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Posts Tagged ‘quantum theory

“The ‘paradox’ is only a conflict between reality and your feeling of what reality ‘ought to be’”*…

John Stewart Bell (1928-1990), the Northern Irish physicist whose work sparked a quiet revolution in quantum physics

Elegant experiments with entangled light have laid bare a profound mystery at the heart of reality. Daniel Garisto explains the importance of the work done by this year’s Nobel laureates in Physics…

One of the more unsettling discoveries in the past half century is that the universe is not locally real. “Real,” meaning that objects have definite properties independent of observation—an apple can be red even when no one is looking; “local” means objects can only be influenced by their surroundings, and that any influence cannot travel faster than light. Investigations at the frontiers of quantum physics have found that these things cannot both be true. Instead, the evidence shows objects are not influenced solely by their surroundings and they may also lack definite properties prior to measurement. As Albert Einstein famously bemoaned to a friend, “Do you really believe the moon is not there when you are not looking at it?”

This is, of course, deeply contrary to our everyday experiences. To paraphrase Douglas Adams, the demise of local realism has made a lot of people very angry and been widely regarded as a bad move.

Blame for this achievement has now been laid squarely on the shoulders of three physicists: John Clauser, Alain Aspect and Anton Zeilinger. They equally split the 2022 Nobel Prize in Physics “for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science.” (“Bell inequalities” refers to the pioneering work of the Northern Irish physicist John Stewart Bell, who laid the foundations for this year’s Physics Nobel in the early 1960s.) Colleagues agreed that the trio had it coming, deserving this reckoning for overthrowing reality as we know it. “It is fantastic news. It was long overdue,” says Sandu Popescu, a quantum physicist at the University of Bristol. “Without any doubt, the prize is well-deserved.”

“The experiments beginning with the earliest one of Clauser and continuing along, show that this stuff isn’t just philosophical, it’s real—and like other real things, potentially useful,” says Charles Bennett, an eminent quantum researcher at IBM…

Quantum foundations’ journey from fringe to favor was a long one. From about 1940 until as late as 1990, the topic was often treated as philosophy at best and crackpottery at worst. Many scientific journals refused to publish papers in quantum foundations, and academic positions indulging such investigations were nearly impossible to come by…

Today, quantum information science is among the most vibrant and impactful subfields in all of physics. It links Einstein’s general theory of relativity with quantum mechanics via the still-mysterious behavior of black holes. It dictates the design and function of quantum sensors, which are increasingly being used to study everything from earthquakes to dark matter. And it clarifies the often-confusing nature of quantum entanglement, a phenomenon that is pivotal to modern materials science and that lies at the heart of quantum computing…

Eminently worth reading in full: “The Universe Is Not Locally Real, and the Physics Nobel Prize Winners Proved It,” from @dangaristo in @sciam.

Apposite: entangled particles and wormholes could be manifestations of the same phenomenon, and resolve paradoxes like information escaping a black hole: “Black Holes May Hide a Mind-Bending Secret About Our Universe.” 

Richard Feynman


As we rethink reality, we might spare a thought for Walter Brattain; he died on this date in 1987. A physicist (at Bell Labs at the time), he worked with John Bardeen and William Shockley to invent the point-contact transistor in 1947, the birth of the semiconductor– work for which the trio shared the Nobel Prize in Physics in 1956.

At college, Brattain said, he majored in physics and math because they were the only subjects he was good at. He became a solid physicist with a good understanding of theory, but his strength was in physically constructing experiments. Working with the ideas of Shockley and Bardeen, Brattain’s hands built the first transistor. Shortly, the transistor replaced the bulkier vacuum tube for many uses and was the forerunner of microminiature electronic parts.

As semiconductor technology has advanced, it has begun to incorporate quantum effects.


