And yet, without "seeing" where our Sun is at this very moment in the present, the Earth is nonetheless drawn not to where the Sun was 8.3 minutes ago, but to where the Sun resides at the present moment.
Hmmm...
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."
And yet, without "seeing" where our Sun is at this very moment in the present, the Earth is nonetheless drawn not to where the Sun was 8.3 minutes ago, but to where the Sun resides at the present moment.
Hmmm...
Sigh.
If you're talking about direction (inward or outward), you must be assigning a velocity to the field propagation, because if it were infinite, there'd be no direction. The whole field would just appear or disappear.
Now let's suppose you turn on your magnet and leave it on for a year. However fast you imagine it to be, the field will reach to some region of space. Since you left it on for a year, it will take a year to collapse at the same speed. But you must admit that the the field close to the apparatus will collape almost immediately after you flick the switch. So in order for the "inward collapse" to reach the apparatus just as you are flicking on the switch, the collapse has to begin much earlier--a year earlier, in fact.
"C" is a velocity, not an acceleration.
Interestingly, one "g" (32.174 ft/s/s) equals 1.03 light years/year/year.
Merely accelerate at one g for one year and--neglecting relativistic effects--you will be "near" c and half a light-year out.
Each kilogram of mass (again neglecting Einstein) will have 4.89 x 10^17 joules of kinetic energy. Since one year is about pi x 10^7 seconds, this works out to about 1500 megawatts operating over one year to accelerate your kilogram.
To account for various inefficiencies, call it 2000 MW. Or two San Onofre nuclear power plants.
If you plan for any payload or structure on your 1-kg spaceship, and you plan to have the powerplant on board, the problem is reduced to stuffing two nuclear power stations in--say--100 grams and a few cc. Scale up until you hit 'Enterprise'.
The problem is that humans are too puny to deal with such power and power densities; it is like stuffing the Sun into the Rose Bowl.
Among the questions I mean to ask the Almighty is: "Why did You make us so short-lived?" and "Why did you put everything so freeping far apart?!?" It is almost as if the Universe is designed to prevent communication/contact among intelligent species--assuming that we are not alone.
Personally I have been forced to conclude that we are alone or very nearly so.
--Boris
That is certainly correct; he would not even understand it.
--Boris
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