Category Archives: Quantum Physics

The Standard Model of physics is the theory of particles, fields and the fundamental forces that govern them.

It tells us about how families of elementary particles group together to form larger composite particles, and how one particle can interact with another, and how particles respond to the fundamental forces of nature. It has made successful predictions such as the existence of the Higgs boson, and acts as the cornerstone for theoretical physics.

One way to think about the Standard Model is as a family tree for particles. For example, the Standard Model tells us how the atoms that make up our bodies are made of protons and neutrons, which in turn are made of elementary particles called quarks.

Related: What are bosons?

Keith Cooper is a freelance science journalist and editor in the United Kingdom, and has a degree in physics and astrophysics from the University of Manchester. He's the author of "The Contact Paradox: Challenging Our Assumptions in the Search for Extraterrestrial Intelligence" (Bloomsbury Sigma, 2020) and has written articles on astronomy, space, physics and astrobiology for a multitude of magazines and websites.

The Standard Model is considered by physicists, such as Glenn Starkman at Case Western Reserve University, as one of the most successful scientific theories (opens in new tab) of all time, but on the flip-side, scientists have also recognized that it is incomplete, in the same way that Isaac Newton's theory of universal gravitation derived from his laws of motion, while remarkably successful, was not the whole picture and required Albert Einstein's General Theory of Relativity to fill in the missing gaps.

The Standard Model was drawn together in the 1960s and early 1970s from the work of a cadre of pioneering scientists, but in truth its origins extend back almost 100 years earlier. By the 1880s, it was becoming apparent that there were positively and negatively charged particles produced when gasses are ionized, and that these particles must be smaller than atoms, which were the smallest known structures at the time. The first subatomic particle to be identified, in cathode rays (opens in new tab), was the negative electron in 1897 by the British physicist and subsequent Nobel Prize winner, J. J. Thomson (opens in new tab).

Then, in 1911, Hans Geiger and Ernest Madsen, under the supervision of the Nobel Laureate Ernest Rutherford (opens in new tab) at the University of Manchester, performed their famous 'gold foil' experiment, in which alpha particles (helium nuclei) were fired at a thin gold foil. Some of the alpha particles passed right through the atoms in the foil, while others were scattered left and right and a small fraction bounced right back.

Rutherford interpreted this as meaning that atoms contained a lot of empty space that the alpha particles were passing through, but that their positive charge was concentrated in a nucleus at their center, and on the occasions an alpha particle hit this nucleus dead on, it was scattered. Further experimentation by Rutherford in 191920 found that an alpha particle fired into air could knock a positively charged particle out of a nitrogen atom in the air, turning it into carbon in the process. That particle was the proton (opens in new tab), which gives the atomic nucleus its positive charge. The proton's neutrally charged partner, the neutron, was identified in 1932 by James Chadwick (opens in new tab) at Cambridge, who also won the Nobel Prize.

So, the picture of particle physics in the early 1930s seemed relatively straightforward atoms were made of two kinds of 'nucleons', in the guise of protons and neutrons, and electrons orbited them.

But things were already quickly starting to become more complicated. The existence of the photon was already known, so technically that was a fourth particle. In 1932 the American physicist Carl Anderson discovered the positron (opens in new tab), which is the antimatter equivalent of an electron. The muon was identified in 1936 by Anderson and Seth Neddermeyer (opens in new tab), and then the pion was discovered in 1947 (opens in new tab) by Cecil Powell. By the 1960s, with the advent of fledgling particle accelerators, hundreds of particles were being discovered, and the scientific picture was becoming very complicated indeed. Scientists needed a way of organizing and streamlining it all, and their answer to this was to create the Standard Model, which is the crowning glory of the cumulative work of the physics community of that era.

According to the Standard Model, there are three families of elementary particles. When we say 'elementary', scientists mean particles that cannot be broken down into even smaller particles. These are the smallest particles that together make up every other particle.

The three families are leptons, quarks and bosons. Leptons and quarks are known as Fermions because they have a half-integer spin. Bosons, on the other hand, have a whole-integer spin. What does this mean?

Spin, in the context of quantum physics, refers to spin angular momentum. This is different to orbital angular momentum, which describes Earth's spin around the sun, Earth's spin around its rotational axis, and even the spin of a spinning top. On the other hand, spin angular momentum is a quantum property intrinsic to each particle, even if that particle is stationary. Half-integer spin particles have spin values that are half-integers, so 1/2, 3/2, etc. The bosons have whole integer spin values, eg 1, 2, 3 etc.

Leptons include electrons, muons, tau particles and their associated neutrinos. Quarks are tiny particles that, when joined together, form composite particles such as protons and neutrons. Particles that are made of quarks are called hadrons (hence the Large Hadron Collider), with composite particles formed of odd numbers of quarks, usually three, being called baryons, and those made of two quarks called mesons. Bosons are force carriers they transfer the electromagnetic force (photons), the weak force (Z and W bosons), the strong nuclear force (gluons), and the Higgs force (Higgs boson).

Each 'family' consists of six known particles (except the bosons, which we'll explain later) that come in pairs called 'generations.' The most stable and least massive particles of the family form the first generation. Because of their stability, meaning that they don't decay quickly, all stable matter in the universe is made from first generation elementary particles. For example, protons are formed of two 'up' quarks and one 'down' quark, which are the two most stable quarks.

There are 17 known elementary particles 6 leptons, 6 quarks, but only 5 bosons. There's one force carrier missing the graviton. The Standard Model predicts that gravity should have a force-carrying boson, in the guise of the graviton. Gravitational waves are, in theory, formed from gravitons. However, detecting the graviton will be no mean feat. Gravity is the weakest of the four fundamental forces. You might not think so, after all it keeps your feet on the ground, but when you consider that it takes the entire mass of the planet to generate enough gravity to keep your feet on the ground, you might get a sense that gravity isn't as strong as, say, magnetism can be, which can pick up a paperclip against the gravitational pull of Earth. Consequently, individual gravitons do not interact with matter that easily they are said to have a low cross section of interaction (opens in new tab). Gravitons may have to remain hypothetical for the time being.

As wonderful as the Standard Model is, it describes only a small fraction of the universe. The European Space Agency's Planck spacecraft (opens in new tab) has confirmed that everything that we can see in the cosmos planets, stars and galaxies accounts for just 4.9% of all the mass and energy in the universe (opens in new tab). The rest is dark matter (26.8%) and dark energy (68.3%), the nature of which are completely unknown and which are definitely not predicted by the Standard Model.

That's not all that's unknown. One big question in physics is whether the elementary particles really are elementary, or whether there is hidden physics underlying them. For example, String Theory posits that elementary particles are made from tiny vibrating strings. Then there's the question of antimatter equal amounts of matter and antimatter (opens in new tab) should have been created in the Big Bang, but this would mean we should not be here at all, because all the matter and antimatter should have annihilated each other. Today we see that the universe contains mostly matter, with very little antimatter. Why is there this asymmetry?

Then there's the question of why particles have the masses that they do, and why the forces have the strengths that they have, and why particles are broken down into the three families of leptons, quarks and bosons. That they just are isn't a good enough answer for physicists they want to understand why, and the Standard Model does not tell them.

In an effort to bring the Standard Model up to speed to face these challenges, scientists have introduced the idea of supersymmetry. If true, then supersymmetry would mean that every particle in the Standard Model has a supersymmetric partner with a much greater mass, and a spin that is different by one-half to their Standard Model partners. This would unify fermions with bosons, since the integer-spin fermions would have half-integer-spin super-partners, and the half-integer-spin bosons would have integer-spin super-partners. The least massive and most stable supersymmetry particles would also have no electric charge and interact only very weakly with normal matter, which sounds very much like the properties of dark matter.

Meanwhile, at the very highest energies analogous to those that existed in the first moment after the Big Bang, supersymmetry predicts that the weak force, the strong force and the electromagnetic force would all have the same strength, and essentially be the same force. Scientists call such a concept a 'Grand Unified Theory'.

According to the CERN website, supersymmetry could also help explain the surprisingly small mass of the Higgs boson (opens in new tab), which is 125 GeV (125 billion electronvolts). While this is relatively high, it is not as high as expected. The existence of extremely massive supersymmetric partners would balance things out. And they must be extremely massive, because the Large Hadron Collider (LHC), nor any other particle accelerator before it, has found any evidence for the existence of supersymmetric partners so far, leading some scientists to doubt that supersymmetry is real. If supersymmetric particles exist, then they must be more massive than the LHC can detect; for example, the mass of the gluino (opens in new tab), which is the supersymmetric partner of the gluon that mediates the strong force binding quarks together inside protons and neutrons, has been ruled out up to 2 trillion eV.