“‘Space-time’ – that hideous hybrid whose very hyphen looks phoney”*…

Space-time curvature [source: ESA]

Space and time seem about as basic as anything could be, even after Einstein’s theory of General Relativity threw (in) a curve. But as Steven Strogatz discusses with Sean Carroll, the reconciliation of Einstein’s work with quantum theory is seeming to suggest that space and time might actually be emergent properties of quantum reality, not fundamental parts of it…

… we’re going to be discussing the mysteries of space and time, and gravity, too. What’s so mysterious about them?

Well, it turns out they get really weird when we look at them at their deepest levels, at a super subatomic scale, where the quantum nature of gravity starts to kick in and become crucial. Of course, none of us have any direct experience with space and time and gravity at this unbelievably small scale. Up here, at the scale of everyday life, space and time seem perfectly smooth and continuous. And gravity is very well described by Isaac Newton’s classic theory, a theory that’s been around for over 300 years now.

But then, about 100 years ago, things started to get strange. Albert Einstein taught us that space and time could warp and bend like a piece of fabric. This warping of the space-time continuum is what we experience as gravity. But Einstein’s theory is mainly concerned with the largest scales of nature, the scale of stars, galaxies and the whole universe. It doesn’t really have much to say about space and time at the very smallest scales.

And that’s where the trouble really starts. Down there, nature is governed by quantum mechanics. This amazingly powerful theory has been shown to account for all the forces of nature, except gravity. When physicists try to apply quantum theory to gravity, they find that space and time become almost unrecognizable. They seem to start fluctuating wildly. It’s almost like space and time fall apart. Their smoothness breaks down completely, and that’s totally incompatible with the picture in Einstein’s theory.

s physicists try to make sense of all of this, some of them are coming to the conclusion that space and time may not be as fundamental as we always imagined. They’re starting to seem more like byproducts of something even deeper, something unfamiliar and quantum mechanical. But what could that something be?….

Find out at: “Where Do Space, Time and Gravity Come From?, ” from @stevenstrogatz and @seanmcarroll in @QuantaMagazine.

* Vladimir Nabokov


As we fumble with the fundamental, we might send far-sighted birthday greetings to Jocelyn Bell Burnell; she was born on this date in 1943. An astrophysicist, she discovered the first pulsar, while working as a post-doc, in 1957. She then discovered the next three detected pulsars.

The discovery eventually earned the Nobel Prize in Physics in 1974; however, she was not one of the prize’s recipients. The paper announcing the discovery of pulsars had five authors. Bell’s thesis supervisor Antony Hewish was listed first, Bell second. Hewish was awarded the Nobel Prize, along with the astronomer Martin Ryle.

A pulsar— or pulsating radio star– a highly magnetized, rotating neutron star that emits a beam of electromagnetic radiation. The precise periods of pulsars make them very useful tools. Observations of a pulsar in a binary neutron star system were used to  confirm (indirectly) the existence of gravitational radiation. The first extrasolar planets were discovered around a pulsar, PSR B1257+12.  And certain types of pulsars rival atomic clocks in their accuracy in keeping time.

Schematic rendering of a pulsar


Jocelyn Bell Burnell


Written by (Roughly) Daily

July 15, 2022 at 1:00 am

“Nothing in life is certain except death, taxes and the second law of thermodynamics”*…

The second law of thermodynamics– asserting that the entropy of a system increases with time– is among the most sacred in all of science, but it has always rested on 19th century arguments about probability. As Philip Ball reports, new thinking traces its true source to the flows of quantum information…

In all of physical law, there’s arguably no principle more sacrosanct than the second law of thermodynamics — the notion that entropy, a measure of disorder, will always stay the same or increase. “If someone points out to you that your pet theory of the universe is in disagreement with Maxwell’s equations — then so much the worse for Maxwell’s equations,” wrote the British astrophysicist Arthur Eddington in his 1928 book The Nature of the Physical World. “If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.” No violation of this law has ever been observed, nor is any expected.

But something about the second law troubles physicists. Some are not convinced that we understand it properly or that its foundations are firm. Although it’s called a law, it’s usually regarded as merely probabilistic: It stipulates that the outcome of any process will be the most probable one (which effectively means the outcome is inevitable given the numbers involved).

