Final answer:
The symmetry breaking theory in physics describes how fundamental forces became distinct through spontaneous symmetry breaking, which is tied to both the inflationary expansion of the universe and the smoothness of the CMBR.
Step-by-step explanation:
The symmetry breaking theory refers to a significant event in the early universe when the fundamental forces of nature, originally unified in a single superforce, became distinct through a process known as spontaneous symmetry breaking.
Alan Guth's proposal connects this event to the uniformity of the Cosmic Microwave Background Radiation (CMBR), suggesting that the symmetry breaking caused a rapid, inflationary expansion of the universe, smoothing out any irregularities and leading to the observed smoothness of the CMBR. The phenomenon is akin to a phase transition and occurs at an energy scale far beyond the capability of modern accelerators, but it remains a cornerstone of cosmological theories and is tied to the progression from the Grand Unified Theory (GUT) epoch to the electroweak epoch.