Posts Tagged ‘quantum mechanics’
“How many general-relativity theorists does it take to change a light bulb?”*…
Jokes are where one finds them…
Heisenberg, Schrodinger, and Ohm are driving along the road together – Heisenberg is driving. After a time, they are stopped by a traffic cop. Heisenberg pulls over, and the cop comes up to the driver’s window.
“Sir, do you know how fast you were driving?” asks the cop.
“No” replies Heisenberg “but I know precisely where I am”
“You were doing 70.” says the cop
“Great!” says Heisenberg “Now we’re lost!”
The cop thinks this is very strange behaviour and so he decides to inspect the vehicle. After a time he comes back to the driver’s window and says
“Do you know there’s a dead cat in the trunk?”
“Well, now we do!!” yells Schrodinger.
The cop thinks this is all too weird, so he proceeds to arrest the three. Ohm resists.
source
[Image above: source]
* “How many general-relativity theorists does it take to change a light bulb? Two: one to hold the bulb and one to rotate space.” (source)
###
As we chortle, we might spare a thought for Louis de Broglie (or as he was known more officially, Louis Victor Pierre Raymond, 7th Duc de Broglie); he died on this date in 1987. An aristocrat and physicist, he made significant contributions to quantum theory. In his 1924 PhD thesis, he postulated the wave nature of electrons and suggested that all matter has wave properties— a concept known as the de Broglie hypothesis, an example of wave–particle duality— a topic that occupied both Heisenberg and Schrodinger and that forms a central part of the theory of quantum mechanics. After the wave-like behavior of matter was first experimentally demonstrated in 1927, de Broglie won the Nobel Prize for Physics (in 1929).
Louis de Broglie was the sixteenth member elected to occupy seat 1 of the Académie française in 1944, and served as Perpetual Secretary of the French Academy of Sciences. He was the first high-level scientist to call for establishment of a multi-national laboratory, a proposal that led to the establishment of the European Organization for Nuclear Research (CERN).
“In our society (that is, advanced western society) we have lost even the pretence of a common culture”*…
In 1959. C.P. Snow gave a now-famous series of lectures (quickly published): The Two Cultures, lamenting the cleaving of Western culture into spheres of science and humanities, neither of which could clearly understand, thus effectively communicate with the other. Jeroen Bouterse reminds us that Snow had a predecessor…
Several years before C.P. Snow gave his famous lecture on the two cultures, the American physicist I.I. Rabi wrote about the problem of the disunity between the sciences and the humanities. “How can we hope”, he asked, “to obtain wisdom, the wisdom which is meaningful in our own time? We certainly cannot attain it as long as the two great branches of human knowledge, the sciences and the humanities, remain separate and even warring disciplines.”
Rabi had been interested in science since his teenage years, and grown up to be a Nobel-prize winning physicist. He had also been an important player in the Allied technological effort during World War II, as associate director of the ‘Rad Lab’: the radiation laboratory at MIT that developed radar technology. The success of Rad Lab, Rabi later reflected, had not been a result of a great amount of theoretical knowledge, but of the energy, vitality, and self-confidence of its participants. In general, Rabi’s views on science and technology were somewhat Baconian: science should be open to the unexpected, rather than insisting on staying in the orbit of the familiar.
In Rabi’s accounts of his time leading Rad Lab, he would also emphasize the way in which he insisted on being let in on military information. “We are not your technicians”, he quoted himself, adding: “a military man who wants the help of scientists and tells them half a story is like a man who goes to a doctor and conceals half the symptoms.” Indeed, the key to understanding Rabi’s worries about the two cultures – he would go on to embrace Snow’s term – is his view of the role science ought to play in public life. Scientists should not just be external consultants, delivering inventions or discoveries on demand or listing the options available to the non-specialist. In some stronger sense, they should be involved in directing policy decisions.
