> I have degrees in mathematics and some understanding of physics, but I've watched a few lectures of Ed Witten before, and he might as well be just making it all up. I know, it can all be backed out such that it all follows from known mathematics and physics,
As someone with a degree in mathematical physics, my experience with many string theorists in general (however ā and I want to stress this ā not with Ed Witten in particular) is that their statements and claims don't all strictly follow from known math and physics. Quite often there are huge logical gaps, implicit assumptions or implicit
redefinitions of commonly used terminology. For instance, when a string theorist says that "We know that quantum theory dictates XY" or that "Any theory of quantum gravity needs to obey XY", then it might very well be that their implicit assumption is that string theory is the right fundamental theory of nature (i.e. that it makes correct predictions) and that they rather mean something like "We know that quantum theory dictates XY if we model the universe as AdS_5 Ć Sāµ" or "Any stringy theory of quantum gravity needs to obey XY".
More generally, my experience has been that a significant number of people doing string theory lack a sufficiently deep mathematical foundation. Theoretical physicists in general are already quite cavalier when it comes to mathematical rigor and in string theory it's even worse because most quantum field theories are not even mathematically well-defined. So everyone grows up learning to ignore mathematical issues and a large number of people then end up thinking they can just "wing" the math and pick up the required mathematical bits and pieces on the go. So they end up using the same terminology as mathematicians while not really understanding it and/or not really being precise with their words nor in their arguments. At least for me this makes it extremely difficult to tell whether someone is (unknowingly) bullshitting or their claims need to be taken seriously.
As someone with a degree in mathematical physics, my experience with many string theorists in general (however ā and I want to stress this ā not with Ed Witten in particular) is that their statements and claims don't all strictly follow from known math and physics. Quite often there are huge logical gaps, implicit assumptions or implicit redefinitions of commonly used terminology. For instance, when a string theorist says that "We know that quantum theory dictates XY" or that "Any theory of quantum gravity needs to obey XY", then it might very well be that their implicit assumption is that string theory is the right fundamental theory of nature (i.e. that it makes correct predictions) and that they rather mean something like "We know that quantum theory dictates XY if we model the universe as AdS_5 Ć Sāµ" or "Any stringy theory of quantum gravity needs to obey XY".
More generally, my experience has been that a significant number of people doing string theory lack a sufficiently deep mathematical foundation. Theoretical physicists in general are already quite cavalier when it comes to mathematical rigor and in string theory it's even worse because most quantum field theories are not even mathematically well-defined. So everyone grows up learning to ignore mathematical issues and a large number of people then end up thinking they can just "wing" the math and pick up the required mathematical bits and pieces on the go. So they end up using the same terminology as mathematicians while not really understanding it and/or not really being precise with their words nor in their arguments. At least for me this makes it extremely difficult to tell whether someone is (unknowingly) bullshitting or their claims need to be taken seriously.