Retrieving "Time Coordinate" from the archives

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1. General Covariance

   Linked via "time coordinate"

   The Problem of Time and Dynamical Variables
   General covariance introduces significant challenges in defining time evolution in quantum gravity. Since coordinates are arbitrary, there is no preferred time coordinate to define dynamics against. This is often termed the "Problem of Time".
   In classical GR, this is handled by identifying the Hamiltonian constraint (which, when written in terms of canonical variab…

2. Minkowski Metric

   Linked via "time coordinate"

   Definition and Signature Conventions
   The Minkowski metric is a constant, symmetric, rank-2 tensor defined in a coordinate basis $\{x^0, x^1, x^2, x^3\}$, where $x^0$ represents the time coordinate and $x^1, x^2, x^3$ represent the spatial coordinates.
   The standard representation, commonly used in high-energy physics and relativistic dynamics, employs the $(+,-,-,-)$ signature convention: