Tag Archives: physics

Loop quantum cosmology connects the tiniest with the biggest in a cosmic tango

Caption: Tiny quantum fluctuations in the early universe explain two major mysteries about the large-scale structure of the universe, in a cosmic tango of the very small and the very large. A new study by researchers at Penn State used the theory of quantum loop gravity to account for these mysteries, which Einstein’s theory of general relativity considers anomalous.. Credit: Dani Zemba, Penn State

A July 29, 2020 news item on ScienceDaily announces a study showing that quantum loop cosmology can account for some large-scale mysteries,

While [1] Einstein’s theory of general relativity can explain a large array of fascinating astrophysical and cosmological phenomena, some aspects of the properties of the universe at the largest-scales remain a mystery. A new study using loop quantum cosmology — a theory that uses quantum mechanics to extend gravitational physics beyond Einstein’s theory of general relativity — accounts for two major mysteries. While the differences in the theories occur at the tiniest of scales — much smaller than even a proton — they have consequences at the largest of accessible scales in the universe. The study, which appears online July 29 [2020] in the journal Physical Review Letters, also provides new predictions about the universe that future satellite missions could test.

A July 29, 2020 Pennsylvania State University (Penn State) news release (also on EurekAlert) by Gail McCormick, which originated the news item, describes how this work helped us avoid a crisis in cosmology,

While [2] a zoomed-out picture of the universe looks fairly uniform, it does have a large-scale structure, for example because galaxies and dark matter are not uniformly distributed throughout the universe. The origin of this structure has been traced back to the tiny inhomogeneities observed in the Cosmic Microwave Background (CMB)–radiation that was emitted when the universe was 380 thousand years young that we can still see today. But the CMB itself has three puzzling features that are considered anomalies because they are difficult to explain using known physics.

“While [3] seeing one of these anomalies may not be that statistically remarkable, seeing two or more together suggests we live in an exceptional universe,” said Donghui Jeong, associate professor of astronomy and astrophysics at Penn State and an author of the paper. “A recent study in the journal Nature Astronomy proposed an explanation for one of these anomalies that raised so many additional concerns, they flagged a ‘possible crisis in cosmology‘ [emphasis mine].’ Using quantum loop cosmology, however, we have resolved two of these anomalies naturally, avoiding that potential crisis.”

Research over the last three decades has greatly improved our understanding of the early universe, including how the inhomogeneities in the CMB were produced in the first place. These inhomogeneities are a result of inevitable quantum fluctuations in the early universe. During a highly accelerated phase of expansion at very early times–known as inflation–these primordial, miniscule fluctuations were stretched under gravity’s influence and seeded the observed inhomogeneities in the CMB.

“To understand how primordial seeds arose, we need a closer look at the early universe, where Einstein’s theory of general relativity breaks down,” said Abhay Ashtekar, Evan Pugh Professor of Physics, holder of the Eberly Family Chair in Physics, and director of the Penn State Institute for Gravitation and the Cosmos. “The standard inflationary paradigm based on general relativity treats space time as a smooth continuum. Consider a shirt that appears like a two-dimensional surface, but on closer inspection you can see that it is woven by densely packed one-dimensional threads. In this way, the fabric of space time is really woven by quantum threads. In accounting for these threads, loop quantum cosmology allows us to go beyond the continuum described by general relativity where Einstein’s physics breaks down–for example beyond the Big Bang.”

The researchers’ previous investigation into the early universe replaced the idea of a Big Bang singularity, where the universe emerged from nothing, with the Big Bounce, where the current expanding universe emerged from a super-compressed mass that was created when the universe contracted in its preceding phase. They found that all of the large-scale structures of the universe accounted for by general relativity are equally explained by inflation after this Big Bounce using equations of loop quantum cosmology.

In the new study, the researchers determined that inflation under loop quantum cosmology also resolves two of the major anomalies that appear under general relativity.

“The primordial fluctuations we are talking about occur at the incredibly small Planck scale,” said Brajesh Gupt, a postdoctoral researcher at Penn State at the time of the research and currently at the Texas Advanced Computing Center of the University of Texas at Austin. “A Planck length is about 20 orders of magnitude smaller than the radius of a proton. But corrections to inflation at this unimaginably small scale simultaneously explain two of the anomalies at the largest scales in the universe, in a cosmic tango of the very small and the very large.”

The researchers also produced new predictions about a fundamental cosmological parameter and primordial gravitational waves that could be tested during future satellite missions, including LiteBird and Cosmic Origins Explorer, which will continue improve our understanding of the early universe.

That’s a lot of ‘while’. I’ve done this sort of thing, too, and whenever I come across it later; it’s painful.

Here’s a link to and a citation for the paper,

Alleviating the Tension in the Cosmic Microwave Background Using Planck-Scale Physics by Abhay Ashtekar, Brajesh Gupt, Donghui Jeong, and V. Sreenath. Phys. Rev. Lett. 125, 051302 DOI: https://doi.org/10.1103/PhysRevLett.125.051302 Published 29 July 2020 © 2020 American Physical Society

This paper is behind a paywall.

“The earth is mostly made of cubes,” said Plato in 5th Century BCE. Turns out, he was right!

Theories from mathematics, physics, and geology have been used to demonstrate that the earth’s basic shape is, roughly speaking, a cube. From a July 20, 2020 news item on ScienceDaily,

Plato, the Greek philosopher who lived in the 5th century B.C.E. [before the common era], believed that the universe was made of five types of matter: earth, air, fire, water, and cosmos. Each was described with a particular geometry, a platonic shape. For earth, that shape was the cube.

Science has steadily moved beyond Plato’s conjectures, looking instead to the atom as the building block of the universe. Yet Plato seems to have been onto something, researchers have found.

In a new paper in the Proceedings of the National Academy of Sciences [PNAS], a team from the University of Pennsylvania, Budapest University of Technology and Economics, and University of Debrecen [Hungary] uses math, geology, and physics to demonstrate that the average shape of rocks on Earth is a cube.

A July 17, 2020 University of Pennsylvania news release (also on EurekAlert but dated July 20, 2020), which originated the news item, goes on to describe the work as “mind-blowing,”

“Plato is widely recognized as the first person to develop the concept of an atom [Maybe not, scroll down to find the subhead “Leucippus and Democritus”], the idea that matter is composed of some indivisible component at the smallest scale,” says Douglas Jerolmack, a geophysicist in Penn’s School of Arts & Sciences’ Department of Earth and Environmental Science and the School of Engineering and Applied Science’s Department of Mechanical Engineering and Applied Mechanics. “But that understanding was only conceptual; nothing about our modern understanding of atoms derives from what Plato told us.

“The interesting thing here is that what we find with rock, or earth, is that there is more than a conceptual lineage back to Plato. It turns out that Plato’s conception about the element earth being made up of cubes is, literally, the statistical average model for real earth. And that is just mind-blowing.”

