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Gravitational Wave Detection Imminent?
Seumas Hyslop writes "The UK Telegraph is reporting that we may finally have equipment that are sensitive enough to measure gravitational waves, which are incredibly small and have evaded detection despite the theories that they are present as a way of explaining gravitational effects. Basically, a laser beam is split into two branches that are sent down two identical 2000 feet long tubes and back again via mirrors. Assuming the two arms remain exactly the same distance, they will cancel each other out. But the scientists think that the beams will interfere with each other owing to the effect of gravity, meaning the length of the branches is altered and a gravitational wave has been detected."
The word is imminent. immanent means something completely different.
How we know is more important than what we know.
Bring out your gravity surfboard and roll on!
bash$
Maybe the gravitational waves changed the i into an a.
i won't even get into it.
anyways, the purpose of the interferometer is to measure the differential gravitational strain between two remote masses. as a gravity wave passes (supposedly), two masses will be driven to oscillate in quadrature with one another. that means that relative to some fixed point, one mass will be drawn closer, and at a right angle another mass will be pushed further away. IIRC.
luckily a michelson interferometer is a great way to detect these small changes, where the remote masses are mirrors. the extremely long beam paths increase the sensitity of the device. and two remote locations are needed for local error cancellation. if you have three locations (there is a LIGO opening in louisiana soon. uh, maybe) then you can actually do gravitiational wave astronomy.
probably some LIGO person will write a better explanation, but it's late.
m
Gravitational Radiation - the cosmological reference, not the meteorology ones.
Some other gravitational wave detection projects
Some anomalies in gravity theory
and, of course, Einstein@Home
Mongrel News all the news that fits and froths
Both sites are asking for public help processing the data, via a special screensaver called Einstein@Home.
--Greg
I imagine that you've stumbled upon the flaw overlooked by teams of experts on General Relativity.
It's obvious to anyone who's read this site for a while that an admin just burned 20 or 30 of his unlimited mod points to bitch slap all of the "you spelled it wrong" posts. It wasn't regular readers with mod points.
The interferometric GW detection systems have been under development for quite a while. These include the LIGO project in the US, the GEO in the UK/Germany, and Australia and I believe Japan and Italy have their own versions. LIGO started collecting data a couple of years ago. So now the guys in the UK turned on their instrument.
So what's the big deal?.. Well, there isn't one. Today's instruments are pretty damn bad. I don't remember the numbers, but you'd have to run them for quite a few decades in a row for a good chance to observe one event (it would have to be something big falling into a black hole somewhere relatively close to us, or a major supernova, or something equally rare.) Essentially, you are trying to measure a ludicriously small displacement (10^-16 cm) of a macroscopic object.
The good thing is, technology is continuing to improve, increasing the sensitivity. Furthermore, there's hope (subject to funding) of creating a space-based version of the experiment by bouncing laser beams between three satellites millions of kilometers apart. So is the GW detection imminent?.. Considering the scale and cost of the projects, it better be, but I (being a scientist and all) prefer to steer clear of that word. So provided the funding doesn't get cut, we'll very likely detect gravitational waves in a few years. But be prepared to wait.
For more deets, check out www.ligo.caltech.edu
i will try again here. so one case of the "gravitational wave" theory is that when two black holes spiral around one another (or any two large masses), they will emit energy in the form of gravitational waves, like two boats circling in a lake. physicists would like to detect this energy.
let me digress for a second to radio. normal EM radiation is in the dipole form. which means the radiation makes charges (electrons in an antenna) oscillate up and down. gravitational waves (i think) hit us in the higher order quadrupole mode, which instead of "up and down" is more like "in and out". or taking a circle and squishing it along one axis, and then the other.
so lets say you are standing on a field. then you have two stones hanging on strings, one 100m north, and the other 100m east. when a gravitational wave passes, if you were God, you would be able to notice that the north stone was pushed closer while the east one was pushed away, then the east one was pulled toward you while the north one was pushed away.
to detect this *infinitesimally* small force, you replace the rocks with mirrors. and put the mirrors in vacuum to prevent them being jittered by air molecules and strange index of refraction effects with the air. then put the mirrors really far apart to increase the relative sensitivity to the same strain.
