From Sabine Hossenfelder at her blog BackRe(Action), responding to a physics major who has heard from cosmologist Brian Greene that string theory can be a grand theory of everything:

Greene states very carefully that superstring theory “has the capacity to embrace” gravity as well as the other known fundamental forces (electromagnetic, weak, and strong). What he means is that most string theorists currently believe there exists a specific model for superstring theory which gives rise to these four forces. The vague phrase “has the capacity” is an expression of this shared belief; it glosses over the fact that no one has been able to find a model that actually does what Greene says.

Superstring theory also comes with many side-effects which all too often go unnoticed. To begin with, the “super” isn’t there to emphasize the theory is awesome, but to indicate it’s supersymmetric. Supersymmetry, to remind you, is a symmetry that postulates all particles of the standard model have a partner particle. These partner particles were not found. This doesn’t rule out supersymmetry because the particles might only be produced at energies higher than what we have tested. But it does mean we have no evidence that supersymmetry is realized in nature. More.

String theory is what happens to science when evidence isn’t Cool, like it used to be. Good career choice? Depends on what becomes of science.

Hossenfelder is the author of the forthcoming book Lost in Math: How Beauty Leads Physics Astray (June, 2018)

*See also:* Sabine Hossenfelder: Hawking’s final theory is just one of “some thousand” speculations

and

Post-modern physics: String theory gets over the need for evidence

The lure of string theory was its power to unify gravity with quantum mechanics. It did this basically by allowing fermions (spin 1/2 particles) to be translated into bosons (spin 1) particles, and vice versa. However, this translation came at the cost of having to introduce lots of virtual particles, which were then not found at the LHC.

Yet, I think some of the basics of string theory will eventually win out once a true manner of unifying gravity and quantum mechanics/quantum field theory (GR + QM/QFT) is discovered. Going back to theoretical ways in which this might happen would certainly seem the way to move forward.

Personally, I’m rather convinced that the entire notion of the ‘ether’ must be looked at from a completely new perspective. The idea that the ‘ether’ is superflous has reigned supreme since Einstein’s time and serously hindered the project of unification, IMHO.

Interestingly, though, much of quantum field theory, and string theory as well, involves the use of Green’s functions; and, yet, when you look at Green’s original paper back in the early 1800’s, his basic approach was to build a mathematical model which to our eyes would look like the ‘luminous aether.’

Likewise, SR, special relativity—proposed by Einstein as explaining electrodynamics without the use of ether, comes to us in the mathematical form provided by the mathematician Hermann Minkowski. In his development of what we know as SR, using a conformal theory he introduces, does not involve—from what I can see—a discarding of the ‘ether.’

Einstein was rather forced into once again accepting the idea of an ‘ether’ in the early 1920’a when it was pointed out to him that a completely ’empty’ space would have nothing at its disposal by which it could ‘curve’ itself.

And what is the vector and scalar potentials of EM except a mathematical form ‘standing in’ for the ‘ether’?

In my musings, relying on an emergent, entropic ether, I see solutions to almost all the pressing problems of modern-day physics—conceptually. This even includes why we live in a ‘left-handed’ universe. I hope physicists will take another serious look at the importance of the ‘ether.’ Again, I think its physics’ way forward.

PaV @ 1: “relying on an emergent, entropic ether, I see solutions to almost all the pressing problems of modern-day physics—conceptually. This even includes why we live in a ‘left-handed’ universe.”

How does an emergent, entropic ether solve the “left-handed” universe problem?