Initial Tests Fail To Find Gravitational Waves 553
eldavojohn writes that though gravitational waves are "predicted to exist by Einstein's Theory of General Relativity, the initial tests run by the Laser Interferometer Gravitational-Wave Observatory Scientific Collaboration (LIGO) failed to find anything. It doesn't disprove their existence although it does rule out a subset of string theory. From the article, 'For example, some models predict the existence of cosmic strings, which are loops in space-time that may have formed in the early universe and gotten stretched to large scales along with the expansion of the universe. These objects are thought to produce bursts of gravitational waves as they oscillate. Since no large-amplitude gravitational waves were found, cosmic strings, if they exist at all, must be smaller than some models predict.' The scientists working in Washington and Louisiana (in tandem to rule out flukes) will now move on to Advanced LIGO which will analyze a volume of space 1,000 times larger. If they don't find any gravitational waves in that experiment, the results will be more than unsettling to many theorists."
They exist. (Score:5, Informative)
It should be noted that the existance of gravitational waves is pretty much certain - measurements of pulsars like the Hulse-Taylor binary match up perfectly with the predictions of GR.
What LIGO is about is trying to observe them directly, rather than just observing the effects of them.
Re:what to do, what to do (Score:1, Informative)
Actually, ID proponents tend to outright ignore new evidence, or any evidence, that doesn't fit their theory.
Of course... (Score:2, Informative)
Gravity is related directly to space, which in turn is directly related to time. Time, as we know, is an illusion. Lunchtime, doubly so. Therefore, gravity is an illusion. Q.E.D.
Re:Open or Closed String Models? (Score:2, Informative)
This comes down to how long it is. A cosmic string isn't the same thing as a string in string theory. A cosmic string is very long macro scale topological feature of the universe while a string theory string is a model for subatomic particles. However you can investigate cosmic strings in string theory leading to the theory of stringy cosmic strings of Vafa et al..
Re:what to do, what to do (Score:3, Informative)
Re:I think I see the problem. (Score:4, Informative)
Oblig. XKCD: Lisp [xkcd.com]
Re:Sending the theoreticians back where they belon (Score:3, Informative)
Re:what to do, what to do (Score:2, Informative)
Compare that with dogmatic writings that get promoted as absolute unchanging truth in spite of being full of internal contradictions as well contradictions with history and with science.
Re:Hex (Score:2, Informative)
Morons!
Gravity is a particle!
Re:Just because they failed to detect any (Score:4, Informative)
I think you completely missed the point. If there is a God, then studying what He/She/It created is of far lesser importance than studying God Himself. Once God is found, everything else pales in comparison. The secrets of the universe are not in what it does, or how it works; but who made it. I think that's what Jastrow was saying, anyway.
Re:Maybe they can't be detected (Score:1, Informative)
Keep in mind that gravity waves (and the movement they induce) travels at a finite speed, which is the same as that of the laser light they use.
Re:Sending the theoreticians back where they belon (Score:1, Informative)
Oh, I dunno...this seems pretty interesting to me, and might lead to 'nanomolecular assemblers' as you call them, or 'replicators' ;-), which is my preferred term. Google "DNA origami", etc.
http://en.wikipedia.org/wiki/DNA_origami [wikipedia.org]
Re:Just because they failed to detect any (Score:3, Informative)
This goes along with some of the greatest scientific discoveries .... "HUH!?!?!?!?! THATS ODD?!?!?!"
It is these moments of Whiskey Tango Foxtrot that often give us the greatest insights. The ramifications of these types of discoveries can take decades to fully decode and understand.
I love it when experiments have unexpected results, because those are the most exciting to a scientist.
Re:They exist. (Score:2, Informative)
> Yes, a lot of observations have fit the theory of gravitational waves, but
> this one in particular went against it.
No it didn't. It set an upper limit on them, but that limit is compatible with current theory.
Re:Linearization (Score:5, Informative)
> Which always made me wonder, how do gravity waves escape a black hole?
They don't. While systems involving black holes may emit gravitational waves, the waves don't come from inside the hole.
Re:what to do, what to do (Score:5, Informative)
In a field of grain, you can grow wheat, barley, rye or oats.
That's very true, of course. But you can't grow wheat, barley, and Ford Pintos. I'm arguing that physics, philosophy, and automobile repair are fields of study, while ID is not. It is a platform. An agenda. It's like saying the people paid by the tobacco companies to falsify studies on the effects of tobacco smoke are conducting science. Apples to orangutans.
Clear up a bit of confusion here: (Score:5, Informative)
Disclaimer: I don't work on LIGO, but I work with people who do.
LIGO didn't expect to see a signal above the noise here. What it has done, is largely rule out a lot of 'exotic' sources - sources with equations of state that don't fit the normal matter we see, but some of the more ambitious parts of string theory thought might be possible. What they have achieved is a phenomenal reduction in their 'noise curve' - the background above which a signal must register to be considered real. So far it's only been a one-way test - just ruling out exotic sources, but nothing that we think should necessarily be there.
