Recent content by Halc

It measures a proper rotation rate, which is observer invariant. The axis orientation is also proper, effectively 'thataway', which again is observer invariant. Sure, coordinate orientation differs from one to the next, but the device outputs proper orientation, not numbers, similar to how a...

One of the more precise methods is to use a ring laser gyroscope, which leverages the Sagnac effect to determine rotation rate and axis orientation, all without looking out the window. Now where the axis actually is (not just its orientation) cannot be determined easily from our lab on Earth...

Indeed. It takes more coordinates to define a rotating frame (in say Minkowskian spacetime) that it does to define an inertial one. For one, the velocity of the axis (relative to what?) needs to be defined, which makes it relative to one specific inertial frame more than any of the others...

Good example of why proper acceleration is absolute. As for rotation, I suppose it is because the physics of a rotating frame is different than that of an inertial frame (relative to which linear motion is defined). So for example, in a rotating frame, objects at rest tend not to stay at...

Yea, but the tariffs bring it back up to 5

Maybe because the OP offered only a line and a snip from that link, and no actual commentary from yourself. The pawn thing was interesting, but had little direct relevance to the OP. It has been generally shown (not proven) that no such strategy can exist. Chess is a game of mistakes. If both...

There are countless time lapse simulations of galactic collisions, squashing say 20 billion years into a few minutes or even seconds. Many of these involve the upcoming collision with Andromeda, but my question is more general. No, I don't have a specific video in mind. Most of these show a...

It would indeed then be an invariant that the barn doors both close. It just wouldn't be an invariant that those doors are closed simultaneously.

That is perhaps our disconnect, using the same language to describe both linear and rotational effects. Come on now, that's a coordinate effect, not a physical one, since the pole does not fit in the barn in frames where the barn moves faster. The whole scenario is just an exercise in...

It does happen in any frame: The fitting of more objects on the circular track. OK, the size/shape of the track and the size of any specific object moving along it is all frame dependent. It's how many more you can pack in that is invariant. Likewise, consider two identical thin rings (thin...

The one I linked, indirect through usenet, on math.ucr,edu Best one is this "Real (not pseudo) gravitational time dilation (i.e., fields due to matter) is a different story. These fields are never uniform, and the derivations just mentioned don't work.". This explicitly states that since the...

Thanks Perter for the replies. I was unaware that 'gravitational strength' and 'gravitional potential' meant the same thing. The topic did not make it that clear. I took 'strength' to mean how much the potential changes locally over distance, the derivative of the potential. I could not find...

This topic is not about the pinned pages, but I went to the dilation page on the FAQ and it seemed incomplete. https://www.physicsforums.com/threads/time-dilation-definition-what-is-time-dilation.763074/ A quick review since the page is locked "Time dilation is the factor by which an inertial...

There was that rabbit...

Indeed. To illustrate, I did a spacetime diagram illustrating the view of the tunnel from a moment in time when the train is sticking out both ends. The stationary train is the red bar at the top. I did not show its position in the past since it doesn't move, so the lines would go straight...