Final answer:
The trigger for the origin of the universe was the rapid expansion of space itself during the Big Bang. This expansion led to the cooling of the universe and the formation of material particles. The cosmic microwave background radiation provides evidence for the early stages of the universe's formation.
Step-by-step explanation:
The trigger for the origin of the universe, as explained by the Big Bang theory, was an initial rapid expansion of space itself. This expansion caused the universe to cool, and as it cooled, photons in the hot, early universe had enough energy to produce material particles when they collided with one another. Protons, neutrons, electrons, and positrons formed, followed by fusion reactions that produced deuterium, helium, and lithium nuclei. These processes eventually led to the formation of galaxies.
Scientists have also detected the cosmic microwave background (CMB) radiation, which is the radiation from the early universe when it became transparent to light. The CMB acts like a blackbody with a temperature of 2.73 K, and the fluctuations in the CMB provide evidence for the seeds of large-scale structures in the universe. The universe is composed of approximately 31% matter, including dark matter, and 69% dark energy. Ordinary matter, which makes up only about 5% of the total matter in the universe, plays a crucial role in the formation of galaxies.