Let us consider a shut and such compartment that is incommunicable with its exterior. A g gravitational field is there measured by mechanical means. In agreement with Einstein Equivalence Principle there is not as distinguishing this gravitational field of a possible acceleration of the compartment.

A classical physicist, placed inside the compartment, decides then to study the behavior of an electric charge and, verifying that it doesn't emit electromagnetic radiation, he concludes that the acceleration is purely gravitational. If the conclusion is true, Einstein Equivalence Principle is wrong; if the conclusion is false, the classic electromagnetism is wrong.

I ask: Who is wrong?: Me? The classical physicist? The classical electromagnetism? Or General Relativity Theory?

Observation: Being General Relativity Theory autonomous, I would be hoping its defense didn't depend on quanta effects.

Alberto Mesquita Filho

01/07/98

Alberto Mesquita Filho wrote:

*Let us consider a shut and such compartment that is incommunicable with its exterior. A g gravitational field is there measured by mechanical means. In agreement with Einstein Equivalence Principle there is not as distinguishing this gravitational field of a possible acceleration of the compartment.*

Right, there is nothing distinguishing this gravitational field from acceleration of the compartment. If the compartment were large enough, supposedly there is a way to detect a gravitational field, but that doesn't mean the thought experiment is invalid.

*A classical physicist, placed inside the compartment, decides then to study the behavior of an electric charge and, verifying that it doesn't emit electromagnetic radiation, he concludes that the acceleration is purely gravitational. If the conclusion is true, Einstein Equivalence Principle is wrong; if the conclusion is false, the classic electromagnetism is wrong.*

I ask: Who is wrong?: Me? The classical physicist? The classical electromagnetism? Or General Relativity Theory?

I don't think it's that simple. Accelerating an electron without an electric field may not produce any radiation, do you know of any such experiments?

*Observation: Being General Relativity Theory autonomous, I would be hoping its defense didn't depend on quanta effects.*

Alberto Mesquita Filho

I don't think so. And I would not like to think the Equivalence Principle is wrong.

Sincerely,

Ken Fischer

01/07/98

Alberto Mesquita Filho wrote:

*Let us consider a shut and such compartment that is incommunicable with its exterior. A g gravitational field is there measured by mechanical means. In agreement with Einstein Equivalence Principle there is not as distinguishing this gravitational field of a possible acceleration of the compartment.*

Right.

*A classical physicist, placed inside the compartment, decides then to study the behavior of an electric charge and, verifying that it doesn't emit electromagnetic radiation, he concludes that the acceleration is purely gravitational.*

The observer's instruments are stationary in the stationary frame of reference of the compartment. So are the electric charge. Maxwell's equation will predict that the instruments will detect no radiation.

Maxwell predict that no radiation will be detected, regardless of whether the compartment is accelerated of a rocket, or are at the surface of Earth. GR does not change that.

So why do you think the 'classical' observer can conlude what you say?

If the conclusion is true, Einstein Equivalence Principle is wrong; if the conclusion is false, the classic electromagnetism is wrong.

I can only guess why you think so. I presume you think that classical theory say that the charge will radiate if it is accelerated by a rocket. But then you are forgetting that our observer's instruments are moving along with the charge. Classical theory predicts that those instrument will detect nothing regardless of how they and the charge are moved, as long as they are moved together. It does not matter which frame of reference you select to do the calculations in.

Remember that EM-fields are dependent on the frame of reference. If the compartment is accelerated by a rocket, an external observer in an inertial frame would (with instruments stationary in his frame) see a changeing EM-field. Right. But the instruments moving along with the charge will see no fields.

*I ask: Who is wrong?: Me? The classical physicist? The classical electromagnetism? Or General Relativity Theory?*

You.

Paul B. Andersen

01/07/98

"Alberto Mesquita Filho" wrote:

*A classical physicist, placed inside the compartment, decides then to study the behavior of an electric charge and, verifying that it doesn't emit electromagnetic radiation, he concludes that the acceleration is purely gravitational.*

This issue is discussed in the preprint gr-qc/9303025, "Radiation from a Uniformly Accelerated Charge and the Equivalence Principle" by Steven Parrott. Here is the abstract:

We argue that purely local experiments can distinguish a stationary charged particle in a static gravitational field from an accelerated particle in (gravity-free) Minkowski space. Some common arguments to the contrary are analyzed and found to rest on a misidentification of "energy". **[http://xxx.lanl.gov/abs/gr-qc/9303025]**

I haven't studied it in detail, but it sounds intriguing.

