LIGO Fails To Detect Gravity Waves

planckscale writes "Last weekend, LIGO (the Laser Interferometer Gravitational-Wave Observatory) did not detect gravitational radiation in association with a gamma ray burst (GRB). The non-detection was actually a valuable contribution, as it helped to distinguish between competing models for what powers GRBs. The detector is due to be upgraded this year for even more accurate measurements. The interferometer is constructed in such a way that it can detect a change in the lengths of the two arms relative to each other of less than a thousandth the diameter of an atomic nucleus."

diameter?

[bwd234]

"...of less than a thousandth the diameter of an atomic nucleus."

Would that be a hydrogen nucleus... a uranium nucleus? Please be more specific.

Re:Fails?

[killmofasta]

Failed to detect. The theory said something should be there, but at what relitive strenght? How much closer (Newtonionan) object be to have to eminate a wave that can be measured. They are looking on the order of a thousanths of a diameter of a neculus, over the length of 4Km.

Is Mickelson Morley repeathing itself?

"The Mickelson-Morley Experiment failed to recognize that the round trip regardless of the direction would be the same and yet at the same time we know ..."

Couldnt we just look at their data? Did a large event happen when they were looking at light beams? We just repeated their experment to an extrodinary accuracy.

Re:Two...arms.

[Anonymous Coward]

That must be the most useless analogy ever.

Analogy?

Re:Fails?

[Anonymous Coward]

Does it detect any gravitational wave at all? According to this wikipedia article [wikipedia.org], "... gravitational radiation has not yet been directly detected". I assume this means that no instrument can directly detect gravitational waves at all.

As far as I understand from the wikipedia article, they have deduced the existence of gravitational waves by the orbitals drawing closer of large rotating binary starts, but no instrument has ever detected any gravitational wave.

Please correct me if I am wrong - some links might help.

Re:Fails?

[smilindog2000]

Actually, I don't think the article is saying that any rethinking of GRBs needs to be done here. The non-detection just proves the burst was from a lot farther than the Andromeda galaxy. That's a good thing, and in-line with some theories if I'm not mistaken. Last I'd read, these bursts can be so violent that they might kill all life forms in the galaxy where they occur. We really don't want them to be common enough to ever happen in our neck of the woods.

Re:Fails?

[bluFox]

Any instrument needs to be calibrated before it can be used for detection. Which means that it has to detect gravitational waves *directly* on some event that is known to produce gravity waves. Apparently LIGO [wikipedia.org] has not been able to detect *any* waves directly until now. Until it does that I think the grandparents question (If the gravity waves exist at all) holds good. Since LIGO has not been able to detect any waves, I do not understand how they can claim tha non-detection is a major event.

Re:As a matter of interest...

[master_p]

Other types of waves (e.g. sound waves, energy waves etc) are composed of particles. What is a gravitational wave composed of? of gravitons? gravitons are not proven to exist. If a gravitational wave has energy (as well as momentum and angular momentum) then what kind of energy is contained in the wave? where does this energy come from?

All that and fun too!

[sd.fhasldff]

What we would replace it with that could explain all of the observations that GR predicts I don't personally know, but it's a good day in physics when a theory is proved wrong because it means that we've done our job.

Not only does it mean we've done our job, it's also a whole lot of fun. Suddenly there's a whole new theory (or even better, lack of one) to test. Lots of new experiments to do. More hours to spend in basement labs...

ID'ers just don't know the fun they're missing.

Re:Of couse, they could *both* have it wrong...

[dlevitan]

Maybe it's just the skeptic in me, but did you just claim that it's a very clear and well understood prediction? Doesn't that imply hypothesis phase? Isn't LIGO part of the observation phase? I have a hard time swallowing the idea that it's a solid theory when we haven't even been able to create any reliable, reproducible scientific observations.

There are "clear and well understood" theories and there are not clear and poorly understood theories. GR has made several correct predictions that have been tested. The same theory has also predicted gravitational waves of which there is indirect observation (merging binaries). We haven't made any direct observations but that's only a matter of time and money.

Looking at not clear and poorly understood theories, there is string theory, which has changed so many times that its not even close to the original anymore. The latest on string theory is that certain parts of it mimic what we know already, but exactly how it operates no one has any idea of. Another example is quantum gravity. Again, we have a general idea, but nothing concrete. However, just because we don't know the more correct theory doesn't mean we can't use the initial theory. Newtonian mechanics did not become wrong after QM and GR. Its just not as accurate.

can it?

[nguy]

What you apparently do not understand is that this device can detect gravitational waves.

That has never been demonstrated. For all we know, gravitational waves may simply not exist.

Re:what if gravitational waves already passed?

[rasputin465]

but I can recall someone arguing that gravity has the estrange property of been instantaneous.

Actually, it's the opposite. Prior to GR, Newton's theory of gravitation predicted that gravitational effects travel instantaneously. After Einstein developed the theory of Special Relativity which, among other things, forbids energy/information from traveling faster than the speed of light, he spent the next ~10 years developing a theory of gravity which was consistent with this (in physics-speak, we say that such a theory is "Lorentz-invariant").

In a vacuum, gravitational waves and photons travel at exactly the speed of light. This can change if the waves encounter obstacles (i.e. how light refracts in a lense, or water, etc.) like dust or other material in its path.

Re:As a matter of interest...

[demallien2]

That would be true, provided that we knew that LIGO actually worked. As it has to date failed to detect any gravity waves, we can not eliminate the possibility:
  - that gravity waves don't exist (ie that GR is wrong)
  - that the calculated sensitivity of LIGO is wrong by orders of magnitude

As a result, this study really doesn't tell us very much at all.

No one has detected gravitational waves... Yet

[mbone]

There have been no direct detections of gravitational waves so far. There have been indirect detections (most robustly with the various binary millisecond pulsars, whose orbits slowly decay due to their radiating energy away in gravitational waves), but no direct detections. However, this was not really seen as an issue, as gravitational wave searches before LIGO suffered from the problem that there were no known sources strong enough for them to detect with good probability. You have to start somewhere, and there is always the chance of either good luck, say a close supernova, or some unknown source that is stronger than expected, but I believe that this is the first actual event whose gravitational waves, by a reasonable model, had a chance of being detected with existing equipment. One such non-detection means nothing - maybe the Gamma Ray Burst occurred way behind the Andromeda Galaxy, for example. If this is consistently repeated, we will eventually conclude that there is something wrong with our physics or our astrophysics, but it is much too soon for that.

Graviatational radiation

[rotenberry]

Many persons have implied that not detecting gravitational radiation will somehow invalidate General Relativity. Unless I am mistaken, every theory of gravitation that requires that

1. Forces due to massive bodies (gravity) to propagate at the speed of light, and
2. Energy to be conserved

must also have gravitational radiation. Information propagates at infinite speed in Newton's theory of gravity, so there is no gravitational radiation.