Gravitational Wave Detection Imminent? 326
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."
hehe (Score:2, Informative)
Re:hehe (Score:3, Funny)
Forget slashdot spelling... look at the science (Score:3, Interesting)
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
Re:Forget slashdot spelling... look at the science (Score:3, Informative)
Re:Forget slashdot spelling... look at the science (Score:2)
Re:Forget slashdot spelling... look at the science (Score:5, Informative)
Re:Forget slashdot spelling... look at the science (Score:4, Interesting)
any disturbance will likly make them vibrate at a very specific fequency. Signals at that frequency are ignored.
Re:Forget slashdot spelling... look at the science (Score:3, Informative)
There are huge seismic isolation system that damp any movement of the test masses, but they don't remove all the seismic noise - that is why the LIGO data is only really useful from about 40Hz upwards.
> Temperature changes?
Again the test masses are isolated and in vaccum so that temperature flucuations don't effect the sensitivty that much, however this is a problem and is a limiting factor in the overall sensitvity of the interfermeter.
> Planes flying overhead? (sound)
This has b
Re:hehe (Score:5, Funny)
The few readers who will actually know what "immanent" means will also know that it was actually supposed to be "imminent", so no harm done. The rest will just see it spelled as usual.
Live with the times !
Re:hehe (Score:5, Funny)
That's the most rediculous thing I've ever heard!
Re:hehe (Score:2)
wat nounseanze!!!11 amereikan shood b riten coretcktly buy evrywon on teh internet. none of thes deegenarate english shood be aloud!`1!
Re:hehe (Score:3, Interesting)
I usually mod down language gripes (and dupe complaints) whenever I can, and I'm sure many other moderators do too. Yes, we know there was a misspelt word there, and yes, we know there was a similar post a while ago. So what? No need to point it out. Over. And. Over. Again.
Re:hehe (Score:3, Informative)
Re:hehe (Score:2, Insightful)
It is when nothing has been moderated up.
And naturally, this whole discussion right here fully deserves to get modded down too.
Crap. Discussing the summary is just as valid as discussing the article. Discussing the weather or Bill Gates' haircut is Offtopic, this aint.
Re:hehe (Score:2)
Because computers read differently than people?
Spelling errors usually make much less difference to a person than they do to a computer.
Re:hehe (Score:2, Offtopic)
I wish I was so smart that a simple spelling error rendered it impossible for me to process the content of the article.
"My built in spell checker is going bezerk! ARRGH!!"
Waves? (Score:5, Funny)
such poor writing in the summary (Score:5, Informative)
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
Re:such poor writing in the summary (Score:4, Interesting)
Now if we can only get rid of the strong local influances such as the sun and moon, then we might get some sensitivity.
The influence of these make detecting very weak waves difficult. It is like detecting the change in sea level due to a rain storm or evaporation. Local wind caused waves and tides make detecting these minute changes difficult.
Re:Can someone please explain this (dumbed down)? (Score:5, Informative)
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
Re:Can someone please explain this (dumbed down)? (Score:4, Informative)
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).
Re:Can someone please explain this (dumbed down)? (Score:5, Informative)
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.
Re:Can someone please explain this (dumbed down)? (Score:4, Informative)
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. [fourmilab.ch]
But there's no way of demonstrating that such curvature will ripple across space-time.
Re:Can someone please explain this (dumbed down)? (Score:3, Interesting)
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 i
Re:Can someone please explain this (dumbed down)? (Score:5, Informative)
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.
Possible problem with the whole idea? (Score:4, Interesting)
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! :)
Re:Possible problem with the whole idea? (Score:4, Informative)
The speed of light will not change no matter what, but otherwise I agree completely with your description, we should not be able to detect a raw change in length due to gravitational waves, however we should be still able to detect a local change in gravitational field, i.e. the local metric, precisely because the change is local due to the waves.
Intuitively this might be why two interferometer arms are necessary.
Re:Possible problem with the whole idea? (Score:3, Interesting)
Re:Possible problem with the whole idea? (Score:2, Informative)
One you look at the output of a Michelson interferometer, there are differences in intensity because one arm may have accrued more phase than the other one. You can think about it in the time domain, measuring length of the arms, or in the frequency domain, be
GW doing work (Score:3, Interesting)
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 b
Re:GW doing work (Score:5, Interesting)
Gravitational waves are predicted to weakly interact with everything which is matter-energy. For that matter, gravity interacts with itself (which is why GR predicts black holes and other such singularities). However, in the weak-field regime (that is, space-time is flat except for a deviation which is orders of magnitude less, meaning we can take the leading term in the expansion, so the theory is linear), gravitational waves just pass through everything. Since they pass through things, their energy falls off like the square of distance from the source. In the strong-field interacting picture, they certainly should exhibit non-linear exotic behaviour, but those are precisely the parts of GR we are trying to probe with LIGO.
