Examining Gravity Waves 61
Joseph "JoeDaMac" Haake writes "Sometime within the next two years, researchers will detect the first signals of gravity waves -- those weak blips from the far edges of the universe passing through our bodies every second. Predicted by Einstein's theory of general relativity, gravity waves are expected to reveal, ultimately, previously unattainable mysteries of the universe."
What if they don't find the gravity waves? (Score:5, Funny)
Think of all the fun that would be! Think of the chaos, the pontificating, the explanations, the TV specials! Think of all the dissertations that would generate! Yes sir, that would be wonderful.
Re:What if they don't find the gravity waves? (Score:4, Funny)
Praise and honor to that new generation of phycisists, and shame on those old school amateurs!
There would be new popular books on how "close" we are to have a GUT explaining "everything". Super egos like Stephen Hawking would say: "I told you so" (even though he didn't).
A bunch of Nobel prizes currently in an undetermined Schrödinger state will await those who are lucky enough to be where the action is.
Unfortunately, the Chinese and Japanese scientists that will provide the framework of the New Theory will not end up on the cover of Time (that will instead be Steve Ballmer or some other American/Western savior of the world).
Re:What if they don't find the gravity waves? (Score:5, Interesting)
We didn't do that to Issac Newton did we?
I am very firmly convinced that the universe is far stranger than even the most brilliant minds alive today or yesterday ever give it credit for. I'm also very firmly convinced that no matter what mathmatical model we try to cram the universe into, we'll always find exceptions and things we don't understand. We'll find evidence to back up existing theories and postulates, yes, but we will also find evidence that takes current theories in a back alley, beats them across the head with a lead pipe, and then steals their credit cards.
Look at the research being done on gravity suppression or-- dare I say it-- anti-gravity. This research is considered quackerie and bad science by legitimate scientists who come across it. The fact remains, however, that this guy's research [bbc.co.uk] has such a huge potential to undermine existing theory and completely rewrite the books concerning propulsion that Boeing has made a major investment in his work.
One day, maybe one day soon, some scientist or group of scientists will make a major refinement on Einsteinian 'General Relativity' just as Einstein made a major refinement on Newtonian 'Classical Physics'. That doesn't mean that the work Newton did or the work Einstein did weren't major acheivments in and of themselves. It doesn't mean that they don't predict a great deal of what's going on, both out there in the cold reaches and here on Earth.
If you beleive that Einstein is 100% correct about everything he theorized then you're going to be in the same boat as people who beleived Newton was 100% correct. We don't know everything and we never will. Get over it already.
Re:What if they don't find the gravity waves? (Score:2, Insightful)
Well, in the mind of the commoner, Einstein is the scientist par excellence.
You can't buy t-shirts or posters with Newton. You can with Einstein. Ask people if they know a physical formula, and they'll say E=mc^2, not F=GMm/r^2 or F=ma. Say 'genius', and people think of Einstein, not Newton (although Newton probably was more ingenious than Einstein). Hell, think about it; they'd have to change the scientist icon in games like Civilization to something else...
Re:What if they don't find the gravity waves? (Score:2, Funny)
Because Einstein had really weird *wild* hair. Newton looks like any other bloke from that era.
Ask people if they know a physical formula, and they'll say E=mc^2, not F=GMm/r^2 or F=ma.
The second one is too hard to be catchy. The third looks like an abbreviation for "fuck mamma", and some might be offended or think it is graffity gang-talk short-hand.
It could also be that Einny is associated with nukes, while Newty is only associated with things like catapults. Nukes are more awe inspiring and intimidating that catapults. (However, isn't Iraq possibly building a nuclear catapult according to German sources?)
Re:What if they don't find the gravity waves? (Score:2, Interesting)
Could Einstein have come up with the mathematical models if Newton hadn't beat him to it? I don't know, but I'm also not positive that, given the solid foundation Einstein had, Newton could have predicted relativity.
Re:What if they don't find the gravity waves? (Score:3, Informative)
Einstein in turn took Lorenz' equations and Maxwells theory of electromagnetism as a starting point. Remeber that c is defined as constant in electromagnetism, so what Einstein really did was just to combine this fact with the relativity equations. This is of course ingenious, and even more so to use Non-Euclidean geometry to extend SR to GR by curved spacetime.
Newton did away with absolute space and Einstein did away with absolute time, so their contributions are very similar in structure.
