A Galaxy-Sized Observatory For Gravitational Waves 190
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."
Usefulness (Score:3, Funny)
>>> "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.
Re:Usefulness (Score:4, Insightful)
*take "validates" in this context to mean that there is no experiment or information in disagreement with the theory, therefor going by science's falsification requirement, science considers the theory to be currently valid.
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Personally, I don't believe in something like gravitational waves, but I'm more inclined to trust his intelligence more than mine.
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I feel the same way, you can bet your money on Einstein every time, but we have to test anything we can anyway to verify everything and hope to learn more.
Re:Usefulness (Score:5, Insightful)
Personally, I don't believe in something like gravitational waves
Science: You're doing it wrong.
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I've never asked him why; I'm afraid that if he gave me the answer, I'd have to get him Sectioned.
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Is thisntest desing in such away (Score:2)
that is could falsify the theory? if so then go for it.
I mean, they don't have to exist, there are other theories out there.
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Is thisntest desing in such away
Is your title designed in such a way that could falsify your hopes of being taken seriously?
....
Yes.
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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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It says "GAHHHHH FUGGIN PIGEONS GET OFF MY HAT... I love you."
A complementary approach (Score:5, Interesting)
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.
Re:A complementary approach (Score:4, Interesting)
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Not a very good clock, now is it. ^_^
Well I never thought of that - n/t (Score:2)
Re:A complementary approach (Score:5, Informative)
The good thing is that the pulsars which glitch are the young ones (hundreds to millions of years old). The pulsars that we are using for NANOGrav are millisecond pulsars which are hundreds of millions or billions of years old, have much smaller magnetic fields than young pulsars, and basically never glitch. They are extremely stable rotators -- much better than normal pulsars.
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what ever it is... adjustment of the crust, startquakes, or what the theory of the month is.
The stopquakes are the ones you have to watch out for.
Re:A complementary approach (Score:4, Interesting)
IOW, because gravitational waves travel at light speed (general theory of relativity), then a "stretch and squeeze" at one pulsar would reach the more distant pulsar many years later. The observed delay is of course a function of the distance between the pulsars, the angle of the wave and the angle of them to earth.
OTOH, a gravitational wave train with a wavelength much shorter the the distance between the pulsars could also be observed if a lot of pulsars were involved -- and if the observation period was at least one cycle. The 10^-9 frequency mentioned equates to a 31.7 year period.
Galaxy envy? (Score:3, Funny)
Will beings in larger galaxies taunt us because their gravity-wave detectors are bigger than ours?
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I guess size really does matter.
So what happens (Score:2)
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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 co
Re:So what happens (Score:5, Interesting)
If gravity waves didn't exist, you'd have to find some other explanation for PSR B1913+16 [wikipedia.org], 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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That's a little presumptuous. (Score:3, Insightful)
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"
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Space itself is a theoretical construct and gravitational waves passing through it are part of the same theory. So it is more correct to say:
"Gravitational waves, if they exist, would squash and stretch space, if it exists, as they travel, if travel is possible, through the universe, if it exists."
But that's retarded, so they don't.
Anything else I can help with, just ask.
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Solipsism is a bitch.
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It's not like they've ever detected any.
If only the summary had said so! Wait...
Might I suggest the following wording instead
No, that would be presumptuous.
Perhaps the summary author assumed a level of reading comprehension. It might be presumptuous if we knew there were gravitational waves, but not what their behavior was. However, we know their behavior, but not if they exist.
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Any armchair physicists here? (Score:2)
So, stop me if I'm way off base, but might it be impossible to detect gravity waves? If a gravity wave is a change in the gravitational constant of a finite space, then wouldn't that affect the mass, and the space-time qualities of a sensor within that space, rendering its observations relative, and useless?
Or does my thought experiment lack a certain... Knowledge?
Thanks!
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> So, stop me if I'm way off base, but might it be impossible to detect gravity
> waves?
Proving that they cannot be detected would be exactly the same as proving that they do not exist.
Re:Any armchair physicists here? (Score:5, Informative)
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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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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You, I, and the lasers are inside the three-space being acted upon by the gravitational wave. How the hell are we supposed to measure this phenomenon from the "inside?"
Same way we'd measure the surface of a sphere changing if we were on the surface of the sphere. Just add an extra dimension.
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A gravity wave will change the distance to objects at right angles to its direction of propagation. This effect is biggest when the distance to an object is order the wavelength of the wave, or longer. (Since they travel at the speed of light, the relation between wavelength and frequency is the same as for light.) Likewise, the sensitivity is biggest when the period of the wave is between the frequency of measurement and the total duration of observations. So, pulsars are sensitive to waves with periods be
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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
Gravitational Waves Exist (Score:2)
I believe that any theory of gravity where
1. Energy is conserved
2. Gravitational information propagates at a finite speed (most theories set this speed equal to the speed of light)
will have gravitational waves of some sort.
Is there any physicist who does not believe in both 1 and 2?
