It's Official: LIGO Scientists Make First-Ever Observation of Gravity Waves (economist.com) 460
A few days ago, we posted reports that a major finding -- the discovery of the long-predicted gravity waves -- was expected to be formally announced today, and reader universe520 is the first to note this coverage in the Economist : It is 1.3 billion years after two black holes merged and sent out gravitational waves. On Earth in September 2015, the faintest slice of those waves was caught. That slice, called GW150914 and announced to the world on February 11th, is the first gravitational wave to be detected directly by human scientists. It is a triumph that has been a century in the making, opening a new window onto the universe and giving researchers a means to peer at hitherto inaccessible happenings, perhaps as far back in time as the Big Bang. Reader
DudeTheMath adds: NPR has a nice write-up of the newly-published results: "[R]esearchers say they have detected rumblings from that cataclysmic collision as ripples in the very fabric of space-time itself. The discovery comes a century after Albert Einstein first predicted such ripples should exist. ... The signal in the detector matches well with what's predicted by Einstein's original theory, according to [Saul] Teukolsky [of Cornell], who was briefed on the results."
Update: 02/11 18:08 GMT by T : Worth reading: this letter, inspirational and informative, from MIT president L. Rafael Reif, about the discovery. (Hat tip to Brian Kulak.)
Cool! (Score:5, Insightful)
Nobody actually ever thought that gravity waves wouldn't exist-- it's pretty much impossible to come up with a version of gravity that doesn't include waves.
But it's amazing that we can actually detect it.
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Wouldn't it have been conceivable, assuming some flaw in the theory of relativity, for gravitational effects to occur instantaneously across vast distances instead of limited by the speed of light (and thus causing propagation in the form of waves)? Or they could have discovered that the waves are different from theoretical predictions in some other way.
Re:Cool! (Score:4, Insightful)
Re:Cool! (Score:4, Informative)
If it were possible, you could use gravity for FTL communication, possibly even allowing you to violate causality.
Re:Cool! (Score:5, Funny)
I look forward to the day when I can tell Comcast "sorry, I'm switching to gravity."
Hawking's party (Score:3)
I'll see you and your FTL at Steven Hawking's post-announced party last year.
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What makes you think that this make it inconceivable? I wouldn't find it any more strange than the many-worlds interpretation of quantum theory, and that one has many supporters.
A lack of causality would mean that our perception of causes and effects is just the biased way we see the world, as a projection of a small subset of events (those with a direct causality relation) within a much more co
Causality (Score:3)
It's very difficult to reason about the universe without causality. Personally, I would rather not go there, the possible delights of science fiction notwithstanding.
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I think you meant to say "Inconceivable? You keep using that word, but I don't think it means what you think it means".
Many fictional things are "conceivable", but in terms of real science, no one is going to take a casual "general relativity is totally broken" proposal seriously. General relativity has made more and better predictions (and more unexpected predictions) than just about anything. You can doubt any theory, but the more one has proven itself, the higher the bar to claim "but maybe it's total
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Causality breaking is subtle. For a simple one-way trip, in your reference frame, nothing will seem wrong, but from another reference frame you may appear to go back in time. If you have two pairs of ansibles (FTL telephones), each pair moving relative to the other, it's possible to send a message round trip (FTL to your connection, normal space to another endpoint, FTL to its connection, back to you) in such a way that you receive it before you send it.
Sorry, my English is terrible, so I don't quite get it.
An example would be good. Let us say that Alice is communicating with Bob who is on a planet 12 light years away with messages that travel at 4*c speed. All the while Alice is travelling towards it at 3*c.
I am not sure how this "FTL to your connection, normal space to another endpoint, FTL to its connection, back to you" would end up reaching Alice before she sends the message.
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I have just tried reading the Tachyonic antitelephone wikipedia page and I am even more confused! Particularly since it heavily uses Lorentz transformation, which is also way over my head...
Would anyone please explain in simpler terms without the maths involved? Or is it one of these areas that just can't be explained without it?