Newton _invented_ caclulus as a byproduct, though, while Einstein had to borrow extensively from recent mathematics (Minkowski space, tensors and all), all of which he had to have help with to fully understand in the context of relativity.
This fact justifies Newton being the greater of the two, because mechanics and calculus are fundamental in all of physics, whereas GR is a very specialized field. We went to the moon with the help of Newton, not Einstein.
Re:What if they don't find the gravity waves? (Score:2, Interesting)
Would you still think Newton was a genius if I told you that his Principia was a mere fraction of what he spent his life doing, and in fact was a quite well-known alchemist? How about the fact that he believed that he could predict the future by reading scripture (see: Temple of Solomon). Or read the last bit of the Principia, where he believed that the tails of comets were what provided us with water and nutrients so that we could survive. His work in alchemy and scriptures comprised the vast majority of his life.
But let's remember that prior to Newton (and afterwards, for awhile) there was no such thing as an equals sign. Imagine doing calculus completely geometrically. Also remember that for the first time in history there was a theory that agreed completely with observation. And how about the fact that the Principia was the final nail in the coffin for the geocentricity.
Then there's Einstein, who was ardently opposed to the revolution that he began (Quantum revolution), and which has resulted in the most tested and highly tested theory in scientific history (note that I'm not saying it's correct). Or that as late as 1895 he may have believed in an ether.
Then again, Einstein did "kick off" quantum mechanics with the photoelectric effect. And the fact that he completely "jacked around" with the foundations of physics by redefining things like space, time, and even reality, indicates a view of the world unlike any scientist had before him.
I've listed all of this because what we define as important factors in determining who was greater is inherently and unavoidably biased by our view of the world and the history that we know. Both of these men were revolutionaries who changed the way that we look at the world. They saw a new paradigm that no one else did, and that is something that only happens, oh, every few centuries in physics.
Incidentally, Newton did NOT do away with absolute space, but adamantly believed there to be one (check out Definition 8, Scholium, in the Principia). Oh yeah, and he did account for the retrograde motion of Mars. Galileo did that first (successfully), though.
The fact that GR is a specialized field doesn't say much, considering that Newtonian mechanics has been around for over 300 years, while GR isn't even 100 yet. More time to mull over mechanics has given scientists more time to take avantage of it. Remember we may go to another star with the help of Einstein.
Things aren't so clean in the history of science. There never was, and probably never will be, a single leader in any science who heads up a revolution. To do so is completely unscientific, as science is a society, not a dictatorship. Newton didn't lead the Copernican revolution, and neither did Copernicus, or Galileo, or Brahe, or DesCartes, or Kepler. Einstein (definitely) didn't lead the quantum revolution, just as Bohr, Schrodinger, Pauli, Pauling, Dirac, or Heisenberg didn't. It evolved, it had it's bumps and bruises. Read Thomas Kuhn's "On The Structure of Scientific Revolutions" for more.
I've noticed a lot of people think "this person did this, and this person did this..." instead of "this person was a driving force in this thought, and this person contributed to this scientific program...". I guess that's just a personal thing, and I'm sure someone will argue with me over this, but concepts like calculus or GR aren't invented, they evolve, like animals evolve. And concepts die, too, to be replaced by bigger, more powerful and robust concepts.
That's just my take on science in general, and I'm sure I'll change it at some point, but I figured I'd voice it anyways.
Re:What if they don't find the gravity waves? (Score:2, Informative)
You can't buy t-shirts or posters with Newton.
t-shirt [historyshirt.com]
What if... (Score:1, Offtopic)
Mod parent up (Score:2)
Re:What if they don't find the gravity waves? (Score:1)
You're right . . . Einstein will still be there. However, all of this anti-gravity stuff is bunk. First hint: if you can shield gravity, you can violate energy conservation. Simply build a machine which lets things fall down under normal gravity, extracts the energy, then moves them back up under your shield. Voila! Instant, infinite amounts of energy. I have yet to see anti-gravity that doesn't have these sorts of problems.
All the real refinements to physical theories usually involve cases where the experiments haven't been done before: Einstein's general relativity applies to speeds close to that of light and very strong gravitational fields. Occasionally you get lucky and something which has already been noticed but is not understood (e.g. the precession of Mercury's orbit), but largely new physical theories come from extension to previously under-investigated domains.
