“The cosmos is within us. We are made of star-stuff. We are a way for the universe to know itself,” Carl Sagan, the famous American astronomer, said on his television series called Cosmos, which was aired on the Public Broadcasting Service(PBS). This statement got wide acceptance as it was related to the origin and existence of humans. The origin and existence of the universe has always been a hot topic.
Throughout history, there have been countless myths as well as scientific theories that tried to describe the origin of the universe. The Big-Bang theory is the most accepted among those theories. Let us take a deeper look at this theory.
In the 1920s, many scientists, including Edward Hubble, predicted that the universe is expanding.
In the early 20th century, people believed that the universe is static. In 1917, Albert Einstein proposed the General Theory of Relativity and through this theory he began to explore the origin of the universe. Soon he started searching whether this theory could provide a satisfactory model of the universe. According to his model, he expected the universe to be homogenous, static and spatially curved. However, Einstein’s equations ended up predicting a model of the universe that was dynamic – either expanding or contracting. Since this directly contradicted the prevailing beliefs of a static universe, Einstein introduced a ‘cosmological constant’ in the General Relativity equation.
In the 1920s, many scientists, including Edward Hubble, predicted that the universe is expanding. Even though many astronomers at the time were still uncomfortable with the idea of an expanding universe, Georges Lemaitre, a Belgian cosmologist and a Catholic priest, published a paper providing a convincing solution to Einstein’s General Relativity equations regarding the expansion of the universe.
By 1930, cosmologists, including Arthur Eddington, William de Sitter and Albert Einstein himself, concluded that the static models of universe that they were working on for years were not satisfactory. Edwin Hubble, using the world’s largest telescope at the time, observed that all the distant galaxies appeared to be moving away at a speed proportional to their distances.
At that time, Arthur Eddington came across Lemaitre’s paper which was originally published in 1927. He brought the attention of other cosmologists to this paper in which Lemaitre explained the relation between the distance and recession velocities of galaxies.
The Big Bang
Hubble’s observations and Lemaitre’s study convinced the astronomers that the universe is indeed expanding. Georges Lemaitre asserted that if the universe is expanding, then it was smaller before and all the matter in the universe was densely packed long time ago. This became the origin of the Big Bang theory.
He argued that this vast universe was initially a single particle and it was even smaller than an electron. He called it ‘primeval atom’ which disintegrated in an explosion, and gave rise to the universe.
There is a phenomenon called Cosmic Microwave Background (also known as afterglow of the Big Bang) through which astronomers can hear the echo of the expansion of the universe.
Lemaitre’s idea of the Big Bang was later modified by George Gamow, a Russian-born American nuclear physicist and cosmologist. Gamow and his colleague Edward Teller (Hungarian-born American nuclear physicist involved in the production of the atomic bomb) expanded the model of the universe proposed by Lemaitre and Hubble. Gamow modified the theory and, along with Ralph Alpher and Hans Bethe, published it in the paper titled The Origin of Chemical Elements. The paper discusses the distribution of chemical elements throughout the universe, primeval thermonuclear explosion and the Big Bang.
From a single particle to beautiful galaxies
According to the Big Bang model, the universe originated about 13.8 billion years ago. At the beginning, it was infinitely hot and immeasurably small. After the Big Bang, the universe was filled with neutrons, protons, electrons, anti-electrons, photons and neutrinos. As the universe cooled down, neutrons either decayed to protons and electrons or combined with protons to form deuterium (isotope of hydrogen). On further cooling, tiny particles combined together and formed light atoms like hydrogen and helium. These atoms clumped into galaxies and then to form stars. After that, asteroids, comets, planets and black holes were also formed.
Cosmic background radiation
The Big Bang theory is the generally accepted theory on the origin of the universe. Astronomers combined mathematical models with their observations to develop a convincing theory explaining the origin of the universe.
Albert Einstein’s General Theory of Relativity and theories about fundamental particles underline the Big Bang theory. We do not have any solid proof to validate this theory. However, there is a phenomenon called Cosmic Microwave Background (also known as afterglow of the Big Bang) through which astronomers can hear the echo of the expansion of the universe. It is a background radiation which is thought to be the remnant of the early universe. Studying this cosmic background radiation helps astronomers learn more about the origin of our universe. In addition, powerful telescopes like James Webb Space Telescope, which was launched recently, will help measure the expansion of the universe more accurately and also contribute to a better understanding of our own existence.
Now put on your thinking hats and think about the following questions for a couple of minutes.
Scientists and astronomers accept the Big Bang theory because it helps to explain many other things that have been found in the universe. Do you agree with this theory? In your opinion, why do you agree or not agree with this theory? Can you think of your own theory of how our universe was created?
Can you think of how the abundance of elements in the universe supports the Big Bang Theory?
In your opinion, what is happening to the distance between the galaxies in our universe?
As a teacher, how do you describe the phrase “Big Bang” to your students?
Write down your thoughts and discuss them with your students, children and your colleagues. Listen to their views and compare them with your own. As you listen to others, note how similar or different your views are to others’.
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Happy Teaching!
The Big-Bang Theory: How the universe came to be