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."
ROFLMAO! Not until you tell us what "color" they are...
"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.
Doc Smith, in the classic novel Triplanetary, made the error of taking binding energy to be a positive, exploitable energy. Accordingly, the aliens used iron as fuel for their starships, iron having the maximum binding energy...sucking it, if necessary, out of the hemoglobin of human beings! 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.
Around here, you have achieved Mt. Rushmore status.
I believe the attraction between them is the same, as they have the same strength of charge.
If it is a quark/antiquark (same color) it is called a meson. If its between quarks it is called a baryon (protons and neutrons fall in this category). Here is the rub, baryonic particles can exist if their total color is neutral; i.e. have a red green and blue charge altogether.
Both mesons and baryons are "colorless" with respect to the outside world. In baryons, as you say, red + blue + green = colorless. In mesons, for example, red + anti-red (or, if you like, red - red) = colorless.
Aw, great. Now Daschle represents me. Worms! More worms I say!
Surely you jest.....
;-)
Yes, but the reasons you gave for that announcement were goofy, IMNSHO.
Like the folks doing the experiment, you may have arrived at the right answer more by accident than via correct reasoning.
[Deep-Fried, Insufferable Geek Alert: there are three color charges, each with a corresponding anti-color. Every gluon carries both a color and an anti-color charge. Shouldn't there be nine kinds of gluon? Why are there only eight?
The combination red-antired + green-antigreen + blue-antiblue is colorless. Therefore, if I assign three gluons that are red-antired, blue-antiblue, and green-antigreen, I'm doing something redundant, because blue-antiblue (for example) is just 0 - red-antired - green-antigreen, and so forth. I'm using three vectors to span a two-dimensional space.
So what we do is choose two of the three color-anticolor pairs, and use them to compose two orthonormal basis vectors (such as g1=(red-antired + blue-antiblue)/sqrt(2), g2=(red-antired - blue-antiblue)/sqrt(2)), with the other gluons being g3=red-antigreen; g4=red-antiblue; g5=green-antiblue; g6=green-antired; g7=blue-antired; g8=blue-antigreen.]
[Atomic Wedgie Geek Alert: The symmetry group of Quantum Chromodynamics is SU(3). In the minimal representation of SU(3), there are three generators...the color charges. In the non-minimal representation, there are 3²-1 generators...the eight gluons! This was spookily mirrored by Murray Gell-Mann's original (1964) quark theory, which also exploited the SU(3) symmetry. Only this time, the minimal representation was the three light quark flavors (up, down, strange), and the non-minimal representation was Gell-Mann's famous Eightfold Way, which correctly(!) predicted the properties of all the light hadrons, including some that had not yet been discovered.]
Trivia Of The Day: Because their foot pads end in literally billions of microscopic filaments, geckos use Van Der Waals forces to allow them to stick to just about any surface and climb up walls and across ceilings. They do this so efficiently that the average gecko is "glued" to the wall with about 200 pounds of force.
The same argument could be applied to the force of electromagnetism, but electromagnetism conclusively propagates at the speed of light.
It can't be that simple. Physicists would have nothing to do. You want to be responsible for all these physicists being out of work and on welfare?
Cha, cha, cha... You know,
epicycles can explain
retrograde motion.
If you're willing to
pile complexity onto
complexity, you
need never give up
on Ptolemy's paradigm.
Sorry. Just rambling...
"So Ptolemy adopted an instrumentalist view --- this strange model is only an accurate calculator to predict the planet motions but the reality is Aristotle's model. This apparent contradiction between reality and a calculation device was perfectly fine in his time. Our modern belief that models must characterize the way the universe actually is [!] is a tribute to the even longer-lasting influence of Aristotle's realism."
Van Flandern also now insists that electromagnetism propagates at infinite speed. (Not electromagnetic waves, mind you, but the field...whatever the devil that means.) It's nonsense, but he's forced into it by his own (mistaken) geometrical argument.
Presumably this frees gravitational waves (as opposed to fields) to propagate at c.
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