Re:What if they don't find the gravity waves? (Score:1)
Um, how to you plan to maintain your anit-gravity shield? Since it will probably require more energy to generate the shield than you get from dropping your object (due to friction most likely) it doesn't violate anything.
Re:What if they don't find the gravity waves? (Score:1)
Re:What if they don't find the gravity waves? (Score:1)
The antigravity shield is going to require energy to create an area where there is no gravity, or gravity is reversed.
In this area you put an object, which will then rise up. You turn off the shield, and the object falls, and you capture that energy.
What I'm saying is the energy captured from the falling object will at the very most, be just enough to power the anti-gravity shield long enough to raise the object again.
Now, take into account friction.
If the anti-gravity shield has any moving parts, the amount of energy you got from the falling object will not be enough to lift the object again. Moving parts generate friction. Friction uses energy in the form of heat which is dissapated to the surrounding area. However, this energy (heat) is not used to lift the object again.
Lets try it with numbers (physics majors will probably want to correct some things here)
Lets say it takes 100J to life the object, and you are able to extract 99J of energy, the other 1J is lost to friction (most likely) in taking the energy from the falling object. Now, you're already short 1J to raise the object again. Then when running the anti-gravity shield, you're going to lose another 1J to friction in the shield generator. Down to 98J. How can you lift the object again, when you don't have enough energy?
Re:What if they don't find the gravity waves? (Score:1)
If I understand you correctly, what you're proposing is something distinctly different than any known physical system (which, I suppose, is not very surprising).
You're saying that raising an object over the shield actually destroys energy. In this process, the total energy of the shield+raised object system actually decreases. This balances the increase in energy when the object is allowed to fall again. To make this work right so that it actually balances correctly in all cases, the amount of energy required to power the shield (ignoring friction) will have to depend on the strength of the local gravitational field, the shielding coefficient, the mass of the object, and the distance it travels in the direction of the gravitational field. The shield does a sort of "negative work" on the object.
This patches up the global energy conservation problems. However, I'm still concerned because local energy conservation is violated. Specifically, the "negative work" is done at the shield, but the amount of "negative work" required is determined by the motion of the object, which can be very far away from the shield. While the distinction between local and global energy conservation is probably not as well-known as the general principle of energy conservation, in general all physical principles should be locally conservative (which implies global conservation).
Re:What if they don't find the gravity waves? (Score:1)
Um. A plane?
Are you implying that ALL forms of antigravity you've read about use antigravity shields that don't consume energy? LOL.
Re:What if they don't find the gravity waves? (Score:1)
The original post references one of the spurious forms of antigravity I'm talking about. Why would I bother claiming that planes don't stay up? Is there some logic to taking such an unreasonable position that I'm missing?
Dr Podkletnov (Score:1)
It's not that legitimate scientists didn't take his work seriously - it's that they couldn't reproduce a simple effect. Considering that he himself has not shown this result to anyone else . . . Well, the options are:
A) The scientific community is frightened by a discovery that would bring huge $ amounts into research for further work and innovation
OR
B) This guy's a quack.
I invite you to apply Occam's razor.
Oh, they will, don't you worry... (Score:1, Offtopic)
Re:Oh, they will, don't you worry... (Score:2)
Bit optimistic (Score:5, Insightful)
On the whole, i think that's not necessarily true. There are several mathematically consistent fringe quantum-physical theorys (usually something akin to higher-order-symmetry electrodynamics) in whcih gravity waves are indistinguishable from e.m. waves, or are longitudinal-time e.m. waves.
Re:Bit optimistic (Score:2, Insightful)
Original Story (Score:5, Informative)
Gravity waves (Score:2, Interesting)
On the ither hand, it could be affected by the whole varying-alpha thing. If something that fundamental is wrong, I think their data will be much less useful.
Re:Gravity waves (Score:5, Informative)
No. The waves we're going to see are a prediction of the classical theory of gravitation, general relativity. This is, of course, only an approximation to some "quantum" theory, but on this level of accuracy we're going to see only classical effects.
Compare this with classical electrodynamics (which predicts electromagnetic waves, ie. light): merely detecting gravitational radiation is going to tell you just as much about quantum gravity as seeing sunlight tells you about quantum electrodynamics.
Could it give evidence to bolster string theory?
No.
The results of this experiment should be very interesting.
Yes, but not in the way you seem to be expecting.
