In this article, I will answer 9 questions about the big bang theory.
- What is the big bang theory?
The big bang theory is the theory that we once considered most likely to happen in today’s world and accepted as true; “How did the universe begin?” It is a theory we put forward to answer the question. Although the big bang theory is not the most common idea among physicists today, there is still a significant portion of people who support it. According to this theory: a long time ago, the universe began as a single, tiny point (singularity) and began to expand. As a result, the universe took its present form and continues to expand today. Although the word “explosion” sometimes creates confusion, the Big Bang, unlike the explosions we know, was not the creation of pressure and heat as a result of chemical reactions of some substances, but the expansion of space.
2) What kind of ideas were put forward until we came to the big bang theory?
The big bang theory was put forward in 1927 by a Belgian priest (also an astronomer) named Georges Lemaître. According to this theory: a long time ago, the universe began as a single, tiny point and began to expand. As a result, the universe became what it is today and continues to expand today. However, this expansion theory did not have very solid evidence. This evidence was revealed 2 years later by astronomer Edwin Hubble. Edwin Hubble’s theory is based on fundamental observations. In 1929, Edwin Hubble observed that the distance between galaxies was increasing everywhere in the universe (Explanation about this sentence is in question 4). This meant that galaxies must have been closer to each other in the past. But long before that; There were many ideas that were not fully scientific, consisted only of philosophical thoughts, and were similar to the big bang theory. In medieval philosophy, there were many debates about whether the universe had a finite or infinite past, and the reason for these debates was the idea of “apeiron”, which Anaximander saw as arche and defended by Aristotle. This idea caused problems for medieval Jewish and Islamic philosophers, who were unable to reconcile Aristotle’s understanding of eternity with Prophet Abraham’s view of creation. English theologian Robert Grosseteste explored the nature of matter and the cosmos in his 1225 treatise De Luce (On Light). He attributed the beginning of the universe to an explosion and argued that the arche was light. Grosseteste says this about this issue: “The first corporeal form, which some call being, is, in my opinion, light. Because by its nature, light spreads itself in all directions, and a point of light creates a sphere of light as long as it does not encounter anything opaque on its path. In this case, the three-dimensional extension of matter is a necessary natural consequence for existence… Form cannot leave matter, because it cannot be separated from it, and in the same way matter cannot remain separate from form on its own… Therefore, light, which is the first form created in the first matter, has an infinite number of directions. It multiplies/spreads correctly…” De Luce is the first attempt to describe the heavens and the earth using a single physical law. One of the people who thought about this problem is Johannes Kepler. Kepler’s problem in this regard is the paradox now called the Olbers Paradox. This paradox is no longer a problem thanks to the big bang theory. Olbers paradox is briefly as follows: The basis of this paradox was the question of why the universe is a pitch black place rather than full of light. Because if the universe is infinitely large, there must be an infinite number of stars in it. In this case, wherever we looked, we would definitely expect to see a star, and the lights scattered from these stars would eventually reach us. Therefore, the Universe would be filled with light from beginning to end! Then why is the Universe pitch black? We can solve this as follows: The universe is not full of light, because not all the stars in the universe have existed since eternity. Not enough time has passed for the light of some of them to reach us, and therefore it is not possible for stars to fill the entire Universe with light.
3 )What was before the big bang?
Answers to this question can be divided into 2: Some say, “The big bang is the absolute beginning of the universe and time. “A statement like ‘before the big bang’ doesn’t make much sense because there is no such thing.” they say. (It is not a good idea to stick to this answer for now.) Some people do not try to “make it easy” by putting forward various theories on this subject. For example, famous cosmologist George Gamow, in his book “Creation of the Universe” published in the 1950s, said: “The great pressure and density that occurred at the beginning of the universe were the result of a previous collapse. Today’s expansion is the result of the universe entering the expansion process again with an elastic ‘rebound’ after the density reached a maximum value in this depression.” Famous physicist Steven Weinberg wrote in his book “The First Three Minutes” in 1977: “One possibility is that a period of infinitely large density has never existed. “The expansion of the universe may have begun after the density reached a very large but finite value during an earlier collapse period.” says. Today, there are two theories that can be assumed to be true with our advancing technology and knowledge: Loop Quantum Gravity and Superstring theory. Both of these are, in essence, “Quantic Gravitation Theory”. You may have heard of superstring theory, even if you haven’t heard of it, you may have heard something like space-time has 11 dimensions according to some theories. This 11-dimensional space-time concept is a product of superstring theory. According to this theory: There are 10 space dimensions and 1 time dimension. 7 of the space dimensions have become too small to be observed as the universe cooled, and there are only 3 space dimensions left that we can observe in the space we are in today. According to this theory, elementary particles are not point entities, but are in the form of strings with dimensions less than centimeters, that is, they are not 0-dimensional, they are considered 1-dimensional. There is a very important advantage (convenience) provided by superstring theory: As two point masses get very close, the interaction forces between them become divergent. There is no such singularity problem in superstrings. According to the superstring scenario, in the very high energy period of the universe
seconds ago, the gravitational force was combined with other forces and there was only one super force. I think there is no need to dilute our minds by giving detailed information about the second theory, the loop quantum gravity theory. To put it briefly: loop quantum gravity theory says that the universe went through phases such as the big collapse and the big bounce before the big bang. Since these theories cannot be based on solid observations and experiments, it seems that it does not make much sense to rely on these theories. These two theories try to combine the “Theory of Relativity” developed by Albert Einstein and the “Quantum Mechanics”, which is not compatible with it.