So supersymmetry is in danger and physicists are now scrambling to find a replacement theory that can advance upon the Standard Model and explain the Higgs boson's mass, as well as dark matter, Grand Unified Theories and everything else. There are no strong candidates to replace supersymmetry yet, and supersymmetry may still win out, but for now physicists will have to make do with the imperfect world of the Standard Model.

CERN's website (opens in new tab) features more information about the Standard Model.

The U.S. Department of Energy explains the Standard Model (opens in new tab) on their own site.

The Institute of Physics also describes the Standard Model (opens in new tab) on their website.

Follow Keith Cooper on Twitter @21stCenturySETI (opens in new tab). Follow us on Twitter @Spacedotcom (opens in new tab) and on Facebook (opens in new tab).

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What is the standard model? - Space.com

In a laboratory in Kyoto, Japan, researchers are working on some very cool experiments. A team of scientists from Kyoto University and Rice University in Houston, Texas has cooled matter to within a billionth of a degree of absolute zero (the temperature when all motion stops), making it the coldest matter in the entire universe. The study was published in the September issue of Nature Physics, and opens a portal to an unexplored realm of quantum magnetism, according to Rice University.

Unless an alien civilization is doing experiments like these right now, anytime this experiment is running at Kyoto University it is making the coldest fermions in the universe, said Rice University professor Kaden Hazzard, corresponding theory author of the study, and member of the Rice Quantum Initiative, in a press release. Fermions are not rare particles. They include things like electrons and are one of two types of particles that all matter is made of.

The Kyoto team led by study author Yoshiro Takahashi used lasers to cool the fermions (or particles like protons, neutrons, and electrons whose spin quantum number is an odd half integer like 1/2 or 3/2) of ytterbium atoms to within about one-billionth of a degree of absolute zero. Thats roughly 3 billion times colder than interstellar space. This area of space is still warmed by the cosmic microwave background (CMB), or the afterglow of radiation from the Big Bang about 13.7 billion years ago. The coldest known region of space is the Boomerang Nebula, which has a temperature of one degree above absolute zero and is 3,000 light-years from Earth.

[Related: How the most distant object ever made by humans is spending its dying days.]

Just like electrons and photons, atoms are are subject to the laws of quantum dynamics, but their quantum behaviors only become noticeable when they are cooled to within a fraction of a degree of absolute zero. Lasers have been used for more than 25 years to cool atoms to study the quantum properties of ultracold atoms.

The payoff of getting this cold is that the physics really changes, Hazzard said. The physics starts to become more quantum mechanical, and it lets you see new phenomena.

In this experiment, lasers were used to to cool the matter by stopping the movements of 300,000 ytterbium atoms within an optical lattice. It simulates the Hubbard model, a quantum physics first proposed by theoretical physicist John Hubbard in 1963. Physicists use Hubbard models to investigate the magnetic and superconducting behavior of materials, especially those where interactions between electrons produce collective behavior,

This model allows for atoms to show off their unusual quantum properties, which include the collective behavior between electrons (a bit like a group of fans performing the wave at a football or soccer game) and superconduction, or an objects ability to conduct electricity without losing energy.

The thermometer they use in Kyoto is one of the important things provided by our theory, said Hazzard. Comparing their measurements to our calculations, we can determine the temperature. The record-setting temperature is achieved thanks to fun new physics that has to do with the very high symmetry of the system.

[Related: Chicago now has a 124-mile quantum network. This is what its for.]

The Hubbard model simulated in Kyoto has special symmetry known as SU(N). The SU stands for special unitary group, which is a mathematical way of describing the symmetry. The N denotes the possible spin states of particles within the model.

The greater the value of N, the greater the models symmetry and the complexity of magnetic behaviors it describes. Ytterbium atoms have six possible spin states, and the simulator in Kyoto is the first to reveal magnetic correlations in an SU(6) Hubbard model. These types of calculations are impossible to calculate on a computer, according to the study.

Thats the real reason to do this experiment, Hazzard said. Because were dying to know the physics of this SU(N) Hubbard model.

Graduate student in Hazzards research group and study co-author Eduardo Ibarra-Garca-Padilla added that the Hubbard model aims to capture the very basic ingredients needed for what makes a solid material a metal, insulator, magnet, or superconductor. One of the fascinating questions that experiments can explore is the role of symmetry, said Ibarra-Garca-Padilla. To have the capability to engineer it in a laboratory is extraordinary. If we can understand this, it may guide us to making real materials with new, desired properties.

The team is currently working on developing the first tools capable of measuring the behavior that arises a billionth of a degree above absolute zero.

These systems are pretty exotic and special, but the hope is that by studying and understanding them, we can identify the key ingredients that need to be there in real materials, conculed Hazzard.

Originally posted here:

Scientists used lasers to make the coldest matter in the universe - Popular Science

If you're a fan of ambitious new TV shows based on genre classics you know and love, then the fading days of summer are turning out to be an especially sweet time to tune in. HBO is rekindling that Game of Thrones smolder with House of the Dragon, Amazon is tapping J.R.R. Tolkien with The Lord of the Rings: The Rings of Power, and even as we speak, NBC is putting the final touches on an all-new Imaging Chamber for the hugely hyped series launch of the freshly-revived Quantum Leap.

By the time Quantum Leap skips back to the airwaves with its Sept. 19 debut, all the above-mentioned awesomeness will have arrived in the span of just a single month which is pretty mind-boggling, when you think about it. But before the excitement fades our brain, its probably a good idea to take a deep breath and break down just what we really do know about NBCs new adventures in time travel.

This ones easy: NBC describes the new Quantum Leap as a sequel series thats set 30 years after the original show. Expect a mix of new storylines, as well as a tug or two at threads that the original left dangling: Fans of the original Quantum Leap are in for a few surprises, including the return of some original characters and the continuation of the most popular plot points, the network teases.

If youre a fan of the original series, feel free to skip ahead: This section covers the basics of the old-school Quantum Leap you know, the big-picture stuff about the shows premise and setting that should still apply in its new 2022 incarnation.

Both the original Quantum Leap and NBCs new series are sci-fi shows set in their respective present-day, real-world trappings. Theyre based on the idea that technologys just a little farther ahead than we think it isespecially if youve got the governments super-secret science resources at your disposal.

In both series, the key hero is an accomplished physicist who leaps through spacetime into different eras from humanitys past, courtesy of Project Quantum Leap an insanely sophisticated (and expensive) R&D program tucked away in a remote, hush-hush lab. Scott Bakula played the now-iconic role of Dr. Sam Beckett in the original series as the hero who gets himself stuck in an unending sequence of time leaps. In the new show, the stranded-hero honors fall to new star Raymond Lee in the role of physicist Dr. Ben Song.

Time travel isnt the only big twist, though: For one thing, the leaper in each series, wellthey sort of, kind of go rogue to make their initial jump in the first place. Thats a polite way of saying that the government in no way, shape, or form gave them permission to take its fancy particle machine for a free spin, and losing a star scientist to the invisible ether of spacetime leaves the projects suit-wearing overseers with plenty of stern questions (and probably a touch of high blood pressure).

For another thing, theres no way to control (or even predict) where in humanitys past Project Quantum Leap will spit our hero out, as original series scientist Dr. Sam Beckett learned the hard way in the shows very first 1989 episode. If thats not enough, our hero doesnt even get to inhabit their own flesh and blood once theyve made the jump: Instead, they emerge in the body of a completely different person native to the particular time and place where their latest leap has taken them.

Most importantly, theres no known escape at least, not one that Project Quantum Leap has the advanced technology to devise. Taking that first-episode time dive sets off an endless cycle of leap after leap, with the only real reprieve coming not by going home to the present but to another place (and another body) where the entire process resets while our hero waitsyou guessed it, for the next leap.

In order to even do that, theyve got to identify and solve some kind of pivotal problem unique to their temporary human host one that typically changes the course of that persons life for the better. When that key quandary has finally been fixed, the mysteries of physics kick in and its off to another new time and another new host.

Thankfully, Quantum Leap offers its stranded, time-drifting scientist one emotional lifeline that preserves their ties to the home they know and love. Thanks to a sweet piece of lab tech known as the Imaging Chamber, a human back in our own time is able to see and talk to the leaper via holographic image. In the original series, that honor went to Sam Becketts friend Al Calavicci(the late Dean Stockwell), a colorful character whom only Sam could see and hear (a twist that served up endless opportunities for cool plot twists and tons of comic relief). NBCs new Quantum Leap similarly features a new holographic companion characterbut well get to that in a moment.

Though the cast and characters are new, the upcoming Quantum Leap bears a lot of the same creative DNA that made the original such a 1990s sci-fi favorite. Original show creator Donald P. Bellisario is on board as an executive producer alongside Quantum Leap veteran Deborah Pratt, both of whom were producers on the earlier series (Pratt also voiced the old-school supercomputer Ziggy.)

Heres a quick look at the shows main characters, as well as the actors wholl be playing them:

Raymond Lee as Dr. Ben SongRaymond Lee (Kevin Can F**k Himself) takes center stage as the new series time-leaping scientist Dr. Ben Song, a highly-intelligent quantum physicist who jumps through time to explore the mysteries of the original Quantum Leap experiment, via NBC. While Ben will have the help of the Quantum Leap team, it is up to Ben to finally put things in order after the chaotic events of the original experiment.

Ernie Hudson as Herbert Magic Williams Those poking, prodding government types we mentioned earlier? Theyll be represented in the person of Herbert Magic Williams, played in the new show by Ghostbusters alum Ernie Hudson. Every science fiction story needs an authoritarian figurehead, explains NBC, describing Magic as the leader of the Quantum Leap project, torn between the responsibility of answering to his bosses in the Pentagon or taking care of the Quantum Leap team. Old school fans might also remember the character from one of Sam's leaps during the original series.

Nanrisa Lee as Jenn Chou Working closely alongside Magic will be Jenn Choi (Bosch and Star Trek: Picard alum Nanrisa Lee). Jenn is the head of digital security for the Quantum Leap project, and shes focused on discovering why Ben decided to leap in the first place, according to the networkall in the hope of eventually bringing Ben home.

Mason Alexander Park as Ian Wright As Ian Wright, Mason Alexander Park (The Sandman, Cowboy Bebop) isnt just your typical research project egghead, but the computer whiz responsible for bringing Ziggy out of the 20th Century and into the present day. The projects lead programmer, Ian rebuilds the originals shows Pratt-voiced AI, a bot that provides crucial information about Ben's leaps through time, NBC teases.

Caitlin Bassett as Addison Augustine Last but definitely not least is the character wholl serve as Dr. Songs holographic pal the same position held by Al (Dean Stockwell) in the original series. Addison Augustine (TV newcomer Caitlin Bassett) is an ex-Army intelligence officer who has an important role in the Quantum Leap project, NBC explains, showing up amid Bens travels as a hologram that only he can can see. Like Al before her, Addison will dish up valuable insight into the past that Ben uses as a guide throughout his adventures.

Rounding out the rest of the creative team, the new series is written and executive produced by Steven Lilien and Bryan Wynbrandt, with Bellisario, Pratt, and Martin Gero (Stargate Atlantis, Blindspot) teaming up with Dean Georgaris (Life of Pi, The Meg) as executive producers. Gero will also reportedly serve as showrunner, via Deadline.

The short answer? No, but it always helps! This article outlines the shows premise in strokes broad enough to get any viewer started, though the new Quantum Leap, like its predecessor, will have you oriented in no time even if the dog happened to eat your TV-history homework. But if you really want to go into the new show fully prepared, hit up Peacock, where all five seasons of the original series are streaming round the clock. Pressed for time? Its okay to cheat! Heres our handy crash-course lineup of the five most essential Quantum Leap episodes.

NBC is the place to be to catch all new Quantum Leap episodes as they air. The series premiere is set for 10 p.m. ET on Monday, Sept. 19 (immediately following The Voice), with new episodes arriving weekly through the fall season. If you miss one, theres no need to get your feathers in a ruffle: Peacock has your back with day-after streaming on demand for every episode.

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Everything to know about the new 'Quantum Leap': Where to watch? What's the story? Who returns? - Syfy

The HERMES experiment A Personal Story, by Richard Milner and Erhard Steffens, World Scientific

One hundred years ago, Otto Stern and Walther Gerlach performed their ground-breaking experiment shooting silver atoms through an inhomogeneous magnetic field, separating them according to their spatially quantised angular momentum. It was a clear victory of quantum theory over the still widely used classical picture of the atom. The results also paved the way to the introduction of the concept of spin, an intrinsic angular momentum, as an inherent property of subatomic particles.

The idea of spin was met with plenty of scepticism. Abraham Pais noted in his book George Uhlenbeck and the Discovery of Electron Spin that Ralph Kronig finishing his PhD at Columbia University in 1925 and travelling through Europe, introduced the idea to Heisenberg and Pauli, who dryly commented that it is indeed very clever but of course has nothing to do with reality. Feeling ridiculed, Kronig dropped the idea. A few months later, still against strong resistance by established experts but this time with sufficient backing by their mentor Paul Ehrenfest, Leiden graduate-students George Uhlenbeck and Samuel Goudsmit published their seminal Nature paper on the spinning electron. In the future I shall trust my own judgement more and that of others less, wrote Kronig in a letter to Hendrik Kramers in March 1926.

Spin quickly became a cornerstone of 20th-century physics. Related works of paramount importance were Paulis exclusion principle and Diracs description of relativistic spin-1/2 particles, as well as the spin-statistics theorems (namely the FermiDirac and BoseEinstein distributions for identical half-integerspin and integerspin particles, respectively). But more than half a century after its introduction, spin re-emerged as a puzzle. By then, a rather robust theoretical framework, the Standard Model, had been established within which many precision calculations became a comfortable standard. It could have been all that simple: since the proton consists of two valence-up and one valence-down quarks, with spin up and down (i.e. parallel and antiparallel to the protons spin, respectively), the origin of its spin is easily explained. The problem dubbed spin crisis arose in the late 1980s, when the European Muon Collaboration at CERN found that the contribution of quarks to the proton spin was consistent with zero, within the then still-large uncertainties, and that the so-called EllisJaffe sum rule ultimately not fundamental but model-dependent was badly violated. What had been missed?

Today, after decades of intense experimental and theoretical work, our picture of the proton and its spin emerging from high-energy interactions has changed substantially. The role of gluons both in unpolarised and polarised protons is non-trivial. More importantly, transverse degrees of freedom, both in position and momentum space, and the corresponding role of orbital angular momentum, have become essential ingredients in the modern description of the proton structure. This description goes beyond the picture of collinearly moving partons encapsulated by the fraction of the parent protons momentum and the scale at which they are probed; numerous effects, unexplainable in the simple picture, have now become theoretically accessible.

The HERMES experiment at DESY, which operated between 1995 and 2007, has been a pioneer in unravelling the mysteries of the proton spin, and the experiment is the protagonist in a new book by Richard Milner and Erhard Steffens, two veterans in this field as well as the driving forces behind HERMES. The subtitle and preface clarify that this is a personal account and recollection of the history of HERMES, from an emergent idea on both sides of the Atlantic to a nascent collaboration and experiment, and finally as an extremely successful addition to the physics programme of HERA (the worlds only leptonproton collider, which started running at DESY 30 years ago for one and a half decades).

Milner and Steffens are both experts on polarised gas targets, with complementary backgrounds leading to rather different perspectives. Indeed, HERMES was independently developed within a North American initiative, in which Milner was the driving force, and a European initiative around the Heidelberg MPI-K led by Klaus Rith, with Erhard Steffens as a long-time senior group member. In 1988 two independent letters of intent submitted to DESY triggered sufficient interest in the idea of a fixed-target experiment with a polarised gas target internal to the HERA lepton ring; the proponents were subsequently urged to collaborate in submitting a common proposal. In the meantime, HERMES feasibility needed to be demonstrated. A sufficiently high lepton-polarisation had to be established, as well as smooth running of a polarised gas target in the harsh HERA environment without disturbing the machine and the main HERA experiments H1 and Zeus.

By summer 1993, HERMES was fully approved, and in 1995 the data taking started with polarised 3He. The subsequently used target of polarised hydrogen or deuterium employed the same concepts that Stern and Gerlach had already used in their famous experiment. The next decade saw several upgrades and additions to the physics programme, and data taking continued until summer 2007. In all those years, the backbone of HERMES was an intense and polarised lepton beam that traversed a target of pure gas in a storage cell, highly polarised or unpolarised, avoiding extensive and in parts model-dependent corrections. This constellation was combined with a detector that, from the very beginning, was designed to not only detect the scattered leptons but also the spray produced in coincidence. These features allowed a diverse set of processes to be studied, leading to numerous pioneering measurements and insights that motivated, and continue to motivate, new experimental programmes around the world, including some at CERN.

Richard Milner and Erhard Steffens provide extensive insights, in particular into the historic aspects of HERMES, which are difficult to obtain elsewhere. The book gives an insightful discussion of the installation of the experiment and of the outstanding efforts of a group of highly motivated and dedicated individuals who worked too often in complete ignorance of (or in defiance of) standard working hours. Their account enthrals the reader with vivid anecdotes, surprising twists and personal stories, all told in a colloquial style. While clearly not meant as a textbook indeed, one might notice small mistakes and inconsistencies in a few places this book makes for worthwhile and enjoyable reading, not only for people familiar with the subject but equally for outsiders. In particular, younger generations of physicists working in large-scale collaborations might be surprised to learn that it needs only a small group and little time to start an experiment that goes on to have a tremendous impact on our understanding of natures basic constituents.

