Equivalence Principle

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Larry Burford</i>
<br />Suppose there is a device that can "accurately" measure the strength of the gravitational potential field at a point, analogous to the way a thermometer can measure temperature at a point. This device, sitting still on the surface of Earth, will have a particular reading, and that reading will be constant. Very constant. Out in the depths of space, away from any significant mass, the same device will have a different, lower, reading. And this difference will exist even if the device is accelerating at 1 g.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">A thermometer is a good analog for a potentiometer. As both are taken out into space, the will give higher readings for the stronger potential (denser elysium) and higher temperature nearer the Sun, and lower readings farther from the Sun. So if I'm inside a black box, how can I tell if I'm closer to the Sun or sitting on a planet?

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Another difference: Increasing velocity in a given potential field causes the potential field to seem stronger (more dense). So the device, if accelerating while away from large masses, should show a continuously changing value for potential.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">And items inside a falling elevator will converge as the center of the Earth is approached. But the equivalence principle claims only that the two (gravitational force and uniform acceleration) cannot be distinguished at an instant from inside a black box.

To be clear, I agree with the authors that the Greenberger-Overhauser neutron interferometer experiment has falsified the weak equivalence principle. I'm just arguing the case (as devil's advocate) as Einstein seems to have intended it. -|Tom|-

[tvf] " ... if I'm inside a black box, how can I tell if I'm closer to the Sun or sitting on a planet?"

You can go just about anywhere in (or out of) the solar system and accelerate at 1 g to simulate the force of gravity on Earth.

But there are only a few places where you can accelerate at 1 g and get a gravitational potentiometer to give the same reading it does on Earth.

(And none where that reading will be constant. But I see now that doesn't matter.)

[tvf] " ... the equivalence principle claims only that the two (gravitational force and uniform acceleration) cannot be distinguished at an instant from inside a black box."

Is the definition that specific? Potential is excluded?

[tvf] "I'm just arguing the case (as devil's advocate) as Einstein seems to have intended it."

Thank you.

Regards,
LB

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Larry Burford</i><blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">[tvf]: " ... the equivalence principle claims only that the two (gravitational force and uniform acceleration) cannot be distinguished at an instant from inside a black box."<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Is the definition that specific? Potential is excluded?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Yes, potential is excluded. Otherwise, you would only need to observe any light beam inside the black box. It would bend from acceleration, and it would bend from potential, but the later would be twice as much as the former. -|Tom|-

[tvf] "Yes, potential is excluded."

Hmmm. Many proponents of the geometric interpretation of GR seem to believe that potential and force are just two ways of looking at the same thing. So why would they make a distinction like this?

Why would it even occur to them to do so?

Regards,
LB

[tvf] "Otherwise, you would only need to observe any light beam inside the black box. It would bend from acceleration, and it would bend from potential, but the later would be twice as much as the former."

It is my understanding that the rules of the EP game forbid such an experiment.

I know for sure that you are not allowed to measure gravitational force over a large enough distance to be able to detect the changes that exist in real gravitational force fields. (Such changes do not exist under mechanical acceleration and provide a simple and effective means of detecting the difference between mechanical acceleration and real gravitational fields.)

So why would one be allowed to measure (any property of) light beams over a large enough distance to falsify EP?

LB

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Larry Burford</i>
<br /><blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">[tvf]: Otherwise, you would only need to observe any light beam inside the black box. It would bend from acceleration, and it would bend from potential, but the later would be twice as much as the former.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">It is my understanding that the rules of the EP game forbid such an experiment. I know for sure that you are not allowed to measure gravitational force over a large enough distance to be able to detect the changes that exist in real gravitational force fields. ... So why would one be allowed to measure (any property of) light beams over a large enough distance to falsify EP?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">The "equivalence" in the equivalence principle is between gravitational force and uniform acceleration. There is no such equivalence and no such principle for gravitational potential. So the experiment I mentioned is like the one you mentioned. It allows one to tell if a gravitational field or a uniform acceleration is acting. But it does nothing to falsify EP.

Remember that gravitational force and gravitational potential are different physical phenomena that, in general, do not have the same properties. And their effects have very little in common. Only gravitational force can accelerate a material body. Only gravitational potential can bend or slow or redshift a light wave. Have a look at "Gravitational force vs. gravitational potential" on this web site for an overview of the differences in physical effects of these two phenomena: metaresearch.org/cosmology/gravity/vanflandern.ppt

Force and potential are related as derivative to function. Note that in other cases where there exist physical counterparts, functions and their derivatives are likewise independent phenomena. The simplest classical case is velocity and acceleration. For any value of either, we can have any allowed value of the other.

But a gradient relationship (a type of derivative) implies a causal link between the two. In that case, we need to know which causes which. No experiment has established the direction of the arrow of causality in the relation "force is the gradient of potential". But Le Sage-type models require that force imposes a gradient onto the potential, the latter being equivalent to the "light-carrying medium". Moreover, even in GR, when something disturbs the potential and sets off a gravitational wave, this does not have any influence on the gravitational forces acting. So it is reasonable to conclude that force causes potential gradients and not vice versa.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Many proponents of the geometric interpretation of GR seem to believe that potential and force are just two ways of looking at the same thing. So why would they make a distinction like this? Why would it even occur to them to do so?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Geometric GR denies that gravity is a force, so its proponents give only lip service to EP, speaking ambiguously about "gravitational fields" without specifying what they mean physically. But geometric GR has now been falsified on physical grounds by the arguments Vigier and I presented in our "Foundations of Physics" paper. (Basically, geometric GR provides no cause for acceleration and no source of new momentum.) What Feynman calls "field GR" has no such doubts about gravity being a force, and correspondingly no ambiguity about the meaning of EP. -|Tom|-