Yet physicists don’t just want descriptions of what will probably happen. “We like laws of physics to be exact,” said the physicist Chiara Marletto of the University of Oxford. Can the second law be tightened up into more than just a statement of likelihoods?

A number of independent groups appear to have done just that. They may have woven the second law out of the fundamental principles of quantum mechanics — which, some suspect, have directionality and irreversibility built into them at the deepest level. According to this view, the second law comes about not because of classical probabilities but because of quantum effects such as entanglement. It arises from the ways in which quantum systems share information, and from cornerstone quantum principles that decree what is allowed to happen and what is not. In this telling, an increase in entropy is not just the most likely outcome of change. It is a logical consequence of the most fundamental resource that we know of — the quantum resource of information…

Is that most sacrosanct natural laws, second law of thermodynamics, a quantum phenomenon? “Physicists Rewrite the Fundamental Law That Leads to Disorder,” from @philipcball in @QuantaMagazine.

* “Nothing in life is certain except death, taxes and the second law of thermodynamics. All three are processes in which useful or accessible forms of some quantity, such as energy or money, are transformed into useless, inaccessible forms of the same quantity. That is not to say that these three processes don’t have fringe benefits: taxes pay for roads and schools; the second law of thermodynamics drives cars, computers and metabolism; and death, at the very least, opens up tenured faculty positions.” — Seth Lloyd


As we get down with disorder, we might spare a thought for Francois-Marie Arouet, better known as Voltaire; he died on this date in 1778.  The Father of the Age of Reason, he produced works in almost every literary form: plays, poems, novels, essays, and historical and scientific works– more than 2,000 books and pamphlets (and more than 20,000 letters).  He popularized Isaac Newton’s work in France by arranging a translation of Principia Mathematica to which he added his own commentary.

A social reformer, Voltaire used satire to criticize the intolerance, religious dogma, and oligopolistic privilege of his day, perhaps nowhere more sardonically than in Candide.


“A nothing will serve just as well as a something about which nothing could be said”*…

Metaphysical debates in quantum physics don’t get at “truth,” physicist and mathematician Timothy Andersen argues; they’re nothing but a form of ritual activity and culture. After a thoughtful intellectual history of both quantum mechanics and Wittgenstein’s thought, he concludes…

If Wittgenstein were alive today, he might have couched his arguments in the vocabulary of cultural anthropology. For this shared grammar and these language games, in his view, form part of much larger ritualistic mechanisms that connect human activity with human knowledge, as deeply as DNA connects to human biology. It is also a perfect example of how evolution works by using pre-existing mechanisms to generate new behaviors.

The conclusion from all of this is that interpretation and representation in language and mathematics are little different than the supernatural explanations of ancient religions. Trying to resolve the debate between Bohr and Einstein is like trying to answer the Zen kōan about whether the tree falling in the forest makes a sound if no one can hear it. One cannot say definitely yes or no, because all human language must connect to human activity. And all human language and activity are ritual, signifying meaning by their interconnectedness. To ask what the wavefunction means without specifying an activity – and experiment – to extract that meaning is, therefore, as sensible as asking about the sound of the falling tree. It is nonsense.

As a scientist and mathematician, Wittgenstein has challenged my own tendency to seek out interpretations of phenomena that have no scientific value – and to see such explanations as nothing more than narratives. He taught that all that philosophy can do is remind us of what is evidently true. It’s evidently true that the wavefunction has a multiverse interpretation, but one must assume the multiverse first, since it cannot be measured. So the interpretation is a tautology, not a discovery.

I have humbled myself to the fact that we can’t justify clinging to one interpretation of reality over another. In place of my early enthusiastic Platonism, I have come to think of the world not as one filled with sharply defined truths, but rather as a place containing myriad possibilities – each of which, like the possibilities within the wavefunction itself, can be simultaneously true. Likewise, mathematics and its surrounding language don’t represent reality so much as serve as a trusty tool for helping people to navigate the world. They are of human origin and for human purposes.