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I've never found a good simple explanation. The basic idea is:
<-A--B--
--C--D->
Arrows show motion, close to the speed of light.
A sends to B FTL. In the reference frame of C and D this seems to go back in time.
B sends to D. This takes normal time, but B and D are close.
D sends to C. In the reference frame of A and B this seems to go back in time.
C sends to A. This takes normal time, but C and A are close.
In all reference frames, the message returns to A before it was sent, because everyone sees one
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If I can just use one part of the Lorentz transformation, I can perhaps be clear. I'm going to do this in two parts: first I justify the time part of the Lorentz transformation, and then I show how FTL implies time travel.
Measuring time on different spaceships Light travels at constant speed. We construct clocks on ships that tell time by bouncing photons between detectors and emitters a meter apart and counting a tick every time the light reaches a detector. We construct them to be perpendicular to
Re:Cool! (Score:5, Insightful)
Yes, absolutely.
The thing here is that to date Einstein has a perfect track record. Which is pretty remarkable.
To date, everything they've ever tested says that the theory of relativity, as far as we've been able to investigate, hasn't shown any cracks.
Re:Cool! (Score:5, Informative)
Well, except for the niggling one where it demands a completely different vacuum energy level than the similarly well-tested theories of Quantum Mechanics.
It's an odd situation - we have two well-tested and widely accepted theories, neither of which show any significant cracks, but which are utterly incompatible with each other.
Re: Cool! (Score:2, Informative)
This has happened in science before, with contradictions between Newton and Maxwell. The whole special relativity thing was the reconciliation.
Re:Cool! (Score:4, Interesting)
It still follows basic thermodynamics once you break it down.
No, it does not.
Neither quantum mechanics nor the relativity theory have anything to do with thermo dynamics, basic or not.
Re:Cool! (Score:5, Interesting)
Absolutely. My point was not so much about refuting relativity completely, but observing (at scales far beyond our normal ability to detect) data that suggests that relativity as we know it is an incomplete theory. Which has already happened, mind you, given that relativity did not at the time fully describe quantum physics and other phenomena.
But discovering that gravity waves didn't follow the pattern might have made LIGO a modern Michelson-Morley experiment, leading to completely new physics, just as relativity was a better description of gravitation and spacetime than Newtonian physics.
Michelson-Morley were wrong. Ether exists (Score:5, Interesting)
What's sort of amusing here is that the Michelson-Morley experiment, which is EXACTLY what this experiment is, failed to detect Ether. Yet this experiment is actually detecting ether! it's not the ether distortion MM were looking for which is differences in some vaccum substance that supports electromagnetic wave propagation. Instead it is detecting gravity wiggles in in real matter. Yet those gravity wiggles traveled through vacuum too. And according to general relativity my understanding is that should have distorted the vaccuum too. Thus if MM had had a sufficiently sensitive interferometer they would have detected these and attributed them to Ether fluctuations!
Re:Michelson-Morley were wrong. Ether exists (Score:4, Interesting)
We detected the electromagnetic ether a long time ago. Today we call it "the photon field." If we had a quantum field theory of gravity we'd call the gravity ether "the graviton field" but instead we settle for calling it spacetime.
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No, the MM experiment was measuring the speed of light in different orientations. Just because both used interferometers does not mean that they are measuring the same thing. If the MM experiment were arbitrarily more precise they would not have detected any change in the speed of light regardless of the orientation of their device, and spacetime fluctuations would have been dismissed as noise, and not particularly significant noise at that.
You are deeply confused about pre-Einsteinian theories of light and
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Dude, all both of them detect is phase as a proxy for time delay at arrival. time delay can occur because things got shorter or things went faster. but the experiments are identical in what they actually measure.
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They are different in what they were TRYING to measure. But they ACTUALLY measure the same thing.
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There's no difference between "change in speed of light", "change in distance", and "change in travel time for light". They're all the same thing. Don't both instruments detect very small changes in round-trip travel time for light, comparing one direction to the other?
