A powerful new idea about how the laws of physics work could bring breakthroughs on everything from quantum gravity to consciousness, says researcher Chiara Marletto

By Chiara Marletto

Manshen Lo

QUANTUM supremacy is a phrase that has been in the news a lot lately. Several labs worldwide have already claimed to have reached this milestone, at which computers exploiting the wondrous features of the quantum world solve a problem faster than a conventional classical computer feasibly could. Although we arent quite there yet, a general-purpose universal quantum computer seems closer than ever a revolutionary development for how we communicate and encrypt data, for virtual reality, artificial intelligence and much more.

These prospects excite me as a theoretical physicist too, but my colleagues and I are captivated by an even bigger picture. The quantum theory of computation originated as a way to deepen our understanding of quantum theory, our fundamental theory of physical reality. By applying the principles we have learned more broadly, we think we are beginning to see the outline of a radical new way to construct laws of nature.

It means abandoning the idea of physics as the science of whats actually happening, and embracing it as the science of what might or might not happen. This science of can and cant could help us tackle some of the big questions that conventional physics has tried and failed to get to grips with, from delivering an exact, unifying theory of thermodynamics and information to getting round conceptual barriers that stop us merging quantum theory with general relativity, Einsteins theory of gravity. It might go even further and help us to understand how intelligent thought works, and kick-start a technological revolution that would make quantum supremacy look modest by comparison.

Since the dawn of modern physics in

Originally posted here:

Quantum computers are revealing an unexpected new theory of reality - New Scientist

The Muon g-2 electromagnet at Fermilab, ready to receive a beam of muon particles. This experiment ... [+] began in 2017 and will take data for a total of 3 years, reducing the uncertainties significantly. While a total of 5-sigma significance may be reached, the theoretical calculations must account for every effect and interaction of matter that's possible in order to ensure we're measuring a robust difference between theory and experiment.

In early April, 2021, the experimental physics community announced an enormous victory: they had measured the muons magnetic moment to unprecedented precision. With the extraordinary precision achieved by the experimental Muon g-2 collaboration, they were able to measure the spin magnetic moment of the muon not only wasn't 2, as originally predicted by Dirac, but was more precisely 2.00116592040. There's an uncertainty in the final two digits of 54, but not larger. Therefore, if the theoretical prediction differs by this measured amount by too much, there must be new physics at play: a tantalizing possibility that has justifiably excited a great many physicists.

The best theoretical prediction that we have, in fact, is more like 2.0011659182, which is significantly below the experimental measurement. Given that the experimental result strongly confirms a much earlier measurement of the same g-2 quantity for the muon by the Brookhaven E821 experiment, theres every reason to believe that the experimental result will hold up with better data and reduced errors. But the theoretical result is very much in doubt, for reasons everyone should appreciate. Lets help everyone physicists and non-physicists alike understand why.

The first Muon g-2 results from Fermilab are consistent with prior experimental results. When ... [+] combined with the earlier Brookhaven data, they reveal a significantly larger value than the Standard Model predicts. However, although the experimental data is exquisite, this interpretation of the result is not the only viable one.

The Universe, as we know it, is fundamentally quantum in nature. Quantum, as we understand it, means that things can be broken down into fundamental components that obey probabilistic, rather than deterministic, rules. Deterministic is what happens for classical objects: macroscopic particles such as rocks. If you had two closely-spaced slits and threw a small rock at it, you could take one of two approaches, both of which would be valid.

But for quantum objects, you cant do either of those. You could only compute a probability distribution for the various outcomes that could have occurred. You can either compute the probabilities of where things would land, or the probability of various trajectories having occurred. Any additional measurement you attempt to make, with the goal of gathering extra information, would alter the outcome of the experiment.

Electrons exhibit wave properties as well as particle properties, and can be used to construct ... [+] images or probe particle sizes just as well as light can. This compilation shows an electron wave pattern, which cumulatively emerges after many electrons are passed through a double slit.

