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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."
This is another failiure in the long history of trying to detect gravity waves.
As a matter of interest what would be the consequences to modern physics if Gravity waves do not exist?
Choose your allies carefully, it is highly unlikely you will be held accountable for the actions of your enemies
"...of less than a thousandth the diameter of an atomic nucleus."
Would that be a hydrogen nucleus... a uranium nucleus? Please be more specific.
"I like to lick butts!" by MobileTatsu-NJG (#32700246) (Score:5, Informative)
I'll spell it out for you. This is not a failure of gravitational wave detection technology.
What you apparently do not understand is that this device can detect gravitational waves. However, it did not detect gravitational waves that correlated with a gamma wave burst originating in Andromeda. Normally such bursts arise from well known phenomena, such as a collision of black holes. But in this case, the collision could not have been from one of these well known phenomena.
What the article suffers from is bad writing. It should have been put in the positive--something like "the gamma-ray burst originated from a novel mechanism". Now, because astrophysicists can not account for the burst, they must go back and (1) study other similar phenomena and/or (2) revise astrophysical theory to explain the heretofore inexplicable gamma ray burst. Why is this burst inexplicable at this point? Because they did not detect gravitational waves that correlated with the burst.
Just callin' it like I see it.
Yes Neo, there is no gravity.
If you mod this up, your slashdot background will turn into a beautiful sunset!
They're little plastic blocks that kids build things with. Granted, you can make things like the Millenium Falcon with them but it can't actually fly.
Oh wait, you said LIGO, nevermind.
Summation 2
There is no gravity - Earth sucks!
In Murphy We Turst
1) General Relativity as formulated by Einstein (and a lot of other similar derivates - are there many?) would be in serious doubt. An exam question I had was take GR and show gravity waves exist - you basically show how the wave equation falls out of the formulas and these things carry momentum out of a system.
2) You then need to explain stuff such as Mercury's orbit precession and observed effects of double Neutron stars slowing down - the FSM stirring his planetary meatball lunch slower?
The Singularity is closer than you think
Quant
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.
Beer is proof that God loves us, and wants us to be happy.
licet differant, aequabitur
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 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.
~561
As predicted, the bites are already being ripped out of my flesh...
In Soviet Washington the swamp drains you.
For all the people arguing over whether or not this is a failure of LIGO or not...it doesn't really say much at all. Initial LIGO (which is currently running) is more of a proof of concept sold as a viable project. But if you look at the expected rates of detection, the absolute high end for all binary sources is less than one event/year. The low end is between 4 events every 10000 years and 4 events every 100 years. The other source types are not any better.
This article basically says that because LIGO is known to not be sensitive enough to measure past a certain distance from Earth (which encompasses the Andromeda galaxy, in whose direction this burst occurred) and because no detection was seen, the burst was not caused from a source in the Andromeda Galaxy.
I suppose that after spending all this money its not a bad thing that LIGO can actually produce some useful results (though I doubt they were amazingly useful). Advanced LIGO should be able to do the job - but not for another 5-6 years. At that point, the minimum event rate is supposed to be around 1/year and we should finally get some sort of positive detection.
Personally I'm hoping Advanced LIGO does work, because otherwise all this money will have gone to waste and the field of gravitational wave astronomy will be even more damaged than it already is. The thing is, many people in astronomy who are not affiliated with LIGO are not excited by it. Maybe that interest will be rekindled when Adv LIGO actually works, since right now its more of an engineering problem than an astronomy or physics problem. More people are interested in LISA which (if it ever launches) should have many more interesting sources. Its amusing seeing LIGO people try to point out the flaws of LISA while trying to explain why LIGO doesn't work, but then maybe I'm biased since I am working on LISA (though I have worked on LIGO in the past).
... but I would call this simply "bad" science - You can't use one poorly-understood phenomenon to explore another. You are incorrect. Gravitational waves (the phenomenon) are a very clear and very well understood prediction of the theory of General Relativity. So I would say that this is as far from "bad" science as you can get. If, ultimately, gravitational waves are not detected by LIGO and its successors that would prove GR was incorrect. And that would be a huge scientific advance.Perhaps the LISA (NASA/ESA) project will have more luck (2015+).
At the risk of opening up some sensitive old wounds here, if you had more than one of these...
would they be called LIGOs?
I looked at the Wikipedia article about LIGO and noticed this interesting question in the discussion. No one has answered it there. Apparently it's from some forum somewhere. Maybe someone here can explain the solution to this "conundrum" for me?
I'd be fascinated to see what's wrong with the reasoning here!
Ok - I accept your analogy of the DNA sequencing to explain the usage of "indirect". What I'm not sure is whether the authors of the wikipedia article intended to use the word that way.