The exchange between matter-energy and curvature (gravitational waves) that you are thinking about is from the latter to the former, but just think about the former being turned into the latter - that is the prediction of the source of gravitational waves. However, it works both ways.
On the levels at which LIGO hopes to detect gravitational waves, we will see about 10^53 gravitons. I am quoting this figure without understanding where it comes from, since we certainly don't have a quantum theory of gravity. But gravity is predicted to be quantum in nature as well, but we won't see the quantization from where we stand.
One of the ancestors addressed the issue of measuring while your meter stick is being squashed and expanded, and another about the local speed of light. These issues are related. One of the postulates (argue argue whatever) of GR is that the speed of light is constant in every frame, and it has the same constant value compared between all frames. Light is the perfect meter stick (or clock) for making measurements with.
I had the same thought about measuring the arm lengths as you did for a while until I started taking GR. Here's how the thought goes: "If space is being stretched, and a meter stick is sitting in front of my face, I will always see the meter stick as being one meter long." Here's what GR predicts: the proper distance between free test masses sitting in space as a gravitational wave passes by will exhibit the increase in the X, decrease in the Y and vice versa oscillation pattern. To measure this, you need to use something free, like the mirrors at the ends of the beam tubes (they are really only free in one dimension). To measure distance, you can't use a meter stick, because it is not an ideal measuring device which you need to measure space with in GR. The ideal device is light. To think about it without resorting to a meter stick increasing and decreasing, think about the light travel time. Since light has a constant speed in all frames, if the proper distance is what is really increasing (disregard what happens to the meter stick, since it is made up of fallible matter and might stretch along with space, but light won't), then it will take longer to go down one arm and shorter down the other. Therefore one arm will add phase relative to the other, which will no longer perfectly interfere at the end.
Re:GW doing work (Score:2)
Re:Possible problem with the whole idea? (Score:2)
Re:Can someone please explain this (dumbed down)? (Score:3, Interesting)
Moonbase LIGO (Score:2, Interesting)
Vacuum at no cost, no tectonics(?)
I'm not considering travel expenses and room and board...
Re:Can someone please explain this (dumbed down)? (Score:2, Funny)
There's a TON of sientifffic evidance that counterdicts this, obviously flawed theory, and that PROVES beyond any doubt that intelligent falling [intelligentfalling.org] is just as valid and should be taught as a valid theory right next to this supposed "fact"
Re:Can someone please explain this (dumbed down)? (Score:5, Informative)
try reading http://en.wikipedia.org/wiki/LIGO [wikipedia.org]
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
Re:Can someone please explain this (dumbed down)? (Score:2, Funny)
Re:Can someone please explain this (dumbed down)? (Score:2, Interesting)
BTW, whenever you here someone speaking of physics and using feets , you should doubt that s/he knows anything about the subject.
Averdupois v. Metric (Score:2)
>>
As an engingeer, there's nothing I hate more than working with averdupois/English units, but it happens frequently, even with "physics" type problems. Ballistics, statics/dynamics, radiation... Ugh.
An amusing aside is that the USA officially adopted the metric system [wikipedia.org] in 1893...and then we used it to better define the foot, the pound, etc. *sigh*
Re:Can someone please explain this (dumbed down)? (Score:2)
Re:Can someone please explain this (dumbed down)? (Score:3, Informative)
Re:Interferometer? More like Interociter Am I RITE (Score:2)
Re:such poor writing in the summary (Score:2)
Just because the equipment list doesn't include a massive accelerating body doesn't mean that there are none within range.
Re:such poor writing in the summary (Score:2)
Or so the theory go
Re:such poor writing in the summary (Score:2)
Re:such poor writing in the summary (Score:2)
Actually, the mass of the mirrors doesn't even matter. They're measuring the space between the mirrors -- the gravitational wave doesn't move the mirrors, per se, as shrinking the space between them.
To detect this, it's a bit more complicated than simple interfereometry. They set up a resonance with the light in each arm reflecting 30 times before being compared. Something about the resonance can detect if the space has bee
further reading (Score:4, Informative)
Gravitational Radiation [wikipedia.org] - the cosmological reference, not the meteorology ones.
Some other gravitational wave [caltech.edu] detection projects
Some anomalies [topology.org] in gravity theory
and, of course, Einstein@Home [uwm.edu]
There's two for twice the price (Score:5, Interesting)
Both sites are asking for public help processing the data, via a special screensaver called Einstein@Home [uwm.edu].
--Greg
Re:There's two for twice the price (Score:2, Informative)
Re:There's two for twice the price (Score:2)
Re:There's two for twice the price (Score:2)
GW detection *probable* within the next 10-15 yrs (Score:5, Informative)
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
Re:GW detection *probable* within the next 10-15 y (Score:2, Informative)
Re:GW detection *probable* within the next 10-15 y (Score:5, Informative)
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
"immanent" does not mean what you think it means. (Score:2)
Between the crackpot science and the bad copyediting, I hope Taco beats him upside the head with a raw ham...