Even more than Rabi’s positive experience with the military during the war, his views were informed by his frustration with the lack of agency scientific experts were able to exercise in the immediate aftermath. Already in 1946, he complained in a lecture that scientists had been used to create the atom bomb, but they had not been consulted about its use, and the fact that many of them had been opposed to it had made no difference. “To the politician, the scientist is like a trained monkey who goes up to the coconut tree to bring down choice coconuts.”
This feeling would increase with the decision to develop a hydrogen bomb. In 1949, Rabi was one of eight experts in the General Advisory Committee (GAC) to the Atomic Energy Commission (AEC), in which capacity he co-signed a unanimous report arguing that the ‘Super’ should not be built. (Rabi, together with Fermi, signed a minority opinion to the effect that the US should first get the USSR to pledge that it would not seek to develop an H-bomb.)
Rather than signaling to the world that he sought to avoid an arms race, however, President Truman did the opposite: without knowing that it was even possible, he announced publicly that the US would “continue its work on all forms of atomic weapons, including the so-called hydrogen or super-bomb.” Rabi would never forgive Truman…
… in the context of Rabi’s broader thinking about science in modern culture, as he came to develop and express it in the decades after the war [the] was not just that more technical expertise needed to be brought to the decision tables; the point was that scientists should make their moral views heard. In the atomic age, where science created so much power, science’s representatives should wield some of that power. From the perspective of the scientists, this was because the atom bomb had demonstrated beyond doubt that science was not a disinterested search for objective truth; it had consequences, and scientists should accept responsibility for those consequences. They should consider not just the means, but the goals…
…
It is a soft law in two cultures discourse that precisely those who most bewail the chasm between science and the humanities end up deepening it. In Rabi’s case, the reason is that he believed in the two cultures; he believed there was something special about the culture and tradition of modern natural science that was a source of wisdom and strength, and that in many ways the project of the humanities was its opposite. Understanding of nature was progressive and forward-looking, was a matter of hope and optimism, while understanding of the human world was old, had already been achieved in ancient societies, and was more a matter of transmission than of innovation. Historian of physics Michael Day notes that over time, Rabi talked less about merging the two traditions and more about putting science at the center of education…
In spite of this, I think Rabi saw correctly that picturing science and the humanities as opposing forces helped him to identify a real fault line in modern culture. The notion that science has to stay on one side of the fact-value-distinction, while the humanities are closer to the actual formation of values, was not a figment of his imagination, and it did stand in the way of his cultural ideals. While not quite the synthesis between the two sides that he sometimes claimed to aim for, the answer he gave – that neither science nor the humanities, nor committees ‘discover’ values, but that values are immanent in activities, in ways of life; that the age of science came with the scientific way of life, with its own values, and that these values were potentially culture-defining – was compelling…
… there remains something inspiring in Rabi’s vision of a common quest for knowledge and understanding, of people working together in activities that are both exciting and important, and of a society that takes those people and their projects not as resources to be exploited, but as models to be emulated.
“The atom bomb and the two cultures: I.I. Rabi on the sciences and the humanities,” from @jeroenbou in @3QD. Eminently worth reading in full.
(Image above: source)
* C. P. Snow, The Two Cultures
###
As we search for synthesis, we might send insightful birthday greetings to Walter Kohn; he was born on this date in 1923. A theoretical physicist and theoretical chemist, he shared the 1998 Nobel Prize in Chemistry (with John Pople); Kohn was honored for his development of density functional theory, which made it possible to calculate quantum mechanical electronic structure by equations involving electronic density (rather than the much more complicated many-body wavefunction). This computational simplification led to more accurate calculations on complex systems and to many new insights, and became an essential tool for materials science, condensed-phase physics, and the chemical physics of atoms and molecules.
