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."

[Aric2000]

I always hoped that gravity would be the one thing that we could use to travel faster then light, once we could control it, then we could use the gravitational force itself to travel between the stars.

Oh well, my dreams are now blown away...

Thanks, thanks a lot!! ;)

[RightWhale]

Van Flandern also now insists

Is he insisting now? This is not good news. Insistence could be a symptom of underlying progressive spookiness. That's right, he could soon be a candidate for kookville.

[Aric2000]

What theory are you gonna come up with next?

Evolution?

Then my life won't be worth living......;)

OK, OK, I'll be good now, I promise!! ....

[Southack]

"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."

Ah, you're calling my name. Would you settle for near-infinite rather than "infinite speed"?

How does the speed of light squared strike you, so to speak?

Gravity is the Energy of a Mass (G=E/M).

Energy is equal to the Mass times the speed of light squared (E=MC^2).

Solving the two equations for Gravity yields G=C^2.

Well OK, that would all be fine except the units look pretty funny, so how do we *observe* whether or not the math adds up?

Two observable phenomenon come to mind:

1. recent experiments in which Light was reduced in speed to under 50 mile per hour show that Light is NOT bent by Gravity at slow speeds. This would seem to indicate that *speed* matters. And since Gravity hasn't been shown to be influenced by Light, but Light can be shown to be influenced by Gravity, a reasonable person could speculate that Gravity is either a much stronger force or a much faster force than is Light.

2. The Earth and other planets in our Solar System. We already know that our entire Solar System is hurtling through space in one constant overall direction at some great speed. Fine. We also know that the planets orbit the Sun in a horizontal plane. Now, if there is a *lag* between the time that a Gravity wave leaves the Sun and reaches each planet, then it should be a more pronounced lag as one moves from Mercury to Pluto, simply because there is more distance to cover.

Now keeping in mind that all of those planets are hurtling through space in the same overall direction (let's say, North) along with the Sun, we should see planets orbit where the Sun *was*, rather than where the Sun *is*.

If it takes 18 seconds for Light to reach Earth from the Sun, then the Earth would be orbiting where the Sun was 18 seconds ago if Gravity travels at the speed of Light, with an even more pronounced lag in horizontal plane orbit for Mars, Saturn, etc.

But we don't see that. Instead of successive planets orbiting more Southward as one looks away from the Sun, we see the planets pretty well line up on the same horizontal plane, as if Gravity was MUCH faster than Light.

And this observation agrees with what we see in the first experiment above when we slow Light down in the lab, which also seems to agree with the math above.

so in my opinion Gravity propagates at somewhere around 3.4703029E10 miles per second (or is that per second squared??).

[Southack]

C#84

[boris]

"If it takes 18 seconds for Light to reach Earth from the Sun, then the Earth would be orbiting where the Sun was 18 seconds ago if Gravity travels at the speed of Light, with an even more pronounced lag in horizontal plane orbit for Mars, Saturn, etc."

Every word in your posting is wrong, including "is", "and" and "the".

You cannot even give the correct distance to the Sun in light-seconds. The Sun is about 8.3 light minutes from Earth.

--Boris

[Aric2000]

You mean my dreams may in fact come to reality!!

I hate it when I feel like a ping pong ball, yes, no, yes, no, when you guys decide, will you let me know please? ;)

Just funnin with you guys, Physics is a very hard science, and I find it fascinating. Thanks for teaching me a bit today.

[Southack]

"The Sun is about 8.3 light minutes from Earth."

Relative to its former position, how far will the Sun have moved in 8.3 minutes?

[FreeTheHostages]

In reality, iron is the one nucleus that can't be used for fuel, but I'm glad I didn't know that as a 12-year-old just the same.

LOL. Hmm, I distinctly recall based on an experience of mine as a 12-year old -- my coffee ice cream landed on a corroding iron railing of a bridge in a small Vermont town and I greedily tried to retrieve and consume it -- that iron (especially when it's oxidizing and getting all weirdly brown and just turning rusty-colored, disguising itself well in the ice cream) does NOT taste good. I convulsed immediately, never did swallow, and still can't the taste completely off my tongue.

OK, that was totally off track but there you are. Iron tastes bad. Or, to be scientifically precise, at least when you're 12 years old and you attempt to consume it in a partially oxidized form in combination with coffee ice cream.

[FreeTheHostages]

An equally interesting question is how quickly one stops reading the posts of certain obtuse individuals who curiously stalk these science threads and post silly things.

