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A Galaxy-Sized Observatory For Gravitational Waves
KentuckyFC writes "Gravitational waves squash and stretch space as they travel through the universe. Current attempts to spot them involve monitoring a region of space several kilometers across on Earth for the telltale signs of this squeezing. These experiments have so far seen nothing. But by monitoring an array of pulsars throughout the galaxy, astronomers should be able to see the effects of gravitational waves passing by. They say such an array of pulsars should effectively shimmer as the gravitational waves wash over it, like a grid of buoys bobbing on the ocean. That'll create an observatory that is effectively the size of the entire galaxy. These observations should be capable of monitoring how galaxies and supermassive black holes evolve together, and shed light on the physics of the early universe. Best of all, the next generation of radio-telescope arrays should be capable of making these observations at a cost of around $66 million over ten years. That's a small fraction of the hundreds of millions that Earth-based observatories have already cost."
>>> "Gravitational waves squash and stretch space as they travel through the universe
Gravitational waves are very useful in the kitchen. I use them for juicing oranges.
What do you mean finding absolutely nothing? They just ruled out the higher end of the spectrum for gravitational waves. They learned a lot in building very precisely calibrated instruments to do the gravitational wave detection. They continue to lower the detection threshold.
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Just wanted to point out that the pulsar timing array approach will cover a completely different frequency range (~ 10^-9 to 10^-7 Hz) to existing ground-based detectors (LIGO, Virgo and friends), which operate in the 10^1 to 10^4 Hz range. In between are projects like LISA (http://lisa.jpl.nasa.gov/).
The different frequency ranges mean different astrophysical sources of gravitational waves; generally speaking, the more massive the system, the lower the GW frequency. LISA, for instance, would see the radiation produced by the supermassive black holes at the centres of galaxies, while the other detectors would be targetting much smaller systems.
A human landing on mars gives us pretty pictures and a bunch of cozy, warm feelings.
Understanding fundamental physics (and mathematics) gave us the computer age along with keeping Moore's "law" working for the past 40 years. What did physics ever give to you? Pretty much every major engineering invention since 1950 depends on it in some way or other.
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Be yourself no matter what they say
> We spend billions on observatories, but what's the point?
Calm down. There is a depression going on.
All that money enters the economy employing everyone from astronomer to shoe-shine guys. In the mean time some science gets done.
If your tag line is to be believed, you will forgive us if we wait till you are actually OUT of your mom's basement before we task you with prioritizing our national science budget.
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Will beings in larger galaxies taunt us because their gravity-wave detectors are bigger than ours?
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That's correct. Lack of evidence isn't enough to disprove a theory; what you need is evidence that directly contradicts the theory. In the case of gravity waves, it might be observation of an event that should produce detectable gravity waves, combined with our not detecting them.
And, while I'm at it, I'd like to point out that what Popper taught us was that a theory was useless unless there's a way to falsify it, at least in theory. If you can find a way to show that any conceivable experimental results can be viewed as confirming the theory, it's useless because it can't be tested. In the case of gravity waves, they're but one of many things predicted by General Relativity, and one of the few that's not been observed as yet.
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Since when does everything science accomplish have to have immediate material benefit to humanity? Science is the advancement of Homo sapien knowledge about the universe. If you're going to complain about spending money complain about throwing trillions of dollars at the people who brought down the economy. Some people need to grow up.
If they don't find gravity waves in this attempt, I would suspect the following to happen:
A: One bunch, the Einsteins of the lot will say "Well, I toldja so..."
B: The Quantum types will simple demand more money for an even bigger test that will look at clusters of Galaxies or some such conglomeration of Stuff.
When that test fails, go back to step A. Rinse. Repeat.
RS
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What do you mean finding absolutely nothing?
Judging by his links to thunderbolts.info, what I think he means is "I'm a crazy idiot who doesn't understand anything, and think this is a sound foundation to question the work of scientists everywhere. Solar wind is caused by an electric field! What do you mean it's a plasma with equal amounts of positive and negative charges, and a field can't move opposite charges in the same direction? No really, I have no idea what you're talking about because I never too physics in school! But my theories are right anyway!"
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Is thisntest desing in such away that is could falsify the theory?
What language is this written in?
What does it translate to in English?
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"Gravitational waves squash and stretch space as they travel through the universe."
