Quantum Chaos Unveiled?
August 6, 2008
University of Utah physicist Brian Saam examines tubes of invisible xenon gas that he used to explore the relationship between chaos theory and modern quantum physics. Photo: Eric Sorte
(PhysOrg.com) -- A University of Utah study is shedding light on an important, unsolved physics problem: the relationship between chaos theory - which is based on 300-year-old Newtonian physics - and the modern theory of quantum mechanics.
The study demonstrated a fundamental new property - what appears to be chaotic behavior in a quantum system - in the magnetic "spins" within the nuclei or centers of atoms of frozen xenon, which normally is a gas and has been tested for making medical images of lungs.
The new study - published in the Aug. 8 issue of the journal Physical Review Letters - was led by Brian Saam, an associate professor of physics and associate dean of the University of Utah's College of Science.
Quantum mechanics - which describes the behavior of molecules, atoms electrons and other subatomic particles - "plays a key role in understanding how electronics work, how all sorts of interesting materials behave, how light behaves during communication by optical fibers," Saam says.
"When you look at all the technology governed by quantum physics, it's not unreasonable to assume that if one can apply chaos theory in a meaningful way to quantum systems, that will provide new insights, new technology, new solutions to problems not yet known."
A Chaotic Dance of Nuclear Spins
Just as atomic nuclei and their orbiting electrons can have electrical charges, they also have another property known as "spin." The spin within an atomic nucleus or electron is like a spinning bar magnet that points either up or down.
Saam and graduate student Steven Morgan zapped xenon atoms with a strong magnetic field, laser beam and radio-wave pulse so the nuclear spins were aligned in four different configurations in four samples of frozen xenon, each containing about 100 billion billion atoms [billion twice is correct].
Despite differing initial configurations, the "dances" of the xenon spins evolved so they eventually were in sync with each other, as measured by nuclear magnetic resonance, or NMR. That took a few thousandths of a second - something physicists seriously call "long-time behavior."
"This type of common behavior has been a signature of classically chaotic (Newtonian) systems, mostly studied using a computer, but it never had been observed in an experimental system that only can be described by quantum mechanics," Saam says.
As an analogy, imagine billions of people in a huge, unfamiliar city. They start walking around in different places and directions, with little conversation among them. Yet, eventually, they all end up walking in the same direction.
Such behavior in nuclear spins had been predicted in 2005 by the study's third author, physicist Boris Fine of the University of Heidelberg in Germany. Fine had made the prediction by adapting chaos theory to quantum theory.
Order from Chaos
The evolution of disorder into order by the xenon atoms' nuclear spins is a signature of chaos theory, which, contrary to the popular notion, does not imply complete disorder. Instead, chaos theory describes how weather, certain chemical reactions, planetary orbits, subatomic particles and other dynamic systems change over time, with the changes often highly sensitive to starting conditions.
"When you have a [chaotic] system that is characterized by extreme randomness, it paradoxically can produce ordered behavior after a certain amount of time," says Saam. "There is strong evidence that is happening here in our experiment."
The sensitivity to starting conditions is known popularly as "the butterfly effect," based on the fanciful example that a butterfly flapping its wings in South America might set off subtle atmospheric changes that eventually build into a tornado in Texas.
Saam says chaos theory can make predictions about extremely complex motions of many particles that are interacting with each other. The mathematical notion of chaos first was described in the 1890s. Chaos theory was developed in the 1960s, based on classical physics developed in the late 1600s by Sir Isaac Newton. Classical physics says the motion, speed and location of any particle at any time can be determined precisely.
In contrast, quantum mechanics holds that "when things get atom small, our notions of being able to put a specific particle in a specific place with a specific speed at a specific time become blurry," Saam says. So a particle's speed and location is a matter of probability, and "the probability is the reality."
Details of the Study: ‘These Guys are Dancing Together'
Technically, spin is the intrinsic angular momentum of a particle - a concept so difficult to explain in lay terms that physicists usually use the bar magnet analogy.
A nonmagnetic material normally has random spins in the nuclei of its atoms - half the spins are up and half are down, so the net spin is zero. But magnetic fields can be applied so that the spins are aligned - with more up than down, or vice versa.
Physicists can measure the alignment or "polarization" of the spins using NMR's strong magnetic field. Nuclear spins also are used medically: When a patient lies within a magnetic resonance imaging (MRI) device's large magnet, the spins within atoms in the body generate electrical signals that are used to make images of body tissues. Doctors are testing xenon as a way to enhance MRI images of the lungs.