I wonder if one could even measure the speed with which one such as yourself passes over such obtuse posts.

It may be that a trillion monkeys on a trillion typewriters might somehow lead to the production of Hamlet, but Free Republic seems like a poor place to test the theory, no? ;)

[longshadow]

my coffee ice cream landed on a corroding iron railing of a bridge in a small Vermont town and I greedily tried to retrieve and consume it

"In the news tonite, Ben & Jerry's, Vermont's premiere ice-cream makers, announce the introduction of their newest flavor; 'Railing & Rust'...... stay tuned, filmed report at 11. Meanwhile, former Governor Howard Dean claims he is being followed on the presidential campaign trail by a 30 foot tall fiberglas "Truth Cow that goes "Moooooooo! Moooo!" and poops simulated 'pasture patties' everytime he tells a whopper...." Doctors say Dean should be stabilized enough to be released from the Brattleboro Retreat in time for the New Hampshire Primary."

[FreeTheHostages]

! ;)

Ah, Gov. Dean. He wasn't actually born in "our" state, now, was he?

I'm up to Norwich for the Vermont Quilt Festival this weekend.

[longshadow]

I'm up to Norwich for the Vermont Quilt Festival this weekend.

Anything like the "Tooth Festival" at the Tunbridge Fair, or the "Herpes Festival" in Putney?

[FreeTheHostages]

Nope, it's New England's largest quilt festival. Nice, mostly republican post-menopausal Vermont women. Hardy crowd! ;)

[longshadow]

Nice, mostly republican post-menopausal Vermont women. Hardy crowd!

Yeah, the ones with the moustaches! Now that's what I call "hardy Vermont woman."

[RadioAstronomer]

Binding energy" is a negative energy. If the mass of a nucleus were always less than any sum of its potential components, then it would always take energy to split a nucleus. This is true for any nucleus below iron. For nuclei above iron, the binding energy becomes less and less; the strong nuclear force creates stable minima in which very heavy nuclei can exist, but these are but local minima sitting high on the electromagnetic hill. A uranium nucleus is heavier than thorium plus helium.

One Of the interesting things about the curve of binding energy is the elements that are created in stellar processes:

The weak force is the force that induces beta decay via interaction with neutrinos. A star uses the weak force to “burn” (nuclear fusion). Three processes we observe are proton-to proton fusion, helium fusion, and the carbon cycle. Here is an example of proton-to-proton fusion, which is the process our own sun uses: (two protons fuse -> via neutrino interaction one of the protons transmutes to a neutron to form deuterium -> combines with another proton to form a helium nuclei -> two helium nuclei fuse releasing alpha particles and two protons). The weak force is also necessary for the formation of the elements above iron. Due to the curve of binding energy (iron has the most tightly bound nucleus), nuclear forces within a star cannot form any element above iron in the periodic table. So it is believed that all higher elements were formed in the vast energies of supernovae. In this explosion large fluxes of energetic neutrons are produced which produce the heavier elements by nuclei bombardment. This process could not take place without neutrino involvement and the weak force.

[RadioAstronomer]

Ping! you would like this thread :-)

[RightWhale]

how far will the Sun have moved in 8.3 minutes

Earth is orbiting the sun at about 60,000 mph. Galactic rotation is a big part of the sun's true motion. We go around the core about every 200 million years at a distance of however far we are from the core. Somebody [preferably a 1st year engineering student] should cruch the numbers and tell us the result in feet or miles. They say the Andromeda galaxy is approaching us, but we might be approaching the Andromeda galaxy, so that speed might be added in.

[PatrickHenry]

Galactic rotation is a big part of the sun's true motion.

Too complicated. I regard myself as a privileged frame of reference, and everything is (or is not) in motion relative to me. From my point of view, here on earth, the sun isn't really going anywhere.

[Southack]

"Galactic rotation is a big part of the sun's true motion. We go around the core about every 200 million years at a distance of however far we are from the core. Somebody [preferably a 1st year engineering student] should cruch the numbers and tell us the result in feet or miles. They say the Andromeda galaxy is approaching us, but we might be approaching the Andromeda galaxy, so that speed might be added in."

Fair enough. So relative to its old position, the Sun will have moved some significant, measurable distance in 8.3 minutes.

This brings up the really interesting question: is the Earth orbiting around the position of the Sun 8.3 minutes ago, as it would if Gravity travels as slow as the Speed of Light, or is the earth orbiting around the Sun at some point closer to the Sun's actual position at this moment, which would indicate that Gravity travels some measurable amount faster than Light.