The group’s finding began with geometric models developed by mathematician Gábor Domokos of the Budapest University of Technology and Economics, whose work predicted that natural rocks would fragment into cubic shapes.

“This paper is the result of three years of serious thinking and work, but it comes back to one core idea,” says Domokos. “If you take a three-dimensional polyhedral shape, slice it randomly into two fragments and then slice these fragments again and again, you get a vast number of different polyhedral shapes. But in an average sense, the resulting shape of the fragments is a cube.”

Domokos pulled two Hungarian theoretical physicists into the loop: Ferenc Kun, an expert on fragmentation, and János Török, an expert on statistical and computational models. After discussing the potential of the discovery, Jerolmack says, the Hungarian researchers took their finding to Jerolmack to work together on the geophysical questions; in other words, “How does nature let this happen?”

“When we took this to Doug, he said, ‘This is either a mistake, or this is big,'” Domokos recalls. “We worked backward to understand the physics that results in these shapes.”

Fundamentally, the question they answered is what shapes are created when rocks break into pieces. Remarkably, they found that the core mathematical conjecture unites geological processes not only on Earth but around the solar system as well.

“Fragmentation is this ubiquitous process that is grinding down planetary materials,” Jerolmack says. “The solar system is littered with ice and rocks that are ceaselessly smashing apart. This work gives us a signature of that process that we’ve never seen before.”

Part of this understanding is that the components that break out of a formerly solid object must fit together without any gaps, like a dropped dish on the verge of breaking. As it turns out, the only one of the so-called platonic forms–polyhedra with sides of equal length–that fit together without gaps are cubes.

“One thing we’ve speculated in our group is that, quite possibly Plato looked at a rock outcrop and after processing or analyzing the image subconsciously in his mind, he conjectured that the average shape is something like a cube,” Jerolmack says.

“Plato was very sensitive to geometry,” Domokos adds. According to lore, the phrase “Let no one ignorant of geometry enter” was engraved at the door to Plato’s Academy. “His intuitions, backed by his broad thinking about science, may have led him to this idea about cubes,” says Domokos.

To test whether their mathematical models held true in nature, the team measured a wide variety of rocks, hundreds that they collected and thousands more from previously collected datasets. No matter whether the rocks had naturally weathered from a large outcropping or been dynamited out by humans, the team found a good fit to the cubic average.

However, special rock formations exist that appear to break the cubic “rule.” The Giant’s Causeway in Northern Ireland, with its soaring vertical columns, is one example, formed by the unusual process of cooling basalt. These formations, though rare, are still encompassed by the team’s mathematical conception of fragmentation; they are just explained by out-of-the-ordinary processes at work.

“The world is a messy place,” says Jerolmack. “Nine times out of 10, if a rock gets pulled apart or squeezed or sheared–and usually these forces are happening together–you end up with fragments which are, on average, cubic shapes. It’s only if you have a very special stress condition that you get something else. The earth just doesn’t do this often.”

The researchers also explored fragmentation in two dimensions, or on thin surfaces that function as two-dimensional shapes, with a depth that is significantly smaller than the width and length. There, the fracture patterns are different, though the central concept of splitting polygons and arriving at predictable average shapes still holds.

“It turns out in two dimensions you’re about equally likely to get either a rectangle or a hexagon in nature,” Jerolmack says. “They’re not true hexagons, but they’re the statistical equivalent in a geometric sense. You can think of it like paint cracking; a force is acting to pull the paint apart equally from different sides, creating a hexagonal shape when it cracks.”

In nature, examples of these two-dimensional fracture patterns can be found in ice sheets, drying mud, or even the earth’s crust, the depth of which is far outstripped by its lateral extent, allowing it to function as a de facto two-dimensional material. It was previously known that the earth’s crust fractured in this way, but the group’s observations support the idea that the fragmentation pattern results from plate tectonics.

Identifying these patterns in rock may help in predicting phenomenon such as rock fall hazards or the likelihood and location of fluid flows, such as oil or water, in rocks.

For the researchers, finding what appears to be a fundamental rule of nature emerging from millennia-old insights has been an intense but satisfying experience.

“There are a lot of sand grains, pebbles, and asteroids out there, and all of them evolve by chipping in a universal manner,” says Domokos, who is also co-inventor of the Gömböc, the first known convex shape with the minimal number–just two–of static balance points. Chipping by collisions gradually eliminates balance points, but shapes stop short of becoming a Gömböc; the latter appears as an unattainable end point of this natural process.

The current result shows that the starting point may be a similarly iconic geometric shape: the cube with its 26 balance points. “The fact that pure geometry provides these brackets for a ubiquitous natural process, gives me happiness,” he says.

“When you pick up a rock in nature, it’s not a perfect cube, but each one is a kind of statistical shadow of a cube,” adds Jerolmack. “It calls to mind Plato’s allegory of the cave. He posited an idealized form that was essential for understanding the universe, but all we see are distorted shadows of that perfect form.”

The human capacity for imagination, in this case linking ideas about geometry and mathematics from the 5th Century BCE to modern physics and geology and to the solar system, astounds and astonishes me. As for Jerolmack’s comment that Plato (428/427 or 424/423 – 348/347 BC) was the first to develop the concept of an atom, not everyone agrees.

Leucippus and Democritus

It may not ever be possible to determine who was the first to theorize/philosophize about atoms but there is relatively general agreement that Leucippus (5th cent.BCE) and his successor, Democritus (c. 460 – c. 370 BC) were among the first. Here’s more about Ancient Atomism and its origins from the Stanford Encyclopedia of Philosphy,

Leucippus (5th c. BCE) is the earliest figure whose commitment to atomism is well attested. He is usually credited with inventing atomism. According to a passing remark by the geographer Strabo, Posidonius (1st c. BCE Stoic philosopher) reported that ancient Greek atomism can be traced back to a figure known as Moschus or Mochus of Sidon, who lived at the time of the Trojan wars. This report was given credence in the seventeenth century: the Cambridge Platonist Henry More traced the origins of ancient atomism back, via Pythagoras and Moschus, to Moses. This theologically motivated view does not seem to claim much historical evidence, however.

Leucippus and Democritus are widely regarded as the first atomists [emphasis mine] in the Greek tradition. Little is known about Leucippus, while the ideas of his student Democritus—who is said to have taken over and systematized his teacher’s theory—are known from a large number of reports. These ancient atomists theorized that the two fundamental and oppositely characterized constituents of the natural world are indivisible bodies—atoms—and void. The latter is described simply as nothing, or the negation of body. Atoms are by their nature intrinsically unchangeable; they can only move about in the void and combine into different clusters. Since the atoms are separated by void, they cannot fuse, but must rather bounce off one another when they collide. Because all macroscopic objects are in fact combinations of atoms, everything in the macroscopic world is subject to change, as their constituent atoms shift or move away. Thus, while the atoms themselves persist through all time, everything in the world of our experience is transitory and subject to dissolution.

