## Wednesday, January 13, 2016 ... /////

### Marriage of strings and loops again?

No, thank you.

People often behave in funny ways – and the human chemistry is hard to predict. That's why the marriages may sometimes look surprising to the external world, too. Over the weekend, Rupert Murdoch engaged retired supermodel Jerry Hall,

congratulations, and the wedding is imminent. During her career, she has protested things like the expansion of an airport – it's probably what makes Rupert excited. Well, it's not easy to marry different scientific theories if they're genuinely different. They may only marry if they're shown compatible and, in the case of sufficiently well-defined theories, equivalent – and that occurs rarely.

The Quanta Magazine has absolutely absurdly published a nonsensical essay by Sabine Hossenfelder titled

String Theory Meets Loop Quantum Gravity.
Why do they do such things? The magazine was relatively OK so far. Won't they also publish her recent "musings" discussed here claiming that neither the free will nor any subjective experiences can exist (tell it to those of us who are subjectively aware of ourselves and the world around us) and the experimenters are prevented by Nature's Big Brother from pressing buttons on their gadgets that could reveal the truth about Nature?

I was happy to see that almost all of her commenters understand that her claims about the perception and decisions make no sense. Can someone be so dimwitted not to see the incoherence and incompatibility with the most well-known facts about the world?

In her "marriage" piece, she complains that the researchers of string theory and loop quantum gravity (LQG) have separate conferences. The theories may be two sides of the same coin, she suggests as if it were common sense. (Her former overlord Lee Smolin was the only other person in the world who sometimes liked to say this stupidity.) Thankfully, she also mentions that people generally disagree with the idea that the theories may be equivalent.

Moshe Rozali explains something you have read here many times. If your starting point is a theory that violates special relativity by O(100)% at the fundamental level, and LQG is an example, it's pretty much guaranteed that every "intermediate and final level" of physics derived from the theory will violate the symmetry by O(100)%, too. That's why he doesn't plan to work on LQG anytime soon.

On the crackpot side, Carlo Rovelli defends LQG by saying that the LHC hasn't discovered supersymmetry yet. That's great but supersymmetry will eventually be discovered; and the absence of supersymmetry is extremely far from being the only problem of LQG. It's really the smallest one.

OK, you are surely asking what's Hossenfelder's evidence that strings and LQG may get married. It's supposed to be a 7-page preprint by Pullin and Gambini
Emergence of string-like physics from Lorentz invariance in loop quantum gravity
These guys understood that "if you want to make LQG compatible with relativity, you have to add some nonlocal interactions that exist in [effective descriptions of] string theory into LQG". I will mention the technical issues momentarily.

But when it comes to LQG or its proposed marriage to string theory, you must understand that the "cleverness" of certain nonlocal interactions that these guys have understood has nothing whatsoever to do with LQG. So what they're proposing is just like the following recipe to produce CocaCola from urine:
Take 2 liters of our wonderful urine.

And add 50 liters of PEPSI, including some ingredients that are only found in Coke. Mix it. And the result will taste almost just like CocaCola produced out of urine!
It's wonderful except that the original urine hasn't played any useful role in the production. To say that the good enough taste (and similarly positive features of certain nonlocal interactions in the effective theory) have anything to do with urine (or LQG) is pure demagogy. It's stupidity. Everything that works in the mixture is taken from string theory (or PEPSI or Coke) and everything that doesn't is taken from urine (or LQG).

Pullin and Gambini may permute their restroom and their kitchen in many chaotic ways so that some readers will lose their ability to distinguish these two rooms and the liquids in them. But smarter readers won't lose this ability.

And you may easily check that after 1.5 years, the paper has 3 citations. An even crazier aspect of this fact is that one of the followups was written by Hossenfelder herself. That equally illogical followup is a (valid but absolutely not new) no-go theorem claiming that you can't get the Lorentz invariance from certain discrete starting points. So it's a preprint that contradicts the basic goal of the Pullin-Gambini article as well as her Quanta Magazine review. She contradicts herself.

The content of her skull may be classified as an absolutely, hopelessly unfixable, mess.

Just to mention something about the technical content: Because strings are extended objects, if you rewrite the interactions of the massless fields as if they were interactions of fields creating point-like particles, you will unavoidably obtain some nonlocal interactions as well. The point-like particle is "actually" an extended object so it influences physics (and particles) at other points than just the center-of-mass where you imagined the particle to be located (although it's an extended string). And that's why nonlocal interactions occur if you write string theory in this way.

However, the actual underlying string dynamics is Lorentz-invariant and is, in some sense, perfectly local. The string interactions are local on the world sheet of the strings, and because the world sheet is smoothly embedded in the spacetime, the interactions are local in the spacetime, too. At least in some sense. It doesn't contradict the fact that the theory may look nonlocal in the spacetime if you rewrite this dynamics (or its effective approximation) in a certain way.

These nonlocalities are of a special form. They still know about the perfectly consistent, Lorentz-invariant underlying theory. The full theory could be reconstructed from the full list of the nonlocal interactions between all the fields. But different, generic types of nonlocal interactions remain deadly – generic nonlocality surely contradicts the Lorentz symmetry. Comments like that, with some equations, appear at the beginning of some introductory texts to string theory. Pullin and Gambini have finally understood these sentences. (They have thousands of other basic things they need to understand in front of them.) They got a bit excited and rhetorically complained that their urinated theory, LQG, doesn't have any of these things. It should have. Let's import them, they recommended.

However, LQG is intrinsically incompatible with the Lorentz symmetry. It's also incompatible with the nonlocality of this kind or any similar kind. String theory is perfectly Lorentz-invariant despite the fact that some of its formulations look nonlocal. From that perspective, string theory is a victory despite a bad starting point. On the other hand, due to the discreteness etc., LQG is Lorentz-violating despite the fact that its interactions are by construction "local" (in the discretized spacetime). It's a failure despite a great starting position.

This whole idea by Hossenfelder is just a demagogic point meant to pretend that the LQG folks are basically doing something similar like string theorists. Except that they don't. LQG folks have never written a good paper and they don't have to write any good papers to get LQG jobs – because no one else in LQG has ever done anything of the sort, either. They're hired simply in order to be in "opposition" and to fill the affirmative action quotas (including the quota saying that ignorant, stupid, and lazy people have to be as widespread in the scientific community as the educated, brilliant, and hard-working ones). It's only string theorists who are actually contributing to physics. So how can someone claim that those are "peers" or theories to get married?

String theory conferences don't need to be flooded by hectoliters of urine who have understood at most the first pages of an introductory string theory textbook – and usually much less than that – and who simply have nothing interesting or coherent to say. I am just absolutely disgusted that these fraudulent tricks are tolerated if not encouraged in the Academia and that the Quanta Magazine that has been mostly OK so far is willing to transform itself into another cesspool that publishes indefensible nonsense like the nonsense from Ms Hossenfelder.