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X-ray and gamma-ray observations of distant quasars are being used to test space-time at extremely tiny scales.
Certain models predict tiny bubbles quadrillions of times smaller than the nucleus of an atom exist.
This "space-time foam" is impossible to observe directly so scientists use other methods to test ideas about it.
A new study combining data from NASA's Chandra X-ray Observatory and Fermi Gamma-ray Telescope, and the Very Energetic Radiation Imaging Telescope Array (VERITAS) in Arizona is helping scientists set limits on the quantum nature of space-time on extremely tiny scales, as explained in our latest press release.
Certain aspects of quantum mechanics predict that space-time - the three dimensions of space plus time -- would not be smooth on the scale of about ten times a billionth of a trillionth of the diameter of a hydrogen atom's nucleus. They refer to the structure that may exist at this extremely small size as "space-time foam." This artist's illustration depicts how the foamy structure of space-time may appear, showing tiny bubbles quadrillions of times smaller than the nucleus of an atom that are constantly fluctuating and last for only infinitesimal fractions of a second.
Because space-time foam is so small, it is impossible to observe it directly. However, depending on what model of space-time is used, light that has traveled over great cosmic distances may be affected by the unseen foam in ways that scientists can analyze. More specifically, some models predict that the accumulation of distance uncertainties for light traveling across billions of light years would cause the image quality to degrade so much that the objects would become undetectable. The wavelength where the image disappears should depend on the model of space-time foam used.
The researchers used observations of X-rays and gamma-rays from very distant quasars - luminous sources produced by matter falling towards supermassive black holes - to test models of the smoothness and structure of space-time. Chandra's X-ray detection of six quasars, shown in the upper part of the graphic, at distances of billions of light years, rules out one model, according to which photons diffuse randomly through space-time foam in a manner similar to light diffusing through fog. Detections of distant quasars at shorter, gamma-ray wavelengths with Fermi and even shorter wavelengths with VERITAS demonstrate that a second, so-called holographic model with less diffusion does not work.
These results appeared in the May 20th issue of The Astrophysical Journal and are available online. The authors of this study are Eric Perlman (Florida Institute of Technology), Saul Rappaport (Massachusetts Institute of Technology), Wayne Christensen (University of North Carolina), Y. Jack Ng (University of North Carolina), John DeVore (Visidyne), and David Pooley (Sam Houston State University).
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for the agency's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.
Quelle: NASA
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NASA Telescopes Set Limits on Space-time Quantum "Foam"
A team of scientists has used X-ray and gamma-ray observations of some of the most distant objects in the Universe to better understand the nature of space and time. Their results set limits on the quantum nature, or "foaminess" of space-time at extremely tiny scales.
This study combines data from NASA's Chandra X-ray Observatory and Fermi Gamma-ray Space Telescope along with ground-based gamma-ray observations from the Very Energetic Radiation Imaging Telescope Array (VERITAS).
At the smallest scales of distance and duration that we can measure, space-time - that is, the three dimensions of space plus time - appears to be smooth and structureless.
However, certain aspects of quantum mechanics, the highly successful theory scientists have developed to explain the physics of atoms and subatomic particles, predict that space-time would not be smooth. Rather, it would have a foamy, jittery nature and would consist of many small, ever-changing, regions for which space and time are no longer definite, but fluctuate.
"One way to think of space-time foam is if you are flying over the ocean in the airplane, it looks completely smooth. However, if you get low enough you see the waves, and closer still, foam, with tiny bubbles that are constantly fluctuating" said lead author Eric Perlman of the Florida Institute of Technology in Melbourne. "Even stranger, the bubbles are so tiny that even on atomic scales we're trying to observe them from a very high-flying airplane."
The predicted scale of space-time foam is about ten times a billionth of the diameter of a hydrogen atom's nucleus, so it cannot be detected directly.
However, If space-time does have a foamy structure there are limitations on the accuracy with which distances can be measured because the size of the many quantum bubbles through which light travels will fluctuate. Depending on what model of space-time is used, these distance uncertainties should accumulate at different rates as light travels travels over the large cosmic distances.
The researchers used observations of X-rays and gamma-rays from very distant quasars - luminous sources produced by matter falling towards supermassive black holes - to test models of space-time foam.
The authors predicted that the accumulation of distance uncertainties for light traveling across billions of light years would cause the image quality to degrade so much that the objects would become undetectable. The wavelength where the image disappears should depend on the model of space-time foam used.
Chandra's X-ray detection of quasars at distances of billions of light years rules out one model, according to which photons diffuse randomly through space-time foam in a manner similar to light diffusing through fog.
Detections of distant quasars at shorter, gamma-ray wavelengths with Fermi and even shorter wavelengths with VERITAS demonstrate that a second, so-called holographic model with less diffusion does not work.
"We find that our data can rule out two different models for space-time foam," said co-author Jack Ng of the University of North Carolina in Chapel Hill. "We can conclude that space-time is less foamy that some models predict."
The X-ray and gamma-ray data show that space-time is smooth down to distances 1000 times smaller than the nucleus of a hydrogen atom.
Quelle: SD
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New Constraints on Quantum Gravity from X-ray and Gamma-Ray Observations
One aspect of the quantum nature of spacetime is its "foaminess" at very small scales. Many models for spacetime foam are defined by the accumulation power α, which parameterizes the rate at which Planck-scale spatial uncertainties (and thephase shifts they produce) may accumulate over large path-lengths. Here α is defined by theexpression for the path-length fluctuations, δℓ, of a source at distance ℓ, wherein δℓ≃ℓ1−αℓαP, with ℓP being the Planck length. We reassess previous proposals to use astronomical observations ofdistant quasars and AGN to test models of spacetime foam. We show explicitly how wavefront distortions on small scales cause the image intensity to decay to the point where distant objects become undetectable when the path-length fluctuations become comparable to the wavelength of the radiation. We use X-ray observations from {em Chandra} to set the constraint α≳0.58, which rules out the random walk model (with α=1/2). Much firmer constraints canbe set utilizing detections of quasars at GeV energies with {em Fermi}, and at TeV energies with ground-based Cherenkovtelescopes: α≳0.67 and α≳0.72, respectively. These limits on α seem to rule out α=2/3, the model of some physical interest.
Quelle; Cornell University Library
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