Although the Greek term atomos is most commonly associated with the philosophical system developed by Leucippus and Democritus, involving solid and impenetrable bodies, Plato’s [emphasis mine] Timaeus presents a different kind of physical theory based on indivisibles. The dialogue elaborates an account of the world wherein the four different basic kinds of matter—earth, air, fire, and water—are regular solids composed from plane figures: isoceles and scalene right-angled triangles. Because the same triangles can form into different regular solids, the theory thus explains how some of the elements can transform into one another, as was widely believed.

As you can see from the excerpt, they are guessing as to the source for atomism and thee are different kinds of atomism and Plato staked his own atomistic territory.

The paper

Here’s a link to and a citation for the paper followed by a statement of significance and the paper’s abstract,

Plato’s cube and the natural geometry of fragmentation by Gábor Domokos, Douglas J. Jerolmack, Ferenc Kun, and János Török. PNAS DOI: https://doi.org/10.1073/pnas.2001037117 First published July 17, 2020

This paper is behind a paywall.

Now for the Significance and the Abstract,

We live on and among the by-products of fragmentation, from nanoparticles to rock falls to glaciers to continents. Understanding and taming fragmentation is central to assessing natural hazards and extracting resources, and even for landing probes safely on other planetary bodies. In this study, we draw inspiration from an unlikely and ancient source: Plato, who proposed that the element Earth is made of cubes because they may be tightly packed together. We demonstrate that this idea is essentially correct: Appropriately averaged properties of most natural 3D fragments reproduce the topological cube. We use mechanical and geometric models to explain the ubiquity of Plato’s cube in fragmentation and to uniquely map distinct fragment patterns to their formative stress conditions.

Plato envisioned Earth’s building blocks as cubes, a shape rarely found in nature. The solar system is littered, however, with distorted polyhedra—shards of rock and ice produced by ubiquitous fragmentation. We apply the theory of convex mosaics to show that the average geometry of natural two-dimensional (2D) fragments, from mud cracks to Earth’s tectonic plates, has two attractors: “Platonic” quadrangles and “Voronoi” hexagons. In three dimensions (3D), the Platonic attractor is dominant: Remarkably, the average shape of natural rock fragments is cuboid. When viewed through the lens of convex mosaics, natural fragments are indeed geometric shadows of Plato’s forms. Simulations show that generic binary breakup drives all mosaics toward the Platonic attractor, explaining the ubiquity of cuboid averages. Deviations from binary fracture produce more exotic patterns that are genetically linked to the formative stress field. We compute the universal pattern generator establishing this link, for 2D and 3D fragmentation.

Fascinating, eh?

You need a quantum mechanic for an atom-sized machine

This news comes from the National University of Singapore’s Centre for Quantum Technologies according to a May 4, 2020 news item on Nanowerk (Note: A link has been removed),

Here’s a new chapter in the story of the miniaturisation of machines: researchers in a laboratory in Singapore have shown that a single atom can function as either an engine or a fridge. Such a device could be engineered into future computers and fuel cells to control energy flows.

“Think about how your computer or laptop has a lot of things inside it that heat up. Today you cool that with a fan that blows air. In nanomachines or quantum computers, small devices that do cooling could be something useful,” says Dario Poletti from the Singapore University of Technology and Design (SUTD).

This work gives new insight into the mechanics of such devices. The work is a collaboration involving researchers at the Centre for Quantum Technologies (CQT) and Department of Physics at the National University of Singapore (NUS), SUTD and at the University of Augsburg in Germany. The results were published in the peer-reviewed journal npj Quantum Information (“Single-atom energy-conversion device with a quantum load”).

The researchers have included an exceptionally pretty illustration with the press release,

Caption: Experiments with a single-atom device help researchers understand what quantum effects come into play when machinery shrinks to the atomic scale. Credit: Aki Honda / Centre for Quantum Technologies, National University of Singapore

A May 4, 2020 National University of Singapore press release (also on EurekAlert), which originated the news item, delves further into the work,

Engines and refrigerators are both machines described by thermodynamics, a branch of science that tells us how energy moves within a system and how we can extract useful work. A classical engine turns energy into useful work. A refrigerator does work to transfer heat, reducing the local temperature. They are, in some sense, opposites.

People have made small heat engines before using a single atom, a single molecule and defects in diamond. A key difference about this device is that it shows quantumness in its action. “We want to understand how we can build thermodynamic devices with just a few atoms. The physics is not well understood so our work is important to know what is possible,” says Manas Mukherjee, a Principal Investigator at CQT, NUS, who led the experimental work.

The researchers studied the thermodynamics of a single barium atom. They devised a scheme in which lasers move one of the atom’s electrons between two energy levels as part of a cycle, causing some energy to be pushed into the atom’s vibrations. Like a car engine consumes petrol to both move pistons and charge up its battery, the atom uses energy from lasers as fuel to increase its vibrating motion. The atom’s vibrations act like a battery, storing energy that can be extracted later. Rearrange the cycle and the atom acts like a fridge, removing energy from the vibrations.

In either mode of operation, quantum effects show up in correlations between the atom’s electronic states and vibrations. “At this scale, the energy transfer between the engine and the load is a bit fuzzy. It is no longer possible to simply do work on the load, you are bound to transfer some heat,” says Poletti. He worked out the theory with collaborators Jiangbin Gong at NUS Physics and Peter Hänggi in Augsburg. The fuzziness makes the process less efficient, but the experimentalists could still make it work.

Mukherjee and colleagues Noah Van Horne, Dahyun Yum and Tarun Dutta used a barium atom from which an electron (a negative charge) is removed. This makes the atom positively charged, so it can be more easily held still inside a metal chamber by electrical fields. All other air is removed from around it. The atom is then zapped with lasers to move it through a four-stage cycle.

The researchers measured the atom’s vibration after applying 2 to 15 cycles. They repeated a given number of cycles up to 150 times, measuring on average how much vibrational energy was present at the end. They could see the vibrational energy increasing when the atom was zapped with an engine cycle, and decreasing when the zaps followed the fridge cycle.

Understanding the atom-sized machine involved both complicated calculations and observations. The team needed to track two thermodynamic quantities known as ergotropy, which is the energy that can be converted to useful work, and entropy, which is related to disorder in the system. Both ergotropy and entropy increase as the atom-machine runs. There’s still a simple way of looking at it, says first author and PhD student Van Horne, “Loosely speaking, we’ve designed a little machine that creates entropy as it is filled up with free energy, much like kids when they are given too much sugar.”

Here’s a link to and a citation for the paper,

Single-atom energy-conversion device with a quantum load by Noah Van Horne, Dahyun Yum, Tarun Dutta, Peter Hänggi, Jiangbin Gong, Dario Poletti & Manas Mukherjee. npj Quantum Information volume 6, Article number: 37 (2020) Published: 01 May 2020

This paper is open access.

