Followers

Google+ Followers

Friday, August 21, 2015

Adrian Cho -- Tiny fountain of atoms sparks big insights into dark energy


By dropping atoms just above an aluminum sphere, physicists have tested a hypothesis about what's stretching the universe on the largest scales.
SIMCA BOUMA
By dropping atoms just above an aluminum sphere, physicists have tested a hypothesis about what's stretching the universe on the largest scales.


Staff Writer
It's a study in contrasts. For more than a decade, physicists have been puzzling over dark energy, the mysterious stuff that’s blowing space apart and has been detected only by studying the universe on the largest scales. Now, researchers have probed its properties using about the smallest tools available—atoms falling freely in a vacuum chamber. The experiment, reported today in Sciencedoesn't  reveal what dark energy is, but it helps nail down what it isn't. In particular, it narrows the prospects for one popular idea: that dark energy resides in hypothesized "chameleon particles" hiding in plain sight.


"I find it exciting to be able to use laboratory-scale experiments to test such ideas," says Amol Upadhye, a theoretical physicist at the University of Wisconsin, Madison, who was not involved in the work. The test doesn’t entirely rule out chameleons, he says, but future improvements might put the idea to the ultimate test.

The discovery of dark energy rocked physics and cosmology. Scientists thought the expansion of the universe was slowing, as the galaxies tugged on one another with their gravity and counteracted the expansion that began with the big bang. However, in 1998, two teams of cosmologists showed that in fact the expansion is accelerating by studying stellar explosions called supernovae. The result has been bolstered by analyses of galaxy clusters, the afterglow of the big bang (the cosmic microwave background), and other cosmological phenomena. Physicists attribute the acceleration to some sort of space-stretching dark energy.

But what is dark energy? There are two possibilities. It could be energy hidden in the vacuum of empty space itself—a cosmological constant, as Albert Einstein hypothesized in 1917. Or it could be a quantum field that fills space and blows it up like a balloon. Both alternatives have problems. Given the standard model of particle physics, theorists can calculate what the cosmological constant should be, and they get a value vastly too big to explain the relatively modest acceleration—suggesting some unknown physics just zeroes it out. On the other hand, the presence of a quantum field would affect things like the orbits of the planets in the solar system—but dark energy doesn’t seem to.

That's where chameleon particles come in. The hypothetical particles would make up just such a quantum field, but they would interact with matter in a way that would make the field vanish wherever the density of matter was high. Thus the field would exert no noticeable effect on things like planets. "The chameleon, like many other theoretical ideas, has a small probability of being there," says Justin Khoury, a theoretical cosmologist at the University of Pennsylvania and co-inventor of the concept. "Nonetheless we should test it if we can."

That's just what Khoury, Holger Müller, an atomic physicist at the University of California, Berkeley, and colleagues have done. To search for a chameleon field, they studied the interactions between an aluminum sphere 9.5 millimeters in diameter and a puff of 10 million ultracold cesium atoms within a vacuum chamber. If there were a chameleon field within the vacuum, then the sphere would squash it. And like a bowling ball on a trampoline, the sphere would bend the field just outside its surface, causing the field’s strength to taper to zero. The cloud of atoms would slide down the sloping field, experiencing a short-range force toward the sphere. Crucially, the cloud itself was not dense enough to suppress the field and spoil the effect. "In the simplest terms, we're looking for a funny force between the sphere and the atoms," Müller says.

That force would come in addition to the pull of Earth's gravity. So, the researchers repeated the experiment in two different configurations. In one, they dropped the atoms from 8.8 millimeters above the sphere, close enough for the sloping chameleon field to exert a force. They used an exquisitely sensitive technique called atom interferometry to measure the cesium atoms’ acceleration as they fell for about 20 milliseconds (see figure). In the other configuration, they dropped the atoms well to the side of the sphere, where the chameleon field should have been uniform and produced no force. So, if there were a chameleon field, the atoms would accelerate downward faster when dropped above the sphere. In fact, in both configurations, the atoms accelerated at the same rate to within a precision of 1 part in 1 million.

Curiously, neither Müller nor Khoury thought up the experiment. Instead, it was proposed by Clare Burrage and Edmund Copeland of the University of Nottingham in the United Kingdom and Edward Hinds of Imperial College London, in a paper they posted to the arXiv preprint server a year ago. "Of course I was disappointed that they did it before us," Hinds says, "but they already had a suitable apparatus, while we have had to build an experiment specifically for the purpose."

At its current precision, the experiment rules out only chameleons whose interaction with matter—the thing that makes the field go away where the matter density is high—is much stronger than gravity, Khoury says. Those that interact with matter more weakly are still viable, he says. Müller says that his team aims to improve the precision of their experiment to 1 part in 1 billion, which should put the chameleon to the ultimate test. Hinds is trying to beat Müller to that goal. And even if the chameleon concept dies, there are other ways to hide a quantum field that would produce dark energy.


Posted in Physics

No comments:

Post a Comment

esoteric



SUBTITLES IN ENGLISH, ESPAÑOL, PORTUGUÊS

Click upon the circle after the small square for captions

MUFON

How to Digitally Record/Video a UFO sighting:


Como registar digitalmente ou gravar um vídeo de um avistamento de um UFO:




Stabilize the camera on a tripod. If there is no tripod, then set it on top of a stable, flat surface. If that is not possible lean against a wall to stabilize your body and prevent the camera from filming in a shaky, unsteady manner.