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Hymn to HERMES CERN Courier - CERN Courier

Quantum theory is perhaps the most successful scientific idea ever. So far, it has never been proved wrong. It is stupendously predictive, it has clarified the structure of the periodic table, the functioning of the sun, the colour of the sky, the nature of chemical bonds, the formation of galaxies and much more. The technologies we have been able to build as a result range from computers to lasers to medical instruments.

Yet, a century after its birth, something remains deeply puzzling about quantum theory. Unlike its illustrious predecessor, Newtons classical mechanics, it does not tell us how physical systems behave. Instead, it confines itself to predicting the probability that a physical system will affect us in one way or another. When an electron is fired from one side of a wall with two holes, for instance, quantum theory tells us where it will end up on the other side, stubbornly saying nothing plausible about which hole it has gone through. It treats any physical system as a black box: if you do this to it now, it will react like that later. What happens in between? The theory simply doesnt tell us.

Many scientists are content with this, but others are puzzled. Among the latter, some make hypotheses: they propose complicated stories about parts of nature that are hidden from us for ever, or multiple universes that underpin the part of reality we do see. Others resign themselves to the notion that science is not about what things really are: it is only about what we are able to directly observe.

Another idea has recently begun to catch on. Perhaps there is no need to make anything up about what lies behind quantum theory. Perhaps it really does reveal to us the deep structure of reality, where a property is no more than something that affects something else. Perhaps this is precisely what properties are: the effects of interactions. A good scientific theory, then, should not be about how things are, or what they do: it should be about how they affect one another.

The idea seems radical. It pushes us to rethink reality in terms of relations instead of objects, entities or substances. The possibility that this could be what quantum physics is telling us about nature was first suggested a quarter of a century ago. For a while it remained largely unnoticed, then several major philosophers picked it up and began to discuss it. Nowadays interest in the idea, called the Relational Interpretation of Quantum Mechanics, is steadily growing. It is a possible solution to the puzzle of quantum theory: what quantum phenomena are is evidence that all properties are relational.

There is a strikingly similar definition of existence at the root of the western philosophical tradition. Platos The Sophist contains the following phrase: Anything which possesses any sort of power to affect another, or to be affected by another, if only for a single moment, however trifling the cause and however slight the effect, has real existence; and I hold that the definition of being is simply action. [] And in the eastern tradition, the Buddhist philosopher Ngrjunas central notion of emptiness (nyat) tells us that nothing has independent existence: anything that exists, exists thanks to, as a function of, or according to the perspective of, something else.

So maybe this is not such a radical idea after all. We all know that a chemical substance is defined by how it reacts, a biological species is defined according to the niche it occupies in the biosphere, and what defines us as human beings is our relationships. Think of a simple object such as a blue teacup. Its being blue is not a property of the cup alone: colours happen in our brain as a result of the structure of the receptors in the retina of our eyes and as a consequence of the interactions between daylight and the cups surface. Its being a teacup refers to its potential function as a drinking vessel: for an alien who doesnt know about drinking tea, the very notion of a teacup is meaningless. What is more, its stability as an object depends on the timescale in which we consider it: take a longer view and it is just a fleeting aggregation of atoms. And are these atoms themselves independent elements of reality? No they are not, as quantum theory shows: they are defined by their physical interactions with the rest of the world.

So quantum physics may just be the realisation that this ubiquitous relational structure of reality continues all the way down to the elementary physical level. Reality is not a collection of things, its a network of processes.

If this is correct, I think it comes with a lesson. We understand reality better if we think of it in terms of interactions, not individuals. We, as individuals, exist thanks to the interactions we are involved in. This is why, in classic game theory, the winners in the long run are those who collaborate. Too often we foolishly measure success in terms of a single actors fortunes. This is both short-sighted and irrational. It misunderstands the true nature of reality, and is ultimately self-defeating. I believe, for example, that we make this mistake all the time in international politics. Prioritising individual countries, or groups of countries, over the common good, is a catastrophic error. It leads to the devastation of war and prevents us from addressing the true challenges that all of humankind a node in natures network faces as a whole.

Carlo Rovelli is a professor of physics. To support the Guardian and the Observer buy a copy at guardianbookshop.com. Delivery charges may apply.

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Helgoland: Making Sense of the Quantum Revolution by Carlo Rovelli (Allen Lane, 9.34)

The World According to Physics by Jim Al-Khalili (Princeton, 12.99)

Theaetetus & Sophist by Plato (Cambridge, 17.99)

Meeting the Universe Halfway: Quantum Physics and the Entanglement of Matter and Meaning by Karen Barad (Duke, 23.99)

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The big idea: why relationships are the key to existence - The Guardian

Mayer Hall recognized as the birthplace of density functional theory

(L-R): Dean Boggs, Professor Schuller, Professor Emeritus Sham and Executive Vice Chancellor Simmons hold the plaque commemorating Mayer Hall as a historic landmark. Photos by: Daniel Orren / UC San Diego Health.

Is there magic in the walls of Mayer Hall? This is the question Oleg Shpyrko, chair of the Department of Physics at the University of California San Diego, asked the audience gathered in the auditorium for a daylong series of events to celebrate the buildings designation as a historical site by the American Physical Society (APS).

Mayer Hall, after all, was named after famed theoretical physicist Maria Goeppert Mayerthe second woman ever to win the Nobel Prize in physics. It was also the birthplace of metamaterials which, among other things, have been used to create Harry Potter-like invisibility cloaks. In the labs of Mayer Hall, many novel high-temperature superconductors and quantum materials were developed. It was also in Mayer Hall where Walter Kohn and Lu Jeu Sham created the Kohn-Sham equation as part of their work in establishing density functional theory, or DFT.

Shpyrko concluded that, no, there wasnt magic inside the walls of Mayer Hall, but there was magic in the people who worked there.

And there was magic in the pivotal Kohn-Sham equation. Its subsequent impact on everything from new materials design to drug discovery led APS to designate Mayer Hall a historical site, stating that DFT is the most used technique for calculating the properties of nuclei, molecules, polymers, macromolecules, surfaces and bulk materials in the chemical, biological and physical sciences.

In the early part of the 20th century, the development of quantum mechanics allowed physicists to learn about the properties and behavior of atoms. Traditionally, the Schrdinger equation was used to determine the probabilistic location and behavior of a particle, including the complexity associated with quantum superposition, which is the basis of the famous Schrdingers cat paradox.

As a result, this equation requires a significant amount of computational effort for each individual electron as well as interactions with every other electron and nuclei. Even a single water molecule contains 10 electrons. Thus, determining the electron behavior of larger molecules quickly becomes prohibitive, akin to controlling the behavior of hundreds of quantum-mechanical Schrdingers kittens who are actively interacting with each other while occupying many locations at once.

From 1964-1966, Kohn and Sham laid the foundation of a computation method based on a single-particle approach, which became known as the Kohn-Sham equation and formed the basis of density functional theory.

DFT simplified the previous process by using the density of all the electrons in the system to determine electron behavior. Researchers no longer needed to focus on each individual electron, but used their collective density as the single variable to solve for, transforming the way quantum mechanics research was performed.

DFT is known as an ab initio, or first principle method, because it can predict material properties for unknown systems without any experimental input. So while it does not precisely solve the Schrdinger equation, it does offer a close approximation at a fraction of the computational effort.

Understanding the electronic properties of complex systems is essential to the design and engineering of new materials and drugs. DFT has been used to study and develop the properties of important materials such as novel semiconductors, new catalysts, neuromorphic materials and complex molecules.

For instance, drug discovery uses DFT as a fast and efficient method to limit the number of drugs that must be experimentally tested for their efficacy in the treatment of many diseases. Thanks to DFT, the time and cost of drug development have been considerably reduced.

The UC San Diego School of Physical Sciences and the physics department worked together to create an engaging, informative day of events to celebrate Mayer Halls designation. Although APS officially named Mayer Hall a historic site in 2021, the celebration was postponed until now due to the pandemic.

Distinguished Professor of Physics Ivan Schuller and Shpyrko welcomed attendees before opening the day with a series of lectures on the impacts of DFT. Researchers and experts from around the world provided insight into the ways DFT continues to shape science, engineering and medicine. The talks touched on everything from materials physics and molecular dynamics to drug discovery and supercomputing.

Dean Boggs spoke about the spirit of discovery that exists in the School of Physical Sciences.