2020 The Universe in Verse livestream on April 25, 2020 from New York City

The Universe in Verse event (poetry, music, science, and more) has been held annually by Pioneer Works in New York City since 2017. (It’s hard to believe I haven’t covered this event in previous years but it seems that’s so.)

A ticketed event usually held in a venue, in 2020, The Universe in Verse is being held free as a livestreamed event. Here’s more from the event page on the Pioneer Works website,

A LETTER FROM THE CURATOR AND HOST:

Dear Pioneer Works community,

Since 2017, The Universe in Verse has been celebrating science and the natural world — the splendor, the wonder, the mystery of it — through poetry, that lovely backdoor to consciousness, bypassing our habitual barricades of thought and feeling to reveal reality afresh. And now here we are — “survivors of immeasurable events,” in the words of the astronomer and poet Rebecca Elson, “small, wet miracles without instruction, only the imperative of change” — suddenly scattered six feet apart across a changed world, blinking with disorientation, disbelief, and no small measure of heartache. All around us, nature stands as a selective laboratory log of only the successes in the series of experiments we call evolution — every creature alive today, from the blooming magnolias to the pathogen-carrying bat, is alive because its progenitors have survived myriad cataclysms, adapted to myriad unforeseen challenges, learned to live in unimagined worlds.

The 2020 Universe in Verse is an adaptation, an experiment, a Promethean campfire for the collective imagination, taking a virtual leap to serve what it has always aspired to serve — a broadening of perspective: cosmic, creaturely, temporal, scientific, humanistic — all the more vital as we find the aperture of our attention and anxiety so contracted by the acute suffering of this shared present. Livestreaming from Pioneer Works at 4:30PM EST on Saturday, April 25, there will be readings of Walt Whitman, Emily Dickinson, Adrienne Rich, Pablo Neruda, June Jordan, Mary Oliver, Audre Lorde, Wendell Berry, Hafiz, Rachel Carson, James Baldwin, and other titans of poetic perspective, performed by a largehearted cast of scientists and artists, astronauts and poets, Nobel laureates and Grammy winners: Physicists Janna Levin, Kip Thorne, and Brian Greene, musicians Rosanne CashPatti SmithAmanda Palmer, Zoë Keating, Morley, and Cécile McLorin Salvant, poets Jane Hirshfield, Ross GayMarie Howe, and Natalie Diaz, astronomers Natalie Batalha and Jill Tarter, authors Rebecca Solnit, Elizabeth Gilbert, Masha Gessen, Roxane GayRobert Macfarlane, and Neil Gaiman, astronaut Leland Melvin, playwright and activist Eve Ensler, actor Natascha McElhone, entrepreneur Tim Ferriss, artists Debbie Millman, Dustin Yellin, and Lia Halloran, cartoonist Alison Bechdel, radio-enchanters Krista Tippett and Jad Abumrad, and composer Paola Prestini with the Young People’s Chorus. As always, there are some thrilling surprises in wait.

Every golden human thread weaving this global lifeline is donating their time and talent, diverting from their own work and livelihood, to offer this generous gift to the world. We’ve made this just because it feels important that it exist, that it serve some measure of consolation by calibration of perspective, perhaps even some joy. The Universe in Verse is ordinarily a ticketed charitable event, with all proceeds benefiting a chosen ecological or scientific-humanistic nonprofit each year. We offer this  year’s  livestream freely,  but making the show exist and beaming it to you had significant costs. If you are so moved and able, please support this colossal labor with a donation to Pioneer Works — our doors are now physically closed to the public, but our hearts remain open to the world as we pirouette to find new ways of serving art, science, and perspective. Your donation is tax-deductible and appreciation-additive.

Yours,

Maria Popova

For anyone unfamiliar with Pioneer Works, here’s more from their About page,

History

Pioneer Works is an artist-run cultural center that opened its doors to the public, free of charge, in 2012. Imagined by its founder, artist Dustin Yellin, as a place in which artists, scientists, and thinkers from various backgrounds converge, this “museum of process” takes its primary inspiration from utopian visionaries such as Buckminster Fuller, and radical institutions such as Black Mountain College.

The three-story red brick building that houses Pioneer Works was built in 1866 for what was then Pioneer Iron Works. The factory, which manufactured railroad tracks and other large-scale machinery, was a local landmark after which Pioneer Street was named. Devastated by fire in 1881, the building was rebuilt, and remained in active use through World War II. Dustin Yellin acquired the building in 2011, and renovated it with Gabriel Florenz, Pioneer Works’ Founding Artistic Director, and a team of talented artists, supporters, and advisors. Together, they established Pioneer Works as a 501c3 nonprofit in 2012.

Since its inception, Pioneer Works has built science studios, a technology lab with 3-D printing, a virtual environment lab for VR and AR production, a recording studio, a media lab for content creation and dissemination, a darkroom, residency studios, galleries, gardens, a ceramics studio, a press, and a bookshop. Pioneer Works’ central hall is home to a rotating schedule of exhibitions, science talks, music performances, workshops, and innovative free public programming.

The Universe in Verse’s curator and host, Maria Popova is best known for her blog. Here’s more from her Wikipedia entry (Note: Links have been removed),

Maria Popova (Bulgarian: Мария Попова; born 28 July 1984)[not verified in body] is a Bulgarian-born, American-based writer of literary and arts commentary and cultural criticism that has found wide appeal (as of 2012, 3 million page views and more than 1 million monthly readers),[needs update] both for its writing and for the visual stylistics that accompany it.[citation needed][needs update] She is most widely known for her blog, Brain Pickings [emphasis mine], an online publication that she has fought to maintain advertisement-free, which features her writing on books, and ideas from the arts, philosophy, culture, and other subjects. In addition to her writing and related speaking engagements, she has served as an MIT Futures of Entertainment Fellow,[when?] as the editorial director at the higher education social network Lore,[when?] and has written for The Atlantic, Wired UK, and other publications. As of 2012, she resided in Brooklyn, New York.[needs update]

There’s one more thing you might want to know about the event,

NOTE: For various artistic, legal, and technical reasons, the livestream will not be available in its entirety for later viewing, but individual readings will be released incrementally on Brain Pickings. As we are challenged to bend limitation into possibility as never before, may this meta-limitation too be an invitation— to be fully present, together across the space that divides us, for a beautiful and unrepeatable experience that animates a shared moment in time, all the more precious for being unrepeatable. “As if what exists, exists so that it can be lost and become precious,” in the words of the poet Lisel Mueller. 

Enjoy! And, if you can, please donate.

The physics of Jackson Pollock’s painting technique

I long ago stumbled across the fascination that Jackson Pollock’s art work exerts over physicists but this work from Brown University adds some colours to the picture (wordplay intended).

