cianfa72's latest activity
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cianfa72 replied to the thread Graduate About the definition of Born rigidity.Yes, in cylindrical coordinates ##(t,r,\phi)## for (2+1)d Minkowski spacetime, the points on the concentric circle drawn on the... -
cianfa72 replied to the thread Graduate About the definition of Born rigidity.Back to your example, consider now in (2+1)d Minkowski spacetime a piece of a concentric annulus on the rotating disk. At any point P on...
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cianfa72 reacted to PeterDonis's post in the thread Undergrad Euclidean geometry and gravity with
Like.
That's not what I said. What I said is that, if you're observing from a distance objects that are at rest fairly close to a black hole's... -
cianfa72 replied to the thread Graduate About the definition of Born rigidity.Quoting Wikipedia - kinematical decomposition In the notation used there, ##X^a_{;b}## should be the (1,1) tensor ##\nabla_b X^a##...
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cianfa72 reacted to PeterDonis's post in the thread Undergrad Is Covariant Derivative Notation Misleading in Vector Calculus? with
Agree.
But there is no "which index is which"; that's the point. It's not like one index "belongs" to the ##\nabla## operator and one index... -
cianfa72 reacted to pervect's post in the thread Graduate About the definition of Born rigidity with Like.
I had to look this up. My source is not the best, but it says the indices in h_ab do run from 0..3. I'm not sure if I actually said...
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cianfa72 replied to the thread Undergrad Ships passing each other at near light speed.Even in the context of relativity, relative vector velocities entering the definition of separation rate as vector sum, are not...
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cianfa72 reacted to Ibix's post in the thread Undergrad Ships passing each other at near light speed with Like.
You need two separate concepts, relative velocity and separation rate. Relative velocity is the speed one object measures another to...
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cianfa72 replied to the thread Graduate About the definition of Born rigidity.You said ##h_{ab}## is a spatial 3-metric tensor. Your definition of it is ##h_{ab} = g_{ab} + {u_a}{u_b}##. However the indices ##a,b##...
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cianfa72 replied to the thread Graduate About the definition of Born rigidity.Ah ok, basically your point is that if we look at 1d lines, then for any timelike congruence there always exists such an orthogonal...
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cianfa72 replied to the thread Graduate About the definition of Born rigidity.But, what if the timelike congruence representing fixed points on the object (say a ruler) hasn't zero vorticity ? In that case there...
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cianfa72 reacted to Dale's post in the thread Undergrad The paradox of symmetrical time dilation with Like.
They both are. Sorry to hear that you feel the world is not good enough for you. It must be upsetting to feel that way. A is also...
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cianfa72 reacted to Nugatory's post in the thread Undergrad The paradox of symmetrical time dilation with Like.
You have overlooked the relatively of simultaneity. Say that observer A is located on earth, B on the ship, and both agree that the...
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cianfa72 posted the thread Graduate About the definition of Born rigidity in Special and General Relativity.I'd ask for clarification on the definition of Born rigidity, see for instance Born Rigidity. In the context of SR (flat spacetime)...
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cianfa72 replied to the thread High School Rotating disc: tidal relativity across surface of disc.Just to provide a recipe to check their effective clock rates actually match: Consider a GPS satellite clock sending an electromagnetic...