We were thrilled to welcome everyone in-person for this event, stated Dean of the School of Physical Sciences Steven E. Boggs. More than just background on DFT itself, these talks highlighted the spirit of discovery that is still present on our campus. The School of Physical Sciences has lived at the heart of that spirit since the universitys founding.

After the lectures and a panel discussion, the university held a dedication ceremony and plaque unveiling. From APS, President Jon Bagger and former President Jim Gates commented on how meaningful the designation was and the continuing importance of DFT.

UC San Diegos Executive Vice Chancellor Elizabeth H. Simmons noted that the groundbreaking work of Kohn, Sham and colleague Pierre Hohenberg was only one example of the extraordinary talent found in the School of Physical Sciences.

The efforts of faculty like Kohn, Sham, Mayer, Roger Tsien, Sally Ride, Harold Urey and others are testament to our universitys remarkable history as a community of visionaries who push boundaries and break barriers to change the world, she said. Their transformative impacts across academic disciplines and in the lives of student and faculty colleagues will continue to reverberate into the future.

Excerpt from:

Honoring a UC San Diego Landmark and Its Lasting Impact on Physics - University of California San Diego

Sabine Hossenfelder is a theoretical physicist and creator of the popular YouTube series Science Without the Gobbledygook. In her new book Existential Physics, she argues that some of her colleagues may have gotten a little too excited about wild ideas like multiverse theory or the simulation hypothesis.

If you want to discuss them on the level of philosophy, or maybe over a glass of wine with dinner because its fun to talk about, thats all fine with me, Hossenfelder says in Episode 525 of the Geeks Guide to the Galaxy podcast. I have a problem if they argue that its based on a scientific argument, which is not the case.

Multiverse theory states that an infinite number of alternate universes are constantly branching off from our own. Hossenfelder says its possible to create mathematical models that are consistent with multiverse theory, but that doesnt necessarily tell you anything about reality. I know quite a lot of cosmologists and astrophysicists who actually believe that other universes are real, and I think its a misunderstanding of how much mathematics can actually do for us, she says. There are certainly some people who have been pushing this line a little bit too farprobably deliberately, because it sellsbut I think for most of them theyre genuinely confused.

Hossenfelder is also skeptical of the simulation hypothesis, the idea that were living in a computer simulation. Its an idea thats been taken increasingly seriously by scientists and philosophers, but Hossenfelder says it really amounts to nothing more than a sort of techno-religion. If people go and spit out numbers like, I think theres a 50 percent chance were living in a simulation, Im not having it, she says. As a physicist who has to think about how you actually simulate the reality that we observe on a computer, Im telling you its not easy, and its not a problem that you can just sweep under the rug.

While theres currently no scientific evidence for multiverse theory or the simulation hypothesis, Hossenfelder says there are still plenty of cool ideas, including weather control, faster-than-light communication, and creating new universes, that dont contradict known science. This is exactly what I was hoping to achieve with the book, she says. I was trying to say, Physics isnt just something that tells you stuff that you cant do. It sometimes opens your mind to new things that we might possibly one day be able to do.'

Listen to the complete interview with Sabine Hossenfelder in Episode 525 of Geeks Guide to the Galaxy (above). And check out some highlights from the discussion below.

Sabine Hossenfelder on entropy:

Entropy is a very anthropomorphic quantity. The way its typically phrased is that entropy tells you something about the decrease of order or the increase of disorder, but this is really from our perspectivewhat we think is disorderly. I think that if you were not to use this human-centric notion of order and disorder, you would get a completely different notion of entropy, which brings up the question, Why is any one of them more tenable than any other? Theres just too much that we dont really understand about space and timeand entropy in particular, gravity, and so onto definitely make the statement. I dont think the second law of thermodynamics is as fundamental as a lot of physicists think it is.

Sabine Hossenfelder on creating a universe:

There is nothing in principle that would prevent us from creating a universe. When I talked about this the first time, people thought I was kidding, because Im kind of known to always say, No, this is bullshit. You cant do it. But in this case, its actually correct. I think the reason people get confused about it is, naively, it seems you would need a huge amount of mass or energy to create a universe, because where does all the stuff come from? And this just isnt necessary in Einsteins theory of general relativity. The reason is that if you have an expanding spacetime, it basically creates its own energy. How much mass youd need to create a new universe turns out to be something like 10 kilograms. So thats not all that much, except that you have to bring those 10 kilograms into a state that is very similar to the conditions in the early universe, which means you have to heat it up to dramatically high temperatures, which we just currently cant do.

Sabine Hossenfelder on faster-than-light communication:

I think that physicists are a little bit too fast to throw out faster-than-light communication, because theres a lot that we dont understand about locality. Im not a big fan of big wormholes, where you can go in one end and come out on the other end, but if spacetime has some kind of quantum structureand pretty much all physicists I know believe that it doesits quite conceivable that it would not respect the notion of locality that we enjoy in the macroscopic world. So on this microscopic quantum level, when youre taking into account the quantum properties of space and time, distance may just completely lose meaning. I find it quite conceivably possible that this will allow us to send information faster than light.

Sabine Hossenfelder on community:

When I was at the Perimeter Institute in Canada, they had a weekly public lecture. It was on the weekendso a time when people could actually come, not during work hoursand afterward there was a brunch that everyone would have together, and I know that the people who would attend those lectures would go there regularly, and they would appreciate the opportunity to just sit together and talk with other people who were interested in the same things. This is something that I think scientists take for granted. We have all our friends and colleagues that we talk to about the stuff that were interested in, but its not the case for everybody else. Some people are interested in, I dont know, quantum mechanics, and maybe they dont know anyone else whos interested in quantum mechanics. To some extent there are online communities that fulfill this task now, but of course its still better to actually meet with people in person.

Continued here:

Have Some Scientists Gotten Too Excited About the Multiverse? - WIRED

By Dalian Institute of Chemical Physics, Chinese Academy SciencesSeptember 9, 2022

Lattice distortion in lead halide perovskite quantum dots leads to a fine structure gap and coherent exciton quantum beating. Credit: DICP

Scientists just reported the utilization of lattice distortion in lead halide perovskite quantum dots to control their exciton fine structure. The researchers were led by Prof. Kaifeng Wu from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS), in collaboration with Dr. Peter C. Sercel from the Center for Hybrid Organic Inorganic Semiconductors for Energy (CHOISE). CHOISE is an Energy Frontier Research Center (EFRC) of the U.S. Department of Energys Office of Science.

The study was published in Nature Materials on September 8, 2022.

It is well established that shape or crystal anisotropy in quantum dots, which are tiny semiconductor nanoparticles, results in energy splitting of their optically bright excitons (bound electron-hole pairs). This is known as fine structure splitting (FSS). These excitons form an important playground for quantum information science researchers. For instance, the excitons FSS can be exploited for coherent control of quantum states for quantum computing, or for polarization-entangled photon pairs in quantum optics, although for the latter it is important to suppress the magnitude of splitting.

Traditionally, studying FSS usually requires a single or just a few quantum dots at liquid-helium temperature, because of its sensitivity to quantum dot size and shape. Measuring FSS at an ensemble level, let alone controlling it, appears impossible unless all the dots are made to be nearly identical.

In this study, by using ensemble-level femtosecond polarized transient absorption, the scientists observed clear bright-exciton FSS in solution-processed CsPbI3 perovskite quantum dots, which is manifested as exciton quantum beats (periodic oscillations of kinetic traces).

Even more amazingly, the beat frequency, as determined by the FSS energy, of a given sample can be continuously controlled by changing the temperature. This is an unprecedented result, meaning that now scientists can facilely control FSS through temperature, said Prof. Wu.

The researchers also discovered that the temperature-dependent FSS was related to the interesting, highly-dynamic lattice of lead halide perovskites. Lowering the temperature led to a more distorted lead-iodide octahedral framework.

Calculations suggested that, because these orthorhombic-phase quantum dots were actually still bounded by the pseudocubic family of crystal planes, the lattice distortion results in an avoided crossing fine-structure gap between bright exciton. This gap was responsible for the observed FSS, and it could be detected in spite of quantum dot size and shape heterogeneity across an ensemble sample.

Lattice distortion in CsPbI3 perovskites is well known in the photovoltaic community, as it is connected to the issue of phase stability of perovskite solar cells, but nobody has previously connected it experimentally to the exciton fine structure, said Prof. Wu. Our study demonstrates that this material property can actually be harnessed to control the bright-exciton splitting in quantum dots for quantum information technologies.