now take a laser beam, split it where you stand and send half the beam to each mirror. the beam then returns to you, you recombine it at the same beamsplitter, and the photons in the laser beam will interfere. whether this interference is *bright* or *dark* depends on the relative path length difference of the two arms.
you can detect changes on the order of 1/100 wavelength (actually, much less, but that's more complicated) which is about 1e-8 meters. since the interferometer is 2e3 meters long, that means you can detect a fractional change of about 1 part in 1e11. but it's actually crazy better than that due to many smart inventions the LIGO people created about locking optical cavities. you get the idea.
so then you watch your interference as a function of time, then go to your astronomy books to see what events should create gravitational waves at the frequency you have observed them.
in a nutshell.
m
ps. analogy: a radio telescope uses electronic amplifiers to measure the induced motion of electrons from EM waves : a GW telescope uses a high finesse optical cavity to measure the induced motion of masses from gravitational waves
I was on a lecture about gravity waves, once. This guy showed a lot of interesting stuff, like that a best gravity wave emitter is when you place four bodies each on a node of a square, and then squash/unsquash this fictional square. Then a strong wave is emitted in perpendicular direction.
also he said that some folks are trying to detect gravity waves by sending two laser beams through a very long tunnel, they bounce of mirrors and then interfere, so length of their way can be measured with high precision. Exactly like in the summary above.
And guess what? They got totally different results depending if there are clouds up in the sky or not. The beams were attracted to the clouds because of cloud's mass. Of course it means that they couldn't detect any gravity waves from far away - too strong local effects.
He also said that the only possible gravity wave detector should be placed in the space on lagrangian point.
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#\ @ ? Colonize Mars
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Ok sounds nice and all, but heres some food for thought. In order for this to work you need both 2000ft arms to be the same EXACT length. If they are not EXACT then the whole thing wont work, but in that case how will you know? Or even better when they are making it, how do they know the gravity waves arent throwing off their measurements before its even built!
Everything -- that has mass and that moves -- generates a ripple in gravity. You do it, your mom does it, too. Heck, so does any movement of Earth (e.g., techtonic plate movement, oceanic changes due to El Nino, etc).
Even though these gravitational waves generated from these local sources are weak compared to a truly remarkable astrophysical sources (e.g., mergers of blackholes), these terrestrial sources are closer; hence damned stronger compare to any expected extraterrestrial sources.
And yet, we have not detected a coherent signal of gravitational wave from local sources. This science is that hard. And that's why this is so fascinating. I think physicists have spent the last decade identifying these local sources and how the local signal would manifest itself in their experiment. I'll tell you, having seen some of the modeling, etc., detecting a gravitational wave from an orbiting pulsar is like trying to catch a person who's yelling "Yankees Rule" in the Fenway stadium via TV broadcasting. Oh that may be actually easier (since the guy would be dead on the spot by the mob of the BoSox fans).
I'm still awake and really should be sleeping, but instead I'll simplify even further, for the first year physics guy. Great description, by the way... I didn't know gravitational waves were supposed to be quadrupole.
Any accelerating charge (an electron for instance) will create an electromagnetic wave. A radio transmitter basically causes electrons in its antenna to oscillate at a particular frequency, and this produces radio waves at that frequency. Theoretically the same thing should hold for mass and gravity. If you cause a mass to accelerate (like the charge) then it should produce gravity waves (like the radio waves). Because gravity is so extraordinarily weaker than electromagnetism, the waves are correspondingly smaller, so very difficult to detect. Einstein says gravity causes space-time to curve, so passing gravity waves should stretch and squish space-time a little bit as they pass. Unfortunately you need to be able to measure distances really precisely.
An interferometer is how you do it. You send out two in phase light beams, bounce them off a mirror, then recombine them. If they travelled exactly the same distance then they should still be in phase (peaks and troughs line up) so they'll reinforce each other. If they travel slightly different distances then they won't be quite in phase anymore and the intensity of the recombined beam will be a bit less than it was originally.