Thats the quantum weirdness were used to: quantum mechanics. Generalizing the laws of quantum mechanics to obey Einsteins laws of special relativity led to Diracs original prediction for the muons spin magnetic moment: that there would be a quantum mechanical multiplicative factor applied to the classical prediction, g, and that g would exactly equal 2. But, as we all now know, g doesnt exactly equal 2, but a value slightly higher than 2. In other words, when we measure the physical quantity g-2, were measuring the cumulative effects of everything that Dirac missed.

So, what did he miss?

He missed the fact that its not just the individual particles that make up the Universe that are quantum in nature, but also the fields that permeate the space between those particles must also be quantum. This enormous leap from quantum mechanics to quantum field theory enabled us to calculate deeper truths that arent illuminated by quantum mechanics at all.

Magnetic field lines, as illustrated by a bar magnet: a magnetic dipole, with a north and south pole ... [+] bound together. These permanent magnets remain magnetized even after any external magnetic fields are taken away. If you 'snap' a bar magnet in two, it won't create an isolated north and south pole, but rather two new magnets, each with their own north and south poles. Mesons 'snap' in a similar manner.

The idea of quantum field theory is simple. Yes, you still have particles that are charged in some variety:

but they dont just create fields around them based on things like their position and momentum like they did under either Newtons/Einsteins gravity or Maxwells electromagnetism.

If things like the position and momentum of each particle have an inherent quantum uncertainty associated with them, then what does that mean for the fields associated with them? It means we need a new way to think about fields: a quantum formulation. Although it took decades to get it right, a number of physicists independently figured out a successful method of performing the necessary calculations.

A visualization of QCD illustrates how particle/antiparticle pairs pop out of the quantum vacuum for ... [+] very small amounts of time as a consequence of Heisenberg uncertainty. If you have a large uncertainty in energy (E), the lifetime (t) of the particle(s) created must be very short.

What many people expected to happen although it doesnt quite work this way is that wed be able to simply to fold all the necessary quantum uncertainties into the charged particles that generate these quantum fields, and that would allow us to compute the field behavior. But that misses a crucial contribution: the fact that these quantum fields exist, and in fact permeate all of space, even where there are no charged particles giving rise to the corresponding field.

Electromagnetic fields exist even in the absence of charged particles, for instance. You can imagine waves of all different wavelengths permeating all of space, even when no other particles are present. Thats fine from a theoretical perspective, but wed want experimental proof that this description was correct. We already have it in a couple of forms.

As electromagnetic waves propagate away from a source that's surrounded by a strong magnetic field, ... [+] the polarization direction will be affected due to the magnetic field's effect on the vacuum of empty space: vacuum birefringence. By measuring the wavelength-dependent effects of polarization around neutron stars with the right properties, we can confirm the predictions of virtual particles in the quantum vacuum.

In fact, the experimental effects of quantum fields have been felt since 1947, when the Lamb-Retherford experiment demonstrated their reality. The debate is no longer over whether:

But what we do have to recognize is as in the case with many mathematical equations that we know how to write down that we cannot compute everything with the same straightforward, brute-force approach.

The way we perform these calculations in quantum electrodynamics (QED), for example, is we do whats called a perturbative expansion. We imagine what it would be like for two particles to interact like an electron and and electron, a muon and a photon, a quark and another quark, etc. and then we imagine every possible quantum field interaction that could happen atop that basic interaction.

Today, Feynman diagrams are used in calculating every fundamental interaction spanning the strong, ... [+] weak, and electromagnetic forces, including in high-energy and low-temperature/condensed conditions. The electromagnetic interactions, shown here, are all governed by a single force-carrying particle: the photon.

This is the idea of quantum field theory thats normally encapsulated by their most commonly-seen tool to represent calculational steps that must be taken: Feynman diagrams, as above. In the theory of quantum electrodynamics where charged particles interact via the exchange of photons, and those photons can then couple through any other charged particles we perform these calculations by:

Quantum electrodynamics is one of the many field theories we can write down where this approach, as we go to progressively higher loop orders in our calculations, gets more and more accurate the more we calculate. The processes at play in the muons (or electrons, or taus) spin magnetic moment have been calculated beyond five-loop order recently, and theres very little uncertainty there.

