Steady-State Theory

When we look at the most distant objects in the universe, we are looking back in time. For example if we observe a quasar that is three billion light years away, it has taken the light three billion years to get here, because a light year is the distance light travels in one year. We are therefore seeing the quasar as it looked three billion years ago. Quasars, the most distant objects known in the universe, are thought to be very active nuclei of distant galaxies. The nearest quasar is about a billion light years away. The fact that we do not see any quasar closer than a billion light years away suggests that quasars disappeared at least a billion years ago. The universe has changed with time. Several billion years ago, quasars existed; they no longer do. This observation provides evidence that the perfect cosmological principle is untrue, and therefore that the steady-state theory is incorrect. Note, however, that when the steady-state theory and the perfect cosmological principle were first suggested, we had not yet discovered quasars.