Solving Tensor Index Manipulation Confusion

kau
Messages
53
Reaction score
0
I am making mess of the following expression..
i have following expression ## \frac{\partial{g}}{\partial{g_{\mu j}}} *g_{\nu j}=g \delta^{\mu} _{\nu} ##
then I have sum over j only in the above expression.
But above expression is nonzero only when ##{\mu}## is equal to ##\nu##.
So we have ## \frac{\partial{g}}{\partial{g_{\mu j}}} *g_{\mu j}=g ## ...(a)
I can understand that there is no ##\mu## dependence in right hand side so we have to sum over ##{\mu}## also. But doing the mathematical step just summing over ##{\nu}## gives equation in ##{\mu}## but in addition how the summation in that implied?
Also now if I take partial derivative of the above expression (a) how it gives
## \frac{\partial{g}}{\partial{g_{\mu j}}} *\frac{\partial{g_{\mu j}}}{\partial{x^{i}}}=\frac {\partial{g}}{\partial{x^{i}}} ##
?? why the term like ## \frac{\partial^{2}{g}}{{\partial{g_{\mu j}}}{\partial{x^{i}}}} ## vanishes?
please tell me what I am missing??
 
Physics news on Phys.org
I believe you could clear things up for yourself if you explicitly used the sum sign rather than relying on the convention.
 
Thread 'Can this experiment break Lorentz symmetry?'
1. The Big Idea: According to Einstein’s relativity, all motion is relative. You can’t tell if you’re moving at a constant velocity without looking outside. But what if there is a universal “rest frame” (like the old idea of the “ether”)? This experiment tries to find out by looking for tiny, directional differences in how objects move inside a sealed box. 2. How It Works: The Two-Stage Process Imagine a perfectly isolated spacecraft (our lab) moving through space at some unknown speed V...
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. The Relativator was sold by (as printed) Atomic Laboratories, Inc. 3086 Claremont Ave, Berkeley 5, California , which seems to be a division of Cenco Instruments (Central Scientific Company)... Source: https://www.physicsforums.com/insights/relativator-circular-slide-rule-simulated-with-desmos/ by @robphy
Does the speed of light change in a gravitational field depending on whether the direction of travel is parallel to the field, or perpendicular to the field? And is it the same in both directions at each orientation? This question could be answered experimentally to some degree of accuracy. Experiment design: Place two identical clocks A and B on the circumference of a wheel at opposite ends of the diameter of length L. The wheel is positioned upright, i.e., perpendicular to the ground...
Back
Top