Berkeley Lab Physicist Challenges Speed of Gravity Claim

spacedaily.com ^ | 23 Jun 03 | staff

[boris]

"That delay would permit the Sun to travel 178,000 miles in those 8.3 minutes.

That would mean that the Earth's orbital plane would be centered *not* on the actual location of the Sun, but rather on the location of the Sun from 8.3 minutes back in time, a measurable difference of 178,000 miles."

Tiresome and tendentious. Loudly asserting Newtonian physics in a non-Newtonian situation proves only your ignorance.

--Boris

[Physicist]

A disturbance to a field may very well propagate at Light speed, but that's an entirely different action, in my opinion, than the field *itself* propagating.

But once the field is there, it's there. What aspect of the field needs to propagate, other than any changes to it?

[Southack]

"Going from no field to some field is a change, and that change is what is propagating. It's all that has to propagate for a complete description of what's going on."

That train of thought very likely misses the right track.

It's too easy to think along those lines and confuse the field itself changing or springing into existence with that of an existing field being disturbed.

When we turn ON the electromagnet, the magnetic field suddenly covers a sizeable area where it did not cover in the past when our electromagnet was OFF.

How *fast* did the field cover this new area?

Yet what you seem to be saying is that this "change" in going from "no field" to "some field" is akin to a disturbance in an existing field.

I'm not convinced that's entirely valid or useful. It might be a division by zero event.

Yes, if we have an *existing* magnetic field, then a disturbance in that field should propagate through the field itself at the speed of Light. That's well-known and not under dispute so far as I'm aware.

But what hasn't been conclusively proved or accepted is how fast the field itself covers an area when the field first forms, likewise for when the field ends as to how fast it ceases to cover an area.

[Southack]

"But once the field is there, it's there. What aspect of the field needs to propagate, other than any changes to it?"

That's rich! It's also a bit beyond the scope of this thread.

We're simply trying to answer *how fast* the field gets there, not *why* it needs to continue to do anything.

[sit-rep]

Why, does an object fall only about 145+- MPH to earth?

[Southack]

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

Proves, conclusively proves beyond dispute my ignorance?! My, my, my...

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.

[RightWhale]

Why, does an object fall only about 145+- MPH to earth?

Could you rephrase the question? An object might fall at that speed, another might fall at a different speed.

[aruanan]

Van Flandern alternates in a random pattern between reality and kookism, so it would be well to read the paper for oneself or wait for further letters to the editor.

Ha ha. Sometimes kookism is more a measure of the degree to which the expectations by which one interprets kookism are out of line with reality than the degree to which the presumed kookism actually departs from reality. I haven't seen in any of the Mars photos anything that looks definitively artificial. But then, astronomers with a lot less to go on than Flandern has have thought they saw canals on Mars where none existed. Still, the "seeing faces in the carpet" phenomenon in the interpretation of Mars photographs shouldn't detract from otherwise cogent arguments on the speed of gravity.

[Physicist]

Yet what you seem to be saying is that this "change" in going from "no field" to "some field" is akin to a disturbance in an existing field.

Exactly! Because consider: an observer at rest with respect to an electrical charge will see an electric field and NO magnetic field, while a moving observer (passing arbitrarily close to the first observer's position) will see both an electric and a magnetic field. The two observers will not agree on whether there is a magnetic field or not; they will, however, agree on the dynamics of locally moving charged particles (i.e., the physics works out the same).

So you see, you can practically never say that any region of space is free from a magnetic field, because the magnetic field in that region will be different for different observers. One man's zero field may be another man's strong field. There can't be anything special about turning on a field; it's the same thing as a change to the existing field. The 4-potential is defined everywhere in space. (Homework: look up the terms "Gauge Principle" and "Gauge Invariance".)

[Geek alert 1: The reason that different observers will see different fields is because of special relativity. From a moving frame of reference, time moves more slowly and space is contracted along the direction of motion. If the field is the same for both observers, the motions of a charged particle can't be agreed upon by different observers. The magnetic force is the force that arises that compensates for the difference in motion between the two versions of spacetime. (It's tempting to call the magnetic force an "apparent force", such as the coriolis force, but it is possible--easy, in fact--to construct magnetic fields that can't be zeroed out by a Lorentz boost.)]