No "new" physics is likely to come out of these experiments (at least not directly). The exciting part is, like the article says, that this is going to give us a whole new way of doing astronomy: remember that a century ago the only way to get any information from distant objects was to look at them, but there's a whole lot of objects that are sending stuff at us on wavelengths not visible to the human eye. So, the early astronomers missed many very important things of what we're now able to see.
Being able to observe the whole electromagnetic spectrum has completely revolutionized astronomy in the past 100 years. Just think of cosmic background radiation: for a long time, it was completely missed since nobody was doing astronomy with microwaves. Similarly, there are many interesting things out there that could be sending us a signal through gravitational waves (like, for example, merging black holes) - and soon we'll be able to see that signal and whatever it's telling about these events.
Of course, the resolution will really be of the sort "an event lasting t seconds was recorded...", but we can extract useful information from even this kind of observations, especially if we can combine them with others (like optical telescopes). (This way we may even indirectly discover something totally new.)
Re:Gravity waves (Score:1)
Re:Gravity waves (Score:4, Insightful)
Yeah, and the answer still is "not directly".
More (and better) data at the turn of the century helped scientists discover the inadequacy if Newtonian mechanics,
Yes, that's the usual story. But it's not really that accurate.
the constancy of the speed of light,
Actually, this was a theoretical prediction of classical electrodynamics, not something that was first discovered by experiment. Most physicists of that era just didn't like this prediction, so they tried to interpret it through the ether idea - and then later experiments disproved this idea.
I know you've probably heard the story about how the Michelson-Morley experiment left everyone baffled until Einstein came along and explained everything by taking this observed constancy as a basic postulate of a new theory of mechanics. That's a nice story, but it's not what actually happened! There is little evidence that Einstein was even aware of the whole experiment. His first article on the special theory of relativity doesn't refer to it (some parts of it can be interpreted as evidence that Einstein was aware of the experiments, but not very convincingly).
So it's not like some "new and better data" suddenly made everyone realize there was something wrong with the current theories of physics. There were two basic theories of physics, mechanics and electrodynamics, which weren't compatible (unless you made some additional, artificial postulate, ie. ether). Einstein solved this problem by theoretical thought alone by modifying the other theory; he didn't use any experimental data (expect, of course, the data that verified classical mechanics and electrodynamics in the
first place).
So, the point of this long explanation is that scientific progress doesn't necessarily follow this simple path of "oh, here's the new data... oops, it doesn't fit our theories, we better invent new ones... oh, here's the new data..." (and, in fact, with the most fundamental theories of physics, it never does).
Right now there is a one similar, big inconsistency in modern physics: quantum mechanics and general relativity aren't "compatible". This is not completely analogous to the situation with the ether and all that: since we have succesfully made all the other classical theories (mechanics, special relativity, electrodynamics) compatible with quantum mechanics, we would expect that general relativity we could similarly quantize general relativity and get a "quantum" theory of gravity. We already know which particular feature of general relativity makes the usual quantization methods fail, so many people think this is just a question of finding the right way to do it.
(In fact, in situations in which this annoying feature of general relativity - its "nonlinearity" - isn't important, we can already make some credible calculations "combining" general relativity and quantum mechanics. The best known example is Hawking radiation.)
And, like I said in my previous post, we're not expecting this experiment to show any "quantum" effects. We have already verified general relativity on this scale (and it works - you can't see any quantum gravitational effects in the motion of planets, for example). If general relativity were to fail on this scale, we should already be able to see quantum gravitational effects in other experiments. So, the only way we could see QG in these experiments would be if GR and QM turned out to be completely wrong... and, even though you all non-physicist out there may not believe me when I say this, this is just not going to happen.
Just like I said earlier, you can safely compare this to classical electrodynamics and light: it doesn't take much experimental accuracy to verify the existence of light (ie. electromagnetic waves), but it does take a lot of work to get to the level where you get to see quantum electrodynamics in action. Similarly (this analogy is actually very close to being exact), there's a long gap between being able to merely detect gravitational waves and seeing quantum gravity in action. Even the former is very difficult to do (as should be evident), so it shouldn't be surprising that nobody expects that the latter is going to happen any time soon ("soon" quite possibly meaning many centuries or even millenia).
Like I said, there is always the possibility that we might be able to see some unexpected things through these gravitational waves, but the waves themselves will be just what classical general relativity predicts (and if they aren't, it will not mean we've hit the quantum theory of gravity; it will mean that GR is completely wrong).
