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Weird matter made of partial particles + Search for grand unification of aromaticity

#1
C C Offline
The weirdest matter made of partial particles defies description
http://abstractions.nautil.us/article/72...escription

EXCERPTS: . . . So when a new theoretical state of matter was discovered whose microscopic features stubbornly persist at all scales, many physicists refused to believe in its existence.

“When I first heard about fractons, I said there’s no way this could be true, because it completely defies my prejudice of how systems behave,” said Nathan Seiberg, a theoretical physicist at the Institute for Advanced Study in Princeton, New Jersey. “But I was wrong. I realized I had been living in denial.”

The theoretical possibility of fractons surprised physicists in 2011. Recently, these strange states of matter have been leading physicists toward new theoretical frameworks that could help them tackle some of the grittiest problems in fundamental physics.

Fractons are quasiparticles — particle-like entities that emerge out of complicated interactions between many elementary particles inside a material. But fractons are bizarre even compared to other exotic quasiparticles, because they are totally immobile or able to move only in a limited way. There’s nothing in their environment that stops fractons from moving; rather it’s an inherent property of theirs. It means fractons’ microscopic structure influences their behavior over long distances.

“That’s totally shocking. For me it is the weirdest phase of matter,” said Xie Chen, a condensed matter theorist at the California Institute of Technology.

[...] Say you have four particles arranged in a square, but when you zoom in to each corner you find another square of four particles that are close together. Zoom in on a corner again and you find another square, and so on. For such a structure to materialize in the vacuum requires so much energy that it’s impossible to move this type of fracton. This allows very stable qubits—the bits of quantum computing—to be stored in the system, as the environment can’t disrupt the qubits’ delicate state.

The immovability of fractons makes it very challenging to describe them as a smooth continuum from far away. Because particles can usually move freely [...their...] initial locations cease to matter. But fractons are stuck at specific points or can only move in combination along certain lines or planes. Describing this motion requires keeping track of fractons’ distinct locations, and so the phases cannot shake off their microscopic character or submit to the usual continuum description.

Their resolute microscopic behavior makes it “a challenge to imagine examples of fractons and to think deeply about what is possible,” said Vijay, a theorist at the University of California, Santa Barbara. “Without a continuous description, how do we define these states of matter?”

“We’re missing a big chunk of things,” said Chen. “We have no idea how to describe them and what they mean.”

Fractons have yet to be made in the lab, but that will probably change... (MORE - missing details)


The search for the grand unification of aromaticity
https://www.chemistryworld.com/features/...15.article

EXCERPTS: ‘Controversial’, ‘suspicious’, ‘questionable’ and even ‘an exercise in chemical futility’ – these are only some of the ways scientists have described the concept of aromaticity. And that’s in spite of it being a concept that almost all chemists are familiar with from school or university.

[...] PubChem, the largest public database of chemical compounds, contains almost 110 million structures. There’s an estimate that two-thirds of them are fully or partially aromatic. Understanding how aromaticity influences a compound’s properties allows researchers to design everything from drugs to molecular light emitters...

[...] The problem with aromaticity is that, despite 200 years of research, there’s no clear definition, rules or experiments that can identify it among all compounds. Benzene might look very different from a heptaborate polyhedron B7H72−, the aluminium square Al42– or a gigantic molecular wheel made of more than 1000 carbon atoms – yet they are all considered aromatic by one standard or another.

‘It’s a paradox,’ says Renana Poranne who researches computational physical organic chemistry at ETH Zürich in Switzerland. ‘On the one hand, [aromaticity] is very ill defined, and on the other hand apparently quite useful for identification or having some expectations about the properties of a chemical compound.’ But this is part of what fascinates researchers. ‘People are interested to understand aromaticity because we still don’t,’ she says.

Despite chemists having access to an ever-increasing number of shorthand rules and a vast array of computational methods, they keep finding aromaticity in unexpected places. But with more than 20 different types of aromaticity described so far, how close are chemists to finding a definition that unites all of them?

[...] The problem with aromaticity, says Alonso, is that it’s ‘a concept that we have invented for trying to describe the properties of a compound’. Unlike a melting point or molecular mass, aromaticity is not an observable property that can be measured in the lab – a fact that seems unpalatable to many scientists . ‘We have more than 100 descriptors to quantify aromaticity, but there is not a single one that can be applied universally,’ explains Alonso.

[...] With aromaticity now firmly past being purely an academic argument, is overhauling the definition even needed? Solà thinks so, particularly when it comes to borderline systems like metal clusters. In 2018, he closely examined 19 aromaticity rules, taking the first steps to combine and connect them with the eventual goal to find a single aromaticity theory that unifies them all.

Sun thinks that there eventually will be an update to include these systems, but that, for now, chemist will have to describe new concepts using old words – despite the issues this sometimes causes. ‘I don’t think we will ever get to a time where everybody agrees there’s one correct method that we should all use exclusively,’ says Poranne. ‘I don’t think that exists in science in general.’

‘I think as the field moves forward, the types of questions that are relevant also are evolving,’ says Wu. ‘We’ve evolved past the stage of asking what aromaticity means. Now is the time to ask the question “What do we use it for?”’ (MORE - missing details)
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History of the term "aromatic": The first known use of the word "aromatic" as a chemical term—namely, to apply to compounds that contain the phenyl group—occurs in an article by August Wilhelm Hofmann in 1855. If this is indeed the earliest introduction of the term, it is curious that Hofmann says nothing about why he introduced an adjective indicating olfactory character to apply to a group of chemical substances, of which only some have notable aromas.

Also, many of the most odoriferous organic substances known are terpenes, which are not aromatic in the chemical sense. But terpenes and benzenoid substances do have a chemical characteristic in common, namely higher unsaturation than many aliphatic compounds, and Hofmann may not have been making a distinction between the two categories. Many of the earliest-known examples of aromatic compounds, such as benzene and toluene, have distinctive pleasant smells.

This property led to the term "aromatic" for this class of compounds, and hence the term "aromaticity" for the eventually discovered electronic property.
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#2
Zinjanthropos Offline
Sounds like looking at the reflection between two mirrors, the same image gets smaller and smaller and goes to infinity I’ve heard, not that I’m going to notice.
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