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Posts Tagged ‘quantum mechanics

“Reality is that which, when you stop believing in it, doesn’t go away”*…

Jukka Liukkonen (left) and Jussi Lindgren (right) describe Heisenberg’s uncertainty principle. Photo: Aalto University

Quantum mechanics arose in the 1920s, and since then scientists have disagreed on how best to interpret it. Many interpretations, including the Copenhagen interpretation presented by Niels Bohr and Werner Heisenberg, and in particular, von Neumann-Wigner interpretation, state that the consciousness of the person conducting the test affects its result. On the other hand, Karl Popper and Albert Einstein thought that an objective reality exists. Erwin Schrödinger put forward the famous thought experiment involving the fate of an unfortunate cat that aimed to describe the imperfections of quantum mechanics.

In their most recent article, Finnish civil servants Jussi Lindgren and Jukka Liukkonen, who study quantum mechanics in their free time, take a look at the uncertainty principle that was developed by Heisenberg in 1927. According to the traditional interpretation of the principle, location and momentum cannot be determined simultaneously to an arbitrary degree of precision, as the person conducting the measurement always affects the values.

However, in their study Lindgren and Liukkonen concluded that the correlation between a location and momentum, i.e., their relationship, is fixed. In other words, reality is an object that does not depend on the person measuring it. Lindgren and Liukkonen utilized stochastic dynamic optimization in their study. In their theory’s frame of reference, Heisenberg’s uncertainty principle is a manifestation of thermodynamic equilibrium, in which correlations of random variables do not vanish.

“The results suggest that there is no logical reason for the results to be dependent on the person conducting the measurement. According to our study, there is nothing that suggests that the consciousness of the person would disturb the results or create a certain result or reality,” says Jussi Lindgren…

The full story at: “A new interpretation of quantum mechanics suggests that reality does not depend on the person measuring it.”

* Philip K. Dick

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As we admire amateur achievement, we might spare a thought for another profoundly-gifted amateur, James Prescott Joule; he died on this date in 1889. A seminal physicist and mathematician, he did “his science” in his free time; in his day job, he managed his family’s brewery.

Joule studied the nature of heat, and discovered its relationship to mechanical work– work that was prompted by his concern as a brewer to get the most from his steam (and later electric) engines. This led to the law of conservation of energy, which in turn led to the development of the first law of thermodynamics. The SI derived unit of energy, the joule, is named for him.

Joule’s earliest published work met with substantial resistance, as it depended on very precise measurements of heat that most in his audience believed infeasible– but that Joule, drawing on his brewer’s craft, had in fact achieved.

He worked with Lord Kelvin to develop an absolute thermodynamic temperature scale, which came to be called the Kelvin scale. Joule also conducted experiments on magnetostriction, via which he found the relationship between the current through a resistor and the heat dissipated, which is known as Joule’s first law.

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“Evidently, the fundamental laws of nature do not pin down a single and unique universe”*…

For the World Is Hollow and I Have Touched the Sky Original printing of the Flammarion engraving, from 1888.
Artist unknown; from Camille Flammarion, L’Atmosphère: Météorologie Populaire

The name of the image—the “Flammarion engraving”—may not ring a bell, but you’ve seen it many times. It depicts a traveler wearing a cloak and clutching a walking-stick; behind him is a varied landscape of towns and trees; surrounding all is a crystalline shell fretted with countless stars. Reaching the edge of his world, the traveler pushes through to the other side and is dazzled by a whole new world of light and rainbows and fire.

The image was first published in 1888 in a book by French astronomer Camille Flammarion. (The original engraving was black and white, although colorized versions now abound.) He notes that the sky does look like a dome on which the celestial bodies are attached, but impressions deceive. “Our ancestors,” Flammarion writes, “imagined that this blue vault was really what the eye would lead them to believe it to be; but, as Voltaire remarks, this is about as reasonable as if a silk-worm took his web for the limits of the universe.”

The engraving has come to be seen as a symbol of humanity’s quest for knowledge, but I prefer a more literal reading, in keeping with Flammarion’s intent. Time and again in the history of science, we have found an opening in the edge of the known world and poked through. The universe does not end at the orbit of Saturn, nor at the outermost stars of the Milky Way, nor at the most distant galaxy in our field of view. Today cosmologists think whole other universes may be out there.