Through a herculean effort of the part of theoretical physicists, the muon magnetic moment has been ... [+] calculated up to five-loop order. The theoretical uncertainties are now at the level of just one part in two billion. This is a tremendous achievement that can only be made in the context of quantum field theory, and is heavily reliant on the fine structure constant and its applications.

The reason this strategy works so well is because electromagnetism has two important properties to it.

The combination of these factors guarantees that we can calculate the strength of any electromagnetic interaction between any two particles in the Universe more and more accurately by adding more terms to our quantum field theory calculations: by going to higher and higher loop-orders.

Electromagnetism, of course, isnt the only force that matters when it comes to Standard Model particles. Theres also the weak nuclear force, which is mediated by three force-carrying particles: the W-and-Z bosons. This is a very short-range force, but fortunately, the strength of the weak coupling is still small and the weak interactions are suppressed by large masses possessed by the W-and-Z bosons. Even though its a little more complicated, the same method of expanding to higher-order loop diagrams works for computing the weak interactions, too. (The Higgs is also similar.)

At high energies (corresponding to small distances), the strong force's interaction strength drops ... [+] to zero. At large distances, it increases rapidly. This idea is known as 'asymptotic freedom,' which has been experimentally confirmed to great precision.

But the strong nuclear force is different. Unlike all of the other Standard Model interactions, the strong force gets weaker at short distances rather than stronger: it acts like a spring rather than like gravity. We call this property asymptotic freedom: where the attractive or repulsive force between charged particles approaches zero as they approach zero distance from one another. This, coupled with the large coupling strength of the strong interaction, makes this common loop-order method wildly inappropriate for the strong interaction. The more diagrams you calculate, the less accurate you get.

This doesnt mean we have no recourse at all in making predictions for the strong interactions, but it means we have to take a different approach to our normal one. Either we can try to calculate the contributions of the particles and fields under the strong interaction non-perturbatively such as via the methods of Lattice QCD (where QCD stands for quantum chromodynamics, or the quantum field theory governing the strong force) or you can try and use the results from other experiments to estimate the strength of the strong interactions under a different scenario.

As computational power and Lattice QCD techniques have improved over time, so has the accuracy to ... [+] which various quantities about the proton, such as its component spin contribtuions, can be computed.

If what we were able to measure, from other experiments, was exactly the thing we dont know in the Muon g-2 calculation, there would be no need for theoretical uncertainties; we could just measure the unknown directly. If we didnt know a cross-section, a scattering amplitude, or a particular decay property, those are things that particle physics experiments are exquisite at determining. But for the needed strong force contributions to the spin magnetic moment of the muon, these are properties that are indirectly inferred from our measurements, not directly measured. Theres always a big danger that a systematic error is causing the mismatch between theory and observation from our current theoretical methods.

On the other hand, the Lattice QCD method is brilliant: it imagines space as a grid-like lattice in three dimensions. You put the two particles down on your lattice so that they're separated by a certain distance, and then they use a set of computational techniques to add up the contribution from all the quantum fields and particles that we have. If we could make the lattice infinitely large, and the spacing between the points on the lattice infinitely small, we'd get the exact answer for the contributions of the strong force. Of course, we only have finite computational power, so the lattice spacing can't go below a certain distance, and the size of the lattice doesn't go beyond a certain range.

There comes a point where our lattice gets large enough and the spacing gets small enough, however, that well get the right answer. Certain calculations have already yielded to Lattice QCD that havent yielded to other methods, such as the calculations of the masses of the light mesons and baryons, including the proton and neutron. After many attempts at predicting what the strong forces contributions to the g-2 measurement of the muon ought to be over the past few years, the uncertainties are finally dropping to become competitive with the experimental ones. If the latest group to perform that calculation has finally gotten it right, there is no longer a tension with the experimental results.

