[RightWhale]

Should shifting the reference frame make any difference in measurements?

[PonyTailGuy]

That would sort of contradict the special theory of relativity, wouldn't it? I had the same reaction.

But read closely, it only says he SIMPLIFIED the calculations by computing from the Jupiter frame of reference.

Apparently the mathematics were considered intractable prior to this, and the fellow thought of a clever way around the problem.

In any event, just how central is the speed of gravity to the general theory of relativity? Is it in the hard core of the theory, is it a supporting assumption? a mathematical consequence? I'd be curious to know. I'm well versed in the special theory but only superficially knowledgeable of the general theory.

[martin_fierro]

Albert Einstein may have been right that gravity travels at the same speed as light

That explains why I never see this coming. <|:)~

[Southack]

"In effect, the experiment was measuring effects associated with the propagation of light, not the speed of gravity."

That is *precisely* what I said back in September here on FR, that all they were measuring was the propagation speed of Light, not Gravity.

[martin gibson]

The quasar signals may have broken the speed of the sound of loneliness...

[theDentist]

Hmmm, it seems to me (by no means a physics guru) that reversing the refernce frame would may not be viable. I mean, Eart is moving, Jupiter is moving, even the Sun is moving. And all at different speeds. It seems to me the best frame of reference (locally) would therefore be the Sun. I mean, reversing the reference from Earth to Jupiter does help in observing effects from afar, but you then still muct wonder about the Sun's effects upon gravitational attraction, and how to subtract the difference based upon Earth's motion, (plus the reference point on Earth moving in revolution).

What we gotta do, is get the smartest person on Earth (a Senator from NY, as I recall), put her is a ship, and fire it at the closest star at a constant velocity, then measure increases in velocity at predetermined ranges. She can report back her observations to a device.

[10mm]

Gravity propagates in "waves?" I thought it was simply a curvature of space around a mass. </sigh>

[Flightdeck]

I don't believe in gravity. I say gravity and EM are one and the same.

[Sabertooth]

((((((growl)))))

[boris]

Eddington (innocent of General Relativity) and certain obtuse individuals today argue that gravity must propagate at infinite velocity.

The argument has superficial plausibility but has been convincingly refuted by (e.g.) Prof. Carlip at UC Davis.

The basic argument relies on something like the inverse of the Poynting-Robeson (spelling?) effect. Light moving radially from the sun encounters Earth moving 'forward' and thus falls at a slight angle relative to the radius vector from Earth to Sun. The effect of this is to exert a slight retrograde pressure due to Earth's motion relative to the radial lines from the Sun.

Gravity, it is argued, would have the same vector triangle except that it would be of opposite sign (since gravity 'sucks' and light 'pushes'). This, says the argument, should cause an acceleration of Earth relative to the Sun, which in a remarkably short period of time (a few thousand years) would result in a doubling of Earth's orbital distance, and in millions of years would fling us out of the solar system entirely. Therefore gravity must propagate at infinite speed, QED.

The problem is that it can be shown that under General Relativity, gravity waves are radiated which exactly equal the increased energy due to the 'couple'. The extra momentum, in other words, is leaked away via gravity waves and the solar system remains stable.

--Boris

[Lee'sGhost]

I thought it was proven by liberals that the earth doesn't have gravity -- it sucks.

[Normal4me]

Is Five Trillionths of a second a big deal when measuring something traveling 186,000 miles per second? I say we call it a tie and move along.

[Uncle Miltie]

We cannot judge the science without first asking the race of the scientists involved. If black, we must add weight to their arguments.

- The Supremes

[longtermmemmory]

bump

[semaj]

I think these guys are grasping at straws. Gravity is a force (Not a constant one either)therefore I don't think it has any speed. ie... The force of gravitational body (centrifugal) increases when an object moves away from it and decreases when a certain threshold of distance is reached away from that body. Gravity is still in effect, yet its influence is lessened by the corresponding distance away from the gravitational body. ( I am not a physicist and don't play one on TV) Just my two cents.