He's also got some other papers at:

**http://xxx.lanl.gov/abs/gr-qc/9711027**

**http://xxx.lanl.gov/abs/gr-qc/9308023**

To any expert relativists reading this: could you take a look at this paper and see if the argument looks sound to you? It looks okay to me, but I'm not an expert..

Nathan Urban

On Wed, 7 Jan 1998, Alberto Mesquita Filho wrote:

*Let us consider a shut and such compartment that is incommunicable with its exterior. A g gravitational field is there measured by mechanical means. In agreement with Einstein Equivalence Principle there is not as distinguishing this gravitational field of a possible acceleration of the compartment. A classical physicist, placed inside the compartment, decides then to study the behavior of an electric charge and, verifying that it doesn't emit electromagnetic radiation*

Is the charge moving around inside the compartment? If so, how? As someone said recently in a similar context, the devil is in the details. If you clarify your thought experiment you should be able to convince yourself this situation is consistent with the Equivalence Principle. See for instance D'Inverno, Introducing Einstein's Relativity, for help (you can try to solve some problems and compare with the answers in the back).

Chris Hillman

01/07/98

Chris Hillman wrote:

*On Wed, 7 Jan 1998, Alberto Mesquita Filho wrote:*
*Let us consider a shut and such compartment that is incommunicable with its exterior. A g gravitational field is there measured by mechanical means. In agreement with Einstein Equivalence Principle there is not as distinguishing this gravitational field of a possible acceleration of the compartment. A classical physicist, placed inside the compartment, decides then to study the behavior of an electric charge and, verifying that it doesn't emit electromagnetic radiation*

*Is the charge moving around inside the compartment? If so, how? As someone said recently in a similar context, the devil is in the details. If you clarify your thought experiment you should be able to convince yourself this situation is consistent with the Equivalence Principle. See for instance D'Inverno, Introducing Einstein's Relativity, for help (you can try to solve some problems and compare with the answers in the back).*

Chris Hillman

In my original project I thought of a charge at rest, for example, a loaded spherical conductor on a table and of this separated by an insulating cylinder. However, the experience would be the same case if the charge it was in a rectilinear and uniform movement. Certainly, in the considered frame of reference, it is not being accelerated because "it doesn't emit electromagnetic radiation".

Alberto Mesquita Filho

01/08/98

**E-mail**

From: Chris Hillman

To: Alberto Mesquita Filho

On Thu, 8 Jan 1998, Alberto Mesquita Filho wrote:

*In my original project I thought of a charge at rest, for example, a loaded spherical conductor on a table and of this separated by an insulating cylinder. However, the experience would be the same case if the charge it was in a rectilinear and uniform movement. Certainly, in the considered frame of reference, it is not being accelerated because "it doesn't emit electromagnetic radiation".*

You are still confused. If the table is experiencing stresses because there is a gravitational force (or if you prefer, because the elevator is being accellerated), then the charge will radiate because it to is being accellerated.

Chris Hillman

01/08/98

Fri, 7 Jan 1998

Thanks to all the ones that answered at the presented theme and, especially, to Paul Andersen for convincing me that I was wrong and that the subject is much more complex than I was imagining. I also thank Nathan Urban by the links.

I agree with Ken Fischer's opinion:

"*I don't think so. And I would not like to think the Equivalence Principle is wrong.*"

and I increase: Physics is more beautiful with Einstein Equivalence Principle.

Sincerely

Alberto Mesquita Filho

01/08/98

Now this is the kind of thing that doesn't happen often enough in this newsgroup:

Paul Draper

01/08/98

Alberto Mesquita Filho wrote:

*Thanks to all the ones that answered to the presented theme and, especially, to Paul Andersen for convincing me that I was wrong and that the subject is much more complex than I was imagining.
*

I also thank Nathan Urban by the links. I agree with Ken Fischer's opinion:
*I don't think so. And I would not like to think the Equivalence Principle is wrong.
*

*and I increase: Physics is more beautiful with Einstein Equivalence Principle.*

Sincerely

Alberto Mesquita Filho

**See as well "Einstein-Faraday's Elevator".**