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The Speed Of Gravity Revealed
redwolfoz writes "New Scientist is reporting that the speed of gravity has been measured for the first time. 'The landmark experiment shows that it travels at the speed of light, meaning that Einstein's general theory of relativity has passed another test with flying colours.' Researchers made the measurement of the fundamental physical constant with the help of the planet Jupiter. One important consequence of the result is that it will help constrain the number of possible dimensions in the Universe."
I think a more precise conclusion is "this is consistant with gravity propagating at c." You can't prove gravity propagates exactly at c, you can only ever prove the difference between the speeds is arbitrarily small. Alternatively, they could prove that the speed of gravity != c, which they haven't done either. To do that, the measured speed plus the error bar would need to be less than c.
Well, this says that Einstein's theory of relativity passed another test with flying colours.. but... According to THIS previous article on /. (and the NYT), the theory of relativity is generally flawed, so then did they really find the speed of gravity?
I'm confused...
[sig]www.masterslate.org[/sig]
The same way an electric field doesn't have a charge, but affects objects that do have a charge. Gravitational/electric fields are -created- by masses/charges. And don't confuse gravity with gravity waves (the speed of which being what are measured here).
.25 to be kinda ridiculous? So based on their measurements, the speed of gravity could actually be anywhere from 30% slower to 20% faster than light. I mean, the article makes it sound like they're just assuming the real number is 1.0 c because anything else would be really surprising. Or maybe the article is wrong. Or I'm mis-reading it. But at the moment, it doesn't sound like "passing with flying colors" to me.
By the way, did anyone else find the quoted margin of error of
The enemies of Democracy are
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> Try telling Sonny Bono that.
Au contraire! Blunt force trauma is all about electromagnetsm. (I suppose there are a few places where it's also about electroweak interactions, but that's a hell of a lot more trauma than I care to talk about. *g* :)
At any rate, gravitational forces had accelerated Sonny pretty gently, and he was doing just fine until electrostatic forces from a nearby tree intervened.
Sonny was a silly clam (silly clam? I repeat myself) who tried to make the electrons in his body occupy the same space as the electrons in aforementioned tree. (For a guy who claimed to be a great physicist, L. Ron Hubbard sure didn't teach his disciples much about the Pauli Exclusion principle or Van der Waals forces.) Sonny Bono's failure to grasp rudimentary physics can be seen as yet another case of evolution in action.
From that they worked out that gravity does move at the same speed as light. Their actual figure was 0.95 times light speed, but with a large error margin of plus or minus 0.25.
So, really, they're triumphantly announcing that the speed of the light is somewhere between 0.7 c and 1.2 c, and just supposing it has to be c for everything to make sense.
Physicists have been accused of being loose with rigour, but this is really stretching it.
You can't prove a physical theory - you can either show that it fits experimental evidence (in which case it might be right), or that it doesn't (in which case you've disproved it).
This experiment shows that a key assumption of GR is consistent with real life. That's it. That's all we can do, and that's all that is being claimed - observations of Jupiter give (roughly) the results we'd expect if gravity travels at c.
I think we should assume more of the author. Think of it this way: Using General Relativity, you can predict what the gravitational field will be. His experiment measured what the field actually was. If the predictions match the measurement, the theory is confirmed (or at least not disproven).
You'll find that in the world of experimental physics nothing is ever perfect and for this kind of an experiment a 0.25c error is pretty good all things considered.
The experiment doesn't tell us that gravity travels at the speed of light, it tells us that the current theory which claims that gravity travles at c is consistant with experiment.
To quote Djikstra (more or less) "testing software can only confirm the presence of bugs, never the absence of them". In much the same way a physical experiment won't (in general) tell us that a theory is perfectly correct, only that it is wrong. This happens when an experiment returns results which do not include the predicted results.
This experiment tells us that all theories which predict the speed of g to be outside the range 0.7c - 1.2c are quite probably wrong whereas those in the vicinity of 0.95c are quite possibly right. GR predicts that g==c which is very close to the measured value, so it is in fact quite reasonable to claim that the theory has passed this particular test.
This experiment doesn't *prove* GR, it just goes to show that it is indeed a very good theory as it has shown throughout the past century.
Of course, even if the cord were massless, the effects of the snip would propagate at the speed of light.