Reference: Lattice distortion inducing exciton splitting and coherent quantum beating in CsPbI3 perovskite quantum dots by Yaoyao Han, Wenfei Liang, Xuyang Lin, Yulu Li, Fengke Sun, Fan Zhang, Peter C. Sercel and Kaifeng Wu, 8 September 2022, Nature Materials.DOI: 10.1038/s41563-022-01349-4

Link:

Coherent Quantum Beating Induced by Lattice Distortion of Perovskite Quantum Dots - SciTechDaily

This transcript has been edited for clarity.

Eric J. Topol, MD: Hello. This is Eric Topol for Medscape. I'm with my co-host Abraham Verghese for a new edition of Medicine and the Machine. We have an extraordinary guest today, Professor Christina Pagel. She is a force a professor at University College London with an extraordinary background in math, physics, and even interplanetary space. We've never had a guest with such a diverse background. Welcome, Christina.

Christina Pagel, PhD: Thank you.

Topol: You've provided extraordinary insights throughout the pandemic. But before we get into that, you've had a unique background as a physicist and mathematician. Then, somewhere along the way, after this great training you had in the United Kingdom, you went to Boston and made a switch in your career to using math and artificial intelligence (AI) to help inform data for health. How did that come about?

Pagel: I originally studied maths at university because I wanted to be a theoretical physicist. That was my aim. I always knew the kind of maths you need to do that. Then I earned a master's in quantum theory. But by then, all the bits of quantum theory that I really liked turned out to be solved.

I asked, can I do a PhD in this? And they said no, it's been done; Feynman did it all 30 years ago. So then I thought, I'd also really like to go into space and be an astronaut. I spoke to the European Space Agency, and they said, you need to do a PhD in space physics, which I'd never heard of. But I went to Imperial College London and asked, can I do a PhD in this? And they said yes. One of the benefits of doing maths is that it's actually quite easy to switch fields. So I did my PhD in interplanetary magnetic fields. And then I came to Boston University for 3 years as a postdoctoral researcher working on interplanetary electrons.

It was an amazing 3 years. But I realized two things: First, I was quite good at math but I wasn't a great physicist. Much to my disappointment, I just didn't have a feel for it in the way that some people have. And second, what I was working on, although it was kind of cool, it didn't matter. If I got it wrong, it didn't make a difference. And I wanted to feel that my work was doing that; I wanted to feel that I was contributing more to society than paying my taxes and not committing crimes.

I was looking around, thinking, what can I do? And I found this department at University College London, where they were applying mathematics to healthcare. I could see that some people there had a physics background. I thought it sounded really interesting. I've been there ever since.

Abraham Verghese: Dr Pagel, it's a great pleasure to meet you. Most of us are so narrowly specialized that we need people like you to grasp the entirety of what's going on in this world. Before we get to COVID, I know you also have a master's in medieval history and I'm sure there's a story behind that.

Pagel: Actually, I have two master's degrees in history. I have one in classical civilization, primarily the ancient Greeks and Romans, and then I went back and I did another in medieval history.

When I was 16, I had to choose between an arts or a science path. I loved both history and science. I picked science, but I never lost my love for history. It was the first time I'd chosen to do a course purely for interest. It had no impact on my career. I was doing it only for myself. It takes you back to the meaning of learning, I think, of trying to understand and find out things, and it's just so interesting.

I realized that having a mathematical background makes you quite good at history. It teaches you to look for what's not there as well as what's there, and helps you create logical arguments and understand that causation isn't correlation, which, I think, is important in history.

Verghese: I believe that it's relevant to COVID and everything you're engaged in. Santayana said that if we don't understand history, we're condemned to repeat it. And I think we're seeing a lot of that now.

Topol: By the way, if you don't follow @chrischirp, then you're missing out in terms of COVID she is a go-to for information and perspective. Before the pandemic started, you were and still are involved in work to understand congenital heart disease, and cardiac surgery in children and adults, and I suspect much more than that.

As a cardiologist, I cue into that stuff. Can you tell us about what that work has been like and how that was a background for some things you're doing now?

Pagel: I've been working on congenital heart disease for almost 15 years. It all starts with two facts about the United Kingdom. The first is that we have a national healthcare system, which means that you can organize things at a national scale. The second is that in 1997, there was the Bristol heart scandal. One of the hospitals where heart surgery was performed in babies had much higher than expected mortality rates when compared with other units that were doing the same kinds of operations.

That took a long time to come to light because it's a high-risk, highly specialized area, so you expect, unfortunately, that some children will die. Then you have this whole question of, how many is too many? What does "expected" even mean when you have this group of children who have such diverse health problems and diagnoses, and all these diverse procedures performed on them?

After that came to light, the National Health Service (NHS) decided to centralize the service, so only about 10-12 hospitals offer it. They did that because they wanted to ensure that there are enough operations happening every year in each of those hospitals. And they made it mandatory for everyone to submit their data.

It gets audited. The data are checked. Every year, they publish survival statistics on the grounds that we don't want this to happen again. That's been going on since 2000, and it has meant that congenital heart disease services are one of the best areas, with a long-standing dataset.

Over the years, we've refined the risk models for deciding how risky these surgeries are for different children. How do we know whether some of the units have higher death rates than average? We can show that, since they've started monitoring, results have gotten better pretty much every single year.

Now that the field has come along, we're looking at what other things matter. It's not just about survival. It's about complications, quality of life. How many surgeries do you need over your lifetime? What happens in outpatients? How are people engaging with it? What happens as children become adults?

So we're using these national datasets to really dig into it. It requires quite a lot of careful statistics and data, but also talking to clinicians, talking to patients, talking to parents. We've also built websites trying to explain what the data are and aren't showing. That's how I started thinking about how we present information that matters to people in a way that they find easy to understand and that's fair.

Verghese: Regarding your work in operational research, I'm wondering, is that a common department now in many universities? What is the day-to-day life of an operational researcher like?

Pagel: So few people know what operational research is. It's technically a branch of mathematics, but it can sit in lots of different places. In the United States, it's often called operations research. It's also called systems engineering, and then it sits within engineering faculties. It can also be called management science and is taught as part of an MBA. So it runs this whole gamut of different subjects and techniques. But at its core, you want to use mathematics and data and any kind of other analytical techniques to improve decision-making. That's the idea.

It's meant to be pragmatic, focused on working with people to understand the actual problem they have. The problem often is not what people say it is. It asks, what information do you have, and how can you use that to improve the decisions you're about to make?

That is the core of it. There are standard techniques such as optimization, queueing theory, mathematical modeling or simulation. But the heart of operational research is trying to improve things, and the techniques you use actually aren't part of it. It's just that certain techniques are more common than others.

Topol: That gets us into the pandemic, because this provides a unique background fresh eyes, transdisciplinary experience, and an intergalactic way to understanding health systems.

We are in the third year of the pandemic. You've been a leading light, a spokesperson for your views and data interpretation, not just in the United Kingdom but throughout the world. Can you give us an overview? Obviously, it hasn't gone well in many respects. What are your key takeaways and concerns? Where do you see the United Kingdom as an outlier, if at all, or different from other places like the United States, which is perhaps even worse?

Pagel: A few things stand out in the big picture. Right at the beginning, the rich Western countries weren't prepared. I believe we thought we were, and there was an element of complacency that we knew what to do.

We have the world's leading health systems, so of course we'll be fine. And that wasn't the case. As societies become more medicalized vaccinations, treatments, healthier lives we've become used to a growing life expectancy, not as many infectious diseases, and not as many ubiquitous public health problems.

We became quite complacent about what an infectious disease can do to a population. We had let our public health functions lapse. Certainly, in the United Kingdom, there wasn't that much public health expertise. The public health bodies are much smaller than they used to be, and people just weren't ready. Whereas some of the middle- and lower-income countries that have strong public health systems that are trying to deliver large-scale vaccination and nutrition programs, they had a much better set-up to do things like contact tracing and supporting people who were ill, to think about how to mobilize a population response.

The other thing that struck me was how unwilling the West was to learn from other countries particularly the East Asian countries, places like South Korea, Taiwan, and Japan. We just felt they had nothing to teach us. I think that was a big mistake, and I think that's still the case today.

People talk about the inevitability of COVID. You only have to look at those countries to see how it wasn't inevitable. We have these quite lazy stereotypes we say that wouldn't work over here because they're different over there. Well, how do you know? What did make those countries quite different is that a lot of them had experienced SARS, and they learned from that and applied that knowledge to this new pandemic.

What worries me is that we're not trying to learn from COVID and apply it to a new pandemic.

Another thing that struck me is that you can understand the panic and the mistakes that happened in the first wave in March 2020. But by the time the Alpha wave hit in late 2020, early 2021, it felt like not that much had been learned. We didn't mitigate it, particularly factors around transmission and about it being airborne. By the summer of 2020, it was reasonably clear that it could spread through the air. It was clear that masks helped. It was clear that ventilation helped. It was clear that outside conditions were much safer than inside. But little effort was made to improve indoor air quality. To this day, I do not understand that, because good air quality comes with so many more public health benefits, beyond COVID. Clean indoor air is in the public good, along the same lines as clean water. I can't understand why we've never prioritized it.

