If gravitational lensing proves GR, why isn't it universally accepted?

[atyy]

Isnt it obvious? I am imagining that all these budget approval comissions have received presentations and calculations based on GR, which have suggested that they can detect gravitational waves. But maybe I am just naive, and they routinely spent millions without expecting to receive some results :)

I think that is an interesting question. I haven't been following, but I remember a few years ago they reported a null result, which it seems was consistent with expectations from other data.

http://www.ligo.org/science/Publication-S6CBCLowMass/
"This "null result" allows LIGO and Virgo scientists to set new limits on the rate of compact binary mergers in the universe. These limits are still about 100 times higher than expected rates from astronomical observations, so the fact that no gravitational waves were detected is consistent with expectations."

http://stuver.blogspot.com/2012/06/null-result-not-finding-what-you-were.html (I think this is written by Amber Stuver http://www.phys.lsu.edu/newwebsite/people/stuver.html.)
"My standard response (as of this date, of course) is, "None, and we didn't expect to either." And I say this with a smile on my face. Cue the confused and disappointed expressions..."

 

[wabbit]

Isnt it obvious? I am imagining that all these budget approval comissions have received presentations and calculations based on GR, which have suggested that they can detect gravitational waves. But maybe I am just naive, and they routinely spent millions without expecting to receive some results :)

I don't know, but you are suggesting the promoters of the project obtained funding under false pretenses. Maybe they did, I have no idea. But I would think some kind of evidence would not be unwarranted before assuming that.

I don't know what they said to those commissions (in the 1990s presumably), but this is a paper from 2001 outlining what was expected then.

LIGO's "Science Reach", Lee Samuel Finn

Technical discussions of the Laser Interferometer Gravitational Wave Observatory (LIGO) sensitivity often focus on its effective sensitivity to gravitational waves in a given band; nevertheless, the goal of the LIGO Project is to ``do science.'' Exploiting this new observational perspective to explore the Universe is a long-term goal, toward which LIGO's initial instrumentation is but a first step. Nevertheless, the first generation LIGO instrumentation is sensitive enough that even non-detection --- in the form of an upper limit --- is also informative. In this brief article I describe in quantitative terms some of the science we can hope to do with first and future generation LIGO instrumentation: it short, the ``science reach'' of the detector we are building and the ones we hope to build.

 

[pervect]

My $.02. There is a lot of smoke about GR and QM being incompatible, but as far as I can tell, they are both compatible in the areas where they both work properly. That is that QM works as an effective field theory at low energies, and GR does too. Neither theory can pretend to work at all energies, QM has issues with various sorts of "diveriences" which are still being debated, but most likely lead to a failure of the theory to apply to arbitrarily high energies. Similarly, GR is ill-behaved in some circumstances, which also involve high energies, such as the singularity in a black hole.

If we stick to the "low-energy" area of physics, both GR and QM live together as a quantum field theory in a curved space-time. There are some theoretical issues, such as the lack of any scheme to quantize gravity waves, but these theoretical issues don't have any experimental consequences in the low-energy regime that our current physics describes.

BTW, "low energy" may be a bit misleading, my understanding is that anything we've been able to do with our most energetic super-coliders is still under the umbrella of "low energy".

 

[SpiderET]

I think that is an interesting question. I haven't been following, but I remember a few years ago they reported a null result, which it seems was consistent with expectations from other data.

http://www.ligo.org/science/Publication-S6CBCLowMass/
"This "null result" allows LIGO and Virgo scientists to set new limits on the rate of compact binary mergers in the universe. These limits are still about 100 times higher than expected rates from astronomical observations, so the fact that no gravitational waves were detected is consistent with expectations."

http://stuver.blogspot.com/2012/06/null-result-not-finding-what-you-were.html (I think this is written by Amber Stuver http://www.phys.lsu.edu/newwebsite/people/stuver.html.)
"My standard response (as of this date, of course) is, "None, and we didn't expect to either." And I say this with a smile on my face. Cue the confused and disappointed expressions..."

Thanks for good links, which give good insight into what they expected. Official LIGO page is rather hard to go trough. I don't want to hijack this thread into gravitational waves discusion, so this is my last response to this topic.

 

[atyy]

If we stick to the "low-energy" area of physics, both GR and QM live together as a quantum field theory in a curved space-time. There are some theoretical issues, such as the lack of any scheme to quantize gravity waves, but these theoretical issues don't have any experimental consequences in the low-energy regime that our current physics describes.

The gravitational waves can be quantized, eg. http://luth2.obspm.fr/IHP06/lectures/silk-uzan/IHP_bib/bmf.pdf (sections 9 and 10).