Re:"immanent" does not mean what you think it mean (Score:2)
ScuttleMonkey: OWOWWOOWWWW
Virginia Ham as a LART. I love it.
Soko
cloud problems.. (Score:3, Interesting)
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.
Food For Thought (Score:2, Interesting)
Re:Food For Thought (Score:5, Interesting)
I presume that they have some way of adusting one path - you simply adjust it to peak brightness / least inteference. Then when something happens, it'll be a different distance either way and you'll see a null, or at least a drop.
If you can't get a peak because the damn thing is jiggling all over the place, then it's working
Thnak Yuo! (Score:3, Funny)
What about other interference? (Score:2, Interesting)
What about vibrations in the ground? 4000ft of tubing and NO vibrations? Unless the tubes were also a perfect vaccuum, the resulting pressure waves in the tubes would diffract the laser beams slightly and cause variation. (believe me, I worked for a company that makes laser imaging devices).
Ok... now heat/cold? The length of the tubes, the positioning of the mirrors, deforming of the mirrors, etc. will be affected by this. Over 2000 f
Re:What about other interference? (Score:5, Informative)
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
In other news... (Score:2, Informative)
method of detecting gravity waves when cheap ones somehow already exist.
Build your own gravity wave detector:
http://www.rexresearch.com/hodorhys/remag86/remag
EGO - VIRGO (Score:5, Informative)
What happened to the other experiment? (Score:3, Interesting)
At any rate, I think I read about it on slashdot, so I suppose I could just wait a few months for a dupe.
Re:What happened to the other experiment? (Score:3, Informative)
Waves or Waves (Score:3)
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.
Re:Waves or Waves (Score:3, Informative)
Indeed, correct. Just to put a tangible front on that very valid theoretical answer, light, RF, etc. (the propagation of electromagnetic radiation) does not need a medium to wiggle around in. This is why it can traverse space so efficiently. Instead of a medium, the electic and magnetic fields wiggle each other.
Furthermore, EM emission of "stuff" is a bit weird. I assume you speak of a "photon" as stuff, however a photon can be simply thought of as a packet of energy. But a photon is simply a wave and
Re:Waves or Waves (Score:2)
fantastic! (Score:2, Informative)
Just a thousand billion billion billion billion.. (Score:3, Interesting)
My hat's off to anybody in this business, they must have a lot of time and money and patience!
Gravitational Phlogiston (Score:2)
And if the results are negative? What then? (Score:3, Interesting)
Re:And if the results are negative? What then? (Score:3, Informative)
They can test it with ... (Score:4, Informative)
[ObDisclaimerForTheClueless: No, I don't really believe they reverse engineered UFOs. The patent's real though. Who knows, it might even work.]
2000 feet long tubes (Score:2)
So I guess we're not going to see a portable one any time soon.
gravity wave already detected (Score:2, Funny)
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.
To the gravitational wave doubters: (Score:3, Interesting)
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.
Shielding Gravity? (Score:3, Insightful)
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!
If they get a result.... (Score:3, Interesting)
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.
Re:Obligatory nitpick (Score:5, Funny)
Z-Shift (Score:2)
Obviously an exaple of Z-Shift at work (in reverse).
Huge litagurgical structures, like those at the Telegraph and Oxford University Press, can move the position of alphabetical characters...
Re:IANAP, but... (Score:2, Funny)
Re:IANAP, but... (Score:2)
m
Re:IANAP, but... (Score:2)
Re:IANAP, but... (Score:2, Interesting)
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 meas
Re:fix the title (Score:4, Informative)
Re:LIGO is old news (Score:2)
what's funnier is i'm not kidding. i'm in lab right now. at 2am on a sunday. sigh.
m
Re:difference (Score:5, Funny)
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.
Re:difference (Score:2, Interesting)
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.
Re:difference (Score:3, Informative)
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 p
Re:difference (Score:2)
Re:difference (Score:2)
While wandering around at Cal Tech (which does much of the research involving LIGO), I happened upon an astronomy lounge, where I found a small device that looked like a car battery charger, but on top of it were two metal balls connected by another piece of metal, such that they could be spun around. It was imply labeled "gravitational wave generator." At first I thought it was some kind of ridiculous joke, but now that I think of it, at very close distances that may
Re:Naive question (Score:2, Interesting)
Re:Naive question (Score:2, Interesting)
How to discriminate signal from noise (Score:2, Interesting)
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 a
Feynman lectures - where did you get the tapes (Score:2)
Yeah but (Score:2)
Re:Sure... (Score:2, Informative)
In their document "First report on the S3 analysis" ( http://einstein.phys.uwm.edu/PartialS3Results [uwm.edu]) 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 da