Verghese: You were prescient about the shape of the BA.5 variant and how that might look a couple of months before we saw it. What does your crystal ball show of what we can expect in the United Kingdom and the United States in terms of variants that have not yet emerged?

Pagel: The other thing that strikes me is that people still haven't understood exponential growth 2.5 years in. With the BA.5 or BA.3 before it, or the first Omicron before that, people say, oh, how did you know? Well, it was doubling every week, and I projected forward. Then in 8 weeks, it's dominant.

It's not that hard. It's just that people don't believe it. Somehow people think, oh, well, it can't happen. But what exactly is going to stop it? You have to have a mechanism to stop exponential growth at the moment when enough people have immunity. The moment doesn't last very long, and then you get these repeated waves.

You have to have a mechanism that will stop it evolving, and I don't see that. We're not doing anything different to what we were doing a year ago or 6 months ago. So yes, it's still evolving. There are still new variants shooting up all the time.

At the moment, none of these look devastating; we probably have at least 6 weeks' breathing space. But another variant will come because I can't see that we're doing anything to stop it.

Topol: One word you have used is "complacency," which we still have a lot of a heavy dose of complacency. The other sentiment you're invoking by the unwillingness to accept exponential growth is denialism. There's a lot of that.

Long COVID is another area of concern. It's a softer endpoint than death and hospitalizations, but nonetheless, it's much more prevalent and real. But there's still a lot of denialism. Can you talk about long COVID?

Pagel: Long COVID is interesting because it took a long time for people to accept that it existed at all. And it still is dismissed and ignored.

Vaccination has not made long COVID go away to the same extent that vaccination has massively reduced the number of deaths and of severe, acute illnesses. A recent paper in JAMA showed that vaccination reduced the incidence of long COVID in healthcare workers by up to two thirds. So it helps, but it certainly doesn't make it go away.

What worries me just as much as long COVID are the longer-term problems that are becoming evident through the great work by the Veterans Administration, looking at 1-year and longer follow-up of people who've had COVID and showing elevated levels of organ dysfunction, pretty much anywhere you look.

That's the other thing about complacency: People want to fit COVID into a box they can understand. But this is a brand-new disease, and we don't understand it. As with the pandemic flu in 1918, it's thought to have been associated with a wave of Parkinson's disease about 10-15 years later.

We have no idea whats ahead of us. To me, this idea that we can live with widespread transmission is betting the future on thinking that we understand it, but there's no particular evidence that we do, even with all the new evidence showing longer-term issues with COVID, whether that's long COVID or other kinds of organ problems.

Verghese: One thing that strikes me is that we're not talking enough about indoor air and the difference it makes, and about long COVID in the sense that if the public really knew how fearful we are, perhaps it would change behavior.

From your perspective as someone with a deep understanding of history, this is not new, this disjunction between what we know would help and the public's willingness to accept it, and political opportunism. What can we do differently from what they did in the era of Camus' The Plague, for example? What can we do to impact the science ignorance that hurts us?

Pagel: I wish I knew. The thing about cleaner indoor air is that it works on any variant and any airborne disease; it helps against pollution; it helps against all kinds of things. And it doesn't take away anyone's freedoms.

What I find difficult is that people in the "COVID isn't a problem" spectrum still don't seem to be pro-ventilation. I just cannot understand why, because it doesn't impact anybody's choices for living their lives. All it does is make people slightly healthier and mitigate some harm. So, I can't quite see why we wouldn't do that. The various studies, and there have been many, showed that it's extremely cost-effective.

One of the issues is that a lot of the experts in ventilation are not doctors or clinical experts. They're engineers, architects, chemists, and physicists. They're coming from a different evidential paradigm, if you like. So you get these calls for trials of ventilation. And these nonclinical experts say, because we understand the physics, we know these things work.

It's quite a clash of cultures along those lines that is an issue. People see the pandemic and think the solution has to be medical when the solution is actually engineering. It doesn't fit into how governments prime themselves to respond.

Also, now that most people have had COVID and have recovered from COVID, including me I've had it twice now when people tell you this is a massive issue, it's easy to think, well, but I'm fine.

It's hard to overcome that and explain that you're fine now, but you don't know what the long-term implications are. Is it a question of getting COVID three times in 5 or 6 years? Or getting it twice a year? That can make quite a difference on your health. And do you really want to be taking a week to 10 days off work every single year from COVID? Can you add that to the amount of illness you were suffering before? So there's a strong economic argument for it as well.

Maybe we have to start making these arguments, because it is a different situation now. We're not in the situation we were 2.5 years ago. I think sometimes people believe that when you say anything about controlling COVID, they think you're arguing for lockdowns or something else, when it's not about that.

It's about how we maintain our economy and our quality of life and our health in a way that allows us all to enjoy our lives the way that we want to.

Topol: You are on the SAGE committee. Tell us about how that group reviews science and makes recommendations to your government.

Pagel: There's a bit of a misunderstanding there. SAGE is the Scientific Advisory Group for Emergencies, which is the government's group of experts that does advise on the pandemic, and it was disbanded in March. At some point, probably hundreds of people contributed to that.

There is also a group, which I belong to, called Independent SAGE. That was launched in May 2020 specifically because at the beginning of the pandemic, membership of SAGE, which was advising the government, and all of the minutes of the decision-making were secret. So we had the government saying, we're making decisions based on the science, but we had no idea what that science was. Independent SAGE was formed to bring some of those discussions into the public. Then, SAGE started making their minutes public.

The government used to hold daily press briefings on COVID. They stopped in June 2020. Although the United Kingdom has published lots of data we have strong national data surveillance it's not necessarily published in a particularly friendly form for nonexperts. So what Independent SAGE has been doing is holding weekly online briefings.

I've done a lot of this as well, where I try to collate all of the data that are out there and explain what's happening right now and what it means. We've evolved into being a bit more of a public-facing science body, where we're trying to explain and interpret what's happening for the public. We take public questions and focus on particular issues such as schools or inequality; we've talked about long COVID a lot, and children.

Topol: I wish we had something like this. Right, Abraham?

Verghese: Indeed. But I must say, both of you are doing a great job of explaining the intricacies of the data to the rest of us. It's just that people with fixed mindsets can easily tune out the most obvious facts.

Pagel: I rely on Eric, especially for the literature filtering. It's incredible how you read the papers and then condense them so I can understand them. I'm not an expert in a lot of the science.

I go to my expert friends and say, you're going to have to tell me what this abstract means because I do not understand biology. Then they explain it, and I say, so is this right? And they say yes or no. Unfortunately, on academic Twitter, there are a lot of people who are amazing scientists but cannot understand how much knowledge they have that other people don't have. So I read these long Twitter threads, but I don't understand them.

Or there are people who are very much into performative cleverness. You would think that their job as an academic is to show how clever they are. Their information is not useful. I always try to provide source data and to make sure I'm not excluding people from that knowledge.

Topol: That gets to the dissemination of the information. What is so important about your background is you are into the hard data and evidence, and the interpretation of that the analytics, if you will. Then you go to social media and you get into the cesspool of toxic responses.

By putting a lot of time into trying to help, you get this ridiculous backlash of people who are just there to cause insult and trouble. How do you deal with that? Every day I wonder, what the hell am I doing? There's so much negativism. You're trying to help, and you're putting in the effort and time, and look what you get. Of course, a lot of people appreciate that. But I'm sure you're subject to similar issues.

Pagel: It's gotten a lot easier over time for me, and I imagine for you. Certainly, once you get to a certain number of followers, there's no way you can read all the comments. In fact, mostly, I don't read them.

It means that Twitter stops being a conversation. It becomes more of a broadcast medium. You lose something from that, but at the same time, you can't get too worried about what random people are saying. Right at the beginning, one of my friends who already had a large following he's in politics told me to never, ever engage in Twitter arguments. You will always regret it, and they'll never work. I mainly followed his advice. A couple of times when I didn't, I regretted it, and I still regret it because those conversations are still used against me now.

Never get engaged. If you do, always pretend that the person means well. A lot of people are doing it in bad faith, but if you respond as if they aren't, there's not that much that people do. Also, you have good mute settings.

For the first year, I didn't block anyone on Twitter. That changed when I read more about how Twitter works, and how people see tweets, and how they get amplified. I had a few quite high profile, quite horrible commentators on Twitter throwing pile-ons on me, people with a million followers calling me certifiable and saying I should be in prison. If you block them, their followers can't see it and you just stop it. Someone told me to think of it as if you're walking down the street and someone starts shouting at you. You don't have to listen to it. You have a right to walk away from it.