Sure then 1880s apparatus wasn't going to detect gravity waves, but that's just a matter of sensitivity of the instrument. We still call an electron microscope a microscope.
Re:Cool! (Score:5, Informative)
To date, everything they've ever tested says that the theory of relativity, as far as we've been able to investigate, hasn't shown any cracks.
That's not quite right.
- GR breaks down when you go to quantum levels
- GR does not fully describe black holes (particularly their horizon and the singularity)
- GR is incomplete with regards to explaining the expansion of the universe (the discrepancy is called Dark Energy)
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+1 for Amusement.
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I pay attention to how the inside of my head works. Extreme introspection. I'm kind of obsessed with knowledge, learning, and optimization, so it's become a sort of nervous tick.
The brain is an intuitive tool: you can pick it up and use it to reasonable effect without learning how. As with most intuitive tools, you can use it to *great* effect if you have better understanding of technique. This is why some people have shitty handwriting, and others are scribbling out professional-grade calligraphy jus
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Re:Cool! (Score:4, Informative)
Its possible to formulate theories of gravity that don't have gravity waves, but there was already strong evidence of their existence from measurements of the orbit decay of neutron star binaries.
Direct detection was fantastic - but it confirmed what was already believed to be extremely likely.
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Yes. Einstein theorized that spacetime is curved around objects, and so an object, once settled, should have this curvature around it rather than a wave to project. That said, it's like ideal gas laws or my economic theories of wealth: everything *approaches* a certain state, but pushing a piston down into a 1L bottle of gas doesn't instantly make tho whole volume obey ideal gas. You get an average, with high pressure at the point you inserted the force, which then reduces as it compresses stuff furthe
"Curved" space (Score:3)
Yes. Einstein theorized that spacetime is curved around objects...
More accurately, if you chose to define a geodesic as being the path taken by a light ray, then the space-time coordinate system defined by light rays in the presence of gravity obeys a non-Euclidean metric that is described by the metaphor "curved"-- by which we mean, it has the same geometry as a (Euclidean) curved surface in a higher-dimensional embedding space.
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We're talking about the fabric of space-time being curved. That means your 3D space is essentially a hyperplane perpendicular to a particular point on a fourth spatial axis. The word "curved" obviously both does and doesn't have the same meaning.
If you flex a 2D plane and draw a straight line across it, you get a curve because the plane is curved. This is trivially demonstrated by drawing a straight line on a sphere. What you just described is, essentially, a 3D space being curved in the same way, an
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I didn't think they existed. After all I can't see them. Unless I can put it in my pocket I don't believe it exists.
So you don't believe in the sun as you are unable to put it in your pocket?
Re: Cool! (Score:3, Funny)
Re: Cool! (Score:4, Funny)
Or houses, or cars, or trees, or manhole covers, or other people... Lots of things don't fit in pockets ;-)
does he actually believe his own pockets exist as he would not be able to put them in side themselves.
Re:Cool! (Score:5, Informative)
Finding them means we can start developing better instruments. Primordial gravity waves are our best shot at understanding the inflationary epoch and understanding the Big Bang itself. This is one of physic's greatest triumphs.
And, of course, it confirms once again that Einstein remains one of the titans of human thought.
Compare prediction to reality [Re:Cool!] (Score:4, Informative)
> Nobody actually ever thought that gravity waves wouldn't exist
Which is precisely why this is such a non-important result. You don't learn much about the universe by demonstrating something everyone already knew is true. It would be much, MUCH more interesting if it didn't work.
To the contrary. Now that we have detected gravitational waves, we can start comparing the predictions to the measured data. Until we had detected them, we couldn't compare theory to data. Now we we have a possibility to do so.
That's why the MMX is cool, and this isn't.
>But it's amazing that we can actually detect it.
From a technology point of view, yes. From a theoretical perspective, not so much.
