Testing the Theory of Relativity 169
HD 456 wrote to us with an MSNBC story about the new observatories that are starting to come online for the purpose of gravity wave research. One is located outside New Orleans, the other in Washington State, the facilities will shoot lasers down 2.5 mile tunnels in an attempt to detect changes in gravity caused by black holes. Redundancy in facilities is being used to avoid having false background noise skew results. In addition to garnering more information on black holes, the scientists also hope to collect data concering the origin of matter.
I thought of this first! (Score:1)
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Nice (Score:1)
... (Score:3)
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Gravity waves @ home! (Score:1)
This seems to lend itself to the kind of distributed effort seen by seti@home - which does a lot of the same things (mainly filtering out background noise & analyzing for signals). On the other hand, it might not be quite so complex. I don't know if I'm giving up on detecting extraterrestrial life from my desktop just yet, but analyzing gravity waves would be a very fun thing to have my computer doing!
Gravity Wave? (Score:1)
I thought Relativity described gravity in terms of warped space, not particle/waves.
Panic. (Score:1)
great... that's the kind of irresponsible science that goes on, eh? Putting black holes in 2.5 mile tunnels? Someone could get hurt!
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Re:I thought of this first! (Score:1)
This isn't to say that you didn't come up with it independently. I invented it in high school, and quickly found out it was already proposed. Makes you think they already had all the good ideas eh ?
Re:I thought of this first! (Score:1)
Never mind that these guys are trying to answer a different question, but I am intrigued: how a magnet was going to help you decide whether light is matter or energy? And what would happen if it's both?
Kaa
Universal observations from inside a tunnel (Score:3)
Of course, since everything in the universe interacts with everything else gravitationally, I ought to be able to deduce the superstructure of the universe and the motion of anything and everything in it by observing how my tea leaves settle on the bottom of my cup. With sensitive enough instruments, of course. My grandmother, for instance...
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Time Travel? (Score:1)
small mistake (Score:2)
There was a tiny mistake in dialect translation during the production of this story, they aren't working on any high-level theoretical physics down in Louisiana, they are working on something much more down to earth:
Backhoes.
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We cannot reason ourselves out of our basic irrationality. All we can do is learn the art of being irrational in a reasonable way.
Gravitational Waves Exist! (Score:5)
Despite the suggestion to the contrary in the MSNBC story, gravitational waves have already been shown to exist. Joe Taylor and Joel Weisberg and their collaborators have demonstrated, using a binary star system, that Einstein's prediction of the rate at which energy is radiated away by accelerating masses is correct to better than one half of one percent. (This was the subject of the 1993 Nobel Prize in Physics [nobel.se], awarded to Taylor and Hulse.) These results also prove, for example, that gravitational waves travel at the same velocity as electromagnetic waves (ie, the speed of light, or 300,000 km/s).
LIGO is an exciting project that may open a whole new field of gravitational wave astronomy and directly probe the properties of such exotic objects as black holes and neutron stars. But it will do it using well-established physical principles.
Re:Universal observations from inside a tunnel (Score:1)
On a somewhat related note, I asked my high school phyics teacher (possibly my best teacher throughout my 4 years) about this, and he told me that this had been thought of back when Newton came up with his original laws. Someone back then said something along the lines of "It's all a matter of decimal places." Dunno why, but there is some reason this won't work. Possibly because it yields an infinate number of simultaneous equations which would require an infinate number of infinately accurate, infinately precise data points to reconcile.
What about the eclipse ? (Score:2)
Relativity FAQ (Score:4)
Here's some info on black holes [ucr.edu] too, while I'm at it.
How about space probes? (Score:2)
Isn't this redundant? (Score:1)
How it works (Score:4)
Re:Grav wave from passing bus vs. distant black ho (Score:2)
Several detectors 100s of miles apart will get the same signal from a distant black hole, but will get very different signals from local perturbations.
