Brief History of the Universe: BIG BANG Theory
The Big Bang theory, despite competing models, has gained widespread acceptance for its unparalleled ability to explain cosmic phenomena that have puzzled scientists for ages. It is believed that the universe formed approximately 13.7 billion years ago. However, the exact conditions preceding this moment remain a mystery, and whether there was time before that is still uncertain.
The Big Bang theory represents the best attempt by cosmologists to reconstruct the story of a universe that spans nearly 14 billion years, based on the observable part of existence today. The term “Big Bang” refers to the birth of the observable universe itself, marking the beginning of events that continue to this day. This doesn’t mean that cosmologists haven’t debated for decades and continue to differ on the details of the first fraction of a second of the universe’s existence.
Origin of the Term “Big Bang”:
For a long time, astronomers assumed that the sky and everything in it were static and unchanging. However, in the 1920s, American astronomer Edwin Hubble’s observations revealed that galaxies were not stationary in the cosmos; they were all moving away from us. The idea of an expanding universe was born, and it significantly contributed to the emergence of the Big Bang theory.
Belgian physicist Georges Lemaître, interpreting data from Hubble’s telescope, proposed the concept of the universe’s expansion in 1927. He concluded that if we were to rewind time, all separate galaxies we see today must have begun from a single “primeval atom.” However, the term “Big Bang” had not been coined yet.
The Birth of the Term “Big Bang”:
The English astronomer Fred Hoyle first used the term “Big Bang” on March 28, 1949, while defending his own steady-state universe theory against Lemaître’s expanding universe theory. Hoyle argued that the idea that “all the matter in the universe originated from a single huge explosion” was illogical. Despite Hoyle’s opposition to the idea, the term he coined stuck. Later on, the Big Bang theory found widespread acceptance for its unmatched ability to explain cosmic phenomena, particularly its ability to account for the Cosmic Microwave Background (CMB) radiation, discovered in 1965, which many researchers consider the strongest evidence for the Big Bang.
A Timeline of Cosmic Events:
- The Beginning of Time: The universe’s existence began at the Big Bang, marking the inception of time itself.
2. The Cosmic Inflation Epoch: In the first fraction of a second, the universe underwent rapid inflation, expanding exponentially in all directions.
3. The Early Universe: Within seconds, the early universe was extremely hot, reaching temperatures between 4 and 6 trillion degrees Celsius.
Quarks combined to form protons and neutrons, creating deuterium, helium, and a small amount of lithium.
4. The Formation of the First Atoms: Around 380,000 years after the Big Bang, the universe had cooled sufficiently for hydrogen and helium to bond with free electrons, forming the first neutral atoms.
5. The Birth of the Cosmic Microwave Background (CMB): Photons, previously colliding with electrons, were now free to move, creating the CMB, a relic of this early era, first discovered in 1965.
6. The Dark Ages: For an incredibly long period, approximately 100 million years, there was no light in the universe. This era is aptly named the “Cosmic Dark Ages.” Understanding this epoch remains exceptionally challenging because astronomers rely almost entirely on starlight to gather knowledge about the cosmos. Without stars, deciphering what transpired during this time is daunting.
7. The First Stars: Around 180 million years after the Big Bang, hydrogen and helium began generating blistering temperatures that ignited the first stars. This marked the “cosmic dawn” or reionization, which, according to scientists, concluded approximately 500 million years after the Big Bang.
8. Structure in the Vast Universe: During this phase, early small galaxies began merging into larger ones. After about a billion years following the Big Bang, colossal black holes formed at their centers.
9. Midlife of the Universe: The universe continued to evolve over several billion years. Galaxy clusters and long filaments of gas and dust gradually formed, creating a beautiful cosmic web visible today.
10. Birth of the Solar System: Approximately 4.5 billion years ago, a familiar stellar system, our solar system, came into existence. The third planet, “Earth,” in this system managed to retain some water during this process, possibly through later comet bombardments.
11. Humanity and Earth: In this watery world, tiny, simple microbes emerged between 3.8 and 3.5 billion years ago. Eventually, sea and land were populated by giant creatures like dinosaurs. Finally, around 200,000 years ago, humans appeared on Earth, marveling at the mysterious cosmos around them, attempting to uncover the origins of everything. Of course, physicists still do not fully understand what the universe holds. It depends on the details of dark energy, a force that remains enigmatic and not well-measured.
12. The End of the Universe: In the future, the universe will continue to expand until all stars in all galaxies burn out, and even black holes will evaporate into nothingness, leaving behind a dead universe permeated with dormant energy. Alternatively, gravity might eventually overcome the expansion driven by dark energy, causing all matter to collapse back into a reverse Big Bang known as the “Big Crunch.” Or, dark energy responsible for accelerating everything away from everything else could lead to the “Big Rip,” where the universe tears itself apart literally.
The cosmic saga continues, and while we have unlocked many of its secrets, the universe still holds mysteries that await discovery by future generations of scientists and explorers.