[metalboy]

Well in this following mathematical model, one can see the formulae of the gravitational force on objects of varying amounts of mass; Both Michael Moore and Pee Wee Herman are standing on top of the Empire State building. Pee Wee jumps first but barely cracks the cement when he hits, but when Michael Moore fictitiously jumps and hits the cement with his brick like head, a force equal to that of a 20 megaton thermonuclear explosion levels every square mile of the east coast, from the top of Maine to the tip of Florida and shock waves are felt globally.

[Old Professer]

Mirror, mirror, on the wall...

[sandydipper]

Hello! Hello! Can you hear me now??

[dalereed]

"Should shifting the reference frame make any difference in measurements?"

I think he should shift his reference frameto the tallest building on the Berkley campus and jump off with his new money grant request in hand and test his theory!

[rockfish59]

Do you fall slower when you're drunk?

[aruanan]

"Einstein may be correct about the speed of gravity but the experiment in question neither confirms nor refutes this," says Samuel. "In effect, the experiment was measuring effects associated with the propagation of light, not the speed of gravity."

Tom Flandern said exactly this the day the announcement was made. What's with these folks taking so long to get the message?

Kopeikin's latest paper on the internet, giving the basis for his findings announced at the AAS meeting, contains some egregious errors. The following claims appear therein: "… a moving gravitating body deflects light not instantaneously but with retardation caused by the finite speed of gravity propagating from the body to the light ray. … We calculated this correction for Jupiter by making use of the post-Minkowskian approximation based on the retarded Lienard-Wiechert solutions of the Einstein equations. … Speed of gravity cg must enter the left side of the Einstein equations (2) … This will lead to the wave operator depending explicitly on the speed of gravity cg." 

None of these statements is correct even in GR, provided only that "the speed of gravity" retains its classical meaning for the past two centuries of force propagation speed. The Einstein equations require the potential field of all bodies to act from the body's instantaneous direction, not its retarded direction, because they set propagation delay for the gradient to zero. But Kopeikin adopts the Sun acting from its instantaneous position and Jupiter acting from its retarded position, which is inconsistent. In fact, although the Sun moves 1000 times more slowly than Jupiter, it is 1000 times more massive, making any hypothetical retardation effects comparably important. The Lienard-Wiechert equations consider retardation in mutual distance, but not in direction – the latter being a much larger effect of propagation delay. And the parameter on the left side of the Einstein equations is c2, and therefore has nothing to do with the speed of gravity, as we noted above. This does not prevent Kopeikin from calling it "cg" and solving for this parameter as if it were the speed of gravity, which is what he has done. 

            Sadly, Kopeikin here ignores both the existence of a long-standing controversy about the speed of gravity (defined as the propagation speed of gravitational force) [5] and the aforementioned arguments raised against his original interpretation by others. Kopeikin used the notion that this experiment might determine "the speed of gravity" to aggrandize the experiment, and perhaps also to justify funding for doing it. Yet the cg parameter measured is more closely related to the speed of light per se than anything else. 




____________

            However, the misrepresentation in this new paper and announcement is more serious than mixing speed-of-light and speed-of-gravity parameters. Kopeikin's new paper has modified the equations to be used in determining the speed of gravity in a fundamental way. His own formalism now rules out the possibility of cg = infinity or cg >> c in his results even before the experiment is performed. Here is why. Kopeikin now defines a new time tau = (c/cg) t to replace the coordinate time t in the Einstein equation. However, because (c/cg) is obviously forced to become very small or zero for large or infinite cg, the role of the time coordinate is diminished or suppressed altogether by this substitution, which effectively eliminates many relativistic effects already verified in other experiments. So even if the speed of "gravitational waves" had been much faster than the speed of light, Kopeikin's experiment is incapable of showing that with his present method of analysis. More than that, Kopeikin has violated scientific protocol by changing the equations to be used for the analysis after the results are in, thereby presumably avoiding the embarrassment of having to announce an unexpected result. We were also unable to verify one of his key references in the December 30 paper, "E. Fomalont & S. Kopeikin (2002)" which says simply "submitted to Science". But as of January 6, Science magazine has no record of such a submission.