Does anyone else find these words to be a little presumptuous. It's not like they've ever detected any. Might I suggest the following wording instead:
"Gravitational waves would squash and stretch space as they travel through space, if they exist"
He's 15 years old. It's much easier for him to understand and critique something that has been summed up than to spend the time and critical thought necessary to understand our present economy. Let's give the little bastard^Wwhippersnapper a break, he's trying.
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Exactly. So, why should we be spending money that we don't have?
Finding gravitational waves isn't going to help 99.99% of the population.
How about you look at this this way instead:
There is a lot of money going around to try to help a flailing economy. Why should that money go ONLY to those who have been bad at their business? Automakers that don't make the right cars? Banks that don't have solid lending strategies? Why NOT give some of that money that's all going to the same economy to scientists who quietly go about their business and get things done?
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LIGO and Pulsars set limits (or could detect) gravitational waves in very different parts of their frequency spectra - periods of milli seconds versus periods of months. The sources are different, the detection physics is different, etc. It's certainly worth trying both.
Also, none of the existing detectors are good enough that you can say for certain that there are known or likely astrophysical sources bright enough that they should see them. You can't talk about falsifiability until you cross that threshold, which I would expect to see happen in a decade or so.
> They just ruled out the higher end of the spectrum for gravitational waves.
No. They failed to detect high-frequency gravitational radiation above a certain level. Conventional theory predicts that the radiation they failed to detect should be fairly rare, so the result tends to confirm the established theory while leaving the proponents of some alternative theories with some explaining to do.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
I seem to recall an experimental observation in the last few years involving Jupiter, through which they verified with about 90% certainty that the speed at which gravity propagates through space/time is equal to the speed of light.
A little googling turned this up:
http://www.nrao.edu/pr/2003/gravity/index-p.shtml
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A gravity wave, as derived from the theory of relativity, doesn't specify that the gravitational constant would oscillate - simply that the shifting of large masses, like co-orbital black holes and such, will distort spacetime in wavelike manner. Those perturbations of spacetime would travel from their origin outward at the speed of light.
It's best to think of it in terms of the bowling-ball-on-a-rubber-sheet analogy of space-time. If you take a large mass like a bowling ball and set it in the middle of a large rubber sheet, it will depress deeply nearby and taper off the further away from it you go on that sheet. If that bowling ball magically disappeared, there would be a wave that travelled across that sheet as well as if you had 2 bowling balls spinning around each other.
The way we've been trying to detect gravity waves so far (LIGO) uses lasers set up at right angles so if space were to compress or stretch in one dimension, the beams the were previously in phase would shift apart. This can detect a stretching of spacetime equal to a fraction of the wavelength of light used in the lasers.
In actuality, it is the change in the behavior of spacetime that lets us measure in that manner, but if the wave were to stretch spacetime in all dimensions, LIGO couldn't work. Hope that explains it.
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DarrenBaker, a gravity wave is not a change in the gravitational constant; it is a deformation of the space-time fabric itself. So it doesn't change the gravitational (attractive) force between masses but simply moves the "fabric" on which they lie.
Imagine a stretchy, rubber fabric that you pull/push or move upward/downward from one side such that a wave propagates through. Then two masses lying on this fabric, link ping pong balls that you would stick on, would move closer/further apart. That's basically the effect that people are trying to measure. Of course, if these "test" objects are perfect in such that they're infinitely small, everything behaves in a trivial way. The catch is when your object is not "perfect" anymore and possesses some finite size. This seems to be concept that you worry about and you are right. Because of it's finite size, the object itself would change size. However, it does not matter at all because this change is not significant. Here's why:
The amplitude of a gravity wave is express in a weird unit expressing the ratio of the spatial compression in one direction to the stretching in the orthogonal direction (see the nice animation here). A typical gravity wave would have an amplitude of 10^-20., which basically mean that any object would change size by this fraction. So this is practically undetectable unless you consider something really big like the "arms" of the LIGO gravity wave detectors or this pulsar timing array. The other thing to take into account is the fact that what you are trying to detect acts like a wave. Waves that this pulsar array is after have frequencies of nanohertz, or wavelengths of 3*10^17 meters (this is about 32 light-year!). For LIGO, frequencies are the order of 1 hertz, so 300 000 km. Hence if your object, the pulsar for the pulsar array, or the mirror/detector for LIGO is much smaller that the wavelength that you attempt to detect, it really doesn't have any effect on what you are trying to measure.
The guy you're responding to, tjstork, is an idiot, not worth your time. He's also a conservative, but I repeate myself. The only reason it's relevant is that his opinions come from his ideology. In his mind, you are already wrong because you like science, and science is paid for in large part by public dollars. This makes science the enemy to him.