Saam and colleagues used xenon because its spins can be aligned relatively easily.
In each experiment, Saam and Morgan used a magnetic field and a laser to align or "hyperpolarize" the spins in a sample of about 100 billion billion xenon gas atoms so a majority of the spins either were aligned "up" or "down." Then, they froze the gas into a solid at a temperature of 321 degrees below zero Fahrenheit.
Then they applied a radio wave pulse, which "flips" the spins so they all are perpendicular to the magnetic field instead of parallel to it. That makes them start circling around the magnetic field axis like spinning tops.
In this manner, the physicists created four frozen xenon samples. Within each sample, the spins were aligned, but different radio pulses were used to make the initial alignment or configuration of the spins different from one sample to the next.
The scientists then used NMR to watch the spins decay or fade over thousandths of a second.
"Although they are held in place in the crystal structure, the spins can interact with each other and change the direction in which they're pointed in much the same way that magnets interact with each other when brought close together," Saam says.
The initial configuration of spins in each xenon sample evolved in extremely complicated ways due to the presence of billions of interacting spins, and each sample rapidly "lost its memory" of where it started. Such behavior has been known for 60 years.
The surprise was that while each sample's initial NMR signal was radically different from the other, they displayed "identical long-time behavior," says Saam.
"Somehow despite the fact these spins have very complicated interactions with each other and started out in completely different orientations, they end up all moving in the same way after several milliseconds," he says. "That's never been seen before in a quantum mechanical system. These guys are dancing together."
Saam says the technical achievement was that the huge amount of polarization made it possible for NMR to measure an extremely weak spin signal - only one-thousandth as strong as the original signal by the time the samples appeared to behave chaotically.
Provided by University of Utah
Oct 09, 2009 |
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I don't understand. What is new?
Are they saying that the nuclear precessions of the 4 samples were initially different but then all temporarily became the same as the precession decayed. Until finally the precessions decayed to zero.
But as always, independent reproducibility is the key, regardless of the effect.
Actually, you are right--on both counts. I had forgotten who was involved in the whole thing. I just remembered University of Utah and Cold Fusion. Either way, there have been things over the years from various departments on that campus that have raised my eyebrows several times.
Funny thing was, BYU got blamed for many of these blunders when it was the U of U that made the blunders. The U of U even have a few CO2 monitors scattered around the various locations in the Salt Lake Valley. These are a joke. They are almost never current and the one that claims to be located in downtown keep shutting down regularly when the temperature gets to a certain point. I found out that they never placed a cover over the thing to keep out solar radiation. It sits out in the open weather and sun, as well as the heat radiating off the top of the building where it sits!
Makes me laugh when I think about it. But, hey, either school makes me laugh for varying reasons. :)
The first line is retarded1!
I WON'T go further...
They need some new writers.
Or at least train the one's they got.
Yeah... I'll train 'em.
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For example, the above sequence of pictures contains a random dots composed of limited number of colors. If the number of colors would be infinite, the resulting color will be uniformly gray. But because the number of colors in limited picture area is limited too, some scale invariant patterns will appear, no matter, how much the picture is averaged/blurred. This effectively leads to the concept of fractal Universe, composed of many levels of scale invariant fluctuations, similar to Perlin noise. These fluctuations appears stringy for us because of high degree of compactification of Aether, by the same way, like the density fluctuations inside of highly compressed gas.
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It means, our Universe as a whole can be completely chaotic probably, but we cannot observe it so, because of limited speed of information spreading. Such chaos violation is the reason of perceived regularity and causuality, which in consequence leads to all physical laws observed under assumption of very low number of initial postulates.
The issue is that we cannot "probe" inside neutrons protons etc. Because of this limitation physics has focussed on mathematical models instead of physical models. Whilst this is a logical approach it makes progress slow and frustrating. Even QED does not have a physics model.
The author hints at that but never comes right out and says it, unless he hid this claim in the technical jargon which obscures the second half of the article. He just says "quantum mechanics holds that... the probability is the reality" in a way that suggests he will later contradict this claim... and then he doesn't.
I did not understand the article.
Chaos theory tries to understand how order emerges out of random events. If you grab a handful of sand. Then trickle it into a pile on the desk then it forms a mound. The shape of the mound is mathematically simple (cone) and is reproducible. However the position of each grain of sand is random and not reproducible.
To me it is simply fluid dynamics. The sand forms the shape of the container. The container being the gravitational field acting on the particles of sand.
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While the AWT model implies, every chaos is formed by density fluctuations of another generation of ordered foam, I don't think, the article intepretation goes so far.