To shut up and calculate, then, recognizes that there are limits to our pathways for understanding. Our only option as scientists is to look, predict and test. This might not be as glamorous an offering as the interpretations we can construct in our minds, but it is the royal road to real knowledge…

A provocative proposition: “Quantum Wittgenstein,” from @timcopia in @aeonmag.

* Ludwig Wittgenstein, Philosophical Investigations


As we muse on meaning, we might recall that it was on this date in 1954 that the official ground-breaking for CERN (Conseil européen pour la recherche nucléaire) was held. Located in Switzerland, it is the largest particle physics laboratory in the world… that’s to say, a prime spot to do the observation and calculation that Andersen suggests. Indeed, it’s been the site of many breakthrough discoveries over the years, maybe most notably the 2012 observation of the Higgs Boson.

Because researchers need remote access to these facilities, the lab has historically been a major wide area network hub. Indeed, it was at CERN that Tim Berners-Lee developed the first “browser”– and effectively fomented the emergence of the web.

CERN’s main site, from Switzerland looking towards France

“I visualize a time when we will be to robots what dogs are to humans. And I am rooting for the machines.”*…

Claude Shannon with his creation, Theseus the maze-solving mouse, an early illustration of machine learning and a follow-on project to the work described below

Readers will know of your correspondent’s fascination with the remarkable Claude Shannon (see here and here), remembered as “the father of information theory,” but seminally involved in so much more. In a recent piece in IEEE Spectrum, the redoubtable Rodney Brooks argues that we should add another credit to Shannon’s list…

Among the great engineers of the 20th century, who contributed the most to our 21st-century technologies? I say: Claude Shannon.

Shannon is best known for establishing the field of information theory. In a 1948 paper, one of the greatest in the history of engineering, he came up with a way of measuring the information content of a signal and calculating the maximum rate at which information could be reliably transmitted over any sort of communication channel. The article, titled “A Mathematical Theory of Communication,” describes the basis for all modern communications, including the wireless Internet on your smartphone and even an analog voice signal on a twisted-pair telephone landline. In 1966, the IEEE gave him its highest award, the Medal of Honor, for that work.

If information theory had been Shannon’s only accomplishment, it would have been enough to secure his place in the pantheon. But he did a lot more…

In 1950 Shannon published an article in Scientific American and also a research paper describing how to program a computer to play chess. He went into detail on how to design a program for an actual computer…

Shannon did all this at a time when there were fewer than 10 computers in the world. And they were all being used for numerical calculations. He began his research paper by speculating on all sorts of things that computers might be programmed to do beyond numerical calculations, including designing relay and switching circuits, designing electronic filters for communications, translating between human languages, and making logical deductions. Computers do all these things today…

The “father of information theory” also paved the way for AI: “How Claude Shannon Helped Kick-start Machine Learning,” from @rodneyabrooks in @IEEESpectrum.

* Claude Shannon (who may or may not have been kidding…)


As we ponder possibility, we might send uncertain birthday greetings to Werner Karl Heisenberg; he was born on this date in 1901.  A theoretical physicist, he made important contributions to the theories of the hydrodynamics of turbulent flows, the atomic nucleus, ferromagnetism, superconductivity, cosmic rays, and subatomic particles.  But he is most widely remembered as a pioneer of quantum mechanics and author of what’s become known as the Heisenberg Uncertainty Principle.  Heisenberg was awarded the Nobel Prize in Physics for 1932 “for the creation of quantum mechanics.”

During World War II, Heisenberg was part of the team attempting to create an atomic bomb for Germany– for which he was arrested and detained by the Allies at the end of the conflict.  He was returned to Germany, where he became director of the Kaiser Wilhelm Institute for Physics, which soon thereafter was renamed the Max Planck Institute for Physics. He later served as president of the German Research Council, chairman of the Commission for Atomic Physics, chairman of the Nuclear Physics Working Group, and president of the Alexander von Humboldt Foundation.

Some things are so serious that one can only joke about them

Werner Heisenberg


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