FEATURE | Beyond the Big Bang: The Search for the Origin of the Universe

Abstract 

Understanding the origins of the cosmos has long been one of the greatest mysteries in the world of astrophysics. This article explores three major theoretical ideas - Chaotic Boundary Conditions, the Anthropic Principle, and the Inflation Theory - that attempt to explain the initial conditions of the universe and how it has evolved into the universe observed today. These models come together to explain issues such as the multiverse and the flat and smooth composition of the universe, bringing scientists one step closer to understanding the vast cosmos. While each theory offers compelling insights, none can yet fully answer the question of how the cosmos began. Yet it is within the unknown that the true beauty of infinite possibility, discovery, and imagination unfolds.

Introduction 

The Big Bang that happened 13.8 billion years ago was the beginning of everything. Because physical laws break down at a singularity, predicting what happened during and before the singularity is nearly impossible; therefore, it is safe to assume in this case that the universe did indeed start at the Big Bang. But the questions don’t end there. What triggered the Big Bang? Who or what set the initial conditions that allowed the cosmos to evolve as it has? Was it purely luck, some deeper law of physics, or something beyond science entirely? And if it was something greater, like a divine force, why design a universe this way? Yet within the endless questions lie wondrous possibilities. These possibilities all tell their own story, each of them getting one step closer to answering the final question: How did the universe begin, and why does it have the conditions observed today?

Stellar Nursery NGC 3324 found in the Carina Nebula

Chaotic Boundary Conditions

The Chaotic Boundary Conditions are one of the many possibilities from which the universe could have arisen. This theory assumed that the cosmos either stretched infinitely in each direction or there were infinitely many universes, meaning that any possibility of the universe was infinitely possible, and thus the initial conditions in which the universe originated would have been chosen at random. However, if the universe is as chaotic as the theory suggests, it wouldn’t have been able to create the smooth and uniform universe seen in the present. 

Anthropic Principle 

The second possibility for the origins of the universe is the Anthropic principle, which contains two versions: weak and strong. The weak Anthropic principle claims that the universe is either infinitely big in size or infinitely big in time, and only certain regions of the universe would have the correct conditions for life to form. And the strong Anthropic principle states that the universe is the way it is because if it were different, humans would not exist, suggesting that cosmic space was fine-tuned just for humans. The weak Anthropic principle fits in with the initial state of the universe because if the cosmos is truly infinite in size then there must be parts of the universe that started out smooth and uniform and some parts that started out chaotic, and it just so happens that humans live in one of the smooth areas. In the strong Anthropic principle it is believed that the reason why cosmic space is so smooth and has the correct conditions for life to form is because humans exist. However it is hard to believe that the universe, which contains hundreds of billions of planets and hundreds of billions stars, was just created for humans. As a result of this, the weak Anthropic principle is generally more accepted. 

Inflation Theory

Any attempt to understand how the universe came to be must start with a careful look at its initial conditions. In order for the universe to behave like it does today, the initial state of the universe had to have the same temperature everywhere to agree with the cosmic microwave background which is uniform, and the rate of expansion needed to be just right to avoid recollapse due to gravitational forces. To check off these requirements, Alan Guth, a scientist at MIT, discovered the Inflation Theory in 1979. He theorized that the cosmos went through a time of rapid expansion in which the universe increased by a million million million million million times in a fraction of a second. He speculated the universe had the right conditions for the inflation theory to happen so it could explain the problems that occurred from the Hot Big Bang Theory but he didn’t explain exactly where the inflation came from or what triggered it.

Inflation: Supercooling 

The right condition for inflation to start consisted of a region of strange, high-energy field called the inflaton field. This field is stuck in a false vacuum which has a high energy but unstable state. This vacuum also has a repulsive gravity causing exponential expansion of the universe, leading to inflation. At this very high energy, it is predicted that the strong, weak, and electromagnetic force would unify as one. Eventually the forces would break but it was 

Timeline of the Big Bang expansion including Inflation

hypothesized that the universe could have been supercooled. Supercooling in water means that if the water was pure enough and in a controlled and undisturbed state, one could make water stay liquid below freezing point. A similar process could have been done in the universe during inflation where the temperature might drop below critical temperature because of the expansion without the symmetry between the forces breaking. The result of this would be a very unstable universe with more energy than if the forces were to separate. The energy supercooling created along with the unstable false vacuum would have an anti-gravitational effect like Einstein’s cosmological constant which is a repulsive force balancing out the gravitational pull of space. This repulsive force pushing things outward along with the already expanding effect of the Big Bang created an accelerating inflationary manner. Everything would be smoothed out by this expansion like how space is today, therefore, the cosmos could have evolved from many chaotic and non uniform origin states. Additionally, the Inflation Theory answered three questions that the Big Bang Theory did not: Why the universe is so uniform, why the cosmos is flat, and why there is so much matter in space.