Let's forget wikipedia for a second. Let me ask:
1. Has a man-made grativational wave been detected by LIGO (or any other gravitational wave instrument)? If so, I'd appreciate links to authoritative sources.
2. Has a natural event which has been corroborated by other sources been detected by LIGO (or any other gravitational wave instrument)?
Both the above tests have are true for DNA sequencing - man made and natural mutations can be detected "indirectly". If neither of the two conditions hold true for LIGO, then how do we know that it even detects gravitational waves?
Ofcourse, if my question appears ignorant - please understand that I'm a general slashdot reader and not a physicist. I'd appreciate your effort in helping me understand.
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.
From the wiki GW and here : The gravitational wave has been indirectly shown to exist by showing that the evolution of orbit of the binary system is in precise agreement with the loss of energy predicted by gravitational waves. Note that this was not done by LIGO. It was observed using convensional Radio telescopes. More over the LIGO is a *direct* detector of Gravitational waves. So I would like to know if LIGO has ever detected gravitational waves. If not the claim is questionable.
~561
Terrorists can't threaten a country's freedom and democracy. Only lawmakers and voters can do that.
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.
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.
Yes. This is no failure in the dectection technology. People at LIGO have estimated what they can detect and what they cannot. This puts an upper bound in the energy of the gravitational waves that were emitted by the GRB source. If it emitted more they would have detected them. This shows GRBs theories have a long way to go. We dont even know the total intrinsic amount of energy of a GRB source. If the source radiates in a polar pattern (like a lighthouse) we only see a small fraction of the GRB sources that exists (when the beam is directed toward the earth), in this case the intrinsic amount of energy is much smaller. If the GRB radiates like a star in all directions the intrinsic amount of energy is MUCH bigger. We can estimate the maximum size of the source bases in the timing of the event (if it has very fast variations it must be smaller because the information to coordinate this variation cannot propagate faster than light). But we dont know much more. This "failed" experiment is as important fot GRBs theory as the "failed" experiment in detecting the aether wind by Michelson and Morley was for the birth of Relativity. It shows we must review our theories. Airton da Fonseca Granero
Well, light is sort of separated. You won't feel the gravitational wave passing through you because the effect is so small and everything will be stretched along with you. However, light has no width and so when the distance between the mirrors increases, it goes out of phase with the cavity and turns up as a signal. Remember that light always travels at the same speed in vacuum, which is why this works.
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.
There are others? I've never heard of any.
http://en.wikipedia.org/wiki/Alternatives_to_general_relativity
http://en.wikipedia.org/wiki/Parameterized_post-Newtonian_formalism
At least not as an overall theory.
I don't know what that means. How is one field theory more "overall" than another? People have attempted to apply GR to many more problems than any of the others, but that doesn't make GR any more complete than any of the others.
The argument is that since binary systems which include a neutron star steadily lose energy it must leave in the form of gravity waves.
Einstein predicted transverse gravitational waves. This post questions whether LIGO is capable of detecting transverse or only longitudinal waves. The poster also points out that two waves would be generated and says that the longitudinal waves cancel at large distances.
Only his tendency toward a dazed stupor prevented him from screaming aloud.
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.
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.
The General Theory of Relativity says they should move at the speed of light. They are simply warps in space-time that are caused events involving really big masses (like black holes colliding). They are basically changes in gravitational forces as very massive object move. A classical example is two black holes rotate around each other and approach and collide. The gravitational forces vibrate up and down in magnitude as the objects move towards and away from us. That is the wave we're trying to detect.
....The General Theory of Relativity says they should move at the speed of light......
If gravity is confined to the speed of light, the Sun should have lost its planets long ago. For example, simple Newtonian math tells us that the Sun and Jupiter "KNOW" about each other right NOW or in a very short amount amount of time, not 43 minutes later. the Earth and the Sun "feel" each other's gravity instantaneously, not with an eight minute delay. The sun and the center of our galaxy communicate by gravity without a many light year time delay. Otherwise, the galaxy would fly apart.
Matter and electromagnetic energy have a speed limit, but gravity either doesn't have a limit at all, or it is incredibly high. Gravity equations do not contain any time values, only mass and distance.
All theory is gray
Unfortunately, too many physicists aren't very familiar with the theory of information.
If one can state the one basic principle in that theory it is that to send or store information you have to spend energy, increasing the entropy in the universe. However, thermodynamics is a macroscopic phenomenon, at quantum dimensions all phenomena are reversible. In quantum dimensions one could say that time is bidirectional. Coincidentally or not, it seems that in quantum dimensions there is no limitation in speed, information can be transmitted instantly. And, what is more, there are experimental results confirming this.
