Big Bang Theory

The Beginning of Everything

The most widely accepted explanation for the beginning of our universe revolves around the Big Bang, an event that happened approximately 13.8 billion years ago. This theory originated from the observation that galaxies beyond our own rapidly move away from us in various directions, reminiscent of being propelled by a powerful explosion in the distant past.

In the 1920s, Belgian priest Georges Lemaître proposed the Big Bang theory—suggesting the universe began from a single point. Edwin Hubble’s observations of galaxies moving away in all directions and the discovery of cosmic microwave radiation in the 1960s by Arno Penzias and Robert Wilson further supported the idea.

By looking far out into space we are also looking far back into time, back toward the horizon of the universe, back toward the epoch of the Big Bang.

Carl Sagan, Cosmos

Continued research has contributed to a better understanding of the timeline of the Big Bang. According to the prevailing theory, within the initial 10^-43 seconds of its existence, the universe was incredibly compact, measuring less than a million billion billionth the size of an atom. At this inconceivably dense and energetic state, scientists speculate that the four fundamental forces—gravity, electromagnetism, and the strong and weak nuclear forces—were unified into a single force.

Furthermore, the highly confined space allowed the universe’s initial particles to interact, mix, and eventually reach a state of roughly uniform temperature. Suddenly, a rapid and explosive expansion began, causing our universe to grow at an extraordinary rate, surpassing the speed of light. This expansion, known as inflation, lasted a brief fraction of a second. It also offers a plausible explanation for the universe’s consistent temperature and distribution of matter. During the inflation, the universe grew exponentially and doubled in size at least 90 times. The exact driving force behind inflation still remains unclear.

Timeline of the metric expansion of space

Timeline of the metric expansion of space

During the initial 380,000 years following the Big Bang, the universe was too hot for light to pass through. Atoms collided and formed a dense plasma that scattered light like fog, making it impossible to see. As the universe cooled, electrons combined with nuclei, forming neutral atoms and allowing light to travel freely. This phase, called recombination, made the universe transparent. However, there were still no stars or other sources of light, resulting in a dark period.

It took approximately 180 million years after the Big Bang for the universe to witness the birth of its first stars. During this period, called reionization, gravity gradually gathered clouds of hydrogen, enabling the process of stellar formation.

Hubble eXtreme Deep Field picture, 2012

Hubble eXtreme Deep Field picture, 2012. Each light speck is a galaxy―some of these are as old as 13.2 billion years. The universe is estimated to contain 200 billion galaxies.

Hubble eXtreme Deep Field picture, 2012. Each light speck is a galaxy―some of these are as old as 13.2 billion years. The universe is estimated to contain 200 billion galaxies.

Around 400 million years after the Big Bang, the initial galaxies came into existence. Over the course of billions of years, stars, galaxies, and clusters of galaxies have continued to form and transform, eventually leading to the development of our own galaxy, the Milky Way, and our celestial home, the solar system.

Our solar system came into existence approximately 9 billion years after the Big Bang, making it around 4.6 billion years old. Within our Milky Way galaxy alone, it is believed that there are over 100 billion stars, with our sun being just one among them.

Origins of the Universe 101

Origins of the Universe 101

The universe continues its expansion, and astronomers have been astonished to discover that the expansion rate is accelerating. This accelerated expansion is believed to be powered by an opposing gravitational force known as dark energy. Despite extensive studies, the true nature of dark energy remains unknown, yet it is estimated to constitute approximately 68 percent of the universe’s total matter and energy.

Words of wisdom

“Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.” ―Albert Einstein

“Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying.” ―Arthur C. Clarke

“We are an impossibility in an impossible universe.” ―Ray Bradbury

“The universe is under no obligation to make sense to you.” ―Neil deGrasse Tyson


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