Estabilize a camera com um tripé. Se não tiver um tripé, então coloque-a em cima de uma superfície estável. Se não for possível, então encoste-se a uma parede para estabilizar o corpo e evitar que a camera registe de maneira tremida e instável.

Provide visual reference points for comparison. This includes the horizon, treetops, lampposts, houses, and geographical landmarks (i.e., Horsetooth Reservoir, Mt. Adams, etc.) Provide this in the video whenever is appropriate and doesn’t detract from what your focus is, the UFO.

Forneça pontos visuais de referência para comparação. Isso inclui o horizonte, cimo das árvores, postes de iluminação, pontos de referência geográficos (como o Reservatório de Horsetooth, Mone Adams, etc) Forneça esses pontos no vídeo sempre que for apropriado e não se distraia do que é o seu foco, o UFO/a Nave.

Narrate your videotape. Provide details of the date, time, location, and direction (N,S,E,W) you are looking in. Provide your observations on the weather, including approximate temperature, windspeed, any visible cloud cover or noticeable weather anomalies or events. Narrate on the shape, size, color, movements, approximate altitude of the UFO, etc and what it appears to be doing. Also include any unusual physical, psychological or emotional sensations you might have. Narrate any visual reference points on camera so they correlate with what the viewer will see, and thereby will be better able to understand.

Faça a narração do vídeo. Forneça pormenores sobre a data, hora, local e direcção (Norte, Sul, Este, Oeste) que está a observar. Faça observações sobre as condições atmosféricas, incluindo a temperatura aproximada, velocidade do vento, quantidade de nuvens, anomalias ou acontecimentos meteorológicos evidentes. Descreva a forma, o tamanho, a cor, os movimentos, a altitude aproximada onde se encontra o UFO/nave, etc e o que aparenta estar a fazer. Inclua também quaisquer aspectos pouco habituais de sensações físicas, psicológicas ou emocionais que possa ter. Faça a narração de todos os pontos de referência visual que o espectador irá ver e que, deste modo, será capaz de compreender melhor.

Be persistent and consistent. Return to the scene to videotape and record at this same location. If you have been successful once, the UFO sightings may be occurring in this region regularly, perhaps for specific reasons unknown, and you may be successful again. You may also wish to return to the same location at a different time of day (daylight hours) for better orientation and reference. Film just a minute or two under “normal” circumstances for comparison. Write down what you remember immediately after. As soon as you are done recording the experience/event, immediately write down your impressions, memories, thoughts, emotions, etc. so it is on the record in writing. If there were other witnesses, have them independently record their own impressions, thoughts, etc. Include in this exercise any drawings, sketches, or diagrams. Make sure you date and sign your documentation.

Seja persistente e não contraditório. Volte ao local da cena e registe o mesmo local. Se foi bem sucedido uma vez, pode ser que nessa região ocorram avistamentos de UFOs/naves com regularidade, talvez por razões específicas desconhecidas, e talvez possa ser novamente bem sucedido. Pode também desejar voltar ao mesmo lugar a horas diferentes do dia (durante as horas de luz)para ter uma orientação e referência melhor. Filme apenas um ,inuto ou dois em circunstâncias “normais” para ter um termo de comparação. Escreva tudo o que viu imediatamente após o acontecimento. Logo após ter feito o registo da experiência/acontecimento, escreva imediatamente as impressões, memórias, pensamentos, emoções, etc para que fiquem registadas por escrito. Se houver outras testemunhas, peça-lhes para registar independentemente as suas próprias impressões, pensamentos, etc. Inclua quaisquer desenhos, esbolos, diagramas. Certifique-se que data e assina o seu documento/testemunho.

Always be prepared. Have a digital camera or better yet a video camera with you, charged and ready to go, at all times. Make sure you know how to use your camera (and your cell phone video/photo camera) quickly and properly. These events can occur suddenly, unexpectedly, and often quite randomly, so you will need to be prepared.

Esteja sempre preparado, Tenha sempre uma camera digital, melhor ainda, uma camera vídeo consigo, carregada e pronta a usar sempre que necessário. Certifique-se que sabe como lidar com a sua camera (ou com o seu celular/camera fotográfica) rápida e adequadamente. Esses acontecimentos podem acontecer súbita e inesperadamente e, por vezes, acidentalmente, por isso, necessita estar preparado.

Look up. Be prepared. Report. Share.

Olhe para cima, Esteja preparado, Relate, Partilhe.

MUFON.COM

ESOTERIC



Pf., clique no símbolo do YouTube e depois no quadrado pequeno, em baixo, ao lado direito para obter as legendas CC, e escolha PORTUGUÊS

埋め込み画像 4埋め込み画像 5

What time is Around the World?

Translate

AND YOU AND I - click image

JAIL THE BANKERS

ET CONTACT MEDITAWTION

NGC - UFO's in EUROPE (Porugal included)

FEBRUARY 7, 2013 - 7:00PM EST

FEBRUARY 7, 2013 - 7:00PM EST
T O R O N T O