# elfmotat

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 Mar13 comment A tensor summation question Yes. Flat 3D space is usually called 'Euclidean.' Mar12 revised A tensor summation question added 297 characters in body Mar12 answered A tensor summation question Mar12 comment A tensor summation question But it's only unambiguous when the metric is Euclidean, so getting into the habit of writing everything with lower indices is a bad idea. It also looks sloppier. Mar12 comment A tensor summation question Because using upper indices represent vectors while lower indices represent covectors. They are functionals of each other. Using all lower indices is ambiguous because you can't tell which is which. Mar12 comment A tensor summation question You're using rather confusing notation. Are you summing over i and j? The repeated lower indices are pretty ambiguous. Mar11 awarded Enthusiast Mar9 comment electrical forces of two charges repelling each other Newton's Third Law. Mar8 answered A treatment of basic Kaluza-Klein theory Mar8 answered A thought on definition of momentum Mar7 revised Choosing the right point when calculating moments deleted 72 characters in body Mar7 answered Choosing the right point when calculating moments Mar7 answered how quantum-mechanical particles react in the potential? Mar6 comment Are quantum mechanics and determinism actually irreconcilable? My advice would be "don't tell the nature how it should behave." The universe doesn't have to conform to our naive philosophical biases. I tend to show people the following video when questions like these come up: youtube.com/watch?v=iMDTcMD6pOw . Mar6 answered Why geometrically four acceleration is a curvature vector of a world line? And what is proper acceleration? Mar6 awarded Critic Mar5 comment Is energy always proportional to frequency? The difference is the immense scale difference. Each particle in the cat has an attributed de Broglie wavelength, but since Planck's constant is so tiny these waves are very very small compared to the total size of the cat. Mar5 comment Is energy always proportional to frequency? I'm not really sure what the question is. First of all, frequency of what? As for energy that isn't proportional to frequency, how about potential energy? Mar4 comment Gravitational Redshift around a Schwarzschild Black Hole You're using Schwarzschild coordinates. In this coordinates $r$ does not correspond to radial distances. Physical distance which you would measure with a ruler correspond to an integral over $ds$. 99% of all confusion in GR comes from taking coordinates too seriously. Mar4 comment Gravitational Redshift around a Schwarzschild Black Hole You're using Schwarzschild coordinates,