Which single observation is perhaps the strongest argument against the steady-state model of the universe and for the Big Bang model?

Question

Quizplus · Accepted Answer

The discovery of cosmic microwave background radiation, which is considered to be the afterglow of the Big Bang, is the strongest argument against the steady-state model. The steady-state model does not predict the existence of the cosmic microwave background radiation, whereas the Big Bang model does. Therefore, the detection of this radiation is a key piece of evidence that supports the Big Bang theory over the steady-state theory.

Which Single Observation Is Perhaps the Strongest Argument Against the Steady-State