Posted on 06/23/2003 9:25:12 AM PDT by RightWhale
Berkeley Lab Physicist Challenges Speed of Gravity Claim
Berkeley - Jun 22, 2003
Albert Einstein may have been right that gravity travels at the same speed as light but, contrary to a claim made earlier this year, the theory has not yet been proven. A scientist at Lawrence Berkeley National Laboratory (Berkeley Lab) says the announcement by two scientists, widely reported this past January, about the speed of gravity was wrong.
Stuart Samuel, a participating scientist with the Theory Group of Berkeley Lab's Physics Division, in a paper published in Physical Review Letters, has demonstrated that an "ill-advised" assumption made in the earlier claim led to an unwarranted conclusion. "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."
According to Einstein's General Theory of Relativity, light and gravity travel at the same speed, about 186,000 miles (300,000 kilometers) per second. Most scientists believe this is true, but the assumption was that it could only be proven through the detection of gravity waves. Sergei Kopeikin, a University of Missouri physicist, and Edward Fomalont, an astronomer at the National Radio Astronomy Observatory (NRAO), believed there was an alternative.
On September 8, 2002, the planet Jupiter passed almost directly in front of the radio waves coming from a quasar, a star-like object in the center of a galaxy billions of light-years away. When this happened, Jupiter's gravity bent the quasar's radio waves, causing a slight delay in their arrival on Earth. Kopeikin believed the length of time that the radio waves would be delayed would depend upon the speed at which gravity propagates from Jupiter. To measure the delay, Fomalont set up an interferometry system using the NRAO's Very Long Baseline Array, a group of ten 25-meter radio telescopes distributed across the continental United States, Hawaii, and the Virgin Islands, plus the 100-meter Effelsberg radio telescope in Germany. Kopeikin then took the data and calculated velocity-dependent effects. His calculations appeared to show that the speed at which gravity was being propagated from Jupiter matched the speed of light to within 20 percent. The scientists announced their findings in January at the annual meeting of the American Astronomical Society.
Samuel argues that Kopeikin erred when he based his calculations on Jupiter's position at the time the quasar's radio waves reached Earth rather than the position of Jupiter when the radio waves passed by that planet. "The original idea behind the experiment was to use the effects of Jupiter's motion on quasar-signal time-delays to measure the propagation of gravity," he says. "If gravity acts instantly, then the gravitational force would be determined by the position of Jupiter at the time when the quasar's signal passed by the planet. If, on the other hand, the speed of gravity were finite, then the strength of gravity would be determined by the position of Jupiter at a slightly earlier time so as to allow for the propagation of gravitational effects."
Samuel was able to simplify the calculations of the velocity-dependent effects by shifting from a reference frame in which Jupiter is moving, as was used by Kopeikin, to a reference frame in which Jupiter is stationary and Earth is moving. When he did this, Samuel found a formula that differed from the one used by Kopeikin to analyze the data. Under this new formula, the velocity-dependent effects were considerably smaller. Even though Fomalont was able to measure a time delay of about 5 trillionths of a second, this was not nearly sensitive enough to measure the actual gravitational influence of Jupiter. "With the correct formula, the effects of the motion of Jupiter on the quasar-signal time-delay are at least 100 times and perhaps even a thousand times smaller than could have been measured by the array of radio telescopes that Fomalont used," Samuel says. "There's a reasonable chance that such measurements might one day be used to define the speed of gravity, but they just aren't doable with our current technology."
General relativity works the same (i.e., it gives a consistent result) in all frames of reference. You are the one saying that coordinate system matters. Why would you expect the orbit to remain stable in the "motionless" coordinate system, but not in a moving coordinate system?
As will the answer to our questions on this thread.
Are the Earth and Sun stationary?
Well, that's not consistent in all frames of reference, so that's probably not our answer.
Could Gravity be moving really, really fast to explain why the Earth appears to be orbiting in a plane around the center of our Sun?
Well, that *IS* consistent with what we see in all frames of reference. Hmmm...
Well, that's not consistent in all frames of reference, so that's probably not our answer.
LOL. That may end up on my office door.
Could Gravity be moving really, really fast to explain why the Earth appears to be orbiting in a plane around the center of our Sun?
Look, if you want to say that roads "move" infinitely fast between cities, that's up to you. The question is how fast the cars go. Assuming that gravitational fields "move" infinitely fast, how fast do gravitational waves (i.e., undulations in the field) move?
(HINT: Tom Van Flandern says that electromagnetic fields move infinitely fast, yet undulations in the field demonstrably move at the speed of light.)
Your office is obviously in a classy neighborhood. On my office door it says: "No Panhandlers!"
You're not following where I'm going with all of this. I'm not saying that roads move infinitely fast. I'm not even saying that road construction moves infinitely fast.
But road construction does move forward at some speed.
Likewise, a magnetic field moves forward at some speed as soon as you turn on the electrical power to the magnet.
And it's a reasonable bet that Gravity propagates its effects outward at some speed once you have assembled a mass.
The Einstein camp seems to hold that magnetic fields are going to propagate outwards at the same speed as do electromagnetic waves, likewise for Gravity.
Both the Einstein and Newton camps seem to hold that Gravity's field propagates faster than Gravity's waves, which seem to have been shown to accelerate at 9.8 m/s^2.
