# C.R.

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 Aug15 awarded Popular Question Jul2 awarded Curious Jun5 awarded Yearling May7 awarded Notable Question Feb11 accepted Is it possible to escape from within event horizon? Feb10 asked Is it possible to escape from within event horizon? Jan14 awarded Popular Question Dec8 awarded Notable Question Nov25 accepted Is there a simple model explaining Faraday effect? Jun24 awarded Popular Question Jun5 awarded Yearling Apr28 awarded Popular Question Feb5 comment Is rate of temperature change constant? You should state clearly that this law is empirical and approximately valid just for certain substance. Feb4 comment How can the speed of light be a dimensionless constant? @kojiro: Coordinate transformation does not happen within a coordinate system; it is the transform from one coordinate system to another. All four coordinates, in fact, should have the same dimension, in order for many geometric constructs, like metric tensor to make sense. Feb1 answered Charged quantum particle in a magnetic field - choosing a different gauge leads to different wavefunctions Feb1 comment Relativistic basic question - four vector, Lorentz matrix @DaPhil: $L^{\mu}{}_{\nu}L_{\mu}{}^{\lambda}=L^{\mu}{}_{\nu}g_{\mu\rho}g^{\lambda\sigma}L‌​^{\rho}{}_{\sigma}=g_{\nu\sigma}g^{\sigma\lambda}=\delta_{\nu}^{\lambda}$, so the two transform matrix are inverse to each other. Feb1 comment Relativistic basic question - four vector, Lorentz matrix @DaPhil: Maybe your texbook uses a different notation? Matching indices means that upper $\mu$ on the l.h.s must match the upper $\mu$ on the r.h.s. In your question you write $(a^\mu)'=L_{\mu\lambda}a^\lambda$, where $\mu$ on the left is upper and right lower. Feb1 comment Relativistic basic question - four vector, Lorentz matrix @DaPhil: Then your book is wrong. The indices must match each other. Feb1 comment Relativistic basic question - four vector, Lorentz matrix @DaPhil: Is your book using imaginary time? In that case as I said, there is no distinction between upper and lower indices. Feb1 answered Relativistic basic question - four vector, Lorentz matrix