But that is almost quotidian compared to what quantum mechanics reveals. It is not just a new opening in the dome, but a new kind of opening. Physicists and philosophers have long argued over what quantum theory means, but, in some way or other, they agree that it reveals a vast realm lying beyond the range of our senses. Perhaps the purest incarnation of this principle—the most straightforward reading of the equations of quantum theory—is the many-worlds interpretation, put forward by Hugh Everett in the 1950s. In this view, everything that can happen does in fact happen, somewhere in a vast array of universes, and the probabilities of quantum theory represent the relative numbers of universes experiencing one outcome or another. As David Wallace, a philosopher of physics at the University of Southern California, put it in his 2012 book, The Emergent Multiverse, when we take quantum mechanics literally, “the world turns out to be rather larger than we had anticipated: Indeed, it turns out our classical ‘world’ is only a small part of a much larger reality.”…

If multiverses seem weird, it’s because we need to revamp our notions of time and space: “The Multiple Multiverses May Be One and the Same.”

* Alan Lightman, The Accidental Universe: The World You Thought You Knew

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As we find one in many, we might send relativistic birthday greetings to Victor Frederick “Viki” Weisskopf; he was born on this date in 1908. A theoretical physicist who contributed mightily to the golden age of quantum mechanics, Weisskopf did postdoctoral work with Werner Heisenberg, Erwin Schrödinger, Wolfgang Pauli and Niels Bohr. He emigrated from Austria to the U.S. in 1937 to escape Nazi persecution. During World War II he was Group Leader of the Theoretical Division of the Manhattan Project at Los Alamos, and later campaigned against the proliferation of nuclear weapons.

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Written by LW

September 20, 2020 at 1:01 am

“If you are not completely confused by quantum mechanics, you do not understand it”*…

 

uchicagoscie

 

If we can harness it, quantum technology promises fantastic new possibilities. But first, scientists need to coax quantum systems to stay yoked for longer than a few millionths of a second.

A team of scientists at the University of Chicago’s Pritzker School of Molecular Engineering announced the discovery of a simple modification that allows quantum systems to stay operational—or “coherent”—10,000 times longer than before. Though the scientists tested their technique on a particular class of quantum systems called solid-state qubits, they think it should be applicable to many other kinds of quantum systems and could thus revolutionize quantum communication, computing and sensing…

Down at the level of atoms, the world operates according to the rules of quantum mechanics—very different from what we see around us in our daily lives. These different rules could translate into technology like virtually unhackable networks or extremely powerful computers; the U.S. Department of Energy released a blueprint for the future quantum internet in an event at UChicago on July 23. But fundamental engineering challenges remain: Quantum states need an extremely quiet, stable space to operate, as they are easily disturbed by background noise coming from vibrations, temperature changes or stray electromagnetic fields.

Thus, scientists try to find ways to keep the system coherent as long as possible…

“This breakthrough lays the groundwork for exciting new avenues of research in quantum science,” said study lead author David Awschalom, the Liew Family Professor in Molecular Engineering, senior scientist at Argonne National Laboratory and director of the Chicago Quantum Exchange. “The broad applicability of this discovery, coupled with a remarkably simple implementation, allows this robust coherence to impact many aspects of quantum engineering. It enables new research opportunities previously thought impractical.”…

Very big news at a very small scale: “Scientists discover way to make quantum states last 10,000 times longer.”

*John Wheeler

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As we strive for stability, we might send calculated birthday greetings to Brook Taylor; he was born on this date in 1685.  A mathematician, he is best known for his work in describing and understanding oscillation.  In 1708, Taylor produced a solution to the problem of the center of oscillation.  His Methodus incrementorum directa et inversa (“Direct and Indirect Methods of Incrementation,” 1715) introduced what is now called the calculus of finite differences.  Using this, he was the first to express mathematically the movement of a vibrating string on the basis of mechanical principles.  Methodus also contained Taylor’s theorem, later recognized by Joseph Lagrange as the basis of differential calculus.

A gifted artist, Taylor also wrote on the basic principles of perspective, including the first general treatment of the principle of vanishing points.

220px-BTaylor source

 

 

“Physics is like sex: sure, it may give some practical results, but that’s not why we do it”*…

 

Feynman and Dirac

Two of Marek Holzman’s photographs of Feynman and Dirac together in Warsaw in 1962

 

Beloved late physicist Richard P. Feynman (1918–1988) first met his hero Paul Dirac (1902–1984) during Princeton University’s Bicentennial Celebration in 1946 and then again at least twice, in 1948 and 1962. Most notably, the two came to heads during the so-called Pocono Conference when Feynman gave a lecture on a nascent “Alternative Formulation of Quantum Electrodynamics”, reformulating the theory which had earned Dirac the Nobel Prize in Physics in 1933. A star-studded audience of 28 of the world’s leading physicists attended the conference, including J. Robert Oppenheimer, Niels Bohr, Eugene Wigner, John von Neumann, Enrico Fermi, Hans Bethe and of course, the inventor of the theory himself, Paul Dirac.

Feynman’s reformulation of Dirac’s theory was not well received at Pocono, as Bohr, Teller and Dirac all raised objections. Feynman’s disappointment from the audience’s reaction motivated him to write up his work for publication instead. He did so, and in the next three years went on to publish four major papers describing his now well-developed theory and its implications…

Feynman and Dirac [met for the last] time, at the International Conference on Relativistic Theories of Gravitation in Warsaw, Poland in 1962… Their conversation, as overheard by a nearby physicist, was so remarkable that he jotted it down:

F: I am Feynman.
D: I am Dirac.
(Silence)
F: It must be wonderful to be the discoverer of that equation.
D: That was a long time ago.
(Pause)
D: What are you working on?
F: Mesons.
D: Are you trying to discover an equation for them?
F: It is very hard.
D: One must try.

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Another of Holzman’s photographs from Warsaw

Feynman’s work earned him a share of the Nobel Prize in Physics in 1965.

Paul Dirac died in 1984 at the age of 82 years old. Two years later, Feynman was invited to give one of three Dirac Memorial Lectures. He did so, with a lecture entitled “Elementary Particles and the Laws of Physics”, which he opened as follows:

When I was a young man, Dirac was my hero. He made a new breakthrough, a new method of doing physics. He had the courage to simply guess at the form of an equation, the equation we now call the Dirac equation, and to try to interpret it afterwards.

 

How Paul Dirac, Richard Feynman’s hero-turned-opponent, motivated a life’s work which not only altered the trajectory of modern physics, but also erected Feynman’s legend as one history’s finest scientist: “When Feynman met Dirac.”

* Richard Feynman

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As we chase after clarity, we might send very tiny birthday greetings to Wolfgang Paul; he was born on this date in 1913.  A physicist, he developed the non-magnetic quadrupole mass filter which laid the foundation for what is now called an ion trap— a device (also known as a Paul trap) that captures ions and holds them long enough for study and precise measurement of their properties.  During the 1950s he developed the so-called Paul trap as a means of confining and studying electrons.  He shared the Nobel Prize in Physics in 1989 for his work.

He humorously referred to Wolfgang Pauli as his imaginary part.

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“Reality is merely an illusion, albeit a very persistent one”*…

 

Science_View-On-G2-Mirror

To look for the strange wave-like properties of quantum particles, physicists hurtle them through a long tunnel-like instrument known as an interferometer

 

Magnify a speck of dirt a thousand times, and suddenly it no longer seems to play by the same rules. Its outline, for example, won’t look well-defined most of the time and will resemble a diffuse, sprawling cloud. That’s the bizarre realm of quantum mechanics. “In some books, you’ll find they say a particle is in various places at once,” says physicist Markus Arndt of the University of Vienna in Austria. “Whether that really happens is a matter of interpretation.”

Another way of putting it: Quantum particles sometimes act like waves, spread out in space. They can slosh into each other and even back onto themselves. But if you poke at this wave-like object with certain instruments, or if the object interacts in specific ways with nearby particles, it loses its wavelike properties and starts acting like a discrete point—a particle. Physicists have observed atoms, electrons, and other minutiae transitioning between wave-like and particle-like states for decades.

But at what size do quantum effects no longer apply? How big can something be and still behave like both a particle and a wave? Physicists have struggled to answer that question because the experiments have been nearly impossible to design.

Now, Arndt and his team have circumvented those challenges and observed quantum wave-like properties in the largest objects to date—molecules composed of 2,000 atoms, the size of some proteins. The size of these molecules beats the previous record by two and a half times. To see this, they injected the molecules into a 5-meter-long tube. When the particles hit a target at the end, they didn’t just land as randomly scattered points. Instead, they formed an interference pattern, a striped pattern of dark and light stripes that suggests waves colliding and combining with each other…

One possibility physicists are exploring is that quantum mechanics might in fact apply at all scales. “You and I, while we sit and talk, do not feel quantum,” says Arndt. We seem to have distinct outlines and do not crash and combine with each other like waves in a pond. “The question is, why does the world look so normal when quantum mechanics is so weird?”…

A record-breaking experiment shows an enormous molecule is also both a particle and a wave—and that quantum effects don’t only apply at tiny scales: “Even Huge Molecules Follow the Quantum World’s Bizarre Rules.”

Read the paper published in Nature Physics by Arndt and his team here.

* Albert Einstein

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As we dwell on duality, we might spare a thought for August Ferdinand Möbius; he died on this date in 1868.  A German mathematician and theoretical astronomer, he is best remembered as a topologist, more specifically for his discovery of the Möbius strip (a two-dimensional surface with only one side… or more precisely, a non-orientable two-dimensional surface with only one side when embedded in three-dimensional Euclidean space).

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Written by LW

September 26, 2019 at 1:01 am

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