Re:Gravity Wave? (Score:2)
Re:What about the eclipse ? (Score:2)
Or maybe they don't... (Score:1)
It increases the likelihood that the theoretical predictions are correct, BUT, I believe to really drive the point home we need to observe localised fluctuations in the S/T continuum.
Of course that's failed miserably so far
Its good to get excited tho
annoying-ass article (Score:4)
A large part of what makes LIGO interesting -- at least to those who believe it will work (see below) -- is the prospect of eventually being able to do some real astronomy with the thing; that is, the idea that particular astrophysical phenomena would send out unique and detectable gravitational wave signatures.
Kip Thorne, one of the world's bad-asses on this subject, I think talks about LIGO in his book from a few years back, Black Holes and Time Warps. Highly recommended if you're interested in this sort of thing.
Finally, it's worth pointing out (as the article did not) that there are real questions about the odds of getting useful data out of the thing. Admittedly, I trust Thorne's opinion on this a lot more than most, but there's definitely a pretty narrow zone where a) we'll detect lots of gravitational waves with LIGO and b) we wouldn't have detected them already. (If I'm not mistaken, there have been small-scale versions of LIGO done already.) I wish I could point you to a link on this, but I can't think of anything useful.
Just my two cents. :-)
Re:What about the eclipse ? (Score:2)
Astronomers first attempted to measure this in an eclipse the year after Einstein published. (1928 or thereabouts). They got results, but it was later found that the measurements they made were smaller than the margin for error.
I think that the effect is pretty much accepted now
Re:Isn't this redundant? (Score:1)
Science is all about redundancy! That's probably for the better too. I remember reading about the atomic clocks experiment, and it did prove Einstein's theories, but this experiment (and I'm sure the many that will follow) prove Einstein's theories from different perspectives. At least that's how I look at it. :-)
Mayhap it'll give us a more interesting glimpse of how things work (which is what it's all about, isn't it?
Re:What about the eclipse ? (Score:1)
What do you get when two black holes collide? (Score:1)
Re:Gravity Wave? (Score:2)
But a little bit of theoretical work with a binary system shows that energy can be lost from the system in the form of ripples in Space/Time - our good old fashioned gravity waves.
By analogy with electromagnetism it was then supposed that these waves take the form of discrete packets of energy - gravitons.
So if we presume that dear old gravity and quantum mech can be married at some level, its reasonable to assume that gravitons behave both like waves and particles (I recommend books by Richard Feynman if you want to get a good feel for this - and avoid Hawking like the plague, he can't write and he gets it wrong. Its amazing what a bit of media manipulation can do).
Richard Feynman - the greatest Physicist of the 20th Century.
Re:Universal observations from inside a tunnel (Score:1)
IIRC, quantum uncertainty is the bugaboo, and not even infinitely precise measurements and calculations will save you: there's a Gedankenexperiment involving dropping an elastic, symmetrical, smooth sphere--precisely vertically--onto a similar hemisphere in a vacuum. How many times will it bounce before it goes off center?
spawn_of_yog_sothoth
Re:Gravitational Waves Exist! (Score:1)
This story from the BBC (Score:2)
Is what you are referring to I think.
V. interesting stuff !
The distinction isn't relevant (Score:3)
Re:How it works (Score:1)
Re:How about space probes? (Score:1)
Only on Slashdot... (Score:1)
Where else will you find "computer, "analysing gravity waves," and "fun" in the same sentence?
Not that that's a bad thing.
Re:What about the eclipse ? (Score:1)
Can light have "rest" anything?
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It's October 6th. Where's W2K? Over the horizon again, eh?
Laser Principles (Score:5)
This theory states that no matter how hard it tries, the cat will never be able to catch a moving laser.
This theory states that no matter how large the warning on the side of the laser, someone will inevitably see what happens when they shine it in their eye.[1]
Shine a laser through a donut and one can theoretically throw a policeman into a brain lock as they try to defend themselves from the obvious sniper while also try to obtain the donut
See number 1, substituting 'stupid person' for 'cat'.