“Reality is merely an illusion, albeit a very persistent one”*…
In an excerpt from his new book, The Rigor of Angels: Borges, Heisenberg, Kant, and the Ultimate Nature of Reality, the estimable William Egginton explains the central mystery at the heart of one of the most important breakthroughs in physics–quantum mechanics…
For all its astonishing, mind-bending complexity– for all its blurry cats, entangled particles, buckyballs, and Bell’s inequalities– quantum mechanics ultimately boils down to one core mystery. This mystery found its best expression in the letter Heisenberg wrote to Pauli in the fevered throes of his discovery. The path a particle takes ‘only comes into existence through this, that we observe it.’ This single, stunning expression underlies all the rest: the wave/particle duality (interference patterns emerge when the particles have not yet been observed and hence their possible paths interfere with one another); the apparently absurd liminal state of Schrodinger’s cat ( the cat seems to remain blurred between life and death because atoms don’t release a particle until observed); the temporal paradox (observing a particle seems to retroactively determine the path it chose to get here); and, the one that really got to Einstein, if the observation of a particle at one place and time instantaneously changes something about the rest of reality, then locality, the cornerstone of relativity and guarantee that the laws of physics are invariable through the universe, vanishes like fog on a warming windowpane.
If the act of observation somehow instantaneously conjures a particle’s path, the foundations not only of classical physics but also of what we widely regard as physical reality crumble before our eyes. This fact explains why Einstein held fast to another interpretation. The particle’s path doesn’t come into existence when we observe it. The path exists, but we just can’t see it. Like the parable of the ball in the box he described in his letter to Schrodinger, a 50 percent chance of finding a ball in any one of two boxes does not complete the description of the ball’s reality before we open the box. It merely states our lack of knowledge about the ball’s whereabouts.
And yet, as experiment after experiment has proven, the balls simply aren’t there before the observation. We can separate entangled particles, seemingly to any conceivable distance, and by observing one simultaneously come to know something about the other–something that wasn’t the case until the exact moment of observing it. Like the beer and whiskey twins, we can maintain total randomness up to a nanosecond before one of them orders, and still what the one decides to order will determine the other’s drink, on the spot, even light-years away.
The ineluctable fact of entanglement tells us something profound about reality and our relation to it. Imagine you are one of the twins about to order a drink (this should be more imaginable than being an entangled particle about to be observed, but the idea is the same). From your perspective you can order either a whiskey or a beer: it’s a fifty-fifty choice; nothing is forcing your hand. Unbeknownst to you, however, in a galaxy far, far away, your twin has just made the choice for you. Your twin can’t tell you this or signal it in any way, but what you perceive to be a perfectly random set of possibilities, an open choice, is entirely constrained. You have no idea if you will order beer or whiskey, but when you order it, it will be the one or the other all the same. If your twin is, say, one light-year away, the time in which you make this decision doesn’t even exist over there yet. Any signals your sibling gets from you, or any signals you send, will take another year to arrive. And still, as of this moment, you each know. Neither will get confirmation for another year, but you can be confident, you can bet your life’s savings on it–a random coin toss in another galaxy, and you already know the outcome.
The riddles that arise from Heisenberg’s starting point would seem to constitute the most vital questions of existence. And yet one of the curious side effects of quantum mechanics’ extraordinary success has been a kind of quietism in the face of those very questions. The interpretation of quantum mechanics, deciding what all this means, has tended to go unnoticed by serious physics departments and the granting agencies that support them in favor of the ‘shut up and calculate’ school, leading the former to take hold mainly in philosophy departments, as a subfield of the philosophy of science called foundations of physics. Nevertheless, despite such siloing, a few physicists persisted in exploring possible solutions to the quantum riddles. Some of their ideas have been literally otherworldly.
In the 1950s, a small group of graduate students working with John Wheeler at Princeton University became fascinated with these problems and kept returning to them in late-night, sherry-fueled rap sessions. Chief among this group was Hugh Everett III, a young man with classic 1950s-style nerd glasses and a looming forehead. Everett found himself chafing at the growing no-question zone that proponents of the Copenhagen interpretation had built around their science. Why should we accept that in one quantum reality, observations somehow cause nature to take shape out of a probabilistic range of options, whereas on this side of some arbitrary line in the sand we inhabit a different, classical reality where observations meekly bow to the world out there? What exactly determines when this change takes place? ‘Let me mention a few more irritating features of the Copenhagen Interpretation,’ Everett would write to its proponents: ‘You talk of the massiveness of macro systems allowing one to neglect further quantum effects … but never give any justification for this flatly asserted dogma.’…
A fascinating sample of a fascinating book: “Quantum Mechanics,” from @WilliamEgginton via the invaluable @delanceyplace.