One: Number 31, 1950. Jackson Pollock (American, 1912–1956). 1950. Oil and enamel paint on canvas, 8′ 10″ x 17′ 5 5/8″ (269.5 x 530.8 cm) Courtesy: Museum of Modern Art (MOMA) [downloaded from: https://www.moma.org/learn/moma_learning/jackson-pollock-one-number-31-1950-1950/]

From an October 30, 2019 Brown University news release (also on EurekAlert),

The celebrated painter Jackson Pollock created his most iconic works not with a brush, but by pouring paint onto the canvas from above, weaving sinuous filaments of color into abstract masterpieces. A team of researchers analyzing the physics of Pollock’s technique has shown that the artist had a keen understanding of a classic phenomenon in fluid dynamics — whether he was aware of it or not.

In a paper published in the journal PLOS ONE, the researchers show that Pollock’s technique seems to intentionally avoid what’s known as coiling instability — the tendency of a viscous fluid to form curls and coils when poured on a surface.

“Like most painters, Jackson Pollock went through a long process of experimentation in order to perfect his technique,” said Roberto Zenit, a professor in Brown’s School of Engineering and senior author on the paper. “What we were trying to do with this research is figure out what conclusions Pollock reached in order to execute his paintings the way he wanted. Our main finding in this paper was that Pollock’s movements and the properties of his paints were such he avoided this coiling instability.”

Pollock’s technique typically involved pouring paint straight from a can or along a stick onto a canvas lying horizontally on the floor. It’s often referred to as the “drip technique,” but that’s a bit of a misnomer in the parlance of fluid mechanics, Zenit says. In fluid mechanics, “dripping” would be dispensing the fluid in a way that makes discrete droplets on the canvas. Pollock largely avoided droplets, in favor of unbroken filaments of paint stretching across the canvas.

In order to understand exactly how the technique worked, Zenit and colleagues from the Universidad Nacional Autonoma de Mexico analyzed extensive video of Pollock at work, taking careful measure of how fast he moved and how far from the canvas he poured his paints. Having gathered data on how Pollock worked, the researchers used an experimental setup to recreate his technique. Using the setup, the researchers could deposit paint using a syringe mounted at varying heights onto a canvas moving at varying speeds. The experiments helped to zero in on the most important aspects of what Pollock was doing.

“We can vary one thing at a time so we can decipher the key elements of the technique,” Zenit said. “For example, we could vary the height from which the paint is poured and keep the speed constant to see how that changes things.”

The researchers found that the combination of Pollock’s hand speed, the distance he maintained from the canvas and the viscosity of his paint seem to be aimed at avoiding coiling instability. Anyone who’s ever poured a viscous fluid — perhaps some honey on toast — has likely seen some coiling instability. When a small amount of a viscous fluid is poured, it tends to stack up like a coil of rope before oozing across the surface.

In the context of Pollock’s technique, the instability can result in paint filaments making pigtail-like curls when poured from the can. Some prior research had concluded that that the curved lines in Pollock’s paintings were a result of this instability, but this latest research shows the opposite.

“What we found is that he moved his hand at a sufficiently high speed and a sufficiently short height such that this coiling would not occur,” Zenit said.

Zenit says the findings could be useful in authenticating Pollock’s works. Too many tight curls might suggest that a drip-style painting is not a Pollock. The work could also inform other settings in which viscous fluids are stretched into filaments, such as the manufacture of fiber optics. But Zenit says his main interest in the work is that it’s simply a fascinating way to explore interesting questions in fluid mechanics.

“I consider myself to be a fluid mechanics messenger,” he said. “This is my excuse to talk science. It’s fascinating to see that painters are really fluid mechanicians, even though they may not know it.”

Here’s a link to and a citation for the paper,

Pollock avoided hydrodynamic instabilities to paint with his dripping technique by Bernardo Palacios, Alfonso Rosario, Monica M. Wilhelmus, Sandra Zetina, Roberto Zenit. PLOS ONE DOI: https://doi.org/10.1371/journal.pone.0223706 Published: October 30, 2019

This paper is open access.

I could not find any videos related to this research that I know how to embed but Palacios, Zetina, and Zenit have investigated Polock’s ‘physics’ before,

If you want to see Pollock dripping his painting in action, there’s a 10 min. 13 secs. film made in 1950 (Note: Links have been removed from text; link to 10 min. film is below),

In the summer of 1950, Hans Namuth approached Jackson Pollock and asked the abstract expressionist painter if he could photograph him in his studio, working with his “drip” technique of painting. When Namuth arrived, he found:

“A dripping wet canvas covered the entire floor. Blinding shafts of sunlight hit the wet canvas, making its surface hard to see. There was complete silence…. Pollock looked at the painting. Then unexpectedly, he picked up can and paintbrush and started to move around the canvas. It was as if he suddenly realized the painting was not finished. His movements, slow at first, gradually became faster and more dancelike as he flung black, white and rust-colored paint onto the canvas.”

The images from this shoot “helped transform Pollock from a talented, cranky loner into the first media-driven superstar of American contemporary art, the jeans-clad, chain-smoking poster boy of abstract expressionism,” one critic later wrote in The Washington Post.

You can find the film and accompanying Open Culture text intact with links here.

Infinity, time, physics, math, and a play at the Vancouver (Canada) East Cultural Centre, January 7 – 19, 2020

Time seems to be having a moment. (I couldn’t resist. 🙂 If Carlo Rovelli’s 2018 book, The Order of Time, is any indication the topic has attained a new level of interest. The only other evidence I have is that I stumble across essays about time in unlikely places.

Infinity, a play about time and more, has been produced and toured on and off since 2015 when it won the Dora Mavor Moore Award for best new play.

Here’s a clip from one of the productions,

Here’s what the publicists at the Cultch (Vancouver East Cultural Centre) have posted about the play on the Events webpage,

A surprising, funny, and revelatory new play about love, sex, and math.

The cynical, skeptical daughter of a theoretical physicist and a composer, Sarah Jean’s clinical approach to love meets with little success. In this absorbing drama infused with science and classical music, three exceptional minds collide like charged particles in an accelerator. Sarah Jean’s hugely talented, yet severely dysfunctional, family will learn that love and time itself are connected in unimaginable ways.

From award-winning playwright Hannah Moscovitch; featuring two of our country’s most esteemed actors, Jonathon Young and Amy Rutherford, up-and-comer Emily Jane King, and violinist Andréa Tyniec; with original music by visionary composer Njo Kong Kie.

“The play makes you feel as much as it makes you think.”—NOW Toronto

There is a December 23, 2019 preview article by Janet Smith for the Georgia Straight which gives you some insight into the playwright and her work (Note: There is some profanity in the second paragraph),

Albert Einstein once called time a “stubbornly persistent illusion”, but tell that to a busy playwright who’s juggling deadlines for TV scripts and stage openings with parenting a four-year-old-boy.

“I’m in an insane relationship with time as a mother—this agonized relationship with time,” writer Hannah Moscovitch laments with a laugh, speaking to the Straight from her Halifax home before her show Infinity opens here after the holidays. “This work-life balance: I was like, ‘What the fuck is everybody complaining about?’ Until I had to do it.