This theory states that, whoa, dude, when you shine the laser up your nose, it glows like Rudolph, man! *puff*[2]
This theory states that sharks with frickin' laser beams on their heads are more deadly than mutated sea-bass.[3]
And yes, I want one of these in pen form.
[1] They go blind
[2] I in no way condone the use of illegal drugs
[3] Being conducted in conjunction with the Darwin Society.
this project is good, but why Hanford?? (Score:1)
I guess I should prefix this with "I am not a physicist, but..."
Consider this quote from the article:
However, small earthquakes, acoustic noises and laser fluctuations can cause a disturbance at one site that could lead scientists to believe they have detected a gravity wave.
Now recall that Hanford was one of the nation's big plutonium production sites back in the day. There's still alot of waste around the site. It is also near a river (acoustic noise).
Certainly these factors are probably much less significant than, say, earthquake-prone California. But if I were tasked with selecting a site, I think I'd prefer somewhere flat and boring. The less disturbances the better. Like I said, though, I'm not a physicist, so perhaps they feel that they can compensate for these factors.
Best regards,
SEAL
Dragging up what little I remember (Score:2)
Einstein described gravity in terms of warped space/time, and the motion of particles through it as the shortest possible path through a curved space. His numbers worked (confirmed as early as the 1920's if I recall) so folks mostly bought it. Einstein hoped to express all forces as some form of curve in space, but that didn't work out for him - other forces are selective in their effects, while gravity happens to everybody.
Now, these days we tend to view things in terms of particles. The reasons are less experimental than logical. We're not talking about tiny billiard balls hurling through space, quantum mechanical particles are a little too weird for that.
Take the following well established notions:
1- Energy does not exist apart from a mass (or alternately that mass and energy are the same thing - the two statements are pretty much the same.)
2- Vacuum has no mass - it isn't a medium that can carry energy.
3- Gravity, like the other three forces, transports energy.
Given these three, we pretty much must conclude that gravity is transported by particles. It might be a particle which, like the photon, has zero rest mass, but if energy is moving through empty space, a particle, by definition, must be carrying it.
Of course, saying so doesn't answer any questions at all. Why should the action of gravity particles distort space/time? If you have a good answer and experimental data to back it up, the Nobel committee has a sizeable cash prize waiting for you.
Re:looking for what?? (Score:3)
The structure of space-time itself. It's not the ether, since electromagnetism propagation is different.
...phil
Re:Grav wave from passing bus vs. distant black ho (Score:1)
Re:The distinction isn't relevant (Score:2)
True (Score:2)
Re:What about the eclipse ? (Score:1)
Relativity tells us that if you're travelling at c, then time stops (for you). Therefore you're everywhere in the universe at the same time. Therefore if you go from a to be, you don't move. Therefore you're at rest.
I rest my case.
Anyway, when was the last time you saw a moving photon?
Gravity: a force or a wave or a particle (Score:5)
As far as I recall, general relativity defines gravity as the curvature of space-time. Gravity waves are the result of changes in the curvature of space time. Gravity waves are theorised have these properties:
Gravity waves will be accompanied by gravitons, a hypothetical particle that has zero rest mass and twice the spin of a photon.
Gravity waves and gravitons propagate outward at the speed of light.
Gravity waves compress mass in one direction perpendicular to the direction they travel, and expand it in a direction perpendicular to both the direction of compression and direction of travel.
Gravity waves are moving ripples in space-time.
Black holes coliding make big gravity waves.
Gravity waves pass through matter.
This experiment it is trying to get empirical evidence on all of the above claims. This has been a goal of some physicists since the theory was proposed in 1916. However, this goal has previously been beyond experimenters technological reach. It takes today's most sophisticated lasers and detectors to isolate a gravity wave from far away. Any local vibrations reaching either the lasers (like noise, or earthquakes) or the detectors will be easily confused with gravity waves. However, the mass of nearby objects does not interfere, just the vibrations they produce.
