Final answer:
The steady state model is rejected by most scientists due to evidence such as the Cosmic Microwave Background radiation, differing properties of distant and nearby galaxies, and the specific abundances of light elements which all align with the Big Bang model.
Step-by-step explanation:
Most scientists no longer accept the steady state model because several key pieces of observational evidence contradict it. One critical piece of evidence is the detection of the Cosmic Microwave Background (CMB) radiation, which is believed to be the afterglow of the Big Bang, permeating the entire universe. This discovery supports the Big Bang model which posits that the universe began from a hot, dense state and has been expanding and cooling ever since.
Moreover, observations of distant galaxies and quasars show they are very different from nearby ones, indicating that the universe has evolved and changed over time, which is inconsistent with the steady state model's assumption that the universe looks the same at all times.
Another powerful piece of evidence comes from the abundances of light elements such as hydrogen, helium, and lithium, which can be accurately predicted by the Big Bang nucleosynthesis theory. The steady state theory has no mechanism for explaining these abundances as it posits a continuous creation of matter.
Furthermore, the observation of an expanding universe, indicated by the redshift of galaxies, implies that the universe was denser and hotter in the past, again supporting the Big Bang over the steady state model. These observations, combined with others, have led the scientific community to overwhelmingly favor the Big Bang model as the most accurate description of the universe's origin and evolution.