4) If galaxies are moving away from each other, how do galaxy collisions occur?
The main reason why there are misunderstandings on this subject is that people do not investigate the background of the sentences they hear and spread them in this way. The statement “Galaxies are moving away from each other” is actually true, but it is normal for it to cause misunderstandings. The things that are moving away are not actually galaxies but galaxy clusters. The formation of galaxy clusters is as follows: 15-20 galaxies, large and small, come together to form small groups. A few of these small groups come together to form larger galaxy clusters. Dozens or hundreds of galaxy clusters come together to form superclusters. The galaxies in our “local galaxy group”, consisting of Andromeda, the Milky Way, the Triangle Galaxy and dozens of dwarf galaxies, are connected to each other by gravitational effects and do not move away from each other. This is true for all galaxy groups in the universe. Galaxies within the group may move apart, get closer, collide or enter each other’s orbits over time due to each other’s gravitational effects, but they do not separate easily. While the galaxy clusters are moving away from each other, the reason why the galaxies within them do not move in this way is that the gravity caused by the distance between the galaxy clusters is very low.
5) Where is the center of the universe?
Actually, this is a very natural question to ask. However, it is not possible to give a clear answer to this question. This result may vary depending on each reference point. I can explain the logic of this as follows: Imagine you have a balloon. This balloon is a balloon that never bursts and there are dots on the balloon. You constantly inflate this balloon with the help of a machine. As you inflate, the distance between the points increases and someone asks you, “Where is the center of this balloon?”. You can’t answer that because that balloon has no center. So, in this scenario, it is most logical to give answers to the center of the universe such as “it does not exist” or “it is everywhere”.
6) What are dark matter and dark energy?
We call the ghostly structure that has mass, is cold, does not move much, and does not emit any light at all, dark matter. In fact, even particle physics is not enough to explain what dark matter is. We infer that dark matter contributes to the shape of the Universe because it increases the density of matter in the Universe due to its mass. Based on our observations, we see that the Universe is expanding at an accelerating rate. For such an expansion to occur, negative pressure must prevail in the Universe. We call what is responsible for this negative pressure “dark energy”. Based on today’s data, we know that 4.6% of our Universe consists of the matter we know, explained by the Standard Model, 24% consists of dark matter, which we do not yet know what it is, and 71% consists of dark energy, which causes the Universe to accelerate and expand.
7) What is the universe expanding into?
The universe is not expanding into anything. What is expanding is the universe itself, not any matter in it. The important thing here is not to take your perspective outside the universe. If you think about it like an observer from outside the universe, it doesn’t make sense. However, if you observe any matter in the universe, there will be no problem. After all, in order to observe the universe from the outside, there must be a concept such as “outside the universe”, but this is not possible. The universe encompasses all space-time.
8) What is cosmic microwave background radiation?
Cosmic microwave background radiation is the photons that reach us from the final scattering surface. In other words, they are photons that have been traveling since the universe was 380,000 years old. Even though we cannot observe the big bang, it provides important evidence for it. After the big bang, our Universe was incredibly hot. It was so hot that protons, neutrons, and electrons were moving too fast to come together to form atoms. Later, as the Universe expanded, matter cooled and protons and electrons came together to form the simplest atoms: hydrogen and helium atoms. Since hydrogen and helium atoms were neutral after they were formed, they could no longer absorb thermal radiation, and the photons that were not absorbed were scattered aimlessly in the Universe. They have been wandering in space ever since.
*Approximately 1% of the sizzle on televisions is caused by cosmic microwave background radiation.
9) If the universe is infinite, how could the universe be in a state of singularity at the time of the big bang?
Before answering this question, the concepts of infinite and unlimited need to be understood well. Let’s explain this with an example: The surface of a basketball ball is a two-dimensional and finite surface, but it has no boundaries. This means that no matter how far you move on the ball, you will never encounter a place like the “end of the surface”. If you move in one direction on the surface of the ball, you will return to where you were.
If we were to adapt this to the universe:
If our Universe is finite, it will be unlimited, so a concept like “the limit of the Universe” is meaningless.
First of all, there is a misconception about singularity such as “the whole Universe is at a single point”, which is not true. It is not known whether our Universe was in a state of singularity at the time of the Big Bang. Our Universe may even be infinite in size at that moment. In the articles you read, the expansion rate of the universe at the time of the big bang is mentioned. What is meant by the size of the universe in those articles is the size of the “observable universe”, not the size of the universe itself. Some theories show that the big bang should have been a singularity, but these often turn out to be errors. I will explain these theories in my future articles. I will also talk about the concept of “Strong Energy” in upcoming articles.
“Where did we come from?” Even though we are curious about the question, it seems very difficult to find a theory that will satisfy us in every respect. But this is not impossible.