Further to which, it’s interesting to recall that, in his 1921 The Analysis Of Mind, Bertrand Russell observed:
What has permanent value in the outlook of the behaviourists is the feeling that physics is the most fundamental science at present in existence. But this position cannot be called materialistic, if, as seems to be the case, physics does not assume the existence of matter…
via Robert Cottrell
See also: “Objective Reality May Not Exist, Quantum Experiment Suggests” (source of the image above).
* Albert Einstein
###
As we examine existence, we might spare a thought for Otto Frisch; he died on this date in 1979. A physicist, he was (with Otto Stern and Immanuel Estermann) the first to measure the magnetic moment of the proton. With his aunt, Lise Meitner, he advanced the first theoretical explanation of nuclear fission (coining the term) and first experimentally detected the fission by-products. Later, with his collaborator Rudolf Peierls, he designed the first theoretical mechanism for the detonation of an atomic bomb in 1940.
“To create something from nothing is one of the greatest feelings”*…
Something from nothing? Not exactly. As Charlie Wood explains, it’s even weirder…
For their latest magic trick, physicists have done the quantum equivalent of conjuring energy out of thin air. It’s a feat that seems to fly in the face of physical law and common sense.
“You can’t extract energy directly from the vacuum because there’s nothing there to give,” said William Unruh, a theoretical physicist at the University of British Columbia, describing the standard way of thinking.
But 15 years ago, Masahiro Hotta, a theoretical physicist at Tohoku University in Japan, proposed that perhaps the vacuum could, in fact, be coaxed into giving something up.
At first, many researchers ignored this work, suspicious that pulling energy from the vacuum was implausible, at best. Those who took a closer look, however, realized that Hotta was suggesting a subtly different quantum stunt. The energy wasn’t free; it had to be unlocked using knowledge purchased with energy in a far-off location. From this perspective, Hotta’s procedure looked less like creation and more like teleportation of energy from one place to another — a strange but less offensive idea.
“That was a real surprise,” said Unruh, who has collaborated with Hotta but has not been involved in energy teleportation research. “It’s a really neat result that he discovered.”
Now in the past year, researchers have teleported energy across microscopic distances in two separate quantum devices, vindicating Hotta’s theory. The research leaves little room for doubt that energy teleportation is a genuine quantum phenomenon.
“This really does test it,” said Seth Lloyd, a quantum physicist at the Massachusetts Institute of Technology who was not involved in the research. “You are actually teleporting. You are extracting energy.”…
“Physicists Use Quantum Mechanics to Pull Energy out of Nothing,” from @walkingthedot in @QuantaMagazine.
Vaguely related (and fascinating): “The particle physics of you.”
* Prince
###
As we demolish distance, we might send insightful birthday greetings to Brain Cox; he was born on this date in 1968. A physicist and former musician (he was keyboardist for Dare and D:Ream), he is a professor of particle physics in the School of Physics and Astronomy at the University of Manchester, and a fellow at CERN (where he works on the ATLAS experiment, studying the forward proton detectors for the Large Hadron Collider there).
But Cox is most widely known as the host/presenter of science programs, perhaps especially the BBC’s Wonders of the Universe series, and for popular science books, such as Why Does E=mc²? and The Quantum Universe— which (he avers) were inspired by Carl Sagan and for which Cox has earned recognition as the natural successor to David Attenborough and Patrick Moore.
Science is too important not to be a part of a popular culture.
“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.
You must be logged in to post a comment.