Gravitational waves exit. The real problem is detecting them and interpreting the waveforms.
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The really interesting thing is that General Relativity predicts two and only two polarizations, while other theories (that cannot be distinguished from G.R. in the usual solar system tests) have more polarizations. If and when we get a good, high SNR, detection of gravitational radiation, a profound test of gravity should follow in short order.
Just because a theory cant be tested (Score:4, Interesting)
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.
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Bear in mind that there's a big difference between a theory which cannot be tested in principle, and one which cannot currently be tested in practice due to limited technology. Actually, it's not even appropriate to use the word "theory" in this context. In the latter case, it's a hypothesis. In the former, it's metaphysics.
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He might not have thought about, but there's actually a fairly simply way to measure the size of an atom.
Take an oil drop and measure its weight. Then drop it on the surface of a very still lake, and leave it to spread it out. It will spread to be about 1 atom thick. Then you can simply look to see how big it spread out, divide by the volume by the area, and the result is the size of the atom.
This gives a result to within an order, which amazing given its simplicity.
adds a whole new dimension to "surf's up" (Score:2)
A Suggestion for 2 New Observatories (Score:2)
Re:Guess LIGO failed too many times (Score:4, Informative)
Re:Guess LIGO failed too many times (Score:5, Insightful)
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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> 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.
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The lack of positive results in gravitational wave detection and the Higgs search reminds me of the Michelson-Morley experiment. Sure I know that we're only scraping the bottom/top of the possible ranges for these phenomena, but I wonder if we aren't just killing time until the next Einstein comes along to explain that there is no luminous aether.
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Is it Crackpot Hour on Slashdot tonight? First electric universe, and now free energy?
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It takes you literally a single mouse click to find out who I am, but I guess that would take a little bit of marbles, huh?
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I really expected that link to redirect to http://www.timecube.com/ [timecube.com]
Re:Guess LIGO failed too many times (Score:4, Insightful)
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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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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Gravitational waves are a consequence of general relativity, so IF gravitational waves don't exist then GR is at least partly wrong. That's a bit stronger than believing in Santa Claus I'd think
Well, if GR was wrong on that score, don't you think physics would suddenly get a lot more interesting? I mean, seriously, its the prospect of Santa Claus popping up and gravity waves not being there that really, fundamentally, the human force that drives science. People want to be surprised by the experiments that
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Eintein's theory of General Relativity (GR) predicts that gravity waves exist, and GR has already made several other verified predictions. It's a bit like a boat in the water. What we've verified with GR already is that the boat displaces water, this is the distortion that objects with mass cause to occur on spacetime. Gravity waves would be the w
Better there are no gravity waves. (Score:2)
Eintein's theory of General Relativity (GR) predicts that gravity waves exist, and GR has already made several other verified predictions. It's a bit like a boat in the water. What we've verified with GR...
No, but my point is that every breakthrough in physics came through because people were ho hum and looking through some theory where they expected to find a result, and didn't. Once upon a time people thought Newtonian mechanics was all there was. We think 100 years of Einstein (wow!), is a long time, b
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So you want all experiments to show something contra to the hypothesis, which suggests some new hypothesis? That's what it sounds like. What do you want to happen when they try to test the secondary hypothesis? Do you want that experiment to fail and sugest something else? If no hypothesis are proven, what's the point of experimenting?
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So you want all experiments to show something contra to the hypothesis, which suggests some new hypothesis? That's what it sounds like
Oh, don't be so sith-like. The situation at hand is that physics has been in confirmation mode for a good long time and it would be fun to see things shaken up a bit.
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I'm really starting to hate the Santa Claus metaphor. There really was a historical person, Nicholas of Cusa, who was Bishop Nicholas in life but became known after his death as Saint Nicolas. That title got shortened and linguistically shifted to Santa Claus.* So technically, there was a Santa Claus, and its just some of the claims made, like his continuing to live today, having flying reindeer or residing at the north pole, that are contra-factuals. Some of the claims, such as his giving a great deal to m
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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.
Re:Guess LIGO failed too many times (Score:5, Informative)
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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That's correct. Lack of evidence isn't enough to disprove a theory; what you need is evidence that directly contradicts the theory.
We are approaching the point where the lack of evidence becomes evidence of non-existance. But as of yet, I know of no alternative theory.
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No, were not. Our instruments are still not nearly sensitive enough to say that.
Re:Guess LIGO failed too many times (Score:4, Informative)
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.
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The theoretical reasons, in this case, include General Relativity, as your first link points out. That's passed a lot of other tests, and dropping it would take some big reasons. Trouble confirming just one of many predictions? Interesting, but not excuse enough to abandon a highly successful theory, not at all. Get a competing theory that has substantially more predictive power, and makes substantially fewer untestable claims, and scientists will generally switch, but none of the electric universe models a
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That position makes science itself entirely useless.
(Unless you can prove scientifically that science is the best way of determining objective truth, and neither we, nor any hypothetical beings living anywhere else in the universe, no matter how powerful their minds are, can ever invent anything better than the scientific method.).