I confess I'm not too confident on those proofs that information cannot be transfered faster than light. Until someone creates a theory that conciliates quantum mechanics with general relativity, I'm willing to believe anything. Maybe irreversible time is just an illusion created by the thermodynamic effects in our macroscopic brains...
Newtonian gravitational equations. In that you are correct. But reality is Non-Newtonian. All Jupiter knows is what the Sun was doing 43 minutes ago. All we know is what the Sun was like 8 minutes ago. Relativity puts a speed limit not just on light but on any type of information transfer. Unless you want to throw out causality. Go read your Einstein again. Or even any introductory physics text on relativity. They explain it quite well. Or here, for anyone who likes small words, try this.
...It is integral to the equations that model electromagnetic phenomenon.....True. It is however NOT integral to equations that describe gravity! There is no time value in them. This is false. Time most definitely appears in the Einstein field equations. The linearized version of them is almost identical to Maxwell's equations.
You are thinking of Newtonian gravity, in which gravity is instantaneous. This is not true of relativistic gravity, in which gravity propagates at the speed of light. Therefore, if someone turned on a gravity generator or suddenly removed a gravity shield, the effects of that should be instantaneous, or at least very fast over large distances. This is false, as can be proven from the Einstein field equations. See here. Until Mr. Roemer first measured the speed of light, it too was thought to be instantaneous. Maybe someday the speed of gravity will be measured. It has been, albeit indirectly. The 1993 Nobel Prize in physics was awarded for this work. It equals the speed of light, plus or minus a few percent experimental error. The sun and the center of our galaxy are in gravitational "touch" with each other NOW, not how they were thousands of light years ago. This too is false. See the paper I cited here.
....But reality is Non-Newtonian.....
For the electromagnetic interaction, relativity has been experimentally shown, but gravity is still pretty much a mystery. We know that matter somehow gives rise to an acceleration we call gravity. There is no way to tell the difference between this acceleration due to gravity and the acceleration of matter by some means. There is no experiment you could do inside, if you were sealed into a closed rocket, to tell whether your cabin was being accelerated through space at 32ft/sec/sec or if that cabin was simply parked on the launch pad on earth.
We also know by experiment, that the gravitational interaction is some 36 orders of magnitude smaller than the electric interaction. Two neutron stars or black holes in close proximity, could have way more influence on each other and the radiation emitted, by way of the electric interactions between them, than by gravity.
Sure, the theory of relativity asserts that gravity is also subject to the speed of light, but that part of relativity has never been experimentally verified. Newtonian mechanics mandate that gravity ITSELF not be in any way be impacted by time. Only the ACCELERATION produced by gravity has a time value. Since the planets and galaxies don't move relative to each other at anywhere close to the speed of light, relativity doesn't enter into the picture here.
All theory is gray
Seriously, what history books have you been reading? You've got parts right. Gravity is indistinguishable from acceleration if you attempt to treat an accelerating body as an inertial reference frame. Yes, an imaginary force does appear if you do the coordinate substitution in this case (see any number of textbook, or, if you enjoy comedy this).
But to assert that the gravitational portions of relativity have never been shown experimentally is ignoring history. I point you towards the precession of Mercury's orbit and the first observation of gravitational lensing in 1919 (See the Story of Eddington and the Eclipse, laid out in many places and quite humorously here. And that's just the simple ones. It's called General Relativity.
Now, let's look at some of your errors here:
1)"Two neutron stars or black holes in close proximity, could have way more influence on each other and the radiation emitted, by way of the electric interactions between them, than by gravity."
Ok, true, given certain things. Even true about the radiation. Except for we're not talking about EM radiation in this context, we're talking about gravitational radiation, which shows no response to EM forces.
2)"Newtonian mechanics mandate that gravity ITSELF not be in any way be impacted by time. Only the ACCELERATION produced by gravity has a time value. Since the planets and galaxies don't move relative to each other at anywhere close to the speed of light, relativity doesn't enter into the picture here."
I'm not even sure where to begin here. Newton is wrong. Sorry to say it. I teach his laws every day in class, and he's wrong. He got damn close but his basic assumptions about the nature of reality are off. Space and time are not static. The force of gravity is only varies with time as the location and the mass creating the space-time curving effect that we see as gravity varies. So, if the object moves (like, oh, I don't know, a binary black hole system) the force we notice will vary. It takes time for the information that the force has changed to reach us. We don't notice instantly. That would mean information has traveled faster than light. Which is not possible.
Oh, and by the way, relativity does enter into this as General Relativity is a description of gravity.
Seriously, go read the first couple of sections ofThe Elegant Universe. And then go read a text book.