And, of course, most importantly, there are a lot of interesting thing out there waiting to be discovered that just aren't the most fundamental things that exist. Not every discovery can lead to a great revolution in fundamental physics, but that doesn't make the discoveries any less exciting! The big revolutions happen so rarely that if that's all you're interested in, you're not going to get much else than disappointment from science.
(Really, a whole new kind of astronomy is being born! It's going to tell us all sorts of interesting things about the universe, even if it doesn't lead to the Theory of Everything. And that's exciting enough for me!)
wave-particle duality, and the structure of the atom.
Now this is getting closer: the Bohr model was rather directly based on experimental evidence. But the experiments were actually very misleading: they made people believe that some kind of discreteness was essential, which made them develop a theory (originally called quantum mechanics) based on some arbitrary "quantization conditions", while the real theory was actually something completely different.
Now we're stuck with the horribly misleading term "quantum mechanics" and a whole lot of people who think "discreteness" is the most essential feature of the theory. But, umm... this is getting offtopic, so I better stop right now...
Re:Gravity waves (Score:2, Insightful)
The theories themselves may have had nothing to do with experimental evidence, but the verification of those theories did. Without more powerful technology, those theories would have been mere conjectures, since they don't significantly differ from classical physics in 'normal' situations. To continue the SR/GR example: I knew that Einstein developed his theory without knowing about Michelson-Morely. The important thing, as I see it, is that the Michelson-Morely experiment provided an experimental validation of one of the postulates of his theory.
Re:Gravity waves (Score:2, Interesting)
OK! Sorry if I got a little carried away with my explanation...
The important thing, as I see it, is that the Michelson-Morely experiment provided an experimental validation of one of the postulates of his theory.
Yes. (Or, perhaps more importantly, it provided evidence that the ether theory in which everyone else believed was wrong and forced them to consider other options. The really convincing proofs of SR came from entirely elsewhere...)
OK, so if you think about these experiments from this point of view, then yes, there will be many theories that they'll be able to validate (or invalidate). The most obvious of all is of course GR and its prediction of gravitational waves... but everybody expects GR to be right anyway, so this isn't the thing we're all so worked up about.
I may be repeating myself, but this is going to provide a whole new channel of information about astronomical events, which will help us verify many astrophysical theories. At first, we'll be on the "edge" of just seeing the waves, so we'll only be able to see signals from the most violent things that happen around the universe: colliding black holes or neutron stars and such stuff. That will help us verify our models of these things, like the article says (they're talking about just this stuff), but not any fundamental theory of physics (or at least that's not expected).
Later, if they can improve the accuracy (I'm not an experimentalist, I don't know how far they can take this), there will be many other interesting things we can see. For example, in the far-off future we might be able to see a gravitational wave background produced in the Big Bang (or soon after it), which actually might provide us some information about quantum gravity. (Right now, many people are excited about the new microwave background data we're about to get from the new experiments; there's some talk about whether string theory might be able to predict some of the fine features seen in the microwave background.) But that really is far off in the future...
Re:Gravity waves (Score:1)
Re:Gravity waves (Score:2)
Re:Gravity waves (Score:1)
LISA (Score:5, Interesting)
In essence, it's just a really, really big version of the Michelson interferometer we all played with in 1st year physics - I remember the thrill back then of realising what tiny changes in distance you could discern with just a couple of mirrors, a lamp and something to measure the recieved intensity.
It's exciting to witness the nascence of an entirely new form of astronomy.
speed of gravity (Score:1)
Arent the results still being crunched?
I believe it was about measuring the speed of gravity.
Hmmm... (Score:2, Insightful)
"When we get a signal, we want to know what is generating that signal," Suen explained. "To determine that, we do a numerical simulation of a system, perhaps a neutron star collapsing, in a certain configuration, get the waveform and compare it to what we observe. If it's not a match, we change the configuration a little bit, do the comparison again and repeat the process until we can identify which configuration is responsible for the signal that we observe."
They will be changing the way they observe in order to conform with what they expect to observe. Doesn't this mean that ultimately they're not really going to discover anything new? I mean, if they set up their observation so that when looking at a neutron star collapse it matches the mathematical model, what's the point? Why not just look at the mathematical model?
Re:Hmmm... (Score:4, Insightful)
It's a classical inverse problem, he's just trying to explain it in layman's terms and making a bit of a hash of it...