So now you send the beams off at ninety degrees to each other and see if the ratio of the distances they travel changes. It will of course, due to all kinds of things, but maybe one of those things is passing gravity waves. So you have detectors on different continents and correlate their measurements. Local things (tiny earthquakes, people walking around above the detector, somebody turning on their washing machine down the street) will not be recorded by both detectors. Things like gravity waves will.
One more interesting thing you can do -- if you have more than two detectors, by watching when the waves are recorded by each detector you can measure the speed of the wave... the speed of gravity, and you can tell what direction the wave came from.
Simplified lots, and I should be sleeping, so that was probably full of errors and you should pay attention to the parent instead, but that's probably as simplified as it can get.
METERS
try reading http://en.wikipedia.org/wiki/LIGO
maybe the european one is 2000 feet, but not the two in th US. actually, the full length of each arm is 4000 m. i've been to the facility, touched a beamtube, drove to the end. meters.
m
I heard they only wanted 10^-12 m (picometer) resolution. And they aren't planning on keeping them fixed at that relative distance; that's impossible without breaking the experiment (if you don't know why, then you don't understand the experiment). The probes are going to be moving at a speed of order meters/second relative to each other. In any case, they don't have to keep the distance fixed so long as they keep track of where the probes are wrt each other. The engineers claim that the optics is the "easy part" (a friend of mine is working on one of the "hard parts"), though it seems anything but easy to me.
...
Also, keep in mind that our wonderful politicians want to build a wind farm next to Hanford since "there's nothing there anyway"
Wouldn't that make the Moon the perfect place to set up a detector?
:-)
Vacuum at no cost, no tectonics(?)
I'm not considering travel expenses and room and board...
Do you seriously think they might have forgotten about callibration? Do you think whoever is in charge of this thing is that dumb? By all means, if you do, pick up a telephone, call them and shout "Remember to do some form of callibration!!!". Be sure to be very emphatic. Science will thank you.
Thnaks to all teh braev suols who wer willign to bern kamra to piont out teh diferense btween "immanent" and "imminent". Othrewise we all wuold haev to RFTA and haev a maeningful dicsussion. Tihs is Slasdhot, and we ca'nt haev taht heer! (Stewpid atricles!)
What if some hungry and / or amorous rabbits are enjoying the beets near the pipes?
Seismic activity?
Temperature changes?
Planes flying overhead? (sound)
I am not sure how they can remove all this tiny tremors and vibrations and details from their detection equipment. I wish they would publish a 'how it works' that deals with stuff like that. It will be on my mind all day now.
please type the word in this image: buffets
random letters - if you are visually impaired, please email us at pater@slashdot.org
#hostfile 0.0.0.0 primidi.com 0.0.0.0 www.primidi.com 0.0.0.0 radio.weblogs.com
LISA satellites need to be stable to within 1 nm per root Hz of bandwidth. (It's been a while since I worked on it, so someone else is welcome to explain what exactly this means.) Suffice it to say that this is a tractable problem, and I would argue no more difficult than the Advanced LIGO designs currently being implemented. And you get more bang for the buck in sensitivity.
Please show me a good reference for LIGO expected detection rates. This is taken from a popular book, but the numbers agree with what I remember hearing from those working on LIGO.
Supernova (within our galaxy)
1 to 3 per century
Black Hole/Black Hole Merger (300 million light-years)
1 per 1,000 years to 1 per year
Neutron Star/Neutron Star Merger (60 million light-years)
1 per 10,000 years to 10 per century
Neutron Star/Black Hole Merger (130 million light-years)
1 per 10,000 years to 10 per century
Source: Einstein's Unfinished Symphony: Listening to the Sounds of Space-Time by Marcia Bartusiak
That's why there are two of them on different parts of the globe. Any gravity-wave phenomenon will affect both, so local effects can be ignored (see how I used affect and effect in the same sentence!)
I assume they would correlate their data with the equivalent agencies around the world. If the gravity waves came from some remote source (like a black hole), their effect could be measured anywhere on Earth. If it was a passing train, that would obviously only occur to one place at a time.
Here's the deal with local sources: their masses are tiny compared to astronomical sources!
But here's a more local source that we have detected: the moon. The moon causes tidal deformations in the Earth's crust, which LIGO (disclosure: I am involved with the LIGO project) and the other large scale interferometers (GEO, VIRGO, TAMA) have to subtract out in order to see anything besides the moon.