“I mean, if I don’t work less I will wreck his childhood. So it’s not like a theoretical ideal that I should have work-life balance,” she continues, sounding as self-effacing, funny, and candidly introspective as some of her best-known female stage characters. And then she reflects more seriously, “Writing Infinity gave me the chance to grapple with that. And now I’m in a constant existential relationship with time; I’m constantly thinking about it. Time is intricately linked to death, they’re inevitably linked. When you come back to time you come back to death.”

In 2008, Ross Manson, artistic director, of Toronto’s Volcano Theatre, approached Moscovitch with an article in Harper’s magazine about the history of timekeeping, with the idea of commissioning her to write on the theme. Moscovitch went on to read Time Reborn: From the Crisis in Physics to the Future of the Universe [2013], in which American theoretical physicist Lee Smolin, of the Perimeter Institute for Theoretical Physics in Ontario, challenges Einstein’s idea of time as illusion.

With Manson’s help, she would go on to meet Smolin as she worked on her play, turning to him as an expert source on the science she was trying to convey in her story. Along the way, she formed a friendship with the man she was once intimidated to meet.

“Oddly enough, while all the specifics are different about what we do, some of the generals are the same,” she explains. “We have no language in common, but we really enjoy hanging out with each other. There’s a critical endeavour in both of our work that is thought-based, and we both very much live in our minds.”

For a more jaundiced view, there’s Conrad Sweatman’s April 5, 2019 review of the play’s script in book form for prairiefire,

The uses and abuses of science in playwriting: a review of Hannah Moscovitch’s play Infinity 

Hannah Moscovitch is an indie darling of Canadian theatre, and her Dora-winning play Infinity reaffirms her reputation as one of Canada’s brightest, most ambitious playwrights. If this sounds like the sort of detached praise one reads on a student report card, it’s partially because throughout my readings of Infinity I wrestled between admiration and annoyance at its rather academic cleverness. While ultimately it earns my letter of recommendation, Infinity sometimes feels like the dramatic equivalent of a class valedictorian’s graduation speech.

Back to Infinity. In his lively introduction to the play’s script, the famous physicist Lee Smolin, who consulted on the play, describes scientists and artists as“explorers of our common future” and pleads for a more open, friendly exchange between these two camps. (Smolin, vi). It comes off as a conciliatory remark after decades of the ‘science wars’ in academia, and Smolin also lauds Moscovitch for bucking the humanities’ postmodernist trend of knocking science and its practitioners. All fine sentiments. But what does this emphasis on the commonality between art and science mean, if anything, about the relationship between the subjective, social stuff of art and the objective, natural stuff of science? Does it suggest that the scientific method should by employed by playwrights and novelists in the fictional study of human nature, as some of the naturalist novelists of the 19th century believed? 

I have no reason to think that either Smolin or Moscovitch really wish for science to colonize the arts and humanities. …

Infinity is a fine addition to the aforementioned genre of smart, humanistic plays about physicists and mathematicians that had its heyday around the turn of the Millennium. It has some of their same flaws and cerebral charms and belongs more, in spirit, to the comparatively untroubled moment, before the Iraq and Afghanistan wars, the Global Recession, and Trump. If, like me, you spent your first years willingly reading serious literature and theatre at length in a humanities department where every text was filtered through the parallax perspectives of postmodern critical theory, you may find refreshing Infinity’s enthusiasm for science and its world of objectivism. You may feel the same way about its avoidance of the crude identity politics, inspired partially by such theory, that’s particularly in vogue in the arts right now: a kind of reactive agitprop in the age of Trump. But with the world staggering right now from one crisis to the next, a contemporary play about Ivy League intellectuals, their theories of time and struggles for authenticity, seems, well, a little untimely. …

Sweatman has identified one of the big problems with using concepts from mathematics and the sciences to inform fiction and art. The romantic poets ran into the same problem as Richard Holmes explores at length in his 2008 book, The Age of Wonder: How the Romantic Generation Discovered the Beauty and Terror of Science. Shelley eventually abandoned his attempts at including science in his poems.

Interestingly, most of us don’t seem to realize that the arts and sciences have been intimately linked for millenia. For example, De rerum natura a multi-volume poem by Roman poet, Lucretius ( (c. 99 BCE – c. 55 BCE), is a philosophical treatise exploring mind, soul, and the principles of atomism (i.e., atoms).

I hope you enjoy the play, if you choose to go. According to the Events webpage (scroll down), the playwright will be present at two post-show talkbacks.

The latest ‘golden’ age for electronics

I don’t know the dates for the last ‘golden’ age of electronics but I can certainly understand why these Japanese researchers are excited about their work. In any event, I think the ‘golden age’ is more of a play on words. From a June 25, 2019 news item on Nanowerk (Note: A link has been removed),

One way that heat damages electronic equipment is it makes components expand at different rates, resulting in forces that cause micro-cracking and distortion. Plastic components and circuit boards are particularly prone to damage due to changes in volume during heating and cooling cycles. But if a material could be incorporated into the components that compensates for the expansion, the stresses would be reduced and their lifetime increased.

Everybody knows one material that behaves like this: liquid water expands when it freezes and ice contracts when it melts. But liquid water and electronics don’t mix well – instead, what’s needed is a solid with “negative thermal expansion” (NTE).

Although such materials have been known since the 1960s, a number of challenges had to be overcome before the concept would be broadly useful and commercially viable. In terms of both materials and function, these efforts have only had limited success.

The experimental materials had been produced under specialized laboratory conditions using expensive equipment; and even then, the temperature and pressure ranges in which they would exhibit NTE were well outside normal everyday conditions.

Moreover, the amount they expanded and contracted depended on the direction, which induced internal stresses that changed their structure, meaning that the NTE property would not last longer than a few heating and cooling cycles.

A research team led by Koshi Takenaka of Nagoya University has succeeded in overcoming these materials-engineering challenges (APL Materials, “Valence fluctuations and giant isotropic negative thermal expansion in Sm1–xRxS (R = Y, La, Ce, Pr, Nd)”).

A June 22, 2019 Nagoya University press release (also on EurekAlert but published on June 25, 2019), which originated the news item, provides more technical detail,

Inspired by the series of work by Noriaki Sato, also of Nagoya University – whose discovery last year of superconductivity in quasicrystals was considered one of the top ten physics discoveries of the year by Physics World magazine – Professor Takenaka took the rare earth element samarium and its sulfide, samarium monosulfide (SmS), which is known to change phase from the “black phase” to the smaller-volume “golden phase”. The problem was to tune the range of temperatures at which the phase transition occurs. The team’s solution was to replace a small proportion of samarium atoms with another rare earth element, giving Sm1-xRxS, where “R” is any one of the rare earth elements cerium (Ce), neodymium (Nd), praseodymium (Pr) or yttrium (Y). The fraction x the team used was typically 0.2, except for yttrium. These materials showed “giant negative thermal expansion” of up to 8% at ordinary room pressure and a useful range of temperatures (around 150 degrees) including at room temperature and above … . Cerium is the star candidate here because it is relatively cheap.

