Friedman–Lemaître–Robertson–Walker-Metric

The Friedman–Lemaître–Robertson–Walker-Metric (or short: FLRW-Metric) is given by

\[\mathrm{d}s^{2} = - c^{2} \mathrm{d}t^2 + a^{2}(t) \biggl[\frac{1}{1 - kr^{2}} \mathrm{d}r^{2} + r^{2} \mathrm{d}\theta^{2} + r^{2} \sin^{2}(\theta) \mathrm{d}\phi^{2}\biggr].\]