[Geek alert 2: Woah! Wait a second! If the relative distortion of spacetime causes an apparent--no, a real--change in the electromagnetic field for relatively moving observers, why doesn't it do the same thing for the gravitational field? It does. It's called the gravitomagnetic effect. Well, doesn't that just prove what Van Flandern is saying? Isn't that just a different formulation of the same effect? No, because first, unlike the "time delay" canard, the gravitomagnetic effect depends on the speed of the observer and not on the distance from the source, and second, because any "time delay" effects (such as the Poynting-Robertson effect, which really does pertain to the light from the sun) would be orders of magnitude greater than the gravitomagnetic effect.]

(I have used the blue font color to denote scientific ignorance, as is customary on FR.)

[Physicist]

We're simply trying to answer *how fast* the field gets there

If it didn't get there at the speed of light, radar wouldn't work.

[sit-rep]

Sorry about that.

I think I am assuming the gravitational force the article is talking about is the speed in which an object will be pulled...

IOW... why, when an apple falls from the tree, it does not leave a 24" crater because it was doing 130,000 MPS and gaining??

[Southack]

"an observer at rest with respect to an electrical charge will see an electric field and NO magnetic field, while a moving observer (passing arbitrarily close to the first observer's position) will see both an electric and a magnetic field. The two observers will not agree on whether there is a magnetic field or not; they will, however, agree on the dynamics of locally moving charged particles (i.e., the physics works out the same). So you see, you can practically never say that any region of space is free from a magnetic field, because the magnetic field in that region will be different for different observers. One man's zero field may be another man's strong field. There can't be anything special about turning on a field; it's the same thing as a change to the existing field."

Ahhh, but there *can* be something special about turning on the field (more below).

Your *observers* in your above example depend upon frames of reference, yet you and I both know that if behavior isn't explained consistently in different frames of reference that someone's equation is wrong. One observer might see a magnetic field, and another observer might not, but that's *not* the same thing as turning on a field in the first place. The two observers won't agree on whether there is or is not a magnetic field in your example, this is true, yet we both know that the field does exist! It just isn't *observable* to one of the participants.

Likewise, the frame of reference doesn't determine the magnetic field of our electromagnet. Regardless of the position of the observer, in reality there is NO field when the electromagnet is OFF, while there is a field that covers a sizeable area when our electromagnet is turned ON.

And what is so special about that fact? Well, that fact means that a magetic field has to propagate outwards over an area in a given amount of time (once we switch the electromagnet ON).

Thus, it is a valid question to ask *how fast* does the field cover that area.

[Southack]

"If it didn't get there at the speed of light, radar wouldn't work."

I don't see where you dug that statement up. I'm not arguing about the speed of *disturbances* in an existing electromagnetic field, but rather how fast a magnetic field covers an area.

[Southack]

"unlike the "time delay" canard, the gravitomagnetic effect depends on the speed of the observer" frame of reference.

Now what do we say about a phenomenon that is not consistently explained in *every* frame of reference, not just one?!

[PatrickHenry]

Because consider: an observer at rest with respect to an electrical charge will see an electric field and NO magnetic field, while a moving observer (passing arbitrarily close to the first observer's position) will see both an electric and a magnetic field. The two observers will not agree on whether there is a magnetic field or not; they will, however, agree on the dynamics of locally moving charged particles (i.e., the physics works out the same).

And because Maxwell's equations showed that they will both agree the charge propagates at c, a certain patent clerk drew some rather interesting conclusions.

[Physicist]

The two observers won't agree on whether there is or is not a magnetic field in your example, this is true, yet we both know that the field does exist! It just isn't *observable* to one of the participants.

By that standard, the field always exists, everywhere. Zero is a perfectly good value for the field to have, as you point out. So if you want to say that a zero-field region of space is not a field-free region of space, I'll accept that.

Now, show me a region of space that is free from all gravitational fields.

[Physicist]

I'm not arguing about the speed of *disturbances* in an existing electromagnetic field, but rather how fast a magnetic field covers an area.

Oh, aye. And as the radar dish sweeps around, shining its beam on regions untouched by magnetic field, is this not the same thing as "turning on the field" there?

[Physicist]

Now what do we say about a phenomenon that is not consistently explained in *every* frame of reference, not just one?!

The phenomenon in question is the motions of physical bodies, and those motions will be agreed upon for all observers. The gravitomagnetic effect guarantees that, even in the face of different spacetime perspectives.

[Physicist]

the charge propagates at c

Smoke what?

[RightWhale]

why, when an apple falls from the tree, it does not leave a 24" crater because it was doing 130,000 MPS and gaining??

That's a good question. We know it doesn't because we haven't seen it happen, but then again, we haven't seen all apples falling. Maybe some make craters.