Recent content by Sam Park

Well, we know that Lorentz invariance fails globally in general relativity, but it remains valid locally. Are you saying there is evidence of violation of Lorentz invariance locally? Many people have searched for such a thing, but as far as I know, there is no evidence that local Lorentz...

I assume when you wrote that Aharoni's non-linear transformation transforms "a" uniform motion along "a" straight line into a similar kind of motion, that you meant to say it transforms ALL uniform motions along straight lines into similar kinds of motion. This is what is required of a...

No, you're confusing classical physics with special relativity. The original poster is saying that in classical physics someone can get hit by a baseball before it is thrown (or equivalently, hit by a "classical light pulse" before it is emitted). This is not true. Classical physics has absolute...

The speed of a baseball thrown at a pedestrian from a moving car is approximately equal to the sum of the car's speed and the speed of the ball relative to the car, but this doesn't imply that the pedestrian will get hit by the baseball before it is thrown.

The description of time dilation and the twin paradox is backwards. It says "when twin B got back to earth, he would be many years older than twin A", but in fact he would be many years younger. The numerical calculation is also backwards. There are quite a few other things wrong with that...

There is an important difference between the energy calculations for a magnetic dipole produced by “free current” and one produced by a magnetized subtance. The distinction is captured by the difference between the B and the H fields. Outside any magnetic material, B and H are strictly...

In case anyone is still interested in the original question, I found another reference (Becker's Electromagnetic Fields and Interactions) that talks specifically about this, and it agrees with what I posted earlier based on Schwartz's treatment. In a nutshell, we can't treat displacements of...

You may be dismissing the textbook explanation of your conundrum too quickly. The interaction between two (or more) current loops is more complicated than one might think. In a set of N current loops, the magnetic flux through the ith loop has a contribution to it arising from the current in...

Yes, I think we all agree that the accepted expression for the energy of a magnetic dipole is correct. The task is to reconcile it with the calculations. I think maybe I can (finally) shed some light on this. There's a discussion of this in Schwartz's "Principles of Electrodynamics". When...

Well, there are multiple distinct field configurations that possesses the same effective dipole moment u, but all of them have potential energy -u*B, so the particular choice of configuration doesn't matter. Since the field configuration I described explicitly has a magnetic dipole moment of...

Yes, I know B is a vector field that varies from place to place. That’s why I said, in order for the integral to give a negative value, the vectors must be pointing in opposite directions somewhere. My intent was to suggest that you check the directions of your vectors at some key points near...

From just a simplistic point of view, the quantity U is being defined as the integral of a squared magnitude, (Bf + Bd)^2, which is obviously positive-definite, but of course the self-terms Bf^2 and Bd^2 are then subtracted from this, leaving just the cross term 2Bf*Bd. The sign of this is...

Hmmm... So you're saying that, with your original approach, the sign came out wrong for both the electric dipole and magnetic dipole, but now with your new approach the sign problem has disappeared from the electric dipole case, but remains unchanged for the magnetic dipole case? So there must...

Do you encounter the same "paradox" in the more general problem of determining the energy of a arbitrary assembly of charges? It's straightforward to determine the energy both in terms of the work required to bring the charges into the final configuration, and in terms of the integral of the...

It's a bit mumbo-jumboish, because you've essentially just re-stated the premise of the question. MTW ask you to show that geodesics on the surface of a cylinder suffer no geodesic deviation, and your answer is "because the cylinder has a quasi rectangular shape, the geodesics which start...