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The phase coherence of light from extragalactic sources – direct evidence against first order quantum gravity fluctuations in time and space

By SpaceRef Editor
January 13, 2003
Filed under , ,

Astrophysics, abstract
astro-ph/0301184


From: Richard Lieu <[email protected]>
Date: Fri, 10 Jan 2003 21:13:54 GMT (9kb)

The phase coherence of light from extragalactic sources – direct
evidence against first order quantum gravity fluctuations in time and space


Authors:
Richard Lieu,
Lloyd W. Hillman

Comments: Accepted for publication by the Astrophysical Journal Letters


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 {f 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.

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