The nature of the phase transition is such that the materials can be powdered into very small crystal sizes around a micron on a side without losing their negative expansion property. This broadens the industrial applications, particularly within electronics.

While the Nagoya University group’s engineering achievement is impressive, how the negative expansion works is fascinating from a fundamental physics viewpoint. During the black-golden transition, the crystal structure stays the same but the atoms get closer together: the unit cell size becomes smaller because (as is very likely but perhaps not yet 100% certain) the electron structure of the samarium atoms changes and makes them smaller – a process of intra-atomic charge transfer called a “valence transition” or “valence fluctuation” within the samarium atoms … . “My impression,” says Professor Takenaka, “is that the correlation between the lattice volume and the electron structure of samarium is experimentally verified for this class of sulfides.”

More specifically, in the black (lower temperature) phase, the electron configuration of the samarium atoms is (4f)6, meaning that in their outermost shell they have 6 electrons in the f orbitals (with s, p and d orbitals filled); while in the golden phase the electronic configuration is (4f)5(5d)1 -an electron has moved out of a 4f orbital into a 5d orbital. Although a “higher” shell is starting to be occupied, it turns out – through a quirk of the Pauli Exclusion Principle – that the second case gives a smaller atom size, leading to a smaller crystal size and negative expansion.

But this is only part of the fundamental picture. In the black phase, samarium sulfide and its doped offshoots are insulators – they do not conduct electricity; while in the golden phase they turn into conductors (i.e. metals). This is suggesting that during the black-golden phase transition the band structure of the whole crystal is influencing the valance transition within the samarium atoms. Although nobody has done the theoretical calculations for the doped samarium sulfides made by Professor Takenaka’s group, a previous theoretical study has indicated that when electrons leave the samarium atoms’ f orbital, they leave behind a positively charged “hole” which itself interacts repulsively with holes in the crystal’s conduction band, affecting their exchange interaction. This becomes a cooperative effect that then drives the valence transition in the samarium atoms. The exact mechanism, though, is not well understood.

Nevertheless, the Nagoya University-led group’s achievement is one of engineering, not pure physics. “What is important for many engineers is the ability to use the material to reduce device failure due to thermal expansion,” explains Professor Takenaka. “In short, in a certain temperature range – the temperature range in which the intended device operates, typically an interval of dozens of degrees or more – the volume needs to gradually decrease with a rise in temperature and increase as the temperature falls. Of course, I also know that volume expansion on cooling during a phase transition [like water freezing] is a common case for many materials. However, if the volume changes in a very narrow temperature range, there is no engineering value. The present achievement is the result of material engineering, not pure physics.”

Perhaps it even heralds a new “golden” age for electronics.

I worked in a company for a data communications company that produced hardware and network management software. From a hardware perspective, heat was an enemy which distorted your circuit boards and cost you significant money not only for replacements but also when you included fans to keep the equipment cool (or as cool as possible).

Enough with the reminiscences, here’s a link to and a citation for the paper,

Valence fluctuations and giant isotropic negative thermal expansion in Sm1–xRxS (R = Y, La, Ce, Pr, Nd) by D. Asai, Y. Mizuno, H. Hasegawa, Y. Yokoyama, Y. Okamoto, N. Katayama, H. S. Suzuki, Y. Imanaka, and K. Takenaka. Applied Physics Letters > Volume 114, Issue 14 > 10.1063/1.5090546 or Appl. Phys. Lett. 114, 141902 (2019); https://doi.org/10.1063/1.5090546. Published Online: 12 April 2019

This paper is behind a paywall.

Whispering in the Dark: Updates from Underground Science a June 12, 2019 talk in Vancouver (Canada)

The Society of Italian Researchers and Professionals in Western Canada (ARPICO) is hosting the intriguing ‘Whispering in the Dark …’ talk about underground science being held prior to the organization’s annual general meeting. From a May 21, 2019 ARPICO announcement (received via email),

… on June 12th, 2019 at the Italian Cultural Centre. ARPICO is proud to host Dr. Silvia Scorza, who will be presenting on the topic of underground science (literally underground) at SNOLAB, where research is conducted in fields of fundamental science that require shielding from external radiation such as cosmic rays. SNOLAB (SNO stands for Sudbury Neutrino Observatory) is a Canadian research laboratory located 2 km underground in Sudbury, Ontario. This presentation will give a unique and interesting perspective into the research that is conducted mostly out of the public view and discussion, but contributes critically to our scientific advances. Applications found in medicine, national security, industry, computing, science, and workforce development, illustrate a long and growing list of beneficial practical applications with contributions from particle physics.

Please read below to learn more about our speaker and topic.

Ahead of the speaking event, ARPICO will be holding its 2019 Annual General Meeting in the same location. We encourage everyone to participate in the AGM, have their say on ARPICO’s matters and possibly volunteer for the Board of Directors. ARPICO is made by all of its members, not just the Board, and it is therefore paramount that you all come, let us know what your wishes are for the Society and tell us how we can do better together as we go forward.

If you are driving to the venue, there is plenty of free parking space.  Please refer to the attached parking map for information on where not to park however, just to be sure.

We look forward to seeing everyone there.

The evening agenda is as follows:
6:00 pm to 6:45 pm – Annual General Meeting  [ Doors Open for Registration at 5:50 pm ]
7:00 pm – Start of the evening event with introductions & lecture by Dr. Silvia Scorza [ Doors Open for Registration at 6:45 pm ]
~8:00 pm – Q & A Period
to follow – Mingling & Refreshments until about 9:30 pm
If you have not already done so, please register for the event by visiting the EventBrite link or RSVPing to info@arpico.ca.

Further details are also available at arpico.ca and Eventbrite.

Whispering in the Dark: Updates from Underground Scienc

Based at a depth of 2 km in the Vale Creighton mine near Sudbury, Ontario, SNOLAB is an underground scientific environment that provides the conditions necessary for experiments dealing with rare interactions that have to be shielded from external radiation. The lab hosts an international community involved in a number of fundamental physics (neutrino and dark matter) as well as new biology and genomic experiments making use of the unique facility. In this lecture, Dr. Scorza will offer an overview on the life of an “underground scientist” and the immense possibilities of discovery that facilities like SNOLAB make available to our society.

