[tt] Physorg: New-School 'Aether' May Shed Light on Neutron Stars

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New-School 'Aether' May Shed Light on Neutron Stars
http://www.physorg.com/news111249257.html
7.10.10

by Laura Mgrdichian

Among scientists, it is widely believed that there is no such thing
as an aether - a medium pervading all space that allows light waves
to propagate, similar to how sound needs air or water - but a part
of its spirit may live on. A group of University of Maryland (UM)
physicists have proposed a modern spin on the aether of old and
have used it to make new predictions about the behavior of neutron
stars.

Physicists once thought light waves propagated in a special medium,
the "luminiferous aether." This implied that the speed of light
would depend on the reference frame of the observer, but
experiments performed at the turn of the 20th century established
that light in a vacuum always travels at the same speed,
independent of the reference frame. Maxwell's electromagnetic
theory of light, together with Einstein's discovery of special
relativity, provided the explanation: there is no such aether, and
all reference frames are equivalent.

The UM group proposes, however, that an aether concept may still
have a place in physics: not representing a medium for light waves,
but a universal preferred frame of reference that is physical in
nature. As such - although the new aether retains the spirit of the
old - there are few similarities between the two.
The UM researchers - Christopher Eling, Ted Jacobson, and Coleman
Miller - describe their aether as a preferred state of rest at each
point of spacetime. This preferred state would not be the result of
something known, such as a gravitational field or cosmic background
radiation, but may, they say, arise from the structure of empty
space in quantum gravity theory.

The new aether violates Lorentz symmetry, the principle stating
that the laws of physics must have the same form no matter the
reference frame. In other words, if a person drops a ball while
standing in their house, in a moving train, or in a rocket shooting
through space, the laws of physics describing the ball's motion are
the same within each frame. This concept is one of the foundations
of special relativity.

The UM team says their work provides a framework in which to test
whether relativity holds within the context of very strong
gravitational fields. In "weak field" situations - such as the
gravitational bending of light and the orbits of the planets around
the Sun - experiments have upheld relativity in gravitational
physics. But experiments to probe relativity where gravity is much
stronger, such as near neutron stars, are not yet as accurate,
because of both limited observations and incomplete knowledge of
the properties of dense nuclear matter.

The UM team use the new aether to make concrete predictions about
neutron stars that differ from those generated by general
relativity, Einstein's theory of gravity. The group's calculations
show that the maximum mass of neutron stars would be smaller than
in general relativity and the increase in wavelength, or
"redshift," experienced by photons emitted from the stars' surfaces
must be 10 percent larger.

"Our quantitative predictions allow strong field violations of
relativity to be characterized and tested in the extreme
gravitational environment of a neutron star," said Jacobson to
PhysOrg.com.

Upcoming experiments that may provide more insight into relatively
at work in strong-gravity situations include x-ray detectors
capable of tracking the movement of elements in disks around black
holes, which will map out the shape of spacetime around a black
hole; highly sensitive space- and ground-based detectors that will
"see" gravitational waves; and devices that will yield improved
measurements of neutron-star masses and the redshift of photons
emitted from their surfaces as they escape the stars' gravitational
fields.

This research is discussed in the August 17, 2007, online edition
of Physical Review D. In their prior work on the subject, the UM
group carried out a similar analysis for non-rotating black holes,
and found that the deviations from general relativity would be very
hard to detect. They say the case of spinning black holes would
likely produce more dramatic effects, but it is more difficult and
remains to be studied.

Citation: Christopher Eling, Ted Jacobson, and M. Coleman Miller
"Neutron stars in Einstein-aether theory" Phys. Rev. D 76, 042003
(2007)