Essentially, to make gravitational waves large, the conditions which need to be satisfied are 1) large amounts of matter 2) moving quickly. Things which satisfy this are: supernovae core collapses which are sufficiently non-axisymmetric, compact (eg. black hole or neutron star) binary system decay, and maybe some events we don't yet know of.
-Leo
The article is writing about GEO600, whose two arms are 600m which is about 2000ft.
-Leo
Argh - So now the Europan's are using feet and the American's are using metres? I think I must've just walked through a ripple in time-space or something.
the french-italian project VIRGO has two arms , each 3000 METERS long.
BTW, whenever you here someone speaking of physics and using feets , you should doubt that s/he knows anything about the subject.
What I'm thinking is the following, We all know the speed of light is constant for a material (or vacuum). From our frame of reference we will not notice the distortion in spacetime. Our yardstick will shorten and lengthen with the compression and expansion of the waves. which would make it impossible to detect the changes. Of course, I'm probably just not knowledgeable enough to know what's going on here, but then again. I'm curious to see if this idea has been addressed.
If no one has thought of this idea yet, I just did and I claim it! :)
"The bass, the rock, the mic, the treble. I like my coffee black, just like my metal" - Mindless Self Indulgence
Let me put is this way: how do you callibrate something like this. Don't get me wrong, I'm sure they know very well what they are doing but I'm just curious.
This is in reply to this post and a number of others on the same topic.
... so they can correlate with those sources.
:)
Major sources of noise: seismic, acoustic, photon shot noise, thermal noise.
1) Acoustic noise: the entire beam tube system is in vacuum, so the only mechanical vibrations can be coupled in through the mirror supports, which are suspended on thin wire. The pendulum created by the hanging mirror essentially creates a mechanical low-pass filter which reduces the effects of noise above about 10 Hz. The gravitational wave projects (on Earth, not talking about LISA here) are mostly interested in frequencies around a few hundred to a few thousand Hz.
2) Seismic: this can cause pretty large displacement. Each of the mirrors (on its' hanging suspension) is sitting on a system of masses and springs (three levels) which creates a third order lowpass filter which further reduces noise.
3) Photon shot noise: this rises with frequency; essentially, photons are uncorrelated random events which create a Poisson noise distribution. In a Poisson distribution, the standard deviation of count rate is equal to the square root of the count rate, so the variance is decreased by decreasing count rate at the detector. This is why the interferometric detectors operate "in null," meaning they keep the mirrors at a differential path length which is equal plus or minus integer multiples of wavelengths. This way, the output at the point where they interfere is kept dark. The idea is that it's easier to detect a difference between 0 and 1 than between 100 and 101. (There is a ton of feedback to keep the whole system in null. Read up on Pound-Drever locking to understand it.)
4) Thermal noise: the surface of the mirror is made of atoms which jiggle in random Brownian motion. This is unavoidable unless the mirror is cooled sufficiently, which is difficult to do because of how well isolate the mirrors are. However, the Brownian motion can be averaged out over a large area by making the laser's spot size large.
So they've thought about it a little bit. And they are also measuring other non-detector channels like seismic activity and acoustics near the detector and wind speed and
The NSF doesn't go around giving millions to any old project
-Leo
Each of the mirrors have magnets glued to them in a quadrupole configuration (so they are not affected by stray magnetic fields) which are used to move the mirrors around. The mirrors are moved around for a few reasons:
1) The detector works in a closed loop feedback system, so they keep the mirrors they same distance (mod the wavelength) from the source (and the error signal which is used to feed back on them is the actual "gravitational wave" signal.
2) Calibration: during data collection, the mirrors are periodically driven with a known magnetic field by the same set of magnets. Because we know the mechanics of moving a mass with the force of a magnet, we know how far it went. And when we look at the error signal to keep the device in lock while it is being forced, we know the ratio between distance the mirrors travel and digital signal coming out of the detector. So after the data are collected and ready to be analyzed, a lot of people spend lots of time preparing and reducing the data, which includes coming up with a calibration from the forcing.