Popper's falsification was a philosophical concept, and might be falsifiable by logic or philosophical debate, but it's not part of science itself, any more than the claim that sc
Re:I don't get it. (Score:5, Insightful)
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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The sad thing is that I've met plenty of computer geeks who basically say that physics is useless. They then go back to their beloved computers without realizing the tragic irony of what they just said. That's the pathetic thing about compute
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The sad thing is that I've met plenty of computer geeks who basically say that physics is useless. They then go back to their beloved computers without realizing the tragic irony of what they just said.
Still, you're making that remark using a web browser running on top of a software stack made up of at least a multi-tasking OS kernel, a dynamic linker and an assortment of userspace libraries, written in various high-level programming languages with optimising compilers. It's not as if the transistors came up with all that by themselves.
Physics in itself is important, there's just no need for most people to be physicists.
Re:I don't get it. (Score:5, Interesting)
> 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.
Re:I don't get it. (Score:5, Insightful)
Re:I don't get it. (Score:4, Insightful)
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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> Since when does everything science accomplish have to have immediate material benefit to humanity?
To play devil's advocate... it's not so much a matter of "what science accomplishes" as "who pays for it". One is entitled to some sort of opinion when one is paying for it, via tax dollars.
It is, as you point out, shortsighted to assume that all science must have an immediate benefit to be worth it. But it is worth considering whether money spent on basic research might be better spent elsewhere.
(Person
Re:I don't get it. (Score:5, Insightful)
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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So I propose before you take a hit on science, maybe you should look at so much other usless spending and save a few kids from hunger
YEs NO ?
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> Exactly. So, why should we be spending money that we don't have?
Because you can not frugally "save" your way out of a depression. That simply leads to a deeper depression.
Its cheaper to build these things (as well as other infrastructure) in a down economy than wait till everyone if fully employed and demanding big salaries.
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I know it's counter intuitive, and back when I was about your age (that's right, I'm patronising you. Feels good man.) I myself didn't get it, but basic science (the kind that seems like useless theoretical dicking around like that gravitational waves thing) is a sort of long term investment, and a great kind of investment, as you can get several times your investment back.
Think about it, what good was nuclear research in the 19th century? Yet a few decades later they probably kept us safe from an all out
Physics = Useful inventions (Score:3, Funny)
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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"Umm...actually finding gravitational waves would help 100% of the population."
Finding gravity waves is the key to finding anti-gravity waves. You see, every particle has its anti-particle. The are electrons and positrons. The are protons and anti-protons. There are top quarks and there are bottom quarks. There are charming quarks and there are boring quarks. There are gluons and anti-gluons. Just imagine what a beam of these would do to your enemy. Leaves nothing but quarks flying in all directions! Not a
If we learn about gravity.... (Score:2)
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> We spend billions on observatories, but what's the point?
To learn.
> I understand taking an in-depth look at our galaxy, but this is ridiculous.
Why?
> We should concentrate on landing on mars...
Well, then you and your colleagues[1] should concentrate away. Meanwhile, these people choose to concentrate on something else.
[1] I assume you have colleagues: why else do you write "we"?
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If every observatory ever built were using a galaxy as a sort of measuring instrument, then yeah. What's your point?
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Thats what I don't understand - how do you use the galaxy as a measuring instrument?
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Disclaimer: not an astrophysicist, I could be entirely wrong.
Re:And yet we spend only 1.6 million on tracking N (Score:2)
I agree that we should be funding the tracking of NEOs more, but remember that the money for these two projects isn't coming from the same pool. One is a NASA sub-project, the other is an international project conducted by a variety of observatories and funded by a variety of organizations. So it's not as simple as "do this instead of that".
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The speed of light is actually the speed of energy, so if gravity waves are energy, then it will be at or slightly below the speed of light. Otherwise, if it's matter-based, then its maximum speed would be about the speed of sound. I believe.
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Vacuums contain material, dude. My Dyson is almost full.
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The Universe has a foamy head?
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> I would love to know how fast gravity waves travel.
At the speed of light.
> If a black hole can keep light from escaping, that means the speed of light
> isn't escape velocity, and that means that gravity is getting to it faster
> than the speed of light?
Gravitational radiation does not come from inside a black hole any more than electromagnetic radiation comes from inside an electron.
Re:This would be wonderful (Score:5, Informative)
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 [nrao.edu]
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No, not quite.
Remeber that mass causes a curvature in spacetime ( General Relativity ), so inside the event horizion, spacetime is curved in on itself so much that light cannot escape, as all possible directions inside the event horizion point towards the center. While a 'calculated' escape velocity inside the event horizion may turn out to be a speed higher than lightspeed, no matter can ever reach that speed.
As far as we can tell, gravity moves at the speed of light, so therefore gravitational waves will
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Hmm. Please do not explain physics in the future. :-(
Not that relativity is particularly easy, but... just no.