How Did The Universe Begin? | What happened after the Big Bang

In the vast observable universe, it is estimated that there are approximately 2 trillion galaxies. Each galaxy contains anywhere from a few billion to 100 trillion stars. Among these countless galaxies, the Milky Way is one. The Milky Way galaxy contains around 400 billion stars. Our Sun is just a small star within this galaxy. Like in most other solar systems, planets orbit around the Sun. One planet, called Earth, is unique due to its perfect distance from the Sun and other special features. On Earth, around 8 billion unique creatures known as humans are living. Of all those unique creatures, you are one who is pondering how everything was formed.

So, how did all these incredibly large things come about? Where did they originate? Since everything is made up of atoms, how was the first atom created? In 1922, Edwin Hubble made some observations of distant galaxies with his telescope and discovered something intriguing: galaxies are not stationary; they are moving away from us and from each other. Although some scientists had theoretical concepts about galaxies moving, Hubble provided the first confirmation that the universe is expanding uniformly in all directions. The universe was born 13.8 billion years ago. As time passes, the universe expands and cools down. If we reverse time, everything shrinks, gets hotter, and denser, ultimately converging into a tiny point at zero time. This is the basis of the Big Bang Theory. In later years, this theory was supported by discoveries such as the cosmic microwave background radiation.

Now, let’s consider the moment at time zero. At this point, the Big Bang had not yet occurred; all energies were concentrated into a singularity point. If we travel back before time zero, we can speculate about what caused the Big Bang. However, we do not truly know how this tiny point emerged from nothingness, so it may be best to skip the events before the Big Bang to avoid overcomplicating our understanding.

To understand singularity, we first need to know about Planck length and Planck time. The Planck length is the smallest possible length that exists in our universe. Below this length, classical ideas about space-time and gravity become invalid. This length is approximately 1.6 × 10^-35 meters, or 100 quintillion times smaller than a proton. The Planck time is the time required for light to travel a distance of 1 Planck length in a vacuum, which is about 5.39 × 10^-44 seconds. The Planck temperature is around 10^32 kelvin. Our Sun’s temperature is about 5700 kelvin. Planck values are beyond human comprehension, and anything below the Planck length makes calculations impossible. Thus, the time between zero and Planck time is considered the Planck Era. During this time, all four fundamental forces—gravity, the strong nuclear force, the weak nuclear force, and the electromagnetic force—were combined into a single super-force.

To visualize this, think of the different phases of water: ice, water, and vapor are all aspects of the same substance. However, at certain temperatures and pressures, all these phases can exist simultaneously. It’s important to note that this analogy is not entirely accurate for the Planck era, as it is related to quantum phenomena characterized by unimaginable temperature, density, size, and energy. Although this time duration was part of the Big Bang, the actual “bang” occurred after the Planck era.

Between the incredibly short timeline of 10^-44 to 10^-36 seconds, a significant event took place—the Grand Unification Era. During this time, immense energies were packed into a tiny volume, beginning to overcome the Planck limit. At the start of this era, gravitational force separated from the other forces, giving the first real meaning and existence to our universe. By the end of this era, the size of space was sufficient to produce quarks, antiquarks, and gluons from the energies. However, these were massless, meaning there was no theoretical distinction between particles and energy; they were all the same.

At the conclusion of the Grand Unification Era, the strong force successfully began to separate from the unified force. Scientists believe this separation process sparked cosmic inflation, which occurred between the timeline of 10^-36 to 10^-32 seconds, during which the universe expanded in size by at least 10^26 times—growing by 100 million billion billion times within a tiny fraction of time. This expansion occurred much faster than the speed of light. While cosmic inflation exceeded the speed of light, it did not violate any principles of our universe. There is a law that the speed of information cannot exceed the speed of light, but there is no law or speed limit for how quickly space itself can expand.

After this inflation, the temperature dropped to around 10^18 kelvin, but we do not know how far the universe expanded. Now, at 10^-12 seconds, the electromagnetic and weak forces are still combined, referred to as the electroweak force. The temperature of the universe at this stage exceeds 10^15 kelvin, and there are no ordinary particles yet—only massless particles, gluons, and pure energy. Here, quarks and gluons coexist, forming what we call quark-gluon plasma.

