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Saturday, October 24, 2009

Oct. 23 - Rethinking relativity: Is time out of joint?‏

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Rethinking relativity: Is time out of joint?


EVER since Arthur Eddington travelled to the island of Príncipe off Africa to measure starlight bending around the sun during a 1919 eclipse, evidence for Einstein's theory of general relativity has only become stronger. Could it now be that starlight from distant galaxies is illuminating cracks in the theory's foundation?


Everything from the concept of the black hole to GPS timing owes a debt to the theory of general relativity, which describes how gravity arises from the geometry of space and time. The sun's gravitational field, for instance, bends starlight passing nearby because its mass is warping the surrounding space-time. This theory has held up to precision tests in the solar system and beyond, and has explained everything from the odd orbit of Mercury to the way pairs of neutron stars perform their pas de deux.


Yet it is still not clear how well general relativity holds up over cosmic scales, at distances much larger than the span of single galaxies. Now the first, tentative hint of a deviation from general relativity has been found. While the evidence is far from watertight, if confirmed by bigger surveys, it may indicate either that Einstein's theory is incomplete, or else that dark energy, the stuff thought to be accelerating the expansion of the universe, is much weirder than we thought (see "Not dark energy, dark fluid").


The analysis of starlight data by cosmologist Rachel Bean of Cornell University in Ithaca, New York, has generated quite a stir. Shortly after the paper was published on the pre-print physics archive, prominent physicist Sean Carroll of the California Institute of Technology in Pasadena praised Bean's research. "This is serious work by a respected cosmologist," he wrote on his blog Cosmic Variance. "Either the result is wrong, and we should be working hard to find out why, or it's right, and we're on the cusp of a revolution."


If it is wrong, we should be working hard to find out why, but if it's right, we are on the cusp of a revolution

"It has caused quite a furore in astronomy circles," says Richard Massey of the Royal Observatory Edinburgh in the UK. "This paper has generated a lot of interest."


Bean found her evidence lurking in existing data collected by the Cosmic Evolution Survey, a multi-telescope imaging project that includes the longest survey yet by the Hubble Space Telescope. COSMOS, which detected more than 2 million galaxies over a small patch of sky, takes advantage of gravity's ability to bend light. Massive objects like galaxy clusters bend the light of more distant objects so that it is directed towards or away from Earth. This effect, called gravitational lensing, is at its most dramatic when it creates kaleidoscopic effects like luminous rings or the appearance of multiple copies of a galaxy.


The sky is also dominated by the distorting effects of "weak lensing", in which intervening matter bends light to subtly alter the shapes and orientations of more distant galaxies, creating an effect similar to that of looking through old window glass. Since galaxies come in all shapes and sizes, it is difficult to know whether the light from an individual galaxy has been distorted, because there is nothing to compare it with. But by looking for common factors in the distortion of many galaxies, it is possible to build up a map of both the visible and even unseen matterMovie Camera that bend their light.


The weak lensing technique can also be used to measure two different effects of gravity. General relativity calls for gravity's curvature of space to be equivalent to its curvature of time. Light should be influenced in equal amounts by both.


When the COSMOS data was released in 2007, the team - led by Massey - assumed these two factors were equivalent. Their analysis revealed that gravitational tugs on light were stronger than anticipated, but they put this down to a slightly higher concentration of ordinary and dark matter in the survey's patch of sky than had been predicted.


To look for potential deviations from general relativity, Bean reanalysed the data and dropped the requirement that these two components of gravity had to be equal. Instead the ratio of the two was allowed to change in value. She found that between 8 and 11 billion years ago gravity's distortion of time appeared to be three times as strong as its ability to curve space. An observer around at the time wouldn't have noticed the effect because it only applies over large distances. Nonetheless, "there is a preference for a significant deviation from general relativity", says Bean (www.arxiv.org/abs/0909.3853).


Gravity's distortion of time appeared to be three times as strong as its ability to curve space.

At this stage, it's hard to say what would happen if the deviation from general relativity was confirmed. Cosmologists have already considered some modifications to general relativity that could explain the universe's acceleration (see "Not dark energy, dark fluid").


Yet finding a deviation when the universe was less than half its current age is odd - if general relativity had broken down at some level, the signs should be most dramatic more recently, long after the repulsive effect of dark energy overwhelmed the attractive powers of gravity some 6 billion years ago.


Most astronomers, including Bean, are cautious about the results. "Nobody is yet betting money that the effect is real," says cosmologist Dragan Huterer of the University of Michigan in Ann Arbor. Various other explanations, like a bias in the technique used to estimate the distances to galaxies, now need to be ruled out.


Although COSMOS photographed a deep patch of sky, it was fairly small by the standards of modern surveys. This opens up the possibility that this region might be anomalous, notes Asantha Cooray, an astrophysicist at the University of California, Irvine. "You could have a massive galaxy cluster that could boost your weak lensing signal up. Or by random chance you could have more dark matter," says Cooray, part of a team that analysed other survey data taken with the Canada-France-Hawaii Telescope in Hawaii and found no hint of a departure from general relativity. "The only way to take that into account is to look at data in a larger field."


Future projects will scan the sky over much wider areas and collect images of many more lensed galaxies. For example, the Dark Energy Survey is poised to start surveying the sky from 2011 and will build up an even more precise picture of how light has been bent over the course of the universe's history.


Whether these surveys find the effect or not, Bean hopes that her paper will generate more interest in the idea of using weak lensing to test general relativity. "I'm not putting my flag out there and saying this is a real thing," Bean says. "We need to look at more data sets. This is really just the first stage for trying to test gravity in this way."


Massey agrees: "At the moment we're in the mode of just trying to hack into general relativity to find the chinks in its armour, to find any places where it might not be working."


Not dark energy, dark fluid



Dark energy could be weirder than we thought. Evidence that over large distances gravity exerts a greater pull on time than on space (see main story) might not necessarily suggest that the theory of general relativity is wrong. It could instead be a sign that the universe's acceleration may require a more exotic explanation.


The simplest way of explaining the universe's acceleration is to invoke a cosmological constant, originally proposed by Einstein to allow the universe to remain the same size in the presence of matter. This describes a universe filled with uniform, outward-pushing energy. But there are other possible explanations for acceleration.


One idea is that the entire universe exists on a membrane, or brane, floating inside an extra dimension. While matter will be confined to three dimensions, gravity could be leaking into this extra dimension. When the universe becomes large enough, this gravity could interact with matter in the brane, to produce acceleration on large scales.


A deviation could also be a sign that dark energy is a more complex "fluid" that exerts varying pressures in different directions. The snag is that telling the difference between a more exotic form of dark energy and a modification to our understanding of gravity could be tricky.


"If we were to detect a departure," says cosmologist Alessandra Silvestri of the Massachusetts Institute of Technology, we might not be able to tell whether there is a flaw in general relativity or just evidence that dark energy is "some sort of fancy fluid".


From: The New Scientist

http://www.newscientist.com/article/mg20427314.400-rethinking-relativity-is-time-out-of-joint.html?full=true
Author: Rachel Courtland

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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



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