anthropics is no solution, since it doesn’t explain an unnaturally small Higgs mass.
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