Berkeley Lab Physicist Challenges Speed of Gravity Claim

spacedaily.com ^ | 23 Jun 03 | staff

[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."

[Physicist]

The correct answer is:

3. All motion is relative, fields are defined everywhere, even if they're zero, and the only part of a field that needs to propagate is the changes to the field.

[boris]

"OK, rather than respond in kind, I'll simply ask you what specific aspect of the Sun and Earth moving through space that *you* assert is non-Newtonian."

I done tole you and tole you: Newtonian mechanics is oversimplified for this situation; it does not apply. It must be augmented by GR, which shows that the "excess momentum" predicted by boneheaded insistence on Newtonian physics is radiated away as gravity waves.

There are numerous situations known today in which Newton is known not to suffice. In fact, the precession of the orbit of Mercury cannot be accounted for by Newtonian physics, and it was the ability of (I believe) Special Relativity to predict and account for it that confirmed that Einstein was right.

I can cite as many examples as you care to read.

If you want the full rigor, contact Dr. Carlip as I did:

Dr. Carlip at UC Davis.

--Boris

[Physicist]

In fact, the precession of the orbit of Mercury cannot be accounted for by Newtonian physics, and it was the ability of (I believe) Special Relativity to predict and account for it that confirmed that Einstein was right.

Actually, the precession of the perihelion of Mercury was known before GR. (I'll assume you meant GR, as SR isn't enough to predict that quantity.) While the correct calculation was an early success of GR, it doesn't really count as an experimental test, as the result was known before the calculation. The most important early experimental test was Eddington's precision measurement of the abberation of starlight by the sun.

As for SR, there are numerous experimental tests. There are no experimental results that disagree with either SR or GR.

[longshadow]

relativity is batting 1.000 placemarker

[Southack]

"There are numerous situations known today in which Newton is known not to suffice. In fact, the precession of the orbit of Mercury cannot be accounted for by Newtonian physics, and it was the ability of (I believe) Special Relativity to predict and account for it that confirmed that Einstein was right. I can cite as many examples as you care to read. If you want the full rigor, contact Dr. Carlip as I did:"

Sadly, if Dr. Carlip told you the above example, then you are both absolutely wrong. Mercury's orbital precession was known when there was *only* Newtonian physics, long before the General Relativity Theory, much less Special Relativity came into our knowlege.

But it isn't so important that you were wrong. What's important is that Newtonian physics *did* suffice to solve that particular question (among others).

...And even more important is that Newtonian physics may still be quite viable to solve *other* vexing questions, such as where the orbital planes of our planets are centered, and why.

[Southack]

"Loudly asserting Newtonian physics in a non-Newtonian situation proves only your ignorance." - Boris

Proves, conclusively proves beyond dispute my ignorance?! My, my, my...what do we have here? Perhaps someone who will claim that Newtonian physics is insufficient to explain the precession of Mercury's orbit, perhaps? Let me simply ask you *again* what specific aspect of the Sun and Earth moving through space that *you* assert is non-Newtonian.

[Southack]

"3. All motion is relative, fields are defined everywhere, even if they're zero, and the only part of a field that needs to propagate is the changes to the field."

There is a discrepancy with that potential answer (which essentially claims that the only propagation that counts are the *changes* to a field rather than the field's propagation itself).

Since we already know that *changes* to a field propagate at the speed of Light, the above answer can't explain why the planets aren't orbiting the Sun's previous location back when Gravity left the Sun to travel to the planets.

The delay for Light going from the Sun to the Earth is 8.3 minutes, for instance, giving the Sun 8.3 minutes of movement from its old location.

So why isn't the Earth orbiting around the Sun's *old* position rather than around the Sun's present position?

Or put another way, under that potential answer there would be an 8.3 minute delay from the time that the Sun (or an electromagnet in another example) was turned off until those speed of light *changes* reached the Earth to permit the Earth to fly off tangentally to its old orbit...a delay that we do NOT see in respect to where the Earth's horizontal orbitital plane is currently centered.

[martianagent]

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.

If the idea of gravity propagating at light speed is a requirement of relativity, then it's time relativity was dropped. Gravity is known by experiment to propagate either instantaneously or close enough thereto that our best instruments cannot tell the difference.

Tom Van Flandern's page on the topic at Metaresearch notes that:

By contrast, gravitational forces are large, readily detected, and control the dynamics of most of the visible universe. Gravimeters easily detect the gravitational force from, and motion of, a person entering a room, for example. The propagation speed of gravitational force is bounded by six experiments to be much faster than the speed of light.
[[5]]. For example:

• In 1825, Laplace determined that the minimum speed of gravity consistent with observations was at least 10 million times the speed of light, c.
• Modern, high-precision solar system observations show that the direction from which the Sun's light comes, and the direction toward which the Sun's gravity pulls us, are not the same. The former is retarded by the time it takes light to travel from Sun to Earth, 8.3 minutes; and the latter is not retarded by any detectible amount.
• Eclipses of the Sun by the Moon occur about 40 seconds before the time of the Sun's maximum gravitational pull on the Moon. The delay indicates that light and gravity do not have the same propagation speed.
• A 1997 laboratory experiment by Walker & Dual showed that gravitational signals propagated much faster than light signals.
• Binary pulsars (with large masses and speeds) show that the speed of gravity must be at least 20 billion times the speed of light.

