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."

[RadioAstronomer]

And Newton says that Gravity propagates at near instantaneous speeds.

Lets try a different tack.

If you have a flat sheet of rubber and you place a large ball on it, you will see a curve. If you roll a smaller ball near it the smaller ball will curve due to the bend in the sheet. This is a good analogy of a gravity field. This sheet is there all the time. However, a wave can be created in that sheet which will then propagate (but the original curve will still be there) along the sheet. If this is a gravitational field and a gravity wave, that wave will propagate at the speed of light according to General Relativity.

I am not sure I am saying this very well.

[RadioAstronomer]

What about chocolate and menopause?

Hmmmm... Not fond of chocolate and the wrong sex for menopause. Nope, not fundamental! LMAO! :-)

[Southack]

"It wouldn't matter, because even if the gravity that left the sun 8 1/2 minutes ago is what is effecting it, it would have the SAME effect no matter where the earth was in it's orbit"

Unless you think that Gravity can predict *where* the Sun and the Earth will be in the future, then Gravity must pull towards the center of the mass that originated it... where that center of mass was located when the Gravity wave first propagated away from that center of mass.

If the Sun didn't move, then this would yield us no useful information.

But the Sun does move, in fact it is moving rapidly (157 miles per second).

Light, for instance, takes 500 seconds to travel from the Sun to the Earth. In that 8.3 minutes, the Sun will have moved 78,186 miles. Thus, when you "see" the Sun, you are actually seeing where the Sun was located 8.3 minutes ago.

...And if Gravity travels as slow as Light, then the Earth is going to be orbiting in a plane that is centered around where the Sun was located 8.3 minutes ago, too.

And we *can* measure and observe the angle and center of the plane of the Earth's orbit around the Sun, FYI...

[Aric2000]

I seriously doubt it, you need something that is OUTSIDE the system, either moving towards us or away from us, in order to do such a measurement, because you need something outside the sytem to measure against.

[Aracelis]

So it is believed that all higher elements were formed in the vast energies of supernovae.

And thus, speculation is that our Sun is a third-generation star...because we have heavier elements.

[Southack]

You are stating the analogy just fine, but the limits of analogies come into play here because the sheet has no propagation speed and it has no movement of its own, either (nor does the big ball at rest in its center).

Your sheet even has bounds, something that we aren't trying (on this thread) to determine for Gravity.

What we want to know is how fast Gravity's influences propagate. If the Sun simply disappeared, would the Earth shoot off tangentally immediately, or would there be an 8.3 minute delay?

[Southack]

You doubt that we can measure the angle of the Earth's orbit around the Sun??

[Aric2000]

NO, because we can measure that, it is the gravity itelf that we cannot measure without an outside reference to measure against.

Within the system it is at equilibrium no differences, it remains the same,therefore you need something that is not in order to measure it.

[Aracelis]

wrong sex for menopause

Au contrair, mon ami...you gentlemen do indeed go through a similar "menopause". Mostly, it begins in your 40's, and often involves fast computers, younger women and radio telescopes. Telltale signs include (but are not limited to) spending long hours on message boards, stopping at every computer store within a 50 mile radius of home "just to look at what they've got", buying bigger dishes for that backyard radio telescope, jamming every possible new electronic gadget into an already crowded basement lab, and proselytizing others to join in a love of electronics and interferometry.

;^)

[RadioAstronomer]

the Sun simply disappeared, would the Earth shoot off tangentally immediately, or would there be an 8.3 minute delay?

It would take 8.3 minutes. Here is a good link:

http://itss.raytheon.com/cafe/qadir/q629.html

[Aric2000]

LOL!!!

Has she got your number or what?

[Southack]

If you can measure the angle of the plane of the Earth's orbit around the Sun, and if you know where the Sun and Earth are located and how fast they are traveling, what then would stop you from observing if the center of the Earth's orbital plane was focused upon where the Sun was located 8.3 minutes ago?

[Southack]

"It would take 8.3 minutes."

If so, then the orbit of the Earth's plane must be centered around where the Sun was located 8.3 minutes ago (78,186 miles from its present location).

Yet is that what we observe??

[Aracelis]

Hehe...I do indeed have his "number". :^)

[RadioAstronomer]

LMAO!!!!!!!!!!!!

[RadioAstronomer]

If so, then the orbit of the Earth's plane must be centered around where the Sun was located 8.3 minutes ago (78,186 miles from its present location). Yet is that what we observe??

The Earth/Sun SYSTEM is moving.

Its been fun, but I am way up past my bedtime. :-) See you tomorrow evening. Have a great night!

[Southack]

"The Earth/Sun SYSTEM is moving."

Indeed. Observing orbits would be pointless (in the scheme of determining the speed of Gravity) if our System was stationary instead of moving around at 157 miles per second.

[Aric2000]

Like I said, I am an amateur just using the knowledge that I have and a dose of common sense, I think that you are making it far more difficult then it has to be.

If Gravity travels at the speed of light, then the gravity that hits us now, left the sun 8.3 minutes ago. We are always in the same place relative to the sun, it takes us with it, therefore your question makes NO sense to me.

Because No matter what the NOW is, the earth is always on the same orbital plane, because the gravity that effects us NOW, is the same amount of gravity that will effect us 8.3 minutes from NOW. Now if the gravity had different strengths, then we could measure it, and we would bounce all over the place and be VERY uncomfortable.

It's been fun, but time for me to go to bed, have a very BIG 4 days ahead of me.

CQ Field day, CQ field day

Fort Flagler, Here I come!!!

[jwh_Denver]

"glued" to the wall with about 200 pounds of force."

Incredible. My brother had told me about what geckos can do but not how. Fascinating. So the geckos actually use "nuclear forces" to hang from a ceiling with one foot.

[jwh_Denver]

SORRY IF THIS IS GETTING COMPLEX

Fabulous simplification of a complex subject. You answered questions I didn't have before your post. I don't know how anybody could do explain it more simply. Great job!

If I may ask a question that has baffled me for years. My understanding is that the electrons circle the nucleus billions of times per second. That would create tremendous centrifugal force no matter how small the mass. Is it simply the the attraction of negative/positive forces or is there something else going on?