At around 10^-10 seconds, the temperature dropped below 10^15 kelvin, leading to the separation of the electromagnetic and weak forces. This separation allowed massless particles to gain mass, resulting in the formation of initial matter particles. At this stage, other elementary particles, such as electrons, began to form, marking the start of the particle era. When the particle era began, matter particles, quarks, and antiquarks were produced in equal numbers, constantly annihilating each other to revert to pure energy. Fortunately, the universe created slightly more matter particles than antimatter particles, resulting in a surplus of matter. For every billion anti-quarks created, there was one billion and one quarks created. Electrons and anti-electrons were also produced in a similar manner. This imbalance between matter and antimatter creation led to the actual formation of our universe. If they had formed in equal numbers, the particles would have eventually annihilated each other, leaving only energy—no quarks, no electrons, no atoms.

As time progressed, the universe continued to expand and cool down. At 10^-5 seconds, with the universe around 1 trillion kelvin, the quark-gluon plasma began to form into protons and neutrons. Now, the universe is one second old, and the temperature has dropped below 10 billion kelvin. Almost all matter and antimatter particles have annihilated each other, concluding the great struggle between matter and antimatter. Due to the earlier imbalance in matter-antimatter creation, some matter particles remained. Thus, the surviving protons, neutrons, and electrons persisted. Although this may seem like a lengthy process, everything occurred within a second. Just one second after the Big Bang, protons, neutrons, and electrons formed—the building blocks of atoms and everything else.

Now, it’s three minutes after the Big Bang. Our young universe has begun to evolve for the first time. Protons and neutrons come together to form the first nuclei. The universe is still too hot for electrons to capture the nuclei, allowing electrons to move freely through the hot universe. However, free neutrons are not as stable as protons; they decay quickly, within 17 minutes, into protons. When they are paired with another neutron or proton, they become stable. Most neutrons decay into protons, which is why our universe has more protons than neutrons—approximately 87% protons and 13% neutrons. Remarkably, some neutrons managed to bond with adjacent protons before they could decay, resulting in the remaining 13% neutrons.

Twenty minutes after the Big Bang, the neutron decay process concludes. Now, the nuclei of hydrogen and helium have formed. The imbalance of protons and neutrons means the universe has more hydrogen atoms than helium, as helium nuclei require two neutrons while hydrogen nuclei require only one proton or one proton and one neutron. By the end of these 20 minutes, the nuclei ratio appeared as 75% hydrogen and 25% helium.

At this point, all atoms are ionized, meaning they are positively charged. To become neutral, atoms must capture electrons. When a negatively charged electron binds with a positively charged nucleus, it forms a completely neutral atom. However, the universe remains hot enough that electrons cannot orbit nuclei. When electrons attempt to orbit nuclei, the temperature prevents this, causing them to be expelled. As the universe continues to expand and cool, it reaches 380,000 years old, with a temperature of 3000 kelvin. This temperature allows electrons to orbit the nuclei, and the electromagnetic force is now sufficient to bind nuclei and electrons.

Finally, after 380,000 years, the first stable atoms formed, marking the beginning of the era of recombination. Not only were electrons struggling, but so were photons, which represent light. When stable atoms formed, photons were captured by nuclei, and the electron clouds were finally freed after 380,000 years. The high-energy photons traveled through the universe, revealing the first light of the universe and allowing it to become transparent. Today, we can still observe this first light, which appeared 380,000 years ago, thanks to the cosmic microwave background radiation. Although they have lost energy over time, we can still detect them today.

One hundred million years after the Big Bang, the first stars began to emerge from hydrogen gas clouds. Due to the immense pressure at the core of stars, hydrogen atoms fuse into helium and then into heavier elements like oxygen, carbon, and iron. Iron atoms are extremely stable, so the pressure within the star is insufficient to continue the fusion process, leading to the star’s death and subsequent explosion as a supernova. This supernova event disperses heavy elements throughout the universe.

Nine and a half billion years after the Big Bang, our solar system formed. Then, after 10.5 billion years, the first life emerged on Earth as a single-celled organism. Over time, a complex evolutionary process unfolded. Finally, 13.8 billion years after the Big Bang, the most unique creatures yet discovered appeared in the universe—humans, who are capable of analyzing, calculating, and witnessing the existence of the universe.

If we are the only unique, intelligent, conscious beings in the entire universe capable of understanding its existence, did the universe wait for us for 13.8 billion years? Or do others already know about the existence of our universe? Why was the universe created, and why did it erase information about the time before the Big Bang through cosmic inflation? These endless questions may remain unanswered for millions of years, or perhaps even forever.