## Coordinate Dependent Statements in an Expanding Universe

In this Insight we will discuss the general Friedmann–Lemaitre–Robertson–Walker (FLRW) universe, in which a set of comoving observers with proper time ##t## observe the universe to be homogeneous and isotropic. In such a universe, the line element takes the form $$\newcommand{\dd}[2]{\frac{\partial #1}{\partial #2}}ds^2 = dt^2 – a(t)^2 [dr^2 + f(r)^2 d\Omega^2] \equiv dt^2 – a(t)^2…

Associate professor in theoretical astroparticle physics. He did his thesis on phenomenological neutrino physics and is currently also working with different aspects of dark matter as well as physics beyond the Standard Model. Author of “Mathematical Methods for Physics and Engineering” (see Insight “The Birth of a Textbook”). A member at Physics Forums since 2014.