As for the design of the installation: it is in the shape of an L, because (as I mentioned before) gravity waves both compress and expand matter as they pass through it. On laser moves faster, and the other slower. This is different from a Michalson inferometer, which checks if normal gravity (that is: curvature of space-time) bends light. A Michalson inferometer isn't used to determine the nature of gravity waves.
Gravity affects all of the universe simultaneously (although it doesn't affect it much, it does affect it). Gravity waves are held back by the speed of light limit though. So, the two installations would get waves at different times, depending on the orientation of the earth to the event.
Of course, this is all conjecture, and that's why we US taxpayers get this installation. If this had already been proven, we wouldn't need these two new observatories.
PS: Check out the observatories homepage [caltech.edu] for more info!
Re:Gravity Wave? (Score:2)
Re:How about space probes? (Score:1)
They use laser-interferometers. To build one of those you need *two* laserbeams with exactly the same length and at exactly 90 degrees from eachother to form an L shape.
Actually, it's one beam that's reflected down two tubes...
What you do is that you messure the difference in lenght that occurs when a gravitywave passes.
The wave will make the space "compress" in the direction it is travelling.
Using three probes, one for every point in the L , it would be very hard to position them and keep them in place with enough accuracy.
You could, of course, build two rigs in space which then could be a lot larger than the 4 kilometer ones they use for Ligo.
(Longer = higher sensitivity)
You would still need two to filter out satelites and instrumental errors.
Re:Gravitational Waves Exist! (Score:1)
Re:Laser Principles (Score:2)
>This theory states that no matter how large the
>warning on the side of the laser, someone will
>inevitably see what happens when they shine it
>in their eye.[1]
This just reminds me of the old joke disclaimer..
"Do not shine laser into remaining eye"
-LjM
Re:Isn't this redundant? (Score:1)
Also, several different theories (mostly GR variations) can explain nearly all observed gravitational phenomena. Therefore doing new experiments may allow scientists to distinguish these theories.
Re:The Louisanna exp is a HUGE PORK BELLY (Score:1)
Caltech LIGO Info (Score:2)
http://ligo.caltech.edu [caltech.edu]
Caltech's Press Release [caltech.edu]
I don't know why their writing articles on this now. LIGO has been in the works for quite a while now.
Just to give you an idea of how sensitive these things are: my roommate spent the summer working on calculating shifts in the earth's crust caused by the sun and moon, so that the correction factors can be applied. If I remember correctly, at one point Kip Thorne (the Feynman Professor of Physics here at Caltech) was working on correcting for the change in Earth's momentum caused by raindrops hitting the surface.
-ElJefe
Gravity does not move infinitely fast! (Score:1)
Since gravity waves are a feature of any field theory of gravitation, such as GR, they had better be found or not only would GR be ruled out but also any theory of gravity based on our understanding of classical and quantum field theory. Although for LIGO to detect it, the waves will have to be pretty strong (some not-too far supernova for example might do). Next-generation experiments are expected to be able to detect waves that originate from more common sources such as close binaries (mentioned in an earlier post).
On a more fundamental note, you never prove a scientific theory, you only (try to) disprove (falsify) it. In Einstein's words, "no amount of experimentation can ever prove me right, but a single experiment can prove me wrong."
Re:Isn't this redundant? (Score:1)
You can gain evidence that the theory is right and increase your confidence in it though.
It only takes ONE REPEATABLE experiment, though, to refute a scientific theory, so that's reason enough to keep testing a theory's predictions.
Re:Isn't this redundant? (Score:2)
The prediction of gravitywaves has, as stated in an earlier post, been proven by measuring the energyloss caused by gravitywave radiation in binary star systems.
But noone has yet detected *an actual gravitywave*!
Only by second hand observation.
And, of course, a new kind of instrument to look into space with is never wrong.
Look at what the telescope, then the radio-telescope and later x-ray/gamma ray/infra-wave detectors have meant for astronomy and our understanding of the univers!
The introduction of gravitywave observatories will most probably lead to so far unknown discoveries.
