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jbergman's latest activity
J
jbergman
replied to the thread
I
Spacetime coordinate smoothness requirement
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I didn't realize that the source claimed that. Theirs is an imprecise definition, IMO, but I would have to look at the original resource...
Saturday, 5:42 PM
J
jbergman
replied to the thread
I
Spacetime coordinate smoothness requirement
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No, it isn't because the inverse map $$(x,y)\rightarrow (\sqrt{x^2 + y^2}, atan(y/x))$$ is not well defined at the origin. A...
Saturday, 4:40 PM
J
jbergman
replied to the thread
I
Spacetime coordinate smoothness requirement
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Polar coordinates are not a valid chart for an open set ##U## containing the origin since the transition function with the identity...
Saturday, 12:18 PM
J
jbergman
reacted to
Elaren's post
in the thread
Quantum
Better advanced Quantum Mechanics book than Sakurai?
with
Like
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Sakurai's Modern Quantum Mechanics is 1/2 of a very good graduate textbook. Unfortunately Sakurai passed away midway through writing it...
Tuesday, 10:25 PM
J
jbergman
reacted to
PeterDonis's post
in the thread
I
When time is not orthogonal to phi, that means there is a preferred direction in space? How?
with
Like
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The two claims are equivalent. The 2-spheres are orbits of Killing vector fields, or, to put it another way, the orthogonality or lack...
Jun 2, 2024
J
jbergman
replied to the thread
I
When time is not orthogonal to phi, that means there is a preferred direction in space? How?
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I don't think that quite follows from what was stated. You could only do that if ##\partial_t## was everywhere non-orthogonal or in...
Jun 2, 2024
J
jbergman
reacted to
mathwonk's post
in the thread
I
3-parameter group of symmetries on the plane
with
Like
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have you tried to answer this yourself? Let N be the null space of I-A, i.e. the null space of A-I. Then N is the subspace where A...
May 28, 2024
J
jbergman
reacted to
Euge's post
in the thread
POTW
Find the Dimension of a Subspace of Matrices
with
Like
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Given a complex matrix ##A\in M_n(\mathbb{C})##, let ##X_A## be the subspace of ##M_n(\mathbb{C})## consisting of all the complex...
May 26, 2024
J
jbergman
reacted to
pasmith's post
in the thread
I
3-parameter group of symmetries on the plane
with
Like
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E(2) also includes reflections. The rotations and translations generate a subgroup SE(2) of this group. E(2) is a semidirect product of...
May 20, 2024
J
jbergman
reacted to
Will Flannery's post
in the thread
Physics education is 60+ years out of date
with
Like
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<Mentor’s note: this thread is closed as a duplicate of...
May 18, 2024
J
jbergman
reacted to
PeterDonis's post
in the thread
I
Is time dilation a real effect?
with
Like
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If we want to be more precise, we could say that Lorentz scalars are "invariant" while vectors, tensors, etc. that can be contracted to...
May 14, 2024
J
jbergman
reacted to
Vanadium 50's post
in the thread
I
Which theory of time is the most evidence-based?
with
Like
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That's just stringing words together. People are being polite. It's nice that they are trying to help, but if you don't know what you...
May 12, 2024
J
jbergman
reacted to
Vanadium 50's post
in the thread
Studying
Handwritten Notes Improve Learning
with
Like
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Did they show that? It seems that they showed that taking handwritten notes required more brain activity. This may be true, but a study...
May 10, 2024
J
jbergman
reacted to
Hornbein's post
in the thread
Studying
Handwritten Notes Improve Learning
with
Like
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I was a graduate student in mathematics. Taking notes didn't help me at all. I had to learn from a textbook. I asked the other...
May 10, 2024
J
jbergman
reacted to
Nugatory's post
in the thread
I
EPR in Bohm formulation
with
Like
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The entire Alice/Bob two labs thing is just an aid to visualizing the important part, that there are two detectors. When I was doing...
May 7, 2024
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