Tuning (Score:4, Insightful)
I REALLY think that the only way to do this kind of thing correctly when you don't match data, is to go back and look at the set up/first principles... Were your boundary condition assumptions fair? Did you assume anything was insignificant, was it?... that sort of thing. Tuning is something that scares the crap out of me, mostly because it sounds like a good idea to most people.
Re:Tuning (Score:2)
While this may sound fishy at first, remember that no-one is going to accept your model for proven on the basis of a single observational event. Do more observations and show that it fits them without too much fiddling, then you have corroboration. (It's fair game to fit the values of basic parameters though, since these values are usually what you're after in the first place.)
Remember that the inverse problem is basically ill-posed to begin with. You're trying to establish the physical parameters of a process based on some integral measurements of some [usually quite distant] consequences of the process. Because of the integration, information is always reduced. An infinite number of different possible models can give you the same integrated results. That's where regularization and all that voodoo comes in... it's more art than science sometimes, but, in the end, the proof is in the pudding. Once your model becomes good enough to predict future observations reasonably well, that's it, that's as rigorous as you can make it and no-one can ask for more.
(After all, it's going to be a long long time before we can watch a neutron star collapse from up close.)
Re:Hmmm... (Score:2)
Re:Hmmm... (Score:2)
a little overconfident? (Score:1, Offtopic)
Wow. Somebody has a pet theory.
rigged model matching? (Score:4, Interesting)
Jabba-The-Hut doing the Wild Thing.
"When we get a signal, we want to know what is generating that signal," Suen explained. "To determine that, we do a numerical simulation of a system, perhaps a neutron star collapsing, in a certain configuration, get the waveform and compare it to what we observe. If it's not a match, we change the configuration a little bit, do the comparison again and repeat the process until we can identify which configuration is responsible for the signal that we observe."
Sounds to me like they may be changing their model to fit the data in such a way that they won't know for sure it is a match. For example, a signal roughly fits the model of a black-hole forming, but not quite. They then keep tinkering with the black-hole formation model until it matches the signal. But in reality the signal could actually be something not related to black holes. They are putting the cart before the horse it seems.
It seems they would have to match a specific electromagnetic observation(s) to the gravity wave event to verify. Otherwise it is just a guess.
I could see some justifiable confidence if the signals were complex, and were only slightly off the models. In other words, near dead-ringer matches of something that would be too much of a coincidence to be something completely different generating the same (expected) complex signal. But I doubt we are at this stage in both the models and accuracy of the signal detection.
Re:rigged model matching? (Score:5, Insightful)
With regard to gravitational observatories, the data are very rich: polarization, amplitude, phase and frequency spectra will be available, possibly from several detectors with different orientations. Detector response is also extremely well understood. The theoretical physics of the sources--general relativity--is also very well understood, and models of stellar collapse, neutron star collisions, etc, contain few parameters (masses, angular momenta, impact parameter...that's about it.)
As such, we can compare model to reality and produce a statistically valid likelihood that the model is false. The Baysians in the audience will point out that relative to our prior knowledge we can also produce the probability that the model is true.
So it isn't a matter of getting something that "roughly fits"--the analysis either produces a fit within error or it does not. If it does not, we dig more deeply into the possible sources of disagreement. The data are sufficienty rich that many, many types of cross-checking and internal consistency checking will be available.
To a hardened skeptic, this of course will not do. But hardened skepticism is an anti-scientific attitude. Scientists are open-minded skeptics, who are able to keep the contingent nature of their beliefs in mind while at the same time maintaining a commitment to distinguish clearly between probable truth and probable falsehood.
--Tom
Re:rigged model matching? (Score:1)
But aren't these instruments on the "edge" of dectection? If it was easy to build good detectors, others would have succeeded already. There have already been some embarassing false starts and false detections WRT "graviscopes". IOW, the data may be rich, but it will also probably be noisy and "blurry".
It could be comparable to Galelio trying to figure out Saturn's "funny handles" in his little telescope. Our technology capabilities in gravity wave scopes is about where Galelio was; perhaps even more comparible to the naked eye, since nobody has detected them before.
Anyhow, we will see.....
The theoretical physics of the sources--general relativity--is also very well understood
It is? Then how come it has not been integrated with quantum phyz yet? Even the existence of black holes is in contention with the "gravistar" theory, for example.
