cianfa72's latest activity

Actually, if you take any small part of the geodesic, and a small neighborhood around that part, then that geodesic segment is minimal -...

True, but that is just a recipe for constructing a pure Riemannian manifold, that happens to a submanifold. So it is actually covered in...

As far as I can understand, in GR, the spacelike geodesics are (always) saddle points when considering them in the overall 4D spacetime...

No, not longest distance - you can deviate from a non minimal great circle path and make it longer - by any amount with squiggles. In...

Simultaneity is a property of pairs of events not objects even in classical physics where there is no relativity of simultaneity.

Ok, this is similar to the Langevin congruence: take the worldline at the center of the rotating disk as "reference/fiducial" worldline...

The vorticity isn't a cause, it's a description. As I understand it, the rotation of the ISS wrt the gyroscope's axis is maintained by...

Yes the vorticity is small, however it suffices to provide the rotation of the ISS w.r.t. the gyroscope's axis.

Strictly speaking, I suppose this is true, but the proper acceleration will be extremely small, because the only reasons it would be...

Better, I'd say the angular momentum is a bi-vector -- https://en.wikipedia.org/wiki/Angular_momentum

I was taking the more advanced viewpoint in which the momentum ##\boldsymbol p## is actually a co-vector (see for instance MTW chapter 2.5).

By contrast to a rotating frame of reference. It is not spinning. We may take it as an article of faith that any "frame" we speak of...

I mean the frame in which the system's CoM stays always at rest (zero total ##\vec P## w.r.t. it). Basically it shares the system's CoM...

To take it simple, one could reasonably model the walls of the ISS as the rim of a 2D disk in which the center of mass (CoM) is...

He means that it rotates 360 degrees relative to the gyroscope's axis, which is Fermi-Walker transported along the ISS's worldline.