Gravitational radiation

[wolram]

the search for "gravity waves", is ongoing, i cannot comprehend
all the consequences if they are not found, but i understand
they won't be minor.
anyone have thoughts on this?

 

[mathman]

(Written by a non-expert.) General relativity predicts their existence. If they can be proven not to exist (not just hard to find), this will indicate a serious flaw in the theory.

 

[Jonathan]

I think they do exist, but am quite sure that they don't exist in the form that they're looking for them. Of course I have no evidence yet .

 

[selfAdjoint]

They have been looked for for 50 years and not found yet. The failure to find them is blamed on the insensitivity of the detectors, not on GR. You can see the scientists trying to lower the bar on LIGO and prepare the public for a null result. Tis will again be blamed (crrectly) on LIGO, not GR.


Gravity waves are indeed the weakest, faintest large scale phenomena we have ever tried to detect.

 

[wolram]

http://physicsweb.org/article/world/12/5/4/1

The work is a significant step towards achieving the nearly incredible measurement sensitivity aimed for in gravity-wave research - equivalent to detecting a change less than the radius of an atom in a distance as large as that from the Earth to the Sun.
----------------------------------------------------------------------
there is little more on this web site, i picked this quote
to emphasise the accuracy needed to find these waves.

 

[Unkaspam]

We've used stereophotogrammetry to measure pressure waves on mars. Would'nt this help in finding gravity waves? You need a matrix of some sort to see the waves with stereophotogrammetry.

 

[wolram]

We've used stereophotogrammetry to measure pressure waves on mars. Would'nt this help in finding gravity waves? You need a matrix of some sort to see the waves with stereophotogrammetry.

pardon my ignorance but i do not understand "stereophotogrammetry"
can you expand on this?

 

[wolram]

I think they do exist, but am quite sure that they don't exist in the form that they're looking for them. Of course I have no evidence yet

JONATHAN are you waiting for a negative result before you print
your theory, or are you willing to spill the beans now?
"he who dares"

 

[Unkaspam]

Originally posted by wolram
We've used stereophotogrammetry to measure pressure waves on mars. Would'nt this help in finding gravity waves? You need a matrix of some sort to see the waves with stereophotogrammetry.

pardon my ignorance but i do not understand "stereophotogrammetry"
can you expand on this?

Have a look a this for now, http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1229.pdf

Stereophotogrammetry might not be what we need to detect radiation, if gravity is a form of radiation. Pressure is not a form of radiation but does come in the form of radiating waves.

 

[wolram]

sorry i have no idea what this is about

 

[Unkaspam]

I can't say I know what its about either.

Here's another place where stereophotogrammetry was used, note the use of the term "gravity waves" in this passage


Effects of ocean waves on remote imaging sensors (stereophotogrammetry), pp.84-93
Author(s): John W. McLean, Kaman Aerospace Corp., Tucson, AZ,
USA;
Aly Graham, Kaman Aerospace Corp., Tucson, AZ, USA.

Abstract: A simulation model is described which generates
simulated images of underwater objects as viewed
through a wind-roughened ocean surface. The physical
model includes representations for the two-dimensional
wavy surface (gravity waves), beam spread at the
surface due to small scale roughness (capillary waves),
and beam spread and attenuation due to multiple
scattering and absorption in the water. The sensor is
modeled as a monostatic imaging system of arbitrary
incidence angle, with emphasis on LIDAR systems.
Results of the simulations are presented, illustrating
the distortion of images in active seas, and the loss
of resolution due to surface and volumetric scattering.

 

[wolram]

from what i can understand this is a remote mapping system
incorperating stereo photography to define the topography
of a surface.
it seems this system has many uses but finding grvity waves
is not one of them

 

[Ambitwistor]

This is probably a terminological confusion. Geophysicists and oceanographers have a term, "gravity wave", which refers to a kind of water wave. It has nothing to do with gravitational radiation, or the propagation speed of gravity. To avoid confusion, the preferred term for wave solutions of gravitational radiation is "gravitational wave", not "gravity wave", although you will sometimes see the latter (particularly among popularized treatments).

So anyway, no, stereophotogrammetry is not useful to detect gravitational waves.

 

[Unkaspam]

I guess we can leave that instrument to the geophysicists.

What is used in the detection of gravitational waves is the Laser Interferometer Gravitational Wave Observatory.

http://www.ligo.caltech.edu/docs/G/G030024-00.pdf [Broken]

This document is an evaluation of its good and bad points. You need Acrobat to read this.

 

[Nereid]

Originally posted by wolram
the search for "gravity waves", is ongoing, i cannot comprehend
all the consequences if they are not found, but i understand
they won't be minor.
anyone have thoughts on this?

To (hopefully) clarify another possible confusion in terminology:
- "gravitation radiation" (the subject of this thread) has been "observed" in at least one binary pulsar (a pair of closely orbiting neutron stars), in the sense that the orbits appear to be changing in a way which implies a loss of energy in the system. The energy loss is hypothesised to be gravitational radiation, and the observed and predicted changes in the pulsar's orbit are consistent with GR.
- "gravitational waves" have not yet been detected, though LIGO (now up and running) and LISA (set to be launched in 2011) are expected to make positive detections.

The gravitational radiation from binary pulsars - at least, those we've found to date - is too weak to be detected by LIGO. However, if a neutron star binary (or a black hole-neutron star one) were to coalesce, the death spiral would generate strong enough gravitational radiation for LIGO to detect. If a suitably distant* NS-NS coalescence were observed in EM (especially in gamma!), and the expected gravitational radiation were not detected, GR would be likely be in trouble.

By the time LISA goes live, son-of-LIGO should have detected at least one death spiral (and several other violent events besides).

*we don't want it to be close - the gravitational radiation would certainly be detected, but no humans would be left alive to record it!