The fact that people can't differentiate between re-working equations and performing an experiment (to see if the experimental data matches the predicted data) is actually insignificant to the fact that they are making uneducated comments based on a one page article that sums up a complicated experiment in layman's terms.
It is actually comforting to see that people such as these abound everywhere, even in a "smarter" community like Slashdot.
"The unicode stuff in the latest version is working fabulously well. My russian mafia friends are ecstatic."
Almost. If the American GOVERNMENT has anything to do with it. The people and scientists are not on the whole evil and destructive like our government is.
Your definition of evil must be the common "has different priorities or beliefs than I do and isn't perfect"
There are better choices for a definition of evil, like the following that applies to Saddam Hussain:
"kills millions, brutally supresses all opposition and all human rights, hires the worst profesional torturers and rapists in history"
You know I assumed that George Senior was full of shit when he called Saddam "another Hitler".
I was wrong. The problem here is that our media doesn't care enough to actually inform us of all the slaughter and oppression around the world and our local do-gooder activists are so busy hating their republican neighbors that they couldn't be bothered to check out the possibilty that they are occasionally right.
Cognitive dissonance makes it easier to believe whatever propaganda is floating around as long as it isn't our propaganda.
The situation in the Middle east is complicated, so of course we know nothing about it. It's scary but the people currently in the White House actually know more about that issue than the activists.
I don't want the "total information awareness" geeks reading my email. But you know, I can oppose some policies of my government without doing a full "you evil bastard" hissy fit.
Rocky J. Squirrel
That is the single worst pair of hypothetically similar examples I have ever seen.
A better pair of contrasting examples would be two pieces of iron being held together by their combined gravitation (negligable, at small sizes) versus pieces of iron held together by magnetizing both and placing them together so that opposite poles are together. The chemical bonds in the metal of the nail are not at "people" scale.
-Terralthra...
Unless you have a plausible alternative hypothesis, experiments that agree with your hypothesis tell you essentially nothing.
This observation is meaningful only in hindsight. An experiment like this one has the potential to disconfirm the hypothesis as well. The fact that it did not do so is significant, albeit not so significant as the alternative.
The slur against physicists is unjustified, particularly the "elevate it to dogma" line. If you want to test a hypothesis, you first assume that it is correct, then try to prove the assumption wrong. If you have a better method, please share it.
It's much more likely the ringing comes from the air right next to the polished gong surface suddenly heating up.
There's a similar confusion about what drives those "solar radiometer" things - you know, a little black-and-white paddlewheel inside an evacuated glass ball that spins when you shine a light on it? People often say the reason they run is photon momentum, when the actual explanation is that the black sides of the paddles are hotter than the white sides, so when the few gas molecules left inside the ball hit the paddles, they leave the black sides going faster than the white sides.
The proof of this is the direction the paddlewheel turns - it turns white-side-first, and a photon-mass explanation would have the paddle turning black-side-first. If you put a paddlewheel inside a REAL hard vacuum, with a REAL low friction bearing, and REALLY isplate it from outside vibration, it turns the right way. See here for a more coherent and complete explanation.
To a Lisp hacker, XML is S-expressions in drag.
So then does "anti-mass" (ie anti-matter) experience anti-gravity? Would anti-matter repel other anti-matter or repel matter? Is this why we don't get much anti-matter casually passing by?
End of Line.
What if gravity has different properties from a long way away, such as intergalactic distances?
I've often wondered lately if perhaps gravity is both a repulsive and an attractive force. For local (i.e. interstellar) distances, the attractive force prevails. But for really vast (intergalactic) distances, it might act as a repulsive force. This could partly explain why the galaxies are accelerating away from each other.
Physicists don't have much of an idea what dark energy is... maybe it's just gravity, and Newton's law needs an amendment.
I've never heard this idea proposed, but it would make a certain kind of sense to me if it turned out to be the case.
WWJD? JWRTFA!
If the gong is reflective, the air near it gets heated both by the incoming light and by the reflected light. If the gong is sooted, only the incoming light heats the air.
At least, this seems logical to me. A way to test it would be to put a vibration sensor on the gong, and try it both in air, and in a vacuum. If you're right, the sensor should read the same, if I'm right the impact in vacuum should be much less.
To a Lisp hacker, XML is S-expressions in drag.