Re:Cool! (Score:5, Interesting)
Actually, no, this is a very important result. We've been looking for gravity waves for years, and until now had been unable to detect them despite looking at sources that we should have been able to detect. This detection essentially closes an "uncertainty gap" in the theory - think of it like replacing "Here there be Dragons" on an old map with, "Nothing but open ocean here". It doesn't really change much, unless you happen to want to travel across the previously unknown area.
In addition, the article doesn't mention it, but by comparing the measured spatial distortions with he predicted values we open the door on the study of why the waves aren't as strong as predicted. Is there a flaw in the machine, or some hither-to unpredicted attenuation factor? The latter could potentially be every bit as earth-shattering as when the study of black-boy radiation revealed Quantum Mechanics.
It is in looking for confirmation of the predictions in current theory that both confirm that theory, and occasionally expose its flaws, which lays the groundwork for new theories. It may not be as exciting or glamorous as discovering something unexpected and new, but it's the same exact search that does both, and it's largely the luck of the draw as to whether the previously unexplored nook you chose to investigate reveals anything new. Its primarily through the exhaustive search of such nooks that we discover the unexpected phenomena that allows further theoretical growth. And in that pursuit "nothing unexpected here" is vitally important, as it allows future researchers to concentrate their attention elsewhere. Not to mention, it develops the early stages of the technologies that eventually allow us to harness the phenomena for productive uses.
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With advanced LIGO, we might have been able to rule in or out that latter possibility (there are still unknowns that aLIGO could help us clear up).
There's more here than confirming what was already strongly suspected. This
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You seem to have a funny sense of what constitutes "true".
Nobody "knew" gravitional waves were real until they got measured. They believed in it, had convinced themselves of it, but they sure as fuck didn't "know" it. If fit the theory, but it wasn't a fact.
What you do is confirm your theoretical model with more evidence. That's what they've done he
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Because of the huge uncertainty over the strength and frequency of extraordinarily exotic astrophysical circumstances which would make gravitational waves identifiable and detectable experimentally.
It's like saying you're going to take a picture of the camouflaged panther with neutrinos. You think you know how neutrinos work, but you don't know how many of those panthers are there.
So is the 5th or 6th fundamental force? (Score:2)
* Strong Intergalactic Force, or the
* Weak Intergalactic Force.
When are white holes going to be discovered? :-)
Re:So is the 5th or 6th fundamental force? (Score:5, Funny)
When are white holes going to be discovered? :-)
#BlackHolesMatter...
Re:So is the 5th or 6th fundamental force? (Score:5, Funny)
When are white holes going to be discovered? :-)
Watch the Oscars.
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When are white holes going to be discovered? :-)
Racist!
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When are white holes going to be discovered? :-)
They a!ready have been and you can oberve them too! Go to the nearest university they are usually members the Greek fraternities
They did what? (Score:5, Funny)
Re:They did what? (Score:5, Funny)
LEGO Scientists are attempting to detect Agony waves which occur when a foot collides with a brick in the dark. It turns out to be a very interesting problem. While most people have problems with a detector sensitive enough to find weak signals, the LEGO scientists are having the opposite.
Re:They did what? (Score:4, Funny)
They're caltrops and you suffer 1d4 worth of damage as well as having a movement penalty.
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I have a considerable collection of LEGO's at home, which is perhaps the reason why I had to read that headline thrice in incredulity before getting it.
Congrats. (Score:2)
Your post will be used as proof of the name confusion when LEGO goes after LIGO for trademark infringement.
Fast (Score:5, Insightful)
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You can safely assume that a tremendous amount of people have been sitting on the edge of their seats for this.
Confirmation of yet another aspect of Relativity is a big deal -- this is a theory with a perfect track record and which pretty much describes almost everything about the universe.
Disproving any of his stuff would rock the scientific community. Continuing to prove again and again just how right he was? That's worthy of some coverage, and NOBODY who covers this stuff was going to miss it.
Everybody
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Holy shit, maybe the new owners are actually accomplishing something!