Now I have quite a low threshold for blocking people because if they're clearly not trying to engage or be helpful and are just shouting at me, I don't have to listen to it. I've never taken it that personally because these people don't know me.

It's been a hard pandemic. People are angry and upset for all kinds of reasons. I get that. I find it much harder when other scientists are attacking me, maybe more politely. I find that harder because they're my peers, and they're basically trying to damage my reputation.

Verghese: I see a lot of undergraduates at Stanford very narrowly focused on computer science, which is the flavor du jour right now. Your career is a wonderful testament to the importance of a broad perspective, not just math but astronomy and history. I think we're going to need more of your kind of educated people for the complexity of what we're dealing with, and it's not going to be possible otherwise to have civilized conversations.

Pagel: A lot of the time, I end up feeling like a complete idiot. I'm not this super-specialized person. And I've always got my mom, as well, telling me, why is it they are listening to you, Christina? Haven't you said it all already?

Topol: I had the privilege of doing an NHS review just before the pandemic in 2018 or 2019. And I was struck by the strong data-driven culture of the team I got to work with.

I saw it during the pandemic with the UK Health Security Agency Office for National Statistics (ONS) reports that would come out every week, and the Intensive Care National Audit and Research Centre (ICNARC) reports of all the ICU admissions, which we don't have here in the United States. Just extraordinary. And then the government just gave up on all this stuff. It seems premature. They were leading the world. We were all learning every day, every week from the United Kingdom because the data were extraordinary. Can you comment about that?

Pagel: Its sad because I think you're right. One area in which the UK has been leading the world is in surveillance, particularly random testing surveillance, which the ONS is still doing, and also the Imperial REACT study, which, unfortunately, was not funded and ended in April this year. I do think it's short sighted.

Some national data collections, like ICNARC, existed before the pandemic and it exists now. It routinely collects data on every single intensive care admission of adults in England and publishes reports on it; the same with pediatric-intensive care; the same with every hospital admission. We have those data. What happened during the pandemic is that they quickly added extra information relevant to COVID. Within days to weeks, they started collating it, so that capability is still there.

Our surveillance has been so good that it's often felt that we were watching and reporting on the pandemic incredibly carefully, but not actually acting on any of the information that it was showing. So in that sense, we have a very sensitive system that's not informing any decisions.

I'm guessing that's what prompted it closing down. If we're not going to do anything different, why are we measuring it? I hope that the ONS Infection Survey, which measures prevalence in a random subgroup of tens of thousands of people every week, carries on because that's the only thing we've got now. And it's one of the only global measures of national long COVID rates as well.

Topol: I also want to ask about your sense of the field of artificial intelligence (AI) in healthcare. You obviously have the grounding with all aspects of machine learning and the complexities of health data, which is not just from health records but all the different layers of data sensors, genomics, and the microbiome. There are lots of different datasets. Where do you see AI? In your view what can it do to improve healthcare in the future?

Pagel: I believe that it can do both more and not as much as what people think. People sometimes see it as this great savior. It isn't. Sometimes what you need is enough nurses and equipment and just old-fashioned doctoring. AI is never going to give you that. AI is incredibly good at taking complex data and using them to understand what's happening, but only if the data contain what is happening.

It's good at things like imaging. The only place where AI is commonly used in the NHS is for things like imaging. If we're looking at scans and you want to assess a tumor or a difference in a tumor, then it's very good at pattern recognition. That's what it's built for. In a sense, all the information is contained in that image.

AI is less good at routine healthcare, which is messy and dirty and subject to lots of biases as to who put it in, at what time, in which place. How has that changed over time? What is that actually telling you about the patient or the system? There it isn't as good. Also, the information of what's in there doesn't necessarily tell you about the future, which is what people are trying to use it for.

We can't predict, say, occupancy in a year's time because what's going to cause occupancy in a year's time is not contained in those data. And AI can't make that happen for me. So sometimes you have to realize there are limitations to what it can do. I believe that some important areas where it could still help more are in things like physiologic time-series data.

We're doing a project on that now, with incredibly complex data. Patients in ICUs have measurements taken multiple times per second for days on end, but we still don't understand that much about how patients get better when they're severely ill. You can see a situation there where AI could help with spotting early deterioration or spotting when patients are ready to leave the ICU, all kinds of other things.

As it turns out, when I'm working with the AI specialists on time series, it just adds a whole extra level of complexity and makes a lot of the normal ways of doing things not work because your assumptions are robbed of independence. Everything is correlated, so it becomes really difficult. But it could become a big thing.

Topol: We've enjoyed this conversation so much. The contributions you've made in the past few years, beyond everything else in your career, Christina, have been what I consider a positive outlier, even momentous.

We've all learned from you, and we're lucky to have someone of your background to be a leading force. We'll keep following you well beyond the pandemic for things that you're going to do to help healthcare. We're glad you switched from physics to healthcare. It's already made a big difference. And it's going to make even more difference in the decades ahead. Thanks so much for joining us today.

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We Are Failing to Use What We've Learned About COVID - Medscape

An ultracompact circularly polarized light source is crucial component for the applications of classical and quantum optics information processing. The development of this field relies on the advances of two fields, i.e., quantum materials and chiral optical cavities. Conventional approaches for circularly polarized photoluminescence suffer from incoherent broadband emission, limited DOP, and large radiating angles.

Their practical applications are constrained by low efficiency and energy waste to undesired handedness and emission directions. The chiral microlasers can have large DOPs and directional output, but only in specific power ranges. Most importantly, their subthreshold performances plummet significantly. Up to now, the strategy for simultaneous control of chiral spontaneous emission and chiral lasing is still absent.

In a new paper published inScience, researchers from Harbin Institute of Technology and Australian National University employ the physics of chiral quasi bound states in the continuum (BICs) and demonstrate the efficient and controllable emission of circularly polarized light from resonant metasurfaces.

BICs with integer topological charge in momentum space and theoretically infinity Q factor have been explored for many applications including nonlinear optics and lasing. By introducing in-plane asymmetry, BICs turn to be quasi-BICs with finite but still high Q factors. Interestingly, the integer topological charge of BICs mode would split into two half integer charges, which symmetrically distribute in momentum space and correspond to left- and right-handed circular polarization states, also known as C points.

At the C points, incident light with one circular polarization state can be coupled into the nanostructures and produce dramatically enhanced local electromagnetic fields. The other polarization state is decoupled and almost perfectly transmit. Such characteristics are well known but rarely applied to light emissions. "This is mainly because the C points usually deviate from the bottom of band. They have relatively low Q factor and cannot be excited for lasing actions," says Zhang.

To realize the chiral light emission, a key step is to combine the local density of states with the intrinsic chirality at C points. If one C point is shifted to the bottom of the band, the Q factor of the corresponding chiral quasi-BIC can be maximal. According to the Fermi's golden rule, the radiation rate of one circularly polarized spontaneous emission is enhanced, whereas the other polarization is inhibited. Both the Q factor and the radiation rate reduces dramatically with the emission angle.

As a result, high-purity and highly directional light emission can be expected near the point. "Of course, the other C point can support similar high chirality with opposite handedness. However, that point also deviates from the maximal Q factor and less be enhanced. Therefore, our metasurface only produces one near unity circular polarization with high directionality around the normal direction," says Zhang.

The control of C points in momentum space closely relates to the maximization of chirality in normal direction. In principle, the realization of chirality relates to the simultaneous breaking of in-plane and out-of-plane mirror reflection symmetries. In this research, the researchers have introduced an out-of-plane asymmetry, the tilt of nanostructures. For an in-plane asymmetry, there is one out-of-plane asymmetry that can move one C point to point. "We find two types of asymmetries are linearly dependent on one another. This makes the optimization of chirality in normal direction very easy" says Zhang.

In experiment, the researchers have fabricated the metasurfaces with one-step slanted reactive ion etching process and characterized the emissions. Under the excitation of a nanosecond laser, they have successfully demonstrated the chiral emissions with a DOP of 0.98 and a far field divergent angle of 1.06 degree. "Our circularly light source is realized with the control of C point in momentum space and local density of state. It is independent of the excitation power," say Zhang, "this is the reason that we can achieve the high Q, high directionality, and high purity circular polarization emission from spontaneous emission to lasing."

Compared with conventional approaches, the chiral quasi-BIC provides a way to simultaneously modify and control spectra, radiation patterns, and spin angular momentum of photoluminescence and lasing without any spin injection. This approach may improve the design of current sources of chiral light and boost their applications in photonic and quantum systems.

Source:http://en.hit.edu.cn/

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Researchers Employ the Physics of Chiral Quasi Bound States in the Continuum - AZoQuantum