Berkeley Lab Physicist Challenges Speed of Gravity Claim

spacedaily.com ^ | 23 Jun 03 | staff

[Right Wing Professor]

How do you know the cars are moving?

Just set up an interferometer, and measure the speed of light forwards and backwards along three coordinates. The difference, divided by two, will give you the absolute velocity along that coordinate. Add the three vectors, and you have the 'real' velocity.

I'm surprised no one has tried this :-)

[Southack]

We know that the cars are moving in reality because reality is superior to my fictitious model. In my fictitious model, the cars *appear* to be stationary.

In reality, the cars are traveling at 70 miles per hour, as stated in the initial pre-condition above in this thread. Check their speedometers!

[Junior]

But the cars are moving only in relation to something else. If, for instance, you are pacing a car at 60 mph on the interstate, the other car is stationary relative to you. Everything is relative as there is no absolute frame of reference.

[Southack]

Do you agree with the pre-conditions in Post #172?

[Southack]

"But the cars are moving only in relation to something else. If, for instance, you are pacing a car at 60 mph on the interstate, the other car is stationary relative to you."

Indeed. One could even create a *model* in which the two cars were stationary.

But outside of that model, jumping out of one of the cars would soon inform you that you were traveling at 60 mph, with an Ouch!

[Physicist]

Check their speedometers!

But they're running on a big treadmill. Of course their speedometers are going to say that.

[Right Wing Professor]

No. I don't disagree with them either. I never took General Relativity, but I know enough about it to realize that I can't count on my intuition to predict the time dependent behavior of the gravitational field. The ol' brain just never learned to wrap itself around rank-20 tensors.

What I was trying to point out, rather snidely, and mostly for the amusement of Physicist, is that your 'reality' is an idea that was tested and discarded at the end of the 19th Century. The Michelson Morley experiment (which I rather crudely described) was an attempt to measure the absolute movement of the earth through space, and it failed. There is no single reference frame that is 'real', as opposed to any others. You can write a self consistent set of equations for any inertial frame you want, and they'll be just as good as those in any other inertial frame.

[Right Wing Professor]

But outside of that model, jumping out of one of the cars would soon inform you that you were traveling at 60 mph, with an Ouch!

You're not travelling at 60 miles an hour. You're travelling at several hundred thousand miles an hour. Running into a meteorite would tell you that. Mega-ouch!

[Physicist]

rather snidely, and mostly for the amusement of Physicist

FWIW, I did emit a loud guffaw, at some velocity.

[Junior]

But then you would have assumed another frame of reference (and possibly room temperature). It all has to do with frames of reference. You pick the one you want to work from and go from there. In a Solar System model, it is safe to assume the frame of reference wherein the Sun is stationary. In the Earth-Moon system it is safe to assume the frame of reference wherein the Earth is stationary.

[Southack]

"But then you would have assumed another frame of reference (and possibly room temperature)."

Indeed. The new frame of reference would have been "reality" instead of the fictitious model of a portion of reality.

[Right Wing Professor]

The new frame of reference would have been "reality" instead of the fictitious model of a portion of reality.

Your cars are moving at 60 mph w.r.t the earth's surface. But the earth's surface is moving at 1000 mph. around the earth's center. The earth's center is moving at 60,000 mph around the center of mass of the solar system. But the solar system is embedded in a spiral arm of the galaxy, and is moving at some velocity I can't remember around the center of the galaxy, and the galaxy itself is rotating around the center of mass of the local cluster, which itself is moving relative to other clusters, all of which are moving relative to the center of mass of the entire universe, which is moving relative to what?

In other words, which frame of reference is reality?

[Southack]

Rather than toy around forever with neither of you agreeing to the pre-conditions in Post #172, let's try a different approach.

One of two things could explain why the orbital planes of our planets are centered upon the Sun's actual location:

1. The Sun and the Earth are actually *not* moving in tandem, but rather, are motionless save for the Earth's orbit around the Sun itself.

or

2. Gravity travels so fast that there is almost no real delay, as in: the Sun hasn't moved very far relative to *anything* by the time Gravity covers the distance in question.

[Southack]

"In other words, which frame of reference is reality?"

Wrong question. It isn't *reality* that changes based upon your frame of reference. Reality is simply what exists.

What changes (when you change your frame of reference) is your *model* of reality.

[PatrickHenry]

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.

Forget the sun for a moment. Consider only the earth-moon system. Although the earth is in motion (around the sun, etc.) the moon manages to keep up with us. We never outrun the moon, even though, from your viewpoint, the moon should be struggling to stay in orbit around a runaway target.

I think the answer to this awesome problem is that the two components of the earth-moon system are both in orbit around a center of gravity. And that is what orbits the sun. Likewise, the earth-sun system has a center of gravity (probably within or very near to the sun) and that is what is roaming around the galaxy.

As always, if I've goofed it up, Physicist or someone else who knows this better than I do will straighten me out.

[Physicist]

The Sun and the Earth are actually *not* moving in tandem, but rather, are motionless save for the Earth's orbit around the Sun itself.

There's a coordinate system where that's true. There are also coordinate systems where that's not true. The same physical result must be achieved in all possible coordinate systems. (After all, a coordinate system is merely a theoretical construction.) Work it out in the heliocentric coordinate system and you'll have the universal answer.

[Right Wing Professor]

So how fast are we moving relative to reality? And how do we measure that?

[Southack]

PRECONDITION #1:The Sun and the Earth are actually *not* moving in tandem, but rather, are motionless save for the Earth's orbit around the Sun itself.

"There's a coordinate system where that's true. There are also coordinate systems where that's not true. The same physical result must be achieved in all possible coordinate systems." - Physicist

Bingo! If the same physical result isn't true in all possible coordinate systems for that precondition, then that precondition must be false.

Guess what that leaves us with to explain the orbit of the planets around the Sun?!

[Junior]

You appear to have a bias toward particular frames of reference.

[dalereed]

"Should shifting the reference frame make any difference in measurements?"

I think he should shift his reference frameto the tallest building on the Berkley campus and jump off with his new money grant request in hand and test his theory!