Re:looking for what?? (Score:1)
However, a humougous majority of scientists beleive that space time itself is being distorted in a quaesi periodic way and that this is at least theoretically observable.
Re:How it works (Score:1)
No medium necessary (Score:2)
"Gravitons" are what gravity particles are called. In principle, it works the same as radio, except with a different particle. Of course, there are important (and unexplained) differences between radio and gravity - that's what keeps physicists employed.
Re:Gravity does not move infinitely fast! (Score:1)
Re:Gravitational Waves Exist! (Score:2)
That's all well and good (actually, it was a very informative post), except that there was no such suggestion in the article.
Here's what it actually said: "There is evidence that the waves exist, but technology has not been powerful enough to detect them." And that's exactly true: we have evidence that they "must" exist--because we see energy radiated away from a binary star system at the predicted rate--but we have not actually directly detected them yet, which this experiment is designed to do.
On the other hand, I agree that the article didn't do too much to clear up the point.
Re:Gravitational Waves Exist! (Score:1)
Re:How it works (Score:3)
But it is NOT true that LIGO can detect the gravitational pull of a human walking by the end of it. A litte background: gravitational waves are created by changes in the gravitational quadrupole moment of a system. Electromagnetic waves, in contrast, are created by changes in the electrical dipole moment of a system.
Getting changes in the quadrupole moment of a system requires doing something funky with the angular momentum of the system. That can happen when black holes collide (they radiate a bunch of their angular momentum away), and I don't know when else it might happen. But it definitely DOESN'T happen (on any reasonable scale) in any terrestrial processes, or any that we know of in our solar system.
It is true that a passing truck, or even a passing person, can cause mechanical vibrations that will affect LIGO's measurements. LIGO is an incredibly accurate system for measuring differences in distances between its perpendicular lengths. Gravitational waves should, according to GR, cause a change of length in one axis and not the other. Mechanical vibrations will also cause a difference in position for the mirrors, so LIGO has a VERY complicated system of mechanical dampers to minimize this effect.
Finally, the last time I checked, most GR experts were of the opinion that gravity waves propagate at the speed of light, not at infinite speed.
Re:Gravitational Waves Exist! (Score:1)
Re:The distinction isn't relevant (Score:1)
Re:How it works (Score:2)
you mean "pork BARREL" (Score:1)
pork belly [dictionary.com]
pork barrel [dictionary.com]
we clear?
Re:Laser Principles (Score:1)
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Re:How it works (Score:1)
Actually, gravity waves do travel at the speed of light, at least according to the theory of general relativity. Of course, this is subject to experimental verification, which is one of the reasons why these gravity wave detectors are being built.
What's really amazing about this project is the fact that they're going to be looking for an extraordinarily weak signal in a bunch of background noise. So how do they know that what they're looking at is the real thing? Well, that's one of the main reasons for having multiple detectors. With the sites in both Washington and Louisiana, they'll be able to look at coinicdences between the signals to determine if the event was a gravity wave or simply some local fluctations due to seismic activity or fluctuations in the laser or one of the other countless things that might give rise to a false signal. I used to be skeptical that these things would be able to detect anything at all (except noise), given that the amplitude of the waves they're trying to detect is smaller than the size of an atom! But I now know (due to a class that I'm taking that's being taught by Kip Thorne) that a lot of thought has been put into all of this and I'm fairly confident that we'll see gravitational waves with LIGO. For more information on the project, check out the Caltech LIGO website [caltech.edu].
Re:Gravity does not move infinitely fast! (Score:1)
Actually it might be possible to move effectively faster than light WITHIN general relativity.
One idea is wormholes but I believe it is not clear, or rather, doubtful, that wormholes can be generated and made stable at all.
Anyway, the speed limit is a local thing: You are not allowed to move faster than a light beam next to you, but actually if you can warp the spacetime in a clever way you could possibly travel arbitrarily fast, as seen from far away (although a light ray coming in from the behind would be even faster!)