How do they detect them (Score:1)
Re:How do they detect them (Score:5, Informative)
It is only mentioned briefly in the article, but I'll try to elaborate.
Basically gravity waves will stretch space in one direction (say x) and contract space in a perpendicular direction (y). Given this, the "easiest" way to detect gravity waves is to build a very large interferometer. LIGO is the current ongoing gravity wave interferometer, which splits one laser beam into two lasers beams, sending each perpendicularly down a vacuum "hallway" four kilometers long. At the end, the beams are reflected by mirrors. The two lasers meet again after another 4km.
The two beams are recombined afterwards. If the distances the two travel are exactly equal, then the two beams will interfere constructively. But if the lengths which the two beams are stretched/contracted by a passing gravity wave, the beams will interfere since one will be "shifted" (it had to travel a longer/shorter distance. By measuring the interference pattern between theses two beams, and hopefully physicists will be able to detect a gravity wave.
The amount that a gravity wave will shrink/extent one of the beam lines is amazingly small. Each 4km beam line will have it's distance changed by 10^-18 meters, or on the scale of attometers! Because of this, any vibration or local variation will affect the beam length. So the physics who are part of the LIGO collaboration built two such laser devices, one in Livingston, Louisiana and the other in Hanford, Washington. When a gravity wave (from outer space) travels through the earth, hopefully both sites will measure the same small variation, which will correspond to a passing gravity wave.
You can get more information about LIGO at:
LIGO's Home Page [caltech.edu]
LIGO collaboration page. [ligo.org]
Slashdot recently had a science story about LIGO [slashdot.org].
Speed of Gravity (Score:4, Interesting)
Re:Speed of Gravity (Score:2, Informative)
No.
For instance, some spin-2 thermodynamics could be experimentally demonstrated if gravitrons could be isolated and easily detected.
No (see my earlier post on quantum gravity and gravitational waves).
According to current theory, there is absolutely no way we could even begin to dream about detecting individual gravitons, much less confine them. These experiments aren't a step towards this "goal" any more than any other experiment out there: according to current theories of physics (yes, the most fundamental ones), confinement of gravitons is an absolutely unimaginable task for all foreseeable technology.
Compare this with neutrinos. They only interact weakly, through the "weak force" (and, of course, they also interact gravitationally), as opposed to, say, protons and electrons, which interact through the strong force and the electromagnetic force. The important difference is that the weak force is, well, like the name says, weak: the probability of any interaction of neutrinos (with any known form of matter) is much, much lower than the probability of protons or electrons interacting with each other.
Remember that quantum mechanics only predicts probabilities. Imagine a neutrino traveling towards the Earth: it has a very low probability to "collide" with any particles of the Earth, so most likely it will just shoot right through the Earth like it's just empty space. A proton or an electron wouldn't do that (or, at least, this would be very, very improbable): they can also interact through the two stronger forces, which means that they would have a much higher probability to collide with some particle of the Earth. For this reason it takes some incredibly complicated arrangements to detect neutrinos (you need a huge detector to get even a single neutrino collision per day).
Now, while neutrinos can interact through the weak force (and gravitationally), the problem with gravitons is that they can only interact through gravitation. And gravitation is much, much weaker than even the weak force! The difference is actually many, many orders of magnitude larger than the difference between the electromagnetic force and the weak force. So we're not goint to see any gravitons for a very, very long time!
Maybe some time in the future we'll be able to build some galaxy-sized detector in intergalactic space and finally see some gravitons... but, unless the "coming" theory of gravity predicts some totally new effects (and it might), it's really that far off.
Re:Speed of Gravity (Score:2, Informative)
Does anyone know if results have been published yet?
The other gravity wave (Score:2, Informative)
Gravity waves may be very short (Score:2, Interesting)
Re:Gravity waves may be very short (Score:2, Informative)
If what you say is correct, you could in theory send a signal by gravity wave much faster than c. This of course would revolutionize the communications industry when we have sufficiently sensitive gravity wave detectors.
Also, the speed of any wave is the product of its wavelength and frequency (c=lambda*nu). The generator of the wave can only affect the frequency, since the speed is dependent on the medium and the wavelength is therefore determined. So, if the speed of gravity wave propagation is dramatically higher than predicted, the wavelength must be dramatically longer, not shorter. This won't help LIGO out any, since it is sensitive to wave amplitude, not wavelength.
Can you provide any details or links about this effect?
not finding them would be more surprising (Score:2)