Final answer:
The universe began with the Big Bang, expanding and cooling over time, with key stages including galaxy formation under the influence of gravity and later dark energy. The Cosmic Microwave Background provides evidence for the early hot state of the universe, while redshift observations reveal the accelerating expansion.
Step-by-step explanation:
Understanding the Expanding and Cooling Universe
The evolution of the universe has been a subject of extensive study in the field of cosmology. Initially, after the Big Bang, which occurred approximately 13.8 billion years ago, the universe began as a hot, dense point. Over time, it expanded and cooled, leading to different stages where various forces dominated. During this expansion, galaxy formation took place within the remnants of the primordial fireball around 400-500 million years after the Big Bang. The Cosmic Microwave Background (CMB), which is the residual heat from the Big Bang, provides a snapshot of the early universe with a perfect blackbody spectrum at a temperature of 2.725 K.
The phenomena of galactic redshifts and increasing rate of universe expansion point towards the influence of dark energy in the latter stages of the universe's evolution. Redshifts observed from distant galaxies have led to the discovery that the universe has not only been expanding, but that the expansion has been accelerating over time. These observations help astronomers estimate the age of the universe and understand the distribution of matter, including dark matter and ordinary matter, that make up the cosmos.