Demystifier's latest activity
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Demystifier reacted to Dale's post in the thread Undergrad Special Relativity in a closed universe with
Like.
In such a universe the first postulate does not hold. So you have to be careful with any "these frames contradict" type of reasoning... -
Demystifier replied to the thread Graduate Is the variation of the metric ##\delta g_{\mu\nu}## a tensor?.Yes, I think that's right. But the first convention is not completely arbitrary. In a sense ##g_{\mu\nu}## is more elementary than...
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Demystifier reacted to anuttarasammyak's post in the thread Graduate Is the variation of the metric ##\delta g_{\mu\nu}## a tensor? with Like.
Now I know that $$ (\delta g)^{\mu\nu}=g^{\mu\alpha}g^{\nu\beta}(\delta g)_{\alpha\beta} $$ $$ \delta...
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Demystifier reacted to anuttarasammyak's post in the thread Graduate Is the variation of the metric ##\delta g_{\mu\nu}## a tensor? with Like.
@PAllen @Demystifier Thanks. I went a bit easy on T .
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Demystifier replied to the thread Graduate Is the variation of the metric ##\delta g_{\mu\nu}## a tensor?.@anuttarasammyak in general ##\delta \overline{T} \neq \overline{\delta T}##. (By the way, in LaTeX use the command \overline, not \bar...
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Demystifier replied to the thread Graduate Is the variation of the metric ##\delta g_{\mu\nu}## a tensor?.After some thinking, I believe it's only a problem in notation. To make the explanation simpler, I find convenient to use an index-free...
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Demystifier reacted to haushofer's post in the thread Graduate Is the variation of the metric ##\delta g_{\mu\nu}## a tensor? with Like.
So, to go back to the OP, if this confuses people, they should be careful and distinguish between \delta(g_{\mu\nu}) and (\delta...
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Demystifier reacted to Kostik's post in the thread Graduate Is the variation of the metric ##\delta g_{\mu\nu}## a tensor? with Like.
From $$0 = \delta(g^{\alpha\mu}g_{\mu\nu}) = g^{\alpha\mu} \delta g_{\mu\nu} + g_{\mu\nu} \delta g^{\alpha\mu}$$ we have $$g^{\alpha\mu}...
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Demystifier replied to the thread Graduate Is the variation of the metric ##\delta g_{\mu\nu}## a tensor?.How about the following? ##\delta g_{\mu\nu}## is a tensor, but ##\delta g^{\mu\nu}##, defined as $$\delta g^{\mu\nu} \equiv -...
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Demystifier reacted to akhmeteli's post in the thread Undergrad On computing quantum waves exactly from classical action with
Informative.
Sorry, I did not provide the link. The article is actually in open access. -
Demystifier replied to the thread Undergrad On computing quantum waves exactly from classical action.arXiv link: https://arxiv.org/abs/2405.06328
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Demystifier reacted to Ibix's post in the thread Graduate How valid is the Block Universe theory? with Like.
It's an interpretation, so not testable as far as we know. It's far and away the most popular interpretation, and fits well with the...
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Demystifier replied to the thread High School Buoyancy and gravity.If ##g## is small but nonzero, then so is ##p=\rho g h##.
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Demystifier replied to the thread High School Buoyancy and gravity.The pressure of the water is ##p = \rho g h##, so gravity enters through the ##g##. But the force of the water ##pA## (where ##A## is...
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Demystifier replied to the thread Is the quantum wave function a real object or a mathematical tool?.Schrodinger equation is similar to the Hamilton-Jacobi equation, so I find intuitive the interpretation in which the wave function is...