The R-ratio method (red) for calculating the muon's magnetic moment has led many to note the ... [+] mismatch with experiment (the 'no new physics' range). But recent improvements in Lattice QCD (green points, and particularly the top, solid green point) not only have reduced the uncertainties substantially, but favor an agreement with experiment and a disagreement with the R-ratio method.

Assuming that the experimental results from the Muon g-2 collaboration hold up and theres every reason to believe they will, including the solid agreement with the earlier Brookhaven results all eyes will turn towards the theorists. We have two different ways of calculating the expected value of the muons spin magnetic moment, where one agrees with the experimental values (within the errors) and the other does not.

Will the Lattice QCD groups all converge on the same answer, and demonstrate that not only do they know what theyre doing, but that theres no anomaly after all? Or will Lattice QCD methods reveal a disagreement with the experimental values, the same way that they presently disagree with the other theoretical method we have that presently disagrees so significantly with the experimental values we have: of using experimental inputs instead of theoretical calculations?

Its far too early to say, but until we have a resolution to this important theoretical issue, we wont know what it is thats broken: the Standard Model, or the way were presently calculating the same quantities were measuring to unparalleled precisions.

Read more from the original source:

The Big Theoretical Physics Problem At The Center Of The 'Muon g-2' Puzzle - Forbes

Albert Einstein is the genius we all know and love. He was a German theoretical physicist. He is known as one of the greatest physicists of all time and for developing the theory of relativity.

He also made important contributions to the development of the theory of quantum mechanics. He received the 1921 Nobel Prize in Physics for his services to theoretical physics and especially for his discovery of the law of photoelectric effect which was a pivotal step in the development of quantum theory.

April 18 is the death anniversary of this great man.

How did Albert Einstein die?

World-renowned physicist Albert Einstein passed away in Princeton Hospital in New Jersey on 18 April, 1955. The cause of his death was the rupture of an aneurysm, which had already been reinforced by surgery in 1948.

He refused to undergo further surgery saying, "I want to go when I want. It is tasteless to prolong life artificially. I have done my share, it is time to go. I will do it elegantly." He kept working almost to the very end, leaving the Generalized Theory of Gravitation unsolved.

He was 76 years old at the time of his death. However, his last words will forever remain unknown as they were uttered in his native German. On his deathbed, he muttered a few last words in that language and the only witness was his nurse but, unfortunately, she didn't speak the language.

Famous Quotes of Albert Einstein:

1. Imagination is more important than knowledge.

2. If you can't explain it simply, you don't understand it well enough.

3. Life is like riding a bicycle. To keep your balance you must keep moving.

4. Imagination is everything. It is the preview of life's coming attractions.

5. No problem can be solved from the same level of consciousness that created it.

Read more:

Albert Einstein Death Anniversary: How did the greatest physicists of all time die? - Free Press Journal

Every community guards a creation story, a theory of cosmic origins. In much of sub-Saharan West Africa, for the past few thousand years, itinerant storytellers known as griots have communicated these and other tales through song. Cosmologists also intone a theory of cosmic origins, known as the Big Bang, albeit through journal articles and math.

Chanda Prescod-Weinstein is a cosmologist who is adept with both equations and the keeper of a deeply human impulse to understand our universe. In her first book, The Disordered Cosmos: A Journey into Dark Matter, Spacetime, & Dreams Deferred, Prescod-Weinstein also admits she is a griot, one who knows the music of the cosmos but sings of earthbound concerns. She is an award-winning physicist, feminist, and activist who is not only, as she says, the first Jewish queer agender Black woman to become a theoretical cosmologist, she is the first Black woman ever to earn a Ph.D. in the subject.

BOOK REVIEW The Disordered Cosmos: A Journey into Dark Matter, Spacetime, & Dreams Deferred, by Chanda Prescod-Weinstein (Bold Type Books, 336 pages).