Re: Fast (Score:3)
That's OK, we still have four months for the "dust on the detector" story.
Science is continuous, not discrete - stories that begin with "It's Official" can be safely filed under, "we'll see".
Which is a Good Thing.
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If you really are looking for something different [just-think-it.com]...
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Surf's up! (Score:2)
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Why this matters (Score:5, Informative)
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> We had a lot of evidence already but more is good
Oh come on. We have a lot of evidence that the sky is blue, how much money should be spend on gathering more evidence of that?
> Second, if we get more data we might be able to rule out or narrow down our search space for any eventual quantum gravity theory
That would be true if the measurement *disagreed* with the predictions, but it *agrees* with them. That is, this result helps make QG *harder*.
> Third, this gives us insight into stellar objects
Oh
Re:Why this matters (Score:5, Informative)
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The reason this is so important is not the single black hole merger they detected.
AND, it was detected during a shake-down run that wasn't intended for scientific investigation. Either they were incredibly lucky, or these things happen all the frelling time, and we're about to view a cacophony of zip/whip/zuups.
It is because this is the first of what will become a major source of astronomical data.
Indeed -- one of the unaddresed issues (so completely, blatanly unaddresed that I suspect the scientists involved have been blinded by the success) is using gravity waves for real astronomy. Wait, wait, bear with me for a second; I'm not saying what they did wasn't real astronom
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It won't be long before... (Score:2)
The wave motion engine gets built to travel between galaxies to Iscandar and save humanity from the Gamilon radiation bombs.
https://en.wikipedia.org/wiki/Space_Battleship_Yamato_(spaceship) [wikipedia.org]
What is a gravity wave? (Score:3)
Re:What is a gravity wave? (Score:4, Interesting)
Re:What is a gravity wave? (Score:4, Informative)
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It's not something that moves along is it?
Err... I think it's like water waves in that sense. No thing is moving in the same direction as the wave. The water molecules only move up and down, but the combined movement becomes this thing we call a wave.
It's a perceived distortion of time space?
It's perceived as a change in the distortion of spacetime. I'm not sure if we've been able to measure static distortions of spacetime yet (not directly, anyway; we can see gravitational lensing for example, and of course falling is a direct consequence of spacetime distortion).
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No thing is moving in the same direction as the wave.
Not quite an exact analogy. In water waves, an individual molecule moves slightly forward as it goes up and slightly backward as it goes down, following an approximately elliptic path. But yes, it has no mean movement in the wave direction.
It's easiest to think of a wave as a traveling disturbance.
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It not that different from an electromagnetic wave (light). With an electromagnetic wave, if you have two charged objects at different locations they will feel a force that causes them to move relative to each other. In electromagnetism you can also detect the motion with one particle because it feels an acceleration.
With a gravity wave, two massive objects will move relative to each other. Here you can't detect with a single object because it feels no acceleration - the object is in free fall even thoug
Never can have enough legos.... (Score:4, Insightful)
buh? there's non-Human scientists? (Score:5, Funny)
the first gravitational wave to be detected directly by human scientists
I had to go read the linked story to make sure it wasn't typical /. submitter reading failure.
Please, The Economist, do tell more, I think you buried the lead there.
sigh. At least it's not a Forbes link.
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Its yet another proof of the global alien conspiracy. What else? They are among us. They control us. They will make earth their colony.
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It's a perfectly cromulent thing to say. We don't know if we're the first scientists to detect these things. We don't know that there are any non-human scientists, and the wording doesn't imply that we do.
Next question: How do you weaponize gravity waves? (Score:2)
No (Score:3)
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What can't LEGO do? (Score:3)
Randall Monroe, please do the math for us. (Score:3)
I'm guessing you can't build a fusion reactor out of LEGOs.
given enough of them you can.
And now the engineers... (Score:2)
...need to figure out a way to surf these waves.
How do they figure out the distance/time (Score:2)
to the triggering event and the general direction it came from?