And the Newton camp further seems to hold that Gravity propagates at near infinite speed, rather than at the speed of Light claimed by the Einstein camp.
OK, so the Einstein and Newton camps appear to disagree on the propagation speed of Gravity's field (size, boundary, limits, effects, insert your redundant explanation here).
Fair enough. Let's observe a large system and see if we can identify whether Gravity has the same time delay as Light. Let's measure whether we see Gravity from the Sun that is 8.3 minutes old as we currently do for Light.
And this should be able to be measured by looking at where the planes of the orbits of our planets are centered, presuming that the Sun is not *absolutely* stationary.
I thought you had it at 18 seconds...
Aberration of starlight
Displacement of the apparent path of light from a star, resulting in a displacement of the apparent position of the star from its true position; discovered by the English astronomer James Bradley and explained by him in 1729.
"The phenomenon is caused by the orbital motion of the earth; in the same way, vertically falling raindrops appear to fall diagonally when viewed from a moving vehicle. The true path of light from a star to an observer is along the straight line from the star to the observer; but, because of the component of the observer's velocity in a direction perpendicular to the direction to the star, the light appears to be traveling along a path at an angle to the true direction to the star.
"Thus, in order to observe a star the central axis of a telescope must be tilted as much as 20.5 (seconds of arc) from the true direction to the star, the exact amount of the angle depending on the direction to the star relative to the direction of the earth's motion in its orbit. Because of the earth's orbital motion, the stars appear to move in elliptical paths on the celestial sphere. All these ellipses have the same semimajor axis, 20.5 of arc, a value known as the constant of aberration. The tangent of the constant of aberration is equal to the ratio of the earth's orbital speed to the speed of light."
This is all elementary and well understood. Attempting to apply it to the Sun merely shows that you have no understanding of the initial answer: that General Relativty has been shown to completely and fully "null out" the aberration of gravity.
--Boris
Nonsense. Claiming something doesn't simply make it so.
We know that it takes Light 500 seconds to reach the Earth from the Sun.
The paltry few GR claims regarding Gravity simply state that it is presumed that Gravity travels at Light speed.
Yet if those claims were true, then we would experience an 8.3 minute delay in time from which Gravity left the Sun to reach the Earth.
That delay would permit the Sun to travel 178,000 miles in those 8.3 minutes.
That would mean that the Earth's orbital plane would be centered *not* on the actual location of the Sun, but rather on the location of the Sun from 8.3 minutes back in time, a measurable difference of 178,000 miles.
Yet we do NOT see the orbital plane of the Earth to be mis-centered 178,000 miles away from the Sun's center of mass.
What would explain that observation?
There are two potentially acceptable answers (you are welcome to add a third if you can):
1. The Sun isn't moving relative to *anything*
or
2. Gravity travels so fast that the Sun hasn't moved any significant distance by the time Gravity travels from the Sun to the Earth.
Again, FIELDS DON'T PROPAGATE. Changes in fields propagate.
Why don't your (or rather, Van Flandern's) arguments also apply to a central electrostatic field? Explain that to me.
Both the Einstein and Newton camps seem to hold that Gravity's field propagates faster than Gravity's waves, which seem to have been shown to accelerate at 9.8 m/s^2.
=:-O
I'm beginning to suspect that I'm falling for a troll.
Start with an electromagnet in the OFF position.
Magnetic field covers no area.
Now turn it ON.
Magnetic field now covers some finite area.
How did it go from covering no area to covering a finite area if it did not propagate outwards from the electromagnet at some speed, per your claim above?
Now, take an electrically charged object and measure the field at some distance. Then move it to one side, very quickly. How long will it take for the change in the field to register at your apparatus?
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.
Welcome back.
His point was that the equations used in the analysis were incorrect. There are countless numbers of physicists looking at this right now. Van Flandern alternates in a random pattern between reality and kookism, so it would be well to read the paper for oneself or wait for further letters to the editor. I was going to read the paper last night, but the associated diagram will take some time to decipher, and the formulas seem to be scattered into constituent atoms.
Indeed you did, but you *also* claimed that fields themselves don't propagate, something that is conclusively disproved by observing a field go from covering no area to covering a sizeable area.
What I did was to show an example wherein BOTH what you said about "changes" propagating as well as what I said about the field propagating were included in the same analogy.
And that analogy is also reproducable by experiment. We *can* observe that a magnetic field goes from covering no area to covering a sizeable area as soon as our electromagnet switches states from OFF to ON.
With that fact known, it is now reasonable to ask *how fast* did that magnetic field propagate from covering no area to covering its new, sizeable area.
Codswallop. Going from no field to some field is a change, and that change is what is propagating. It's all that has to propagate for a complete description of what's going on.
With that fact known, it is now reasonable to ask *how fast* did that magnetic field propagate from covering no area to covering its new, sizeable area.
The change in field is an electromagnetic wave, and it propagates at the speed of light.
Now: since the changes in an electromagnetic field propagate at c, how is it possible that orbits in a central electrical potential remain stable? Does an electron "see" where the potential well is now, or where it was some time ago?
I don't necessarily accept your premise that the field itself doesn't propagate.
A disturbance to a field may very well propagate at Light speed, but that's an entirely different action, in my opinion, than the field *itself* propagating.
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