Prescod-Weinsteinis an assistant professor of physics and astronomy, and a core faculty member in the department of womens and gender studies at the University of New Hampshire. She thus enjoys a unique frame of reference from which to appraise science and her fellow scientists. She is an insider whom others nonetheless cast as an outsider, because of her identity, orientation, and the tint of her skin. From the outside, however, she admits a fuller view of her field. She perceives the structures that were invisible to people, and reveals them.

The Disordered Cosmos is equal parts critical analysis, personal essay, and popular science. It is an introspective yet revelatory book about the culture of physics and the formative years of a scientific career.

Growing up during the 1990s in East Los Angeles, where at night the dominant lights flashed red and blue, Prescod-Weinstein owned a telescope but rarely saw the stars. She was a born empiricist who decided to become a physicist at the age of 10, after her single mother took her to see the documentary A Brief History of Time. Her mother, the journalist and wage activist Margaret Prescod, continually nourished the young girls passion. She took a teenage Prescod-Weinstein to Joshua Tree National Park, where they spent a night observing the Comet Hyakutake, unblinded by city lights.

After arriving at Harvard University to study physics, Prescod-Weinstein struggled academically, in part because of her own extracurricular advocacy for providing a living wage to campus workers. Yet a classmate tried to help her realize her childhood dream. He offered her a job at a new observatory atop Maunakea in Hawaii, where the view to the heavens was among the most limpid on Earth. There she could earn better than a living wage in the astronomers efforts to gather photons particles of light that will help them tell our cosmological story.

Prescod-Weinstein imagined dedicating herself to pure physics in this idyllic locale, with beaches, amazing tans, and an opportunity to start over. But no physics is pure, no place such an idyll. Astronomers had started building their telescopes on Maunakea during the 1960s against the protests of native Hawaiians, for whom the summit is sacred. Her living wages, she realized, would have underwritten the erasure of another peoples cosmology. I promised myself that I would make more room in my life for my dreams of being a physicist, she wrote. But not like this. She now supports the native Hawaiians who have vowed to protect their unceded lands against the impending construction of the Thirty Meter Telescope, which might yet become the worlds largest.

Prescod-Weinstein not only narrates her struggle to become a cosmologist, she advocates for all peoples whom physicists have undervalued. She praises the assistants and janitors, mostly people of color, whose labor permits theorists to ponder the universe daily, because part of science is emptying the garbage. She elevates her elders, such as Elmer Imes and Ibn Sahl, whose contributions others have disregarded because these forebears were not of European descent.

The beauty of mathematics and the majesty of the stars attracted Prescod-Weinstein to cosmology. They sustain her. Yet, she writes: Learning about the mathematics of the universe could never be an escape from the earthly phenomena of racism and sexism.

So, Prescod-Weinstein unveils the majesty that oppression obscures. In the opening quarter of her book, she hurries readers through a tour of physics, rushing past Bose-Einstein condensates, axions, and inflatons to arrive at her own research into dark matter. Its a brilliant sprint, and the prize for finishers is some of her finest writing about race and science.

I promised myself that I would make more room in my life for my dreams of being a physicist, Prescod-Weinstein wrote. But not like this.

Prescod-Weinstein includes a thunderous essay about scientists historical neglect of the biophysics of melanin and the repercussions today. Later, there is a chapter that she did not want to write about an episode from her life that she did not want to share. She had no choice, she explained, because Rape is part of science and a book that tells the truth about science would be a lie if I were to leave out this chapter. Her account is so fierce and switches registers so regularly, as if gliding between chorus and verse, that the writing becomes incantatory. She saps the events power to define her, transmuting pain into affecting prose.

