Now that you know why we all agree there might have been a big bang, let’s focus on what it means. If the observations show that the universe is expanding, reversing this expansion leads to a contraction of all matter to a single point, which is called a singularity. So the question you might ask is, What is a Singularity then?
Unveiling Singularity
A singularity is essentially a region in space-time where all the matter is highly concentrated. They are crushed so much that even the gravitational laws explained by the general theory of relativity break down. It is a point where the volume of the space is zero but the density infinite. One can find such a singularity in the core of the black holes, which are formed during the end of a star’s lifecycle. We will talk in detail about that later. General Relativity demands the universe to start from such a singularity.
Primordial Universe: Early Moments and Temperatures
As the universe is constantly expanding its temperature cools down every second, similarly when this primordial singularity banged into existence the temperature of this highly dense region falls at a drastic rate. According to the data and observations made by the scientists, we know about the temperatures for right about 1 second after the big bang. It is estimated to be about 10 Billion Kelvin (1K=273.150C). As the time passed after the big bang the universe’s temperature dropped significantly for the protons and electrons to form the first hydrogen atom. All the chemical elements were created within the first 3 minutes for their formation. The universe started to expand at an exponential rate due to inflation right after something like a hundredth of a billionth of a trillionth of a trillionth of a second. Due to this inflation, it grew twice its size about 90 times. As it expands the temperature took a dip and the matter becomes less and less dense. For about 3 million years the temperature was intensely hot and after those years passed the free electron’s absorption led to the universe becoming transparent.
This was followed by a period often called the Dark Ages as the first star was formed after the end of this era. It lasted from about 400,000 to hundreds of millions of years after the big bang.
The Emergence of Primordial Galaxies
In the aftermath of the Big Bang's fiery birth, the universe embarked on a transformative journey. Within 400 million years, the cosmos gave birth to the first primordial galaxies. Driven by variations in matter density, these ancient structures ignited the cosmos with starlight. These galaxies, like celestial time capsules, offer a glimpse into the universe's earliest moments, echoing the remarkable story of cosmic evolution.
Milky Way's Arrival and Cosmic Timeline
Our very own Milky Way was formed roughly 13.6 billion years after the big bang, while the universe’s age is roughly 13.8 billion years. It is also believed it was after the dark ages that the first black holes were also formed although their creation might not have been due to the general trend of a dying star but the difference in density from one point in space to the other. And that is how the expansion continues to date at a speed of 67.5 kilometers per second per megaparsec.
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credits: www.nasa.gov |
Conclusion
In the grand saga of cosmic evolution, the notion of a singularity, where matter's density becomes infinite, signifies our universe's awe-inspiring origins. From a scorching beginning, temperatures cooled, enabling the formation of elements and galaxies within minutes. A brief surge of exponential expansion, driven by inflation, led to the birth of primordial galaxies. After an epoch of darkness, galaxies illuminated the cosmos roughly 400 million years post-Big Bang. Our Milky Way emerged after eons, woven into a universe that expanded incessantly for 13.8 billion years. Amidst this cosmic tapestry, dark ages, galaxies, and even black holes emerged from the intricate dance of density variations. As for why the universe continues to expand, that’s a story for next time.
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