cianfa72's latest activity
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cianfa72 posted the thread Undergrad Raising and lowering indices using metric tensor in Special and General Relativity.I'm in trouble with the notations used to rise or lower indices in tensor calculus. Consider the following: $$g_{\mu \nu} g^{\nu \rho}... -
cianfa72 reacted to PeterDonis's post in the thread High School Further Understanding Simultaneity Conventions with
Agree.
Yes, and "achronal" (or more precisely "acausal" since we want to rule out null separated events as well) is the more precise technical... -
cianfa72 reacted to PeterDonis's post in the thread High School Further Understanding Simultaneity Conventions with
Like.
I already gave it to you, way back in post #2: you don't want events that are causally connected to be simultaneous. The events of... -
cianfa72 reacted to WannabeNewton's post in the thread Graduate The rotating disk of Albert Einstein with Like.
Did you read the attachment at all? I don't know how many more times to repeat it. There's a huge difference between local spatial...
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cianfa72 replied to the thread Graduate About the definition of Born rigidity.Yes, this turns out by looking at the worldsheet of the moving ruler described in the inertial rest frame of the center's disc (cut the...
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cianfa72 replied to the thread Graduate About the definition of Born rigidity.I'm confused about this. We can look at the worldsheets describing the standard rulers held by the Langevin observers riding on the...
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cianfa72 replied to the thread Graduate About the definition of Born rigidity.To me this topic of rotating disc is a bit of a headache. The spacelike blue helix curve in #19 (defined by using Einstein...
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cianfa72 reacted to Ibix's post in the thread Graduate About the definition of Born rigidity with Like.
Locally it is, because the coordinate system is orthogonal. But @A.T. is talking about light pulses emitted by one observer and...
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cianfa72 replied to the thread Graduate About the definition of Born rigidity.I'm trying to understand your claim from Minkowski spacetime in standard cylindrical coordinates. Consider the (subset) of Langevin...
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cianfa72 reacted to Ibix's post in the thread Graduate About the definition of Born rigidity with Like.
Yes. It's obvious from symmetry - the congruence is identical under the combination of time translation and then rotation by ##\Delta...
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cianfa72 replied to the thread Graduate About the definition of Born rigidity.Only later I realized the following: take a set of Langevin observers at fixed radius on the rotating disc (let's call it ##S##). This...
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cianfa72 reacted to A.T.'s post in the thread Graduate About the definition of Born rigidity with Like.
Yes, the string can be a closed loop going all around the rotating disk, thus measuring it's proper circumference. That global geometry...
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cianfa72 reacted to Ibix's post in the thread Graduate About the definition of Born rigidity with Like.
In a cylindrical coordinate system where the disc is rotating with angular velocity ##\omega## about the origin, the line element is...
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cianfa72 replied to the thread Graduate About the definition of Born rigidity.Yes, definitely. Indeed I was wondering whether one could define a sort of "proper area" for 2D object/shapes.
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cianfa72 replied to the thread Graduate About the definition of Born rigidity.As locally measured lenghts, you mean the lenght between marks on the string as measured from an inertial momentarily comoving frame.
