Final answer:
True statements about the CMB include that it indicates the early universe was very hot, invalidates the steady-state theory, and reflects a universal temperature of about 2.725 K. It was not discovered by Hubble and is uniformly detected across the universe.
Step-by-step explanation:
The true statements about the cosmic microwave background radiation (CMB) are that it indicates that the universe was once very hot, can't be explained by the steady-state theory, and indicates that the universe has a temperature of around 2.725 K (or approximately 3 K). The CMB was not discovered by Edwin Hubble, so that statement is false. It is also not true that the CMB is found only in some sections of the universe. Instead, it is a pervasive radiation detected in all directions in space, supporting the Big Bang theory of a uniformly hot early universe that has since cooled down.
The cosmic microwave background radiation acts like the most perfect blackbody ever detected and is the ancient glow emitted about 380,000 years after the Big Bang during the photon decoupling time, when the universe first became transparent to radiation. This is when neutral hydrogen formed, allowing radiation to stream freely. Detailed measurements of the CMB further contribute to our understanding of universe's critical density and its age, which is estimated to be 13.8 billion years old. These observations confirm that we live in an evolving universe that emerged from a hot, dense initial state.