I remember a physicist, M. Alcubierre, describing such a "clever space-time geometry" but unfortunately I can't locate the paper on the web anymore. It's published in Class. Quant. Grav. though, in case you have access to a physics library... That paper was serious, the best thing being that the distortion needed is PURELY LOCAL, just a few meters around the "USS Enterprise". The problem was that in front of the spaceship you need a negative energy density. This is frowned upon in classical physics but possible in principle in quantum theory.
You can also search arxiv.org (aka xxx.lanl.gov), the physics preprint archive, for the word "warp" or "warp drive"; you'll be surprised about the number of titles showing up.
Bad Flashback (Score:2)
I can't even remember where to begin to calculate the photon density in the field. If I did, I might be able to work that half out (although I'd probably get the wrong answer - seem to recall not doing that well on my quantum final either.)
The interference from a field that's parallel to the beam sure as hell won't be much. Of course at the edges it won't be parallel... I think I'll need some extra paper.
Thank God I quit physics.
Alcubierre warps (Score:2)
The New Scientist has an article about it here [newscientist.com].
Re:Gravitational Waves Exist! (Score:2)
Any theory which when linearized gives the same equations will "predict" gravitational waves. (I don't know if any alternatives have been shown to support gravity waves in their non-linear equations.) However, different theories would predict different this in the non-linear regime, presumablely where these gravity waves are being created. Studying the waveforms may allow you to gain some insight about the non-linearities in the equations, thus supporting one theory or another.
This what I was refering to. I don't know of a (possiblely valid) theory that works and doesn't imply some sort of gravity waves. But I'm no expert.
Warp travel links (Score:1)
http://www.lysator.liu.se/~nisse/doc/alcubierre/ [lysator.liu.se]
Also there is a news article mentioning some of the ideas at
[bbc.co.uk]
http://news.bbc.co.uk/hi/english/sci/tech/newsi
Space has an Elasticity (Score:1)
One thing I find interesting by this fact, is that since gravitational waves travel at the speed of light, space therefore has an elasticity.
For example, if a huge black hole were to open up where the sun is, and engulf it, the Earth wouldn't feel the effects of it for 7 minutes (I think its 7 minutes at c to the Sun?). I find that pretty cool.
Re:lame "big bang" theory (Score:1)
Gravity Probe B (Score:3)
Gravity Probe B is a satellite that will be launched in a few years' time. It plans to check for one untested prediction of general relativity (the frame-dragging effect of massive spinning objects like the earth) by placing several hyperaccurate gyroscopes in orbit and measuring the change in the rotation axis of those gyroscopes from this effect.
It's been under works for 30 years now... here's the website [stanford.edu] for the project.
The whole system has to be incredibly accurate... I worked with this over the summer, and the technical details are scary (for example, the gyros used are the smoothest spheres ever made by man... if they were expanded to the size of the earth, the greatest height difference between valleys and peaks would be about 16 ft)
So let me get this right... (Score:1)
Jay (=
Re:The Louisanna exp is a HUGE PORK BELLY (Score:1)
Comparatively, swampland is a GREAT place to put one of these things...
Re:annoying-ass article (Score:1)
Re:lame "big bang" theory (Score:1)
Differing scientific opinion, based on facts, is certainly incredibly important to scientific reasoning. Differing scientific opinion in the absence of facts is just annoying.
Re:How about space probes? (Score:1)
And you thought $3.5e8 was a lot of money...
The big risk with building gravity wave detectors is if they don't detect anything. This would be a really surprising result if it were true, so no one would believe it unless more experiments with bigger instruments were done to confirm it. But getting money to repeat an experiment which didn't work the first time would be next to impossible, so everyone could be left in a frustrating situation.
Re:How about space probes? (Score:1)
In fact, though, there are plans to set up a series of probes in space as part of LIGO to check for lower-frequency waves than the ground-based observatories will detect. I believe the first of the probes is supposed to be launched within a decade or so, but I can't recall all the details.
Re:lame "big bang" theory (Score:1)
"START" reads "the first observable event";
"END" reads "the last observable event."