-Leo
when do we get our impeller drives & Warchowski sails?
-- The Heineken Uncertainty Principle: You can never be sure how many bears you had last night.
Hundreds of scientists spend millions of dollars of money on an incredibly expensive
8 6.htm
method of detecting gravity waves when cheap ones somehow already exist.
Build your own gravity wave detector:
http://www.rexresearch.com/hodorhys/remag86/remag
Non sequitur: Your facts are uncoordinated.
If you can detect the passing Gravitational Wave then does this mean it has done work? If so then the waves should attenuate.
So in what form is the energy of a Gravitational Wave? With EM the energy travels in the form of a photon. Does this mean if we detect a gravitational wave that we have detected a graviton?
If so is it quantized? Also does this mean that somehow the graviton interacts with other mater? Wouldn't this unify gravitation into the EM force?
Well - I don't know enough physics to answer but I suspect that gravitational energy might actually be continuous.
However the mechanizm by which gravitational energy (which should have mass because E=MC^2 - except they are thinking "rest" mass and the rest mass may be zero) gets transfered from the gravitational wave into whatever it gets transfered into may have a consequence. If we have a pair of spinning black holes for instance then this may be a way for them to leak energy and thus they might slowly evaporate.
I seem to recall reading that NASA had sent up a bunch of satellites bearing very sensative equipment that were supposed to detect gravitational waves, though I don't think they were using this method of detection. Does anyone know what happened with that experiment? Do they have the results yet?
At any rate, I think I read about it on slashdot, so I suppose I could just wait a few months for a dupe.
Ok, so are these gravitational "waves" real or just a construct to explain gravity?
Essentially the trigger for this question is the whole sound/EM difference. EM is acutally the emission of "stuff" whilst sound is the propogation of energy through a medium and without the medium there is no sound just the vibration of the original source.
It's been a long time since I read any theoretical physics and so my head hurts a little when I think about this stuff, but the "dents in space time caused by mass as balls on a rubber film" metaphor help explain the "pull" of gravity really quite nicely, if it is even remotely true. But that model suggests a "medium" through which gravity acts.
"The first thing to do when you find yourself in a hole is stop digging."
The other replies are mostly right: you use more than one detector so you can look for a signal in both of them...
/.ers)
then you have the fact that the signal you look for has a very well known shape (it can be calculated in our teoretical framework)
you also expect to observe it toghether with other (indipendent) signatures:
a supernova for example would be observed by all astrophisics experiments sensitive to light (common visible light telescopes, radio/gamma telescopes) and by most of the neutrino experiments around (this is no sci-fi neutrino telescopes already "saw" a supernova a few years ago)
and finally every piece interferometer apparatus is contained in a vacuum tank and suspended at the end of many pendules designed in such a way that it is as decoupled as possible from external vibrations (bunnies humping, trains, earthqakes, everything mentioned by the other
I'm so happy for the GEO600 crew if they are in fact getting close! I've actually seen the facility - pretty amazing stuff and a very good example of how far you can push things using much brain and relatively little dollar. For example, the article didn't mention this but the arms of the interferometer do not intersect at quite 90deg due to the fact that the arms are built along the borders of farm plots.. As for filtering out noise, they filter out everything above and below particular frequencies. It's all extremely sensitive work and I'm glad somebody else is doing it!
My hat's off to anybody in this business, they must have a lot of time and money and patience!
The LSC (LIGO Scientific Collaboration) thinks a little bit different about that.
:-)
In their document "First report on the S3 analysis" (http://einstein.phys.uwm.edu/PartialS3Results) which is based on the Einstein@Home community efforts they say:
"However, the numbers of sources and their distances from us are uncertain, and in their first few years of operation it is quite possible that the LIGO and GEO instruments may not detect anything."
"So far, we have not seen any evidence for pulsar signals in the S3 data. As described earlier, this is not surprising, because LIGO is not sensitive enough to guarantee that we will see one or more pulsars."
LIGO is going to be upgraded ("Advanced LIGO"), which will improve the detection of events by the factor 100-1000.
Maybe the theory of grav-waves is even wrong, who knows...
You look like a million dollars. All green and wrinkled.
