Wednesday, April 20, 2016

Quanta Magazine on triangles in string cosmology

Natalie Wolchover wrote an article
Physicists Hunt for the Big Bang’s Triangles
that mostly focuses on the ongoing theoretical work attempting to produce predictions of non-Gaussianities in the Cosmic Microwave Radiation – signs of the "very early stages" of the life of the Universe. It's interesting to read such texts because of the exciting science but also because I've known basically all the thinkers who are mentioned there.

Wolchover mentions the Juan Maldacena's and Nima Arkani-Hamed's 2015 paper on cosmology (non-Gaussianities determined using the concept of symmetry out of the assumed string-like higher-spin fields of masses comparable to the Hubble scale), Juan's previous work on non-Gaussianity, Nima's ongoing research attempting to link this cosmological topic with the Amplituhedron, some Matt Kleban's fresh work involving triangles and cylinders (I didn't understand enough to see what he may have found), or e.g. the community's reaction to the discovery claim by BICEP2 in Spring 2014.

She manages to sketch many things that are already in the literature as well as some opinions and guesses that are easier to find by personal communication.

Matias Zaldarriaga has a more practical approach to the "limit of knowledge" than others – I actually tend to sympathize with him. He says that the limits of knowledge may exist but they're still very far and we face many more tangible "technical" obstacles before we could be affected by the "limits of knowledge" so it's better to focus on the practical obstacles that are numerous. Nima seems to believe in some Merciful God that protects the mortals from the limits of knowledge and he was even willing to talk about some "completion of quantum mechanics" that could basically suppress the ignorance resulting from the cosmic variance, if I understand it well.

Well, I don't have any rigorous proof but I would bet 20:1 against such things. Cosmic variance is unavoidable and this claim is basically equivalent to "statistics happens". I can't see how it could possibly be avoided. And the proposed "extensions of quantum mechanics" would probably have to be sketched with some details for me to think that they differ from the usual crackpots' anti-quantum nonsense.

The article mentions that Linde's and Kallosh's minimalistic models of inflation – with one scalar field and not much else – are found implausible by others who arguably take the lessons of string theory more seriously than Linde and Kallosh. The inflationary models have to contain some extra structure. And at some level, the non-Gaussianities are basically unavoidable. Whether they're strong enough to be observed soon is a different question.

I agree that the non-Gaussianities are unavoidable. The structure of the Cosmic Microwave Background may be visualized as a quantum field with the Fourier modes \(\zeta(\vec k)\). If you assume that they're modes of a free field, they're basically equivalent to \(x_i\) variables in a higher-dimensional harmonic oscillator. In a harmonic oscillator, you have \(\langle x_a x_b x_c\rangle = 0\) in the ground state and similarly\[

\langle \zeta(\vec k_1) \zeta(\vec k_2) \zeta (\vec k_3) \rangle = 0

\] for all triplets of 3-dimensional vectors \(\vec k_j\). However, if you add some higher-order (cubic...) terms to the Hamiltonian, the correlation function of three zetas above will be nonzero. The momentum conservation (translational symmetry) will still require the correlator to be nonzero only if\[

\vec k_1 + \vec k_2 + \vec k_3 = 0

\] which means that the three vectors \(\vec k_j\) may be drawn as the oriented sides of a triangle. That's why triangles are discussed in this context. When the momentum conservation equation holds, the 3-point function is ultimately predicted by string theory (or any detailed enough theory of the cosmic inflation) to be nonzero, although plausibly very small. No non-Gaussianity has been observed yet but it may change. The situation is somewhat analogous to (but not exactly the same as) the tensor perturbations – those announced by BICEP2 in 2014 in a claim with the certainty that later turned out to be exaggerated, to say the least.

There are some references to experiments and extra thoughts and models that go beyond the paper by Maldacena and Arkani-Hamed, among other things.

However, what I find absolutely frustrating is the reaction by the readers. suggests that the Quanta Magazine – funded by Jim Simons as an editorially independent venue to explain top science to the laymen – has about 4 times as many readers as this blog. So I find it rather likely that the number of readers of this article – I mean people who have opened the separate page – has surpassed 10,000.

However, after one day, there is only one comment, a comment by an extraterrestrial alien with green hair named "Ver Greeneyes" who managed to ignore 99.9% of the content of the article. Instead, the alien found just Eva Silverstein's comment that it's "surreal to suggest that string theory is divorced from the data" because the traditional science is obviously what these folks are doing right now and what is described in this article.

The alien pompously declared zerself to be a "cop" who defends the public against the "ridiculous notion" that one should take string theory very seriously without direct tests. Sorry, dear green extraterrestrial troll, but the best physicists in the world take string theory extremely seriously while the dumbest individuals like you who have no clue usually don't. If you have been told that you have the capacity or credentials to moralize about string theory or be a "cop" above people like Linde, Maldacena, Arkani-Hamed, and others, and that these people need "cops" like you, you have been lied to. You're just a worthless pile of green šit and if you dared to appear on this blog, you would survive outside the blacklist at most for two seconds.

Around 1999 when e.g. Brian Greene released The Elegant Universe, I was inclined to believe that the number of Americans (to make it specific) who are really interested in the fundamental laws of the Universe is several million – because of the number of copies of the book Brian could sell and because of other estimates. These days, it seems that the number of people outside the very narrow circle of a dozen of string theorists or string cosmologists who could be interested in these matters is basically zero.

It has basically become a rule that whenever a high-brow article like that is published, the first comments as well as most of the comments are written by the smelly moronic šitheads similar to "Van Greeneyes" who belong to a cesspool or Peter Woit's den or Lee Smolin's aß rather than to a serious popular server about science.

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