Dr. Silvia Scorza was born and raised in Genoa, Italy. She received her B.Sc. and M.Sc. in Physics from the University of Genoa in 2003 and 2006, respectively. She then moved to the University Claude Bernard Lyon1 (UCBL1), France, where she obtained her Ph.D. in 2009. She has then held postdoctoral positions in France at the Institut de Physique Nucléaire de Lyon, in the U.S. at the Southern Methodist University in Dallas (TX) and later in Germany at the Karlsruhe Institute of Technology. Silvia is currently a research scientist at SNOLAB and adjunct professor at Laurentian University working on the SuperCDMS SNOLAB direct dark matter search experiment and the cryogenic test facility CUTE.
 
WHEN (AGM): Wednesday, June 12th, 2019 at 6:00pm (doors open at 5:50pm)
WHEN (EVENT): Wednesday, June 12th, 2019 at 7:00pm (doors open at 6:45pm)
WHERE: Italian Cultural Centre – Museum & Art Gallery – 3075 Slocan St, Vancouver, BC, V5M 3E4

RSVP: Please RSVP at EventBrite (http://whispersinthedark.eventbrite.ca/) or email info@arpico.ca
 
Tickets are Neede

Tickets are FREE, but all individuals are requested to obtain “free-admission” tickets on EventBrite site due to limited seating at the venue. Organizers need accurate registration numbers to manage wait lists and prepare name tags.

All ARPICO events are 100% staffed by volunteer organizers and helpers, however, room rental, stationery, and guest refreshments are costs incurred and underwritten by members of ARPICO. Therefore to be fair, all audience participants are asked to donate to the best of their ability at the door or via EventBrite to “help” defray costs of the event.
 
FAQs
Where can I contact the organizer with any questions? info@arpico.ca
Do I have to bring my printed ticket to the event? No, you do not. Your name will be on our Registration List at the Check-in Desk.
Is my registration/ticket transferrable? If you are unable to attend, another person may use your ticket. Please send us an email at info@arpico.ca of this substitution to correct our audience Registration List and to prepare guest name tags.
Can I update my registration information? Yes. If you have any questions, contact us at info@arpico.ca
I am having trouble using EventBrite and cannot reserve my ticket(s). Can someone at ARPICO help me with my ticket reservation? Of course, simply send your ticket request to us at info@arpico.ca so we help you.
 
What are my transport/parking options?
Bus/Train: The Millenium Line Renfrew Skytrain station is a 5 minute walk from the Italian Cultural Centre.
Parking: Free Parking is vastly available at the ICC’s own parking lot.  …

We look forward to seeing you there.

ARPICO
www.arpico.ca

You can find out more about SNOLAB here. There’s even a virtual tour.

Electron quantum materials, a new field in nanotechnology?

Physicists name and codify new field in nanotechnology: ‘electron quantum metamaterials’

UC Riverside’s Nathaniel Gabor and colleague formulate a vision for the field in a perspective article

Courtesy: University of California at Riverside

Bravo to whomever put the image of a field together together with a subhead that includes the phrases ‘vision for a field’ and ‘perspective article’. It’s even better if you go to the November 5, 2018 University of California at Riverside (UCR) news release (also on EurekAlert) by Iqbal Pittalwala to see the original format,

When two atomically thin two-dimensional layers are stacked on top of each other and one layer is made to rotate against the second layer, they begin to produce patterns — the familiar moiré patterns — that neither layer can generate on its own and that facilitate the passage of light and electrons, allowing for materials that exhibit unusual phenomena. For example, when two graphene layers are overlaid and the angle between them is 1.1 degrees, the material becomes a superconductor.

“It’s a bit like driving past a vineyard and looking out the window at the vineyard rows. Every now and then, you see no rows because you’re looking directly along a row,” said Nathaniel Gabor, an associate professor in the Department of Physics and Astronomy at the University of California, Riverside. “This is akin to what happens when two atomic layers are stacked on top of each other. At certain angles of twist, everything is energetically allowed. It adds up just right to allow for interesting possibilities of energy transfer.”

This is the future of new materials being synthesized by twisting and stacking atomically thin layers, and is still in the “alchemy” stage, Gabor added. To bring it all under one roof, he and physicist Justin C. W. Song of Nanyang Technological University, Singapore, have proposed this field of research be called “electron quantum metamaterials” and have just published a perspective article in Nature Nanotechnology.

“We highlight the potential of engineering synthetic periodic arrays with feature sizes below the wavelength of an electron. Such engineering allows the electrons to be manipulated in unusual ways, resulting in a new range of synthetic quantum metamaterials with unconventional responses,” Gabor said.

Metamaterials are a class of material engineered to produce properties that do not occur naturally. Examples include optical cloaking devices and super-lenses akin to the Fresnel lens that lighthouses use. Nature, too, has adopted such techniques – for example, in the unique coloring of butterfly wings – to manipulate photons as they move through nanoscale structures.

“Unlike photons that scarcely interact with each other, however, electrons in subwavelength structured metamaterials are charged, and they strongly interact,” Gabor said. “The result is an enormous variety of emergent phenomena and radically new classes of interacting quantum metamaterials.”

Gabor and Song were invited by Nature Nanotechnology to write a review paper. But the pair chose to delve deeper and lay out the fundamental physics that may explain much of the research in electron quantum metamaterials. They wrote a perspective paper instead that envisions the current status of the field and discusses its future.

“Researchers, including in our own labs, were exploring a variety of metamaterials but no one had given the field even a name,” said Gabor, who directs the Quantum Materials Optoelectronics lab at UCR. “That was our intent in writing the perspective. We are the first to codify the underlying physics. In a way, we are expressing the periodic table of this new and exciting field. It has been a herculean task to codify all the work that has been done so far and to present a unifying picture. The ideas and experiments have matured, and the literature shows there has been rapid progress in creating quantum materials for electrons. It was time to rein it all in under one umbrella and offer a road map to researchers for categorizing future work.”

In the perspective, Gabor and Song collect early examples in electron metamaterials and distil emerging design strategies for electronic control from them. They write that one of the most promising aspects of the new field occurs when electrons in subwavelength-structure samples interact to exhibit unexpected emergent behavior.

“The behavior of superconductivity in twisted bilayer graphene that emerged was a surprise,” Gabor said. “It shows, remarkably, how electron interactions and subwavelength features could be made to work together in quantum metamaterials to produce radically new phenomena. It is examples like this that paint an exciting future for electronic metamaterials. Thus far, we have only set the stage for a lot of new work to come.”

Gabor, a recipient of a Cottrell Scholar Award and a Canadian Institute for Advanced Research Azrieli Global Scholar Award, was supported by the Air Force Office of Scientific Research Young Investigator Program and a National Science Foundation Division of Materials Research CAREER award.

There is a video illustrating the ideas which is embedded in a November 5, 2018 news item on phys.oirg,


Here’s a link to and a citation for the ‘perspective’ paper,

Electron quantum metamaterials in van der Waals heterostructures by Justin C. W. Song & Nathaniel M. Gabor. Nature Nanotechnology, volume 13, pages986–993 (2018) DOI: https://doi.org/10.1038/s41565-018-0294-9 Published: 05 November 2018

This paper is behind a paywall.