IANAP, but I like to read books on science, esp. physics, astronomy, cosmology, evolutionary biology, etc. Some people read cheapie novels, I'll read the latest thing from Kaku, Green, Dawkins, Darling, etc. Not that they are necessarily the best books on any given subject at any given time, but for the most part they are fairly accurate. It seems that in string theory gravity is solved in higher dimensions, but the instruments to test that are some time off from development, and so, in terms of testability, we're stuck where we've always been - somewhere between Einstein (relativity) and Bohr (quantum theory). And while everything in terms of matter seems to favour Quantum theory, Relativity is still on top of gravity, as we have yet to find a gravity wave or even a graviton. Therefore, IMHO, we have to come to ask an interesting question: What If Quantum Theory Simply Doesn't Work With Gravity? String Theory might have an explanation, but we're a long way off from being able to test String Theory's ideas about gravity, and (most importantly) a failure of Quantum Physics on Gravity is not necessarily an indication of String Theory's notions. So, if it this test fails (like all the other Gravity Wave Detectors has) when will scientists give up and figure out a new understanding of gravity? This test seems like a good one, so what will happen if it fails? And furthermore, given its expense, how can it be repeatable outside of its own instrumentation? I'm not being a troll - just asking honest questions and trying to get a better conversation in this article beyond a bunch of juvenile carping about spelling errors. RS
Shoes for Industry. Shoes for the Dead.
And yet, we have not detected a coherent signal of gravitational wave from local sources. This science is that hard. And that's why this is so fascinating.
That is the really weird part. The people at fourmilab have a video of a basement torsion bar experiment that demonstrates that objects create their own space-time curvature.
But there's no way of demonstrating that such curvature will ripple across space-time.
Vintage computer adverts: http://www.vintageadbrowser.com/computers-and-software-ads
Time wouldn't have to change. If space stretched, the wavelength would correspondingly change.
Imagine a wave traveling across a lake. What if you were able to stretch the lake? The wave length would be longer.
Now, what if there were two waves traveling across the lake. You wanted to observe the interference pattern of the waves, but since they are BOTH traveling across the same lake, they are both affected the same.
My point being that you can't measure changes in space if the ruler you are using to measure changes also.
... a gravitational wave generator patented by the NSA. I guess reverse engineering all those UFOs paid off.
[ObDisclaimerForTheClueless: No, I don't really believe they reverse engineered UFOs. The patent's real though. Who knows, it might even work.]
Human/Ranger/Zangband
No need for fancy experiments. My wife detected a gravity wave using our car recently. One minute she was driving along minding her own business, next minute she was in a ditch after a rogue wave shifted the entire road out from under her.
Anyway, that's her story and she's sticking to it.
UNIX: 'cuz you can tattoo it on your knuckles!
I see a few posts saying, "Well, we haven't seen gravitational waves yet, so maybe they don't exist." To that, I have several responses:
1. There's no reason why we should have seen them yet; they're so weak that even LIGO I probably won't see them. (LIGO II probably will, if the equipment works as designed.)
2. Gravitational waves have already been detected indirectly: the 1993 Nobel Prize was awarded to Taylor and Hulse for this discovery. They observed a binary star system whose orbits were inspiralling at exactly the rate that general relativity predicts for a binary system that is losing energy via gravitational waves. That rate also gives the rate at which energy is leaving the system, and allowed them to infer the speed of gravitational waves: the speed of light, to within a few percent --- also as predicted by general relativity.
3. Even if general relativity in particular is wrong, pretty much any field theory compatible with special relativity contains wave solutions propagating at the speed of light, for demonstrable reasons of logical consistency. This holds for both classical and quantum theories (e.g. Maxwell's equations, general relativity, the Standard Model of particle physics, etc.), theories of quantum gravity like string theory, and so on. You basically have to throw out all of relativity and go back to Newtonian physics to get field theories without wave solutions.