LIGO primer and vast oversimplification:
LIGO is an interferometer. The way it works is that a laser is split into two parts, each of which goes down an equal length tunnel, at right angles to one another. If the light went the same distance, when it is reflected back, it should still be in phase, and should interfere constructively (think back to intro physics and the way waves on a string add). If a gravitational wave which had the right polarization passed through the region in the time of detection, one tunnel will have been 'shorter' due to the contracting geometry caused by the wave, and hence the beams will no longer be in phase when they return, so will not interfere constructively in the same way.
So why is it so hard to see waves? Well, all kinds of things (drilling, trucks going by, someone sneezing!) can cause a minute wobbling of any part of the equipment and thus will cause the waves to interfere in the wrong way. What LIGO looks for is a specific 'signature' measured at three sites concurrently, the signature being the waves predicted to occur from certain galactic events (two black holes spiraling into one another, for example). They do some pretty impressive data processing to look for this, but so far have only found that they can't see anything above the noise. We've ruled out some of the less likely things that could be going on - types of matter that some string theories allow, but certainly aren't predicted to exist by established theories (like GR).
However, over time with a few additions to 'advanced' LIGO, or the amazing LISA project we should have a two-way test: Either we'll see the wave that GR predicts to exist from standard black hole collisions, or theoretical physicists have a lot of explaining to do.
Re:I think I see the problem. (Score:4, Informative)
Have they tried reversing the polarity of the main deflector array?
That only works if one first applies an ionized tachyon pulse to clear the emitters.
Re:what to do, what to do (Score:2, Informative)
If ID is magic, then it's not science, therefore ID is magic. :)
Now this is a perfect example of begging the question -- you assume the thing you want to prove as a premise in your argument.
Re:They exist. (Score:5, Informative)
Re:Everybody knows (Score:4, Informative)
Gravity sucks.
It always lets us down
Ergo, Gravity != Rick Astley.
Re:what to do, what to do (Score:3, Informative)
You invent experiments to PROOF you theory, not to falsify it.
Sorry, no, that's just wrong. You *can't* prove *any* theory, as there may always be some case that the theory gets wrong. This would be why no modern theory, no matter how well it's predictions match experimental result, has ever been promoted to a law (see General Relativity for an excellent example).
The purpose of experiment, then, is to test the theory and see if reality matches it. If it doesn't, the theory is falsified and you go back to the drawing board, either by revising the theory or positing an entirely new one. If, however, reality does match the prediction, you go on to the next experiment, once again seeing if you can falsify the theory with the next result.
Contrast this with Intelligent Design. ID can certainly posit certain predictions (eg, irreducible complexity of the eye). And you can certainly try to falsify it ("See, look, here are the chain of fossils that show the evolution of the eye"). But an ID proponent can simply declare that God made it that way, and then move on to the next prediction. IOW, the theory is impossible to falsify, as it always gives the believer an "out".
Re:Linearization (Score:4, Informative)
The visualization is sound, for a 3d representation. The problem is that space/time involves the 4th dimension, and we are 3rd demensional beings. It is impossible for us to visualize anything in the 4th dimension in a literal sense - we have no frame of reference.
We can think about it abstractly, in ways we can somewhat understand. That is what the "rubber sheet" model is. Space/time is obviously not a 2d plane in a 3d world, it's a 3d plane in a 4d world. What is actually happening is that rubbersheet exists in every direction - forward, backward, up and down. It's not many sheets, it's not a sphere surrounding everything, it is a plane that exists in all three dimensions. It's a difficult abstraction to make, and it is impossible to accurately and literally conceptualize because we have no 4d frame of reference.
For a good explanation of why that is, check out Carl Sagan's [youtube.com] explanation, it's rather enlightening. He steps it down to a 3d object interacting with a 2d world, so that we have a frame of reference to understand what is happening.
You won't come out understanding the 4th dimension, you'll come out understanding why you can't understand the 4th dimension, and since Space/Time is a 4th dimensional concept, why the explanations don't make sense.
Re:Clear up a bit of confusion here: (Score:4, Informative)
You're almost there - what we're looking for is a contraction along one axis, and an expansion along the other (for the simplest case). Therefore to your observers (remember speed of light is a constant in all reference frames) you would see the light ray along the shorter distance get back before the one along the longer distance. The observer watching from within the system won't see the light go perfectly straight. The curvature of space itself is very much observable to someone living within that space.
An example that might help illustrate this is the first real experimental test of GR - photographs of the sky during a solar eclipse. Here it was seen that stars appeared out of place from where they 'should' be if the light had traveled through a straight (flat/Euclidean) geometry. This effect was the effect of the sun's gravitation bending the light rays.
More recently we've been able to see light from distant stars that goes on either side of a large mass that bends them both towards us, the light from one side traveling further than the other. The lensing effect is now quite famous and is very useful in examining distant events that would otherwise be hard to see (somehow having something 'in the way' of our sight actually improves our ability to see it!).
I hope that helps, though I realize that it might not be as clear as you'd like.
Re:Maybe they can't be detected (Score:3, Informative)
This is why the laser is split, and sent down two perpendicular paths. Sure, a wave might stretch the spacetime of the X axis... but that same stretching wouldn't effect a similar increase in the return time of the Y axis. This very stretching of the measuring device itself against one axis(thus modifying the round-trip time of the split laser as compared to a perpendicular path) is the very thing that they are measuring.
Your pet theory, and their experiment, match. :)