Van Flandern stops just short of calling Kopeikin an outright fraud.

[Southack]

General Relativity and Quantum Cosmology, abstract
gr-qc/9706082

From: Bill Walker <walker@ifm.mavt.ethz.ch>
Date: Fri, 27 Jun 1997 16:29:59 +0200   (69kb)
Date (revised): Mon, 28 Jul 1997 20:37:18 +0200

Propagation Speed of Longitudinally Oscillating Gravitational and Electrical Fields

Authors: William D. Walker, J. Dual
Comments: No changes - better PS, 13 pages, PS

The near-field Lienard-Wiechert potential solution of a longitudinally oscillating electrical field produced by an oscillating charge is presented, and the results are compared to the R. P. Feynman multipole far-field solution. The results indicate that the phase speed of a longitudinally oscillating electrical field is much faster than the speed of light in the near field.

[Southack]

"Modern, high-precision solar system observations show that the direction from which the Sun's light comes, and the direction toward which the Sun's gravity pulls us, are not the same. The former is retarded by the time it takes light to travel from Sun to Earth, 8.3 minutes; and the latter is not retarded by any detectible amount."

And that's *precisely* what we've been discussing on this thread.

[RightWhale]

Gravimeters easily detect the gravitational force from, and motion of, a person entering a room

The person would be so kind as to enter the room 100 times so we can do a least squares analysis.

[RightWhale]

the phase speed of a longitudinally oscillating electrical field is much faster than the speed of light in the near field

Many people will find phase speed confusing since it has nothing to do with wavefront propagation.

[martianagent]

I'm starting to get the impression that the history books are not going to treat Albert Einstein kindly. Is it just me?

[RightWhale]

I'm starting to get the impression that the history books are not going to treat Albert Einstein kindly.

Sure they will. He did much more than the Special Theory, and his influence went far beyond physics and even science. They talk about his lack of skill with mathematics, but many physicists sought his advice. There is theoretical physics, experimental physics, and developmental physics. You could represent these divisions in order by Einstein, Faraday, and Tesla.

[martianagent]

The idea of gravity propagating at light speed seems to be a requirement of relativity, and it also seems to be grossly out of touch with reality and emperical science. Something has to be wrong with the picture.

[RightWhale]

Something has to be wrong with the picture.

More than one thing needs further consideration. First off, SR deals with appearances of electromagnetic phenomena. Second, the speed of light in the vacuum was taken as a constant in the premise, not as something to be proved or demonstrated. There is nothing wrong with SR except that we are using it to limit ourselves. At the same time, putting such a limit on ourselves has historically spurred some to think deeper and wider and pushed our minds to further accomplishment.

[Physicist]

So why isn't the Earth orbiting around the Sun's *old* position rather than around the Sun's present position?

From the perspective of any point in the field, the sun is still in its old position. The field moves along with the sun. If something accelerates the sun, then the field will adjust to reflect the new position...but it will take 8.3 minutes for that change to register out here.

You really need to abandon this idea of absolute motion. Even Galileo knew better than that.

[Physicist]

The idea of gravity propagating at light speed seems to be a requirement of relativity

That's incorrect. It is a consequence of relativity.

and it also seems to be grossly out of touch with reality and emperical science.

There is not a single experimental result that contradicts relativity. This idea of "gravity propagating faster than gravitational waves" is a null concept, with no basis other than a trivial misunderstanding of what a field is. It's like saying that while you may walk at a finite speed, the ground beneath your feet is infinitely fast.

Something has to be wrong with the picture.

In other words, you don't like it. The universe is the way it is, and not how you would wish it to be.

[Physicist]

The results indicate that the phase speed of a longitudinally oscillating electrical field is much faster than the speed of light in the near field.

Homework: understand the difference between "phase velocity" and "group velocity".

[boris]

"Sadly, if Dr. Carlip told you the above example, then you are both absolutely wrong. Mercury's orbital precession was known when there was *only* Newtonian physics, long before the General Relativity Theory, much less Special Relativity came into our knowlege."

Again you are wrong. The phenomenon was known but Newtonian mechanics could provide no explanation of it.

If you think otherwise, please post the Newtonian explanation here. We'd all be interested to see it.

The world was in an uproar when Einstein's predictions were shown to match the actual measured precession.

And Dr. Carlip did not tell me this.

--Boris