Berkeley Lab Physicist Challenges Speed of Gravity Claim

spacedaily.com ^ | 23 Jun 03 | staff

[PatrickHenry]

This then is approximately 565,837 miles per hour or 157 miles per second.

Relative to me, the sun is motionless. It stays right where I want it, one AU from the earth. Nothing else matters. All your computations are for naught! Mrruuuhahahahahaha!

[Physicist]

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).

Those are the aspects of the situation that are analogous to the sun.

The sun, insofar as it is not subjected to accelerations, is at a fixed location in its own reference frame. The sun's gravitational field, as long as the sun hasn't undergone an acceleration for more than 8.3 minutes, is fixed to all points in space, at least as far as the Earth's orbit is concerned. The field, like the sheet, does not need to propagate; it's already where it needs to be. The Earth will "see" the same field at every point, regardless of how fast it's moving (neglecting the "gravitomagnetic" effect, which is a known relativistic correction that is vanishingly small).

Should the sun undergo an acceleration (or, God forbid, disappear), the changes in the field will propagate from the sun outward. These changes are gravitational waves, and they propagate at c. Again: waves propagate, fields do not.

The situation is exactly analogous to the electromagnetic field vs. electromagnetic waves. The same geometrical argument applies. Van Flandern now says that while electromagnetic waves propagate at c, electromagnetic fields propagate infinitely fast. Whatever. It's like saying that while cars drive at finite speeds, the road goes infinitely fast. I suppose that's one way to describe it...just not a very useful way.

(I had promised myself not to respond to this Van Flandern crackpottery any more, but RadioAstronomer has inspired me. For the future, I'll put together a boilerplate response.)

[Doctor Stochastic]

Or in the words of Tom T. Hall: "Faster Horses, Younger Women, Older Whiskey, More Money."

[boris]

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

Define your coordinate system. In a heliocentric system, it does not move at all.

The whole solar system is moving around the center of the galaxy at about 230 km/s. If you use a galactic-centered coordinate system, the Sun moves 114,678 kilometers in orbit around the galaxy in 8.3 minutes.

However, the galaxy is moving toward the "Great Attractor":

"Detailed observations of the galaxies around us indicate that there is superposed on the Hubble flow a large-scale streaming motion of about 600 km/s in the general direction of the constellation Centaurus.

"This mass migration includes the Local Group, the Virgo Cluster, the Hydra--Centaurus Supercluster, and other groups and clusters for a distance of at least 60 Mpc up and downstream from us. It is as if a great river of galaxies (including our own) is flowing with a swift current of 600 km/s toward Centaurus.

"Location of the Great Attractor

"Calculations indicate that ~10^16 solar masses concentrated 65 Mpc away in the direction of Centaurus would account for this. This mass concentration has been dubbed the Great Attractor. Detailed investigation of that region of the sky (see adjacent image of the galaxy cluster Abell 3627) finds 10 times too little visible matter to account for this flow, again implying a dominant gravitational role for unseen or dark matter. Thus, the Great Attractor is certainly there (because we see its gravitational influence), but the major portion of the mass that must be there cannot be seen in our telescopes."

So the Sun moves ~299,196 kilometers toward the Great Attractor in 8.3 minutes.

However, there is another frame of reference, that of the gross motion of the Solar System with respect to the cosmic background radiation field. This motion has been found to be ~371 km/s. So the sun moves 184,980 km in 8.3 minutes relative to the cosmic background radiation.

Satisfied?

--Boris

[sandydipper]

Hello! Hello! Can you hear me now??

[RadioAstronomer]

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

Absolutely. :-)

[RadioAstronomer]

Thanks for the help! I was running out of analogies to describe our system. :-)

[RadioAstronomer]

Nice post. I wasn't even going to go there here on this discussion. :-) (We could also add the effects of the multiple bodies just in this solar system alone, Precession and all the various nutations of our Earth, precession of the Sun, etc.)

[Junior]

A "baby among giants" placemarker.

[RadioAstronomer]

Good morning Junior! :-)

[longshadow]

(I had promised myself not to respond to this Van Flandern crackpottery any more, but RadioAstronomer has inspired me. For the future, I'll put together a boilerplate response.)

Someone has to drive a stake through its heart every so often to make sure it doesn't creep about, snagging unsuspecting, scientifically-challenged lurkers.

;-)

[Southack]

"The sun, insofar as it is not subjected to accelerations, is at a fixed location in its own reference frame. The sun's gravitational field, as long as the sun hasn't undergone an acceleration for more than 8.3 minutes, is fixed to all points in space, at least as far as the Earth's orbit is concerned."

That's an oversimplification, and it misses reality.

The Sun is moving relative to its previous position. It isn't fixed. Likewise, the Earth is moving relative to its previous position, it isn't fixed, either.

The Light that we on Earth see from the Sun is actually from where the Sun was located 8.3 minutes ago. Yes, both the Earth and Sun have moved in tandem during those 8.3 minutes, but that doesn't mean that the Earth and Sun are in a "fixed" location. The *angle* at which we see the Sun from here on Earth is distorted from where the Sun is actually located.

Instead of seeing precisely where the Sun resides, we see where the Sun was located 8.3 minutes ago (some 78,000 to 300,000 miles away, depending upon how fast one can show that the Sun moves).

If *both* the Sun and the Earth are moving Northward at 157 miles per second, even as the Earth simultaneously revolves around the Sun, then the Light that we see from the Sun will be from the location that the Sun was at 8.3 minutes ago, which is 78,186 miles *SOUTH* of its actual current position (because it takes Light 8.3 minutes to reach the Earth).

So forget Gravity. Until we can agree that:

1. The Sun is *moving* relative to it previous position,
2. Light takes 8.3 minutes to travel from the Sun to the Earth

Then we aren't ready to discuss Gravity.

We have to be able to agree that the Sun is moving and that Light takes time to reach the Earth before we can go any further in this debate, and that's because we have to build a framework wherein we agree or disagree that we are viewing the Sun in its old location of 8.3 minutes ago.

[Southack]

C#172

[Southack]

C#172

[Southack]

C#172

[Physicist]

Until we can agree that:

1. The Sun is *moving* relative to it previous position,

There is no such thing as absolute motion. If we don't accelerate the sun, then I am at liberty to choose a coordinate system in which the sun is at rest. So no, the sun does not move, according to my choice of coordinate system...and your arguments have to work in that coordinate system.

[Southack]

"There is no such thing as absolute motion. If we don't accelerate the sun, then I am at liberty to choose a coordinate system in which the sun is at rest."

No, you are not at liberty to change reality.

True, you can create a fictitional *model* in which the Sun and Earth do not "move", just as I could create a fictitious model for two cars that are both traveling together at 70 miles per hour, but it would be erroneous to say that simply because my *model* of those two cars had unchanging reference points that the cars weren't physically moving.

[Physicist]

How do you know the cars are moving?

[Southack]

The cars themselves *are* moving in reality, it is in my fictitious *model* of the cars that they appear to be stationary.

Modeling moving objects to make them appear stationary doesn't make the actual objects themselves stationary, QED.

[Physicist]

How do you know the cars are moving? Moving with respect to what? How fast are they going?