He'll stick to his scientifically ignorant position, and you will fail to educate him.
Just a heads up.
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Like I mentioned in the last sentence, it relies on the expectation that a gravity wave passing through an area would stretch one dimension of space while contracting another perpendicular to it.
If it causes all dimensions (including time) to expand and contract simultaneously, it can't work.
Of course, I have to defer my understanding of gravity waves to those who study this stuff for a living and have experimentally verified a large body of the predictions made by general relativity.
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I really expected that link to redirect to http://www.timecube.com/
Doesnt mean its not true...Democritus 2400 years ago proposed the existence of the atom.
He had no way testing this, he simply used logic to deduce it.
This is precisely this type of condescending, we-are-am-smater-than-you attitude that turns people off on science and scientists. Maybe physicists should concentrate on the foundational issues (e.g., the true nature of motion) first before they go chasing after gravity waves. You folks are not as smart as you think you are.
But of course you are as smart as you think, which is smarter than every other physicist alive or dead (while so pointedly stating that you aren't one), so this is the kind of condescending attitude we need. LOL.
Did you know that over 90% of physicists believe that matter can move in spacetime even though it is known that spacetime is frozen from the infinite past to the infinite future?
Spacetime isn't frozen. It's warped by mass and constantly expanding. "Did you know" indeed. :)
Did you know that most physicists believe that moving bodies remain in motion for no reason at all, as if by magic?
They also believe that bodies at rest remain at rest for no reason at all, as if by magic! This is no more mysterious.
Well, magic, and that and for it to do otherwise in either case would require an expenditure of energy and a transfer of momentum.
I'll admit, I bit and read the blog, and it was highly amusing. It was very humorous reading about how you agree with Aristotle* that there must be a "force" to make an object move at a constant velocity, and the object should instantly stop as soon as that "force" is removed. And therefore there must be "energy" around us to make this happen. As if "force" and "energy" are vague, mysterious entities, like a sci-fi writer referring to a "mysterious force" or "a being of pure energy".
But actually, force is a change in momentum. If there was a net force acting on a moving object, it would accelerate (or decelerate). If there's no force on an object, it can't accelerate or decelerate, i.e. its velocity must be constant. If the speed of the object changes, then there was a transfer of energy. Energy, by the way, is the principle Newton was looking for. It's the transfer and storage of energy in various forms that explains how objects can begin moving, and continue moving. Conservation of energy was formulated not too long after Newton's conservation of momentum and fills in what Newton couldn't.
The problem with upending physics is that you have to understand it first. This has been the case for all the great physicists, and it's the case today. And you don't understand causality. An object changing its speed, going from motion to no motion, is the effect, and for this to happen there must be a measurable cause, specifically a transfer of momentum and energy. So, please, Conservation of Energy demands an answer: in the absence of any outside force, why would an object moving at a constant velocity stop?
* Great thinker but lousy physicist -- thought his ideas were so good they didn't need testing**! Must be why you're drawn to him. ;)
** Maybe if he had, he would have realized that he was close but off on his idea of an object's natural state in the absence of interference being one of rest, when it's really one of constancy, and we would have Aristotle's Laws of Motion.
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If gravity waves didn't exist, you'd have to find some other explanation for PSR B1913+16, which is a pulsar in orbit around another star. The pulsar and its companion are spiraling in together, losing energy in exact agreement with the phenomenon of gravitational radiation predicted by General Relativity. This binary pulsar system has been hailed as sufficiently convincing indirect evidence for the existence of gravity waves that Russell Alan Hulse and Joseph Hooton Taylor Jr. were awarded the 1993 Nobel Prize in Physics for its discovery.
No, it doesn't seem that the existence of gravitational waves is in any question here. The only thing is that there might be much yet we don't understand about gravity that is stifling our ability to observe them directly. It's obvious that General Relativity is far from being the final word on gravitation.
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Saint Nicholas is a historical person who has simply had more myths and legends attach themselves to him than has George Washington, also still a historical person despite the Cherry Tree and Dollar across the Potommac stories.
The myth of Santa Claus has taken such a scale that, though Saint Nicholas might be a historical person, it's fair to say that Santa Claus is a separate entity, a myth based on a historical figure.
So what do you know, maybe when you'll be older you'll owe your flying car to current research on gravitational waves.
And gravity-defying breast implants for your wife...
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