There are no assumptions about what comes "before" and "after," or what this even means in a human sense. It is undefined because we cannot (yet) know. This is very different from START being the absolute beginning of all things.
Physicists are (surprisingly?) flexible about the nature of the universe..
Re:lame "big bang" theory (Score:1)
And I do believe that the Big Band theory is correct; it is simply not whole. The process earth inside of the shell has defined the shell as being the universe -- completely without understanding and beyond the fact that the platform exists, sitting on someone's desk, inside of a corporate network on some strange world.
Gosh, I hope we are on something like LINUX or Open Source. I would be really embarrassed if we were being run on a Windows system. I am getting nervous about a universal abend here.
Damn it Jesse, stop thinking!
Re:How it works (Score:2)
If you want to believe special relativity, EVERYTHING moves at most at the speed of light. Everything. Period. Gravity can indeed be characterized as bending or warping spacetime, but that doesn't exempt it at all. Information, in the form of gravity waves or whatever, cannot travel faster than the speed of light; if you allow any sort of transmission of information or energy (yes,gravity waves carry energy) faster than the speed of light you get yourself into really nasty paradoxes.
The idea is that gravity waves coming from far away will look like the same signal everywhere just delayed a bit, whereas interference from close by will only appear on a single detector or can else be triangulated to a nearby location. Hence we can filter out unwanted signals.
Re:I thought of this first! (Score:1)
as far as I know at least
Re:Universal observations from inside a tunnel (Score:1)
Three things:
One, lack of information. This includes both lack of knowledge about the laws of physics, and the inability to gather the necessary physical data, both because there is so much of it and because it would require observation at the sub-atomic level.
Two, as others have pointed out, you run into problems with the fact that the process of measurement affects the measurement. This encompasses both Heisenburg uncertainty, and it also includes the fact that the computer that holds this information would have to be included as part of the universe. Since it is not possible to make a computer that is "outside" the universe, you cannot model the whole universe without encountering a problem of infinite recursion, sort of like telling a computer to back up the contents of an entire hard drive onto that hard drive. Once it gets to the backup file, it will go into an infinite loop.
Third, you run into problems of chaos theory and spontaneous order. The problem is that a small error in measurement can lead to an enourmous change in the outcome. This is one reason why there is a limit to the accuracy of weather forecasting, for example. No matter how accurate the measurements we make, there will still be a small error, and that error will become larger as you try to predict farther out into the future. So if you make a small error in one measurement, that small error can cause all of your predictions to be off.
yea, (Score:1)
:-s
Re:How about space probes? -> It's called LISA (Score:1)
As you might imagine, the major obstacle to LISA is the expense of the thing. I suspect that the success (or lack thereof) of LIGO will have a big impact on whether LISA ever gets funded. However, all the signals that we know are out there (coalescing neutron stars and the like) are likely to be too weak to detect with LIGO I (only the most optimistic estimates give an appreciable event rate with LIGO I). If LIGO II gets funded, then it will almost certainly see some events, and that could renew interest in LISA. LIGO II isn't scheduled to begin installation until 2004 (assuming it gets funded at all), so I expect we won't see a space-based gravitational wave observatory until sometime after then.
-r
Re:Gravity Probe B - aethernet? *snicker* (Score:1)
If they were to find that there were some frame-dragging effects, wouldn't this throw a humongous monkey wrench into the whole 'there is no aether' thing?
The way I was taught, *There was no "aether"*
To me, any indication of reference frame dragging would indicate otherwise. Maybe not *exactly* the same thing that the MM experiement "disproves", but still.....
Re:Nice (Score:1)
If he's so worried about us pesky humans playing God, why is he publishing on an online medium? I mean, weren't we playing god 100 years ago when Faraday and Maxwell were working out the basics of E&M, and Shockley/Bardeen/others again with solid state research to bring us the transistor, which directly leads to the computer on his desk.