Prescod-Weinstein is attuned to the language of physicists, especially the biases it elides, as when her colleagues speak of colored physics, more commonly known as quantum chromodynamics, which she describes as a theory that uses color as an analogy for physical properties that have nothing to do with color. She is adept at then rephrasing physics to redress those biases. Systemic racism is compared to weak gravitational lensing, the subtle distortion of light owing to the curvature space and time around distant galaxies. Cyclical time is intuitive to a person who menstruates. The wave-particle duality reveals the queer, nonbinary nature of quantum mechanics. Dark matter is not actually dark: Its transparent more like a piece of glass than a chalkboard. Not only is the name antithetical to the science, some physicists have compared such invisible matter, crudely, to Black people.

Studying the physical world requires confronting the social world, Prescod-Weinstein writes. It means changing institutionalized science, so that our presence is natural and our cultures are respected. It also means confronting the privileged stories of science.

The demographics of physicists still reflect the iniquities of the past. And physics remains diminished because of its biases. Whenever we exclude whole peoples, we not only disallow their questions we disavow their knowledge. The field squanders other cultures perceptions of time. And as Prescod-Weinstein notes, physicists may even misinterpret the wave-particle duality and confuse the rotating identities of neutrinos because they are too oriented toward binaries.

Learning about the mathematics of the universe could never be an escape from the earthly phenomena of racism and sexism.

The Disordered Cosmos is not perfect. There are phrases that Prescod-Weinstein might have heated longer or squeezed harder until they crystalized. There are intervals when the pressure of having to cite so many ideas make matters too dense. But these are quibbles. Besides, the defects of an otherwise ideal crystal can render it more colorful and electric.

Prescod-Weinstein aspires to loftier matters. The books frontispiece is a sketch of two women who remind her that even in the worst conditions, Black women have looked up at the night sky and wondered. These women were slaves, who not only navigated the stars to freedom but also wondered at that black expanse. They are as much my intellectual ancestors as Isaac Newton is.

Prescod-Weinsteins most vital work, in the end, is the emancipation of Black and brown children who still cannot see their futures in the stars. She distills this labor in a series of questions: What are the conditions we need so that a 13-year-old Black kid and their single mom can go look at a dark night sky, away from artificial lights, and know what they are seeing? What health care structures, what food and housing security are needed?

Prescod-Weinstein teaches that all humans are made of luminous matter. And she knows just how radiant people can be, despite the obstacles in their way. She understands, intimately, that Black people hunger for a connection to scientific thought and will overcome the barriers placed in front of them in order to learn more.

Joshua Roebke is finishing a book on the social and cultural history of particle physics, titled The Invisible World. He won a Whiting Foundation Creative Nonfiction Grant and teaches literature and writing at the University of Texas at Austin.

Read the rest here:

Book Review: A Cosmologist Throws Light on a Universe of Bias - Undark Magazine

A minimal Weyl semimetal

Many compounds have now been identified as Weyl semimetals, materials with an unusual electronic band structure characterized by the so-called Weyl points. Weyl points always appear in pairs, but the solid-state materials studied so far have at least four. Wang et al. engineered a Weyl semimetallic state with the minimum number of Weyl points (two) in a gas of ultracold atoms trapped in an optical lattice (see the Perspective by Goldman and Yefsah). To do that, the researchers had to create three-dimensional spin-orbit coupling in this system. The relative simplicity of the resulting band structure will make it easier to observe the unusual effects associated with this state.

Science, this issue p. 271; see also p. 234

Weyl semimetals are three-dimensional (3D) gapless topological phases with Weyl cones in the bulk band. According to lattice theory, Weyl cones must come in pairs, with the minimum number of cones being two. A semimetal with only two Weyl cones is an ideal Weyl semimetal (IWSM). Here we report the experimental realization of an IWSM band by engineering 3D spin-orbit coupling for ultracold atoms. The topological Weyl points are clearly measured via the virtual slicing imaging technique in equilibrium and are further resolved in the quench dynamics. The realization of an IWSM band opens an avenue to investigate various exotic phenomena that are difficult to access in solids.

More:

Realization of an ideal Weyl semimetal band in a quantum gas with 3D spin-orbit coupling - Science Magazine