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Exciting, but (Score:3)
I'll wait for the peer review.
Re:Exciting, but (Score:5, Informative)
Gravitational waves (Score:2)
I guess I'll be the pedant here :) It's gravitational waves, the name gravity wave is already taken.
Physicist's commentary and original article (Score:5, Informative)
What would it be like to be close to this event? (Score:3)
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While gravity can be viewed as having an instant effect, the propagation of changes in gravity influence moves at the speed of light. That propagation action can been rationalized like a wave.
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gravity can be viewed as having an instant effect
What does this mean? I think I understand that if the sun moves away quickly we will not notice this for a few minutes (time for the wave to go from the sun to us). I do not know what then is "instant".
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when i said "instant" i meant the current observed effect of gravity. As I move through space i feel gravity everywhere and always and there for the bull feels instant as i move into an area of higher gravity. i guess "constant" would have been a better term to use, but i was trying to phrase it using the words of the GP in order to make a link for the explanation.
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I think s/he also was saying that when the wave (zone of effect) does arrive the implementation does apply instantly.
IANAS so this is my understanding and is possibly me talking out my ass.
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Gravity also propagates at the speed of light. If the sun were split in half, and each half thrown out of the plane of the solar system at near light speed, it would still take the 8 minutes of light travel time to the earth for any effect at all to be detected.
The difference between gravity and gravity waves is like the difference between an electric field and electromagnetic radiation. They are closely related, but one is a static field, the other a propagating wave.
Gravity is not instantaneous (Score:5, Informative)
Are gravitational waves different from gravity? Because this article would have you believe that the speed at which they propagate is speed of light, where as gravity has instant effect AFAIK.
Gravity does not have instantaneous effect.
Nothing physical has instantaneous effect.
In any case, if you're talking about the gravity of something just sitting unmoving, it doesn't really mean anything to say that the gravitational effect is instant, or delayed. It only makes sense to ask the question when something is accelerated away from sitting stationary, and in that case, the effect isn't instantaneous; the change in effect at an observer is at the speed of light.
Re:Be Skeptical (Score:5, Informative)
Any science you can explain in a few sentences to a layman will be so full of holes as to be nothing more than hearsay and astrology.
A big event, that would have created ripples that would arrive here roughly at the time of the experiment, happened. As we listened, at that time, we saw inconsistencies representative of just such a gravitational wave hitting the experiment. It's tiny, but above background noise and experimental error (it's mentioned elsewhere that this basically means 6-sigma certainty), and coincides with a particular event that we were able to "observe" (not literally) in other ways.
The source of the wave barely matters. We detected gravitational fluxes that would otherwise be unexplained. That we are able to correlate them to one single event, that's just of the type of rare event that we predict might be able to cause such signals "loud" enough to be "heard" by us, and match up the timing means that it's the most likely explanation too.
But more importantly - 100-year-old mathematics predicts some absolutely insane, bonkers things that - when we are finally able to look for them - turn out to be true. That's all science cares about.
You can't just make up shit and then - in 100 years - several people invent an instrument that correlates perfectly to the shit you made up, several times, to the satisfaction of major scientific institutions unless - basically - you were absolutely spot-on correct all along.
That's pretty much what happened. The Einstein field equations are fucking bonkers to understand, let alone try and solve the implications of them. And I'm a mathematician. But they predict stuff like this that we then find. When it came from barely matters. A simplification of the definition of "size" in a mass-media article doesn't matter at all (tell people black holes have no size, and they look at you like you're an idiot).
So, no, it's not as bad as you make out.
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Nope, sound waves don't either.
Think of a giant rubber sheet with a ball bearing in every square inch. Squish the sheet and the balls in that part get closer together. Stretch it and they get further apart. Do both to the same sheet and you have a wave and the distance between them is half a wavelength. Repeat it regularly and you have a full, repeating wave of a certain wavelength.
The ball bearings are sound-carrying particles in audio terms, and mass-bearing particles in gravity terms.
Neither of them