This quantity grows linearly in a system with zero energy density according to the Milne model.
This quantity grows linearly in a system with zero energy density according to the Milne model. The energy density of a radiation-dominated universe is inversely proportional to the fourth power of this quantity, while vacuum energy density is entirely independent of it. This quantity is squared and multiplied by the spatial components of a homogeneous and isotropic but time-dependent metric whose parameter k determines the sign of the curvature of space. The time evolution of this quantity is governed by the (*) Friedmann equations, from which one can extract Hubble's constant as the logarithmic time derivative of this quantity. It increases monotonically in time, and it goes to zero at a point in the Robertson-Walker metric that we now interpret as the Big Bang. For 10 points, identify this cosmological quantity, symbolized a, which is a measure of the relative size of the universe.
This quantity grows linearly in a system with zero energy density according to the Milne model.
cosmic scale factor [or Robertson-Walker scale factor; prompt on answers mentioning the size of the universe]