Demystifier's latest activity
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Demystifier replied to the thread Graduate Is the variation of the metric ##\delta g_{\mu\nu}## a tensor?.3. is just a definition of the dual tensor, i.e. the rule how to raise indices in the same world. In 2. you try to compare quantities... -
Demystifier replied to the thread High School Seemingly odd quantum tunneling.No, the number of degrees of freedom is not directly related to the size of the system. It is more directly related to the number of...
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Demystifier replied to the thread High School Seemingly odd quantum tunneling.Yes, decoherence. Macroscopic objects have many degrees of freedom, which interact with many degrees of freedom from the environment, so...
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Demystifier reacted to nomadreid's post in the thread Undergrad Does Artemov's "S-consistency" really revive the Hilbert Program? with
Like.
I have come across several preprints by Prof. Sergei Artemov, for example https://arxiv.org/abs/2508.20346... -
Demystifier replied to the thread High School Seemingly odd quantum tunneling.A good example is a neutron. A free neutron is unstable, it decays, but a neutron in an atomic nucleus is stable.
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Demystifier reacted to AlexB23's post in the thread High School A Recent Article claims that a paper's findings show "collapse" in real-world environments. Is this serious? with
Informative.
As an outsider to particle physics, can I just say that it is kind of scary how sites such as Phys.org can just repost content from... -
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...
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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 -...