Inflation Theory: Isotropic and Homogeneous Universe

Cosmic space is isotropic and homogeneous meaning it is the same in all directions and all places. On a large scale, galaxy clusters are spread out evenly and stars start to look the same. Although the universe could have had a uniform temperature if it was left untouched for a long time, the early cosmos expanded so quickly that there was no time for the temperature to be uniform across space. The reason behind the uniform temperature in the cosmic microwave background was because of the Inflation Theory which suggested that the earliest form of the universe was a region of incredibly small size. Because of the small size of the universe, the temperature was able to reach a uniformity through the whole universe. Then the inflation would happen, allowing for the temperature to also expand and settle in every region of the universe.

Inflation Theory: Flatness of the Cosmos

The second question the Inflation Theory explains is the flatness of the cosmos. In the universe, if the ratio to the density of the universe to the critical density, which is the density when the universe is at balance and expansion stopped, is greater than one it will cause the space to curve and become a sphere shaped universe or a place with finite volume but no edge. This ratio is called Omega. If Omega is less than one, the universe becomes saddle-shaped, infinite, and continues to expand. However, Omega actually equals one in real cosmic space which means that like flat Euclidean geometry, the universe is flat and will barely be able to expand forever. Because the universe likes to 

evolve away from flatness, the early universe needed to be extremely flat for this to work. It was discovered that unlike how space wanted to drift away from flatness, inflation was driven towards flatness, solving this question and the question of why is it so close to critical rate (perfect balance so universe neither collapse or expand forever).

Alan Guth is a physicist and cosmologist 

who proposed the Inflation Theory in 1979

Inflation Theory: The Matter Problem

Inflation Theory also debunked why there is so much matter in the universe. Quantum mechanics stated that particles were created from energy in the form of particle and antiparticle pairs. So where did energy come from? The energy of the cosmos is equal to zero. All the matter in the universe is positive however the gravitational field is negative because when two things are far apart, it takes a lot of energy to pull them apart making the whole field negative. The universe cancels out the negative gravitational energy with the positive matter to result in a universe where the energy is exactly zero. During Inflation Theory, the size of the universe went up, and so did the gravitational field, thus there was more space to increase the amount of matter in the universe to keep that balance of zero.

Inflation Theory: Hot Big Bang

The universe seen today is expanding but not as rapidly as in the Inflation Theory because the symmetry between the forces will have broken during inflation and the extra energy in the unbroken symmetry will eventually be released, reheating cosmic space so all that stored energy turns into hot particles, radiation, matter and antimatter making the universe extremely hot again, marking the beginning of the Hot Big Bang phase. This would prove why the universe is expanding at a critical rate and why different regions of the universe have the same temperature.

Chaotic Inflationary Model

In Guth’s original theory, the breaking of symmetry or the transition from false vacuum to true vacuum would be via bubbles, these bubbles were supposed to expand and meet up with each other so the whole universe would be in a new phase of broken symmetry. However, the universe was expanding so fast that even if the bubbles were moving at the speed of light, they could not meet up. This would mean a very nonuniform universe with areas that still had symmetry between forces. 

Later in 1983, Linde discovered a better model of the Inflation Theory and called it the Chaotic Inflationary Model. This model did not contain phase transition or supercooling and he said that the expansion could have happened in any region of space. In his model, there was a spin 0 field called the Scalar Field, and the energy of this field would have acted just like the cosmological constant, driving expansion. As the universe expanded, the energy of the field would slowly decrease in energy, giving away its energy to form new particles like protons and neutrons.

Subsequently in 1986, Linde came up with the Eternal Chaotic Inflation which suggested that inflation never truly ends everywhere. Instead, it is still going on in some regions, creating a continuous cycle of multiverses with varying properties.

Conclusion

Although these are only a few of the many theories predicting the origins of the cosmos, the Chaotic Boundary, Anthropic, Inflation Theory and many more have filled in many of the gaping holes of the secrets of the universe. But the full truth of the vast cosmos is yet to be discovered. Where did the humans come from? Who created Earth? Who created the universe? Was the world indeed created for humans? In a world with so many unanswered questions lies the true beauty of endless possibilities, discovery, and imagination.