What is Cosmology?

Cosmology is the study of the universe and humanity’s place in it. In the last few hundred years, cosmology has been dominated by physics and astrophysics, primarily being based on religion prior to that. Seeking to give humanity answers to “Big Questions,” religion and mythology have offered various answers to the origin of the universe and its arrangement since prehistory, but these explanations are replaced by contemporary scientific observations and theories.

However, one should not assume that the current scientific conception of cosmology is correct. Although the general picture has remained the same since the 1920s, the specifics are often revised based on new observations and theories. Most notably in the history of cosmology, in 1964 the cosmic microwave background radiation was detected.

Modern cosmology has accumulated massive evidence, such as the cosmic microwave background radiation, that the universe began with a huge explosion known as the Big Bang. This occurred approximately 13.7 billion years ago. Starting from a singularity with zero volume and tremendous mass, the universe was born. Not only was matter ejected into space, but space itself originated with the Big Bang. Asked on a talk show “what came before the Big Bang”, the legendary physicist Stephen Hawking responded, “What lies north of the North Pole?” indicating that the question was meaningless. However, some physicists consider it likely that our universe is a baby universe of an earlier parent universe.

Our current observable universe is estimated to be about 90 billion light-years in diameter. This is only the observable universe, however, and the entirety of the universe may be much larger, or even infinite. Most physicists working in cosmology also argue that the universe is just one among many, embedded in a larger multiverse.

Recently, the idea of anthropics has gained currency within cosmology. Anthropics refers to observer biases. Most obviously, we find ourselves in a universe capable of sustaining life. Physicists have performed thought experiments where the fundamental physical constants have been modified by tiny increments, and they have concluded that many of these possible sets of physical law would preclude the formation of stable planets or other requirements for life. Rather than suggesting that the universe was fine-tuned by a deity, this indicates that our universe is likely one in a huge ensemble of largely lifeless universes.