I've worked on string theory briefly (published one paper that got a respectable number of citations). It is not considered a dead end by people working on it obviously.
Many of the best people in theoretical physics with Edward Witten being the most prominent example have been working on it for ~40+ years now. None of the public detractors have nearly the same stature that Witten has. Of course this is basically an argument by authority and there is a chance that once titans like Witten leave the playing field the following generations will lose more and more influence.
I think there is a fair bit of criticism of String Theory among very good people that is not voiced publicly because there would be no point to it, they have nothing to gain. In many ways it is the "Only Game in Town" (literal quote from my supervisor), just doing high-energy particle phenomenology is not that much more exciting.
String theory has already led to a number of very high profile successes in mathematics (Perelman's Proof of the Poincare Conjecture, Monstrous Moonshine etc.), so it is not like the techniques that have been developed are totally useless.
I wonder if it’s not that string theory gets its more reasonable results simply by reducing the singularity of a particle in one dimension.
If we look at the idea of a ”point particle”, it’s clearly something that is never observed elsewhere.
This is what leads to the whole idea of renormalization: that any force that goes to infinity as r->0.
For string theory, adding a second dimension to the particle adds density, which avoids the same amount of infinites. Similarly, loop gravity’s ”chunky” timespace also prevents infinites by essentially adding a minimum distance.
I feel both approaches are wrong. The conceptual model of the particle as a dot still lives on in some regard.
With M-theory, string theory moved more to something like the concept of a particle with density in multiple dimensions.
However, the extreme complexity and the many assumptions needed in string theory made it very unappealing to me.
I would like to see some theory that used the wave nature of particles resolve the infinities - including quantum gravity, then describe some mechanism how these waves could gain dual particle-like behaviour when leaving the Planck length world.
The starting point of Perelman's proof is the observation that (a modified version of) the Ricci flow is a gradient flow. The connection to 2d non-linear sigma models is briefly discussed in section 2 of the introduction in https://arxiv.org/pdf/math/0211159.pdf and section 1.4*. The overall intuition is that string theory captures the geometry of the back ground Riemannian manifold.
Yeah, loop quantum gravity is pretty badly broken as a theory of gravity. It doesn't have the right classical limit (i.e., general relativity). Doesn't even have thermodynamics compatible with the right classical limit.
I'd be extremely hard pressed to name a significant result loop quantum gravity has exported to the rest of physics and mathematics.
There's also the asymptotic safety program, which isn't completely implausible, but is kind of stuck in the 'steal underpants' phase.
Quantum Loop Gravity is much smaller ~200 people most of them not very famous and it has not produced the same depth of research directions in particular not recently.
Many of the best people in theoretical physics with Edward Witten being the most prominent example have been working on it for ~40+ years now. None of the public detractors have nearly the same stature that Witten has. Of course this is basically an argument by authority and there is a chance that once titans like Witten leave the playing field the following generations will lose more and more influence.
I think there is a fair bit of criticism of String Theory among very good people that is not voiced publicly because there would be no point to it, they have nothing to gain. In many ways it is the "Only Game in Town" (literal quote from my supervisor), just doing high-energy particle phenomenology is not that much more exciting.
String theory has already led to a number of very high profile successes in mathematics (Perelman's Proof of the Poincare Conjecture, Monstrous Moonshine etc.), so it is not like the techniques that have been developed are totally useless.