In fact, metallargusts of antiquity were playing God as well, so we shouldn't use metals, lest we upset the delicate balance of the universe. Wait, he does denounce the combustion engine. I guess this implies he walks/bikes/etc wherever he goes, so as not to upset the ecosystem.
He seems to be the only clear-thinker among us, if it weren't for him I'm sure we'd all be up a paddle.
Re:Nice (Score:1)
Haha, i shouldn't be so hasty to submit my words. Of course, I meant to say, "We'd be all up a certain river without a paddle"
Re:Gravity Probe B (Score:2)
Indeed. Gravitational effects tend to be miniscule, so any noise in the system tends to kill you. Only by filtering out virtually everything can you hope to see the signal from gravitational physics. To give an example from LIGO, the displacements of the test masses in LIGO are roughly 10^-16 cm, or about 10^-8 of the diameter of a hydrogen atom. An interesting bit of trivia Kip Thorne mentioned in one talk he gave was that the test masses behave classically in LIGO I, but by the time LIGO II comes along quantum mechanical effects will start to become measurable. That means that if LIGO II comes to pass, it will be the first time that the quantum mechanical behavior of a macroscopic object has been observed directly. Amazing stuff indeed.
-r
Re:Laser Principles (Score:2)
This theory states that sharks with frickin' laser beams on their heads are more
deadly than mutated sea-bass.
I assume you meant to say "laser" beams, right?
--
grappler
Re:Universal observations from inside a tunnel (Score:1)
This experiment is there to increase our knowledge of the laws of physics. With your reasoning, all experiments would be pointless. Either we already know what the experiment could possible tell us, or we don't, in which case we can't do the experiment.
you run into problems with the fact that the process of measurement affects the measurement
Yes, and if I stand on a scale, that will influence my mass as well. That doesn't mean that the measurement is pointless. The conclusion of the Heisenburg principle isn't "all measurements are pointless". The conclusion is "there is a limit on what you can measure simultaneously".
you run into problems of chaos theory and spontaneous order. The problem is that a small error in measurement can lead to an enourmous change in the outcome.
Yes, and that's true for a lot of problems. But you can also calculate how much errors in your measurement influence the final result. Weather forecasting is a perfect example. There's a limit, but todays limit is further than yesterdays, due to the ability to use more data, and better precision. Nowadays, you see 5 day forecasts. I certainly remember the times you got only 3 days, and the forecast for the third day was much less detailed than you get nowadays for 5 days.
Limits are nothing more than limits. As long as you know what your limits are, you can still do a lot. Limits don't mean "all measurements are pointless". Limits also chance over time.
-- Abigail
Re:Dragging up what little I remember (Score:1)
Ummm, well how about the Voyager spacecraft travelling through space? They have mass, E=mc^2, so they thus have energy, and they surely appear to be 'carried' through this vacuum medium. Of course, one can claim that space isn't a pure vacuum but has a few hydrogen particles per cubic meter, but then again that is what light (and gravity) is travelling through from the sun anyway.
I think you may have meant to accord with the notion that space (vacuum) has no ether, thus the logical way of explaining energy being transferred through it is as a particle, because what can the E&M or gravity waves oscillate to carry them forward?
Sorry if I'm misinterpreting your point. It just strikes me as a not-well-understood notion (from my point of view, that is). I cannot wait to get to grad school and do E&M again (as well as GR and QM)...
In case you didn't know (Score:1)
Re:The Louisanna exp is a HUGE PORK BELLY (Score:1)
Re:yea, (Score:1)
Event rates and LIGO 2 (Score:2)
Y'all should know, though, that the next generations of LIGO are already "in the slot", and they promise to increase the event rates quite a bit. The whole trick is to isolate the mirrors as much as possible from disturbances that aren't gravity waves. Fortunately, there are very clever people working on the problem as we speak.
BTW...perhaps the best isolation would be to shoot the whole Michelson interferometer mess up into orbit. I'm pretty sure that some guys at NASA are working on this too. It's worthwhile to check out the LIGO page. Set