Strange Physical Theory Proved After Nearly 40 Years

Clara Moskowitz
Staff Writer
LiveScience.com clara Moskowitz
staff Writer
livescience.com – Wed Dec 16, 12:20 pm ET

When physicist Vitaly Efimov heard his theory had finally been proven, he ran up to the younger scientist who had verified it and gave him a high five.

Efimov had predicted a quantum-mechanical version of Borromean rings, a symbol that first showed up in Afghan Buddhist art from around the second century. The symbol depicts three rings linked together; if any ring were removed, they would all come apart.

Efimov theorized an analog to the rings using particles: Three particles (such as atoms or protons or even quarks) could be bound together in a stable state, even though any two of them could not bind without the third. The physicist first proposed the idea, based on a mathematical proof, in 1970. Since then, no one has been able to demonstrate the phenomenon in the lab - until recently.

A team of physicists led by Randy Hulet of Rice University in Houston finally achieved the trio of particles, and published their findings in the online journal Science Express.

"It was very exciting, because after 40 years of this prediction being out there, it was finally verified," Hulet told LiveScience.

Hulet presented his work at a meeting in Rome in October that Efimov also attended.

"He gave me a high five after my talk," Hulet recounted. "He was so enthusiastic and so excited to see this prediction become true."

Efimov had calculated that the triplet of bound particles was possible, and that it was repeating: New bound states could be achieved at higher and higher energy levels in an infinite progression. All of the bound states would occur at energy levels that were multiples of 515.

To prove that they had really created the trios, called Efimov trimers, the researchers produced one set of three lithium atoms bound together, and then reproduced it with a binding energy 515 times the first one. (Essentially, binding energy indicates how tightly the particles hold onto one another and how much energy it would take to pull them apart.)

The researchers used a setup called a Feshbach resonance that allowed them to tweak the energy levels of their atoms. They found that when they hit multiples of 515, the particles would bind, but at other energies they wouldn't, proving that the trios really were Efimov trimers.

"It's an amazing effect, really," Hulet said. "A lot of people didn't believe [Efimov] at first. It was a very strange prediction."

The theory is unique because it's a solution to a special case of what's called the "three-body" problem. Scientists have solved the "two-body" problem - that is, they have calculated exactly how two objects should move based on their starting positions, masses and velocities. Scientists can also calculate this scenario for many masses, but a pure solution to the general three-body problem has been elusive.

"Physicists can handle two-body problems quite well, and many-body problems fairly well, but when there are just a few objects, like the three bodies in these Efimov trimers, there are just too many variables," Hulet said.

The Efimov calculation isn't the solution to the general case, but rather a solution to a specific case of three bodies. Thus, discovering a real-life example of three particles fulfilling his prediction is an important step to learning more about few-body physics.

* The Strangest Little Things in Nature
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* How Quantum Physics Could Power the Future

* Original Story: Strange Physical Theory Proved After Nearly 40 Years

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Cerebro y estrés post-traumático

Un nuevo trabajo muestra por primera vez cómo las diferentes regiones del cerebro humano responden cuando se experimenta un evento inesperado o traumático.

En este estudio participaron 15 adultos sanos a los que mientras se les realizaba una resonancia magnética funcional (fMRI), se les pidió que escucharan a una serie de sonidos, en tonos bajos y altos, algunos de los cuales estaban asociados a un sonido fuerte. Se les pidió que calificaran los tonos entre 0 y 100; 0 si no esperaban oír el sonido fuerte, 100 si esperaban oírlo y 50 si no podían hacer una predicción. Además, se midieron otras respuestas, como palmas de las manos sudorosas, para determinar a cuántos de los participantes les molestaba el ruido. Posteriormente se correlacionaron las respuestas de la piel y del cerebro para evaluar cómo la actividad del cerebro influye en la expresión emocional.

El análisis de las imágenes cerebrales mostraron que los acontecimientos desagradables producen actividad en el lóbulo frontal del cerebro. La actividad se redujo cuando los participantes esperaban el evento desagradable, pero no cuando el evento era inesperado.
[NeuroImage 2009]
Knight DC, Waters NS, King MK y Bandettini PA

Memoria a largo y corto plazo

Los hallazgos de un estudio publicado en la revista Proceedings of the National Academy of Science USA muestran que existen dos redes de memoria a corto plazo en el cerebro. Una que funciona de forma independiente del hipocampo y se mantiene intacta en pacientes con déficit de memoria a largo plazo, y otra, que depende del hipocampo y se deteriora al mismo tiempo que lo hace la memoria a largo plazo.

A pacientes con epilepsia del lóbulo temporal con esclerosis bilateral del hipocampo se les pidió que memorizaran fotografías de escenas normales de cada día. A continuación se les pidió que recordasen esas imágenes mientras se registraba su actividad cerebral mediante una magnetoencefalografía. Lo hicieron dos veces: después de un corto período de 5 segundos y pasados 60 minutos.

Comprobaron que en estos pacientes la memoria a corto plazo era buena mientras que la memoria a largo plazo estaba afectada. Sin embargo, cuando a los 5 segundos se les pidió que recordasen los detalles de las escenas que había aprendido de memoria, no podían.
[Proc Natl Acad Sci 2009]
Cashdollar N, Malecki U, Rugg-Gunn FJ, Duncan JS, Lavie N y Duzel E