There's a TON of sientifffic evidance that counterdicts this, obviously flawed theory, and that PROVES beyond any doubt that intelligent falling is just as valid and should be taught as a valid theory right next to this supposed "fact"
actually, local sources of GWs are highly unlikely to produce signals which are detectable. the bigger problem is local sources of vibration: trucks driving on the road, heating and air-conditioning fans, planes flying overhead, etc etc.
saulson's book has an example calculation of what would be needed to generate detectable GWs in the lab. take two steel balls, mass 1000 kg each, 1 meter apart. rotate them around their common center of mass at a frequency 96 Hz (about 600 rad/s). the strain that generates is about (1/r)*1e(-35) where "r" is the distance from the generator to the detector. in comparison, a typical pair of neutron stars, 1.4 solar masses each, 20 km apart, and rotating at about 400 Hz. if the pair is in the Virgo cluster, about 15 megaparsecs away, the strain at the earth would be about 1e(-21). this sort of order of magnitude stuff can't just be handwaved without a few approximate equations.
i did my phd research with ligo, so i have somewhat of an insider's view.
This is a tautology.
Any accelerating charge (an electron for instance) will create an electromagnetic wave. A radio transmitter basically causes electrons in its antenna to oscillate at a particular frequency, and this produces radio waves at that frequency. Theoretically the same thing should hold for mass and gravity. If you cause a mass to accelerate (like the charge) then it should produce gravity waves (like the radio waves). Because gravity is so extraordinarily weaker than electromagnetism, the waves are correspondingly smaller, so very difficult to detect. Einstein says gravity causes space-time to curve, so passing gravity waves should stretch and squish space-time a little bit as they pass. Unfortunately you need to be able to measure distances really precisely.
I have a question for you, the obvious conclusion from what you say is that it seems to me you lose stable orbits now. That is all gravitational orbits should suffer from the same problem as classical electron-nucleus orbit decay. That is, since any 2 body orbiting system is accelerating its total angular momentum should decay, so I looked this up and in fact not only is this true, that is apparantly exactly what the 1993 nobel prize was given out for. Now I have two questions, if this is true, there should be "derivable" an equivalent of maxwell's equations for gravitational waves using the exact same argument that was used in electrodynamics (i.e. reference frame tricks). Also using the orbital decay analogy, w/ point masses shouldn't there also be a "quantization" due to the gravitational potential ala quantum mechanics. i.e. two hypothetical electroneutral point masses (say neutrons) gravitationally orbiting around each other have a "bohr" radius of ?? at the lowest allowed eigenstate? I'm curious what that number is. Is this below the strong/weak nuclear force length scale?
This article got me thinking:
If you can detect a gravity wave then doesn't that mean that some energy is being absorbed from it?
If energy can be absorbed from it, then doesn't it get weaker?
So if a gravity wave can be made weaker, then couldn't you theoretically build a gravity shield?
And if you scaled one up, could I stand on it and float off of the earth?
It doesn't seem right, so where am I going astray? Thanks Physicists!
...then it behooves them to offer alternative explanations for their results. "In experimental philosophy we are to look upon propositions iffered by general induction from the phenomena as accurately as or very nearly true, notwithstanding any contrary hypotheses that may be imagined, till such time as other phenomena occur, by which they may either be made more accurate or liable to exception." -- Isaac Newton, Rule IV of "Rules of Hypothesizing", in Mathematical Principles of Natural Philosophy (1687).
The experimental design is that of the Michealson-Morley experiments. That hypothesis still stands (ie. they failed to reject the null hypothesis, a very different thing than supporting the alternative hypothesis, and the beast of proving the null hypothesis is imaginary). If they get results, it'll be on them to show the effect is due to something other than that which has so far been unable to be detected but previously theorized and hypothesized as causing the same effect they expect to find.
Still awaiting the technology capable of testing it is the hypothesis that ether flows along the lines of a gravitational field, and so must be tested simultaneously parallel and perpendicular to gravity. Getting a vertical structure big enough but stable enough to do this is far harder than getting two perpendiculars.
Keep in mind that in science "out of favor" and "disproven" are not the same, but in peoples minds they are taken as such. Read "The Golem" by Collins & Pinch for many entertaining examples, including the M/M experiments.
"I may be synthetic, but I'm not stupid." -- Bishop 341-B
I'm on pins and needles here. I'm wondering if gravitational waves will be complicated enough to require
an application of the new theory of intelligent design.