12,687 research outputs found
The phase coherence of light from extragalactic sources - direct evidence against first order Planck scale fluctuations in time and space
We present a method of directly testing whether time continues to have its
usual meaning on scales of <= t_P = sqrt(hbar G/c^5) ~ 5.4E-44 s, the Planck
time. According to quantum gravity, the time t of an event cannot be determined
more accurately than a standard deviation of the form sigma_t/t = a_o
(t_P/t)^a, where a_o and a are positive constants ~1; likewise distances are
subject to an ultimate uncertainty c \sigma_t, where c is the speed of light.
As a consequence, the period and wavelength of light cannot be specified
precisely; rather, they are independently subject to the same intrinsic
limitations in our knowledge of time and space, so that even the most
monochromatic plane wave must in reality be a superposition of waves with
varying omega and {\bf k}, each having a different phase velcocity omega/k. For
the entire accessible range of the electromagnetic spectrum this effect is
extremely small, but can cumulatively lead to a complete loss of phase
information if the emitted radiation propagated a sufficiently large distance.
Since, at optical frequencies, the phase coherence of light from a distant
point source is a necessary condition for the presence of diffraction patterns
when the source is viewed through a telescope, such observations offer by far
the most sensitive and uncontroversial test. We show that the HST detection of
Airy rings from the active galaxy PKS1413+135, located at a distance of 1.2
Gpc, secures the exclusion of all first order (a=1) quantum gravity
fluctuations with an amplitude a_o > 0.003. The same result may be used to
deduce that the speed of light in vacuo is exact to a few parts in 10^32.Comment: Title change. One reference added. Final version accepted by ApJ
Quantum Geometrodynamics I: Quantum-Driven Many-Fingered Time
The classical theory of gravity predicts its own demise -- singularities. We
therefore attempt to quantize gravitation, and present here a new approach to
the quantization of gravity wherein the concept of time is derived by imposing
the constraints as expectation-value equations over the true dynamical degrees
of freedom of the gravitational field -- a representation of the underlying
anisotropy of space. This self-consistent approach leads to qualitatively
different predictions than the Dirac and the ADM quantizations, and in
addition, our theory avoids the interpretational conundrums associated with the
problem of time in quantum gravity. We briefly describe the structure of our
functional equations, and apply our quantization technique to two examples so
as to illustrate the basic ideas of our approach.Comment: 11, (No Figures), (Typeset using RevTeX
The Darkies\u27 Cradle Song
https://digitalcommons.library.umaine.edu/mmb-vp/4649/thumbnail.jp
Hidden Dirac Monopoles
Dirac showed that the existence of one magnetic pole in the universe could
offer an explanation of the discrete nature of the electric charge. Magnetic
poles appear naturally in most grand unified theories. Their discovery would be
of greatest importance for particle physics and cosmology. The intense
experimental search carried thus far has not met with success. I proposed a
universe with magnetic poles which are not observed free because they hide in
deeply bound monopole--anti-monopole states named monopolium. I discuss the
realization of this proposal and its consistency with known cosmological
features. I furthermore analyze its implications and the experimental
signatures that confirm the scenario.Comment: Comments: 15 pages, 3 figure
Coming From The Races : Galop
https://digitalcommons.library.umaine.edu/mmb-ps/2985/thumbnail.jp
Pro Patria March : For Native Land
https://digitalcommons.library.umaine.edu/mmb-ps/2617/thumbnail.jp
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