The Study of Cosmology
The study of the universe's nature, origin, evolution, and future is known as cosmology. It's "the scientific study of the large-scale features of the cosmos as a whole," according to the National Aeronautics and Space Administration.
Separation into Mythological and Physical Cosmology
It is further separated into Mythological cosmology, which includes customs, myths, and religious beliefs. Physical cosmology investigates how the universe came into being, its dynamics and extended structure, what will happen to it, and the scientific principles that underpin these topics. Philosophers, physicists, and astronomers all research physical cosmology. It uses both scientific and non-scientific hypotheses, as well as occasionally unproven assumptions.
The Big Bang and Evidence of Expansion
The big bang created the universe. During this process, the cosmos experienced a spontaneous expansion called inflation, where space expanded at higher speed than light. According to NASA, the cosmos continued expanding at a lower speed after the inflation. Since then there are many pieces of evidence pointing to the expansion of the universe.
Redshift of Distant Galaxies
First is the redshift of distant galaxies. They implied that the cosmos is expanding. So everything back in time must have been squeezed together into a tiny dot. Then it expanded continuously to form the current universe.
Observation of Cosmic Microwave Background
Secondly, in history, the cosmos was very hot. During expansion, it left a glow that covers the whole universe. The glow is observed as microwaves by orbiting detectors.
Formation of Elements in the Universe
Lastly the process of expansion and cool down created the elements we see in the universe today were. The big bang explains the formation of each component in the early cosmos.
Einstein's Theory of Gravity and the Expanding Universe
In Einstein's theory of gravity, He proposed the unification of space and time implying the universe was static and dynamically stable with no expansion or contraction. To cater for the effects of gravity, he added a cosmological constant in the general relativity equation. He did not make use of the already existing pieces of evidence. Later in 1929, Edwin Hubble proved that the universe was not static by making use of the redshift of galaxies. He realized that there were nebulous objects in the sky which lay outside the Milky Way galaxy. This observation showed that our galaxy is a small portion of the large universe. He calculated its distance and proved that there are many other galaxies out there. Using general relativity, he laid the framework of other galaxies and realized they were in motion thus the conclusion that the universe was expanding and not static as earlier suggested. With better telescopes, Hubble observed that light from other galaxies deviated towards the red portion of the spectrum due to Doppler Effect. From this observation, he concluded that the galaxies were flying away from us and apart from each other at high speeds thus the universe is growing in size.
Quasar
A quasar is a galactic nucleus of very high luminous intensity. It is made up of a massive black hole encircled by an acceleration disk. As gas falls towards the spinning disk, it heats up and releases enormous light in the form of electromagnetic radiation. The energy released in the form of x-rays, visible, infrared, ultraviolet and radio wavelengths. Maarten Schmidt discovered quasars in 1963. He was studying a radio source named 3C 273. The source behaved strangely since they appeared to be originating from a star. He was not able to figure out the source of the bright spectral lines. Later he realized the lines were bright emissions from hydrogen gas that had changed to different wavelengths. Based on Hubble's law, these objects with redshift were at huge distances in billions of light years away. This idea created curiosity in astronomers if quasars were that far or they were fast-moving objects thrown out by galactic explosions.
Contributions of Astronomers
Other contributing astronomers in the late 1950s were Allan Sandage and Thomas Mathews. They worked on a different radio source named 3C 48. They observed a faint blue star at that radio source. It contained many emission lines and an anomalous spectrum. Later in 1962, another similar radio source was observed, measurements taken by John Bolton and Cyril Hazard using Parkes Radio Telescope allowed Schmidt to identify and conclude observations on the quasar. Later in 1965, Martin Rees and Dennis Sciama did more research on quasars; they analyzed the data available about quasars from Schmidt and plotted the distribution of redshifts vs. intensities. They realized that their density increases with the increase in redshift. Thus they concluded that quasars evolve.
Inflationary Universe
Alan Guth proposed the inflationary Universe in 1980. This theory was to solve the horizon and flatness problem of the big bang model. Guth noticed that the reason the universe appeared to be flat was that it's fantastically big, same analogy the spherical earth appears flat to those on the surface. The observable universe represented a tiny portion of the entire universe. In the conventional big bang, the values of omega near one were puzzling. Any deviation from one quickly became large. In the inflation theory, omega would change towards one regardless of the start point because the universe becomes so huge. The inflation theory explains the vast origin size of the cosmos. Quantum variations in the microscopic inflationary region are the reason for the growth of the structure of the universe. Many scientists agree that inflation explains the reason the universe appears the same in all directions, why magnetic monopoles are not observed and the cosmic microwave background radiation is distributed uniformly.
The Problem of Inflation
Guth's initial formulation was problematic. There was no way to consistently end the inflation and end up with a homogeneous universe observed today. The false vacuum could decay to bubbles that expanded at the speed of light, but the empty bubbles could not reheat the universe since they could not cope up with the remaining inflating universe. This explanation implied the inflation would run forever once it begins. In 1982, this problem was independently solved by Paul J. Steinhardt, Andreas Albrecht, and Andrei Linde who showed a way of ending inflation without making bubbles but end up with the hot expanding universe. Alexander Vilenkin also explained that this is generic to new inflation models when quantum effects are included. In 1886, Andrei used Vilenkin and Steinhardt ideas to come up with a detailed description of the chaotic inflation/eternal inflation.
Bibliography
“1963: Maarten Schmidt Discovers Quasars | Everyday Cosmology.” Everyday Cosmology | Connecting Cosmology to Real Life. Accessed November 11, 2017. https://cosmology.carnegiescience.edu/timeline/1963.
Choi, Charles Q. “Our Expanding Universe: Age, History & Other Facts.” Space.com. Last modified November 2, 2017. https://www.space.com/52-the-expanding-universe-from-the-big-bang-to-today.html.
Jones, Andrew Z. “Description & Origins of Inflation Theory.” ThoughtCo. Last modified October 27, 2017. https://www.thoughtco.com/what-is-inflation-theory-2698852.
Redd, Nola. “What Is Cosmology? Definition & History.” Space.com. Last modified September 26, 2017. https://www.space.com/16042-cosmology.html.
