If we see in the eyes of science then we use two different types of theories to understand the whole universe - the first theory is the General Theory of Relativity and the second is the Quantum Field Theory. If we talk about the bigger objects like stars, planets, etc in this universe then we use the General Theory of Relativity to understand the behavior of this universe. Where we use the Quantum Field Theory to understand the structure of matter and interaction of energies in the atomic and subatomic levels.
Both of these theories work very well within their respective domains. This means that if an object is larger in size, then the General Theory of Relativity will work there. And if an object is smaller in size or very less in mass, then the Quantum Field Theory will work there.
But why there are two different theories for understanding the behavior of the universe?
So, can we not formulate a theory that will be able to explain the bigger levels and quantum levels phenomena occurring in the universe?
This type of thinking of physicists gives rise to a new theory that we know in the name of string theory. The peculiarity of this theory is that it talks about quantum gravity and multiple dimensions.
And it also helps to answer some questions that are related to Big Bang's previous universe, which are still mysterious in modern physics. If you do not know what is string theory then this article is for you. In this article, you will know -
1. What is String Theory?
2. What are the Fundamental Forces?
3. What is the Standard Model of Elementary Particles?
4. What does String Theory say?
5. What are Multiple dimensions in string theory?
6. What is Quantum gravity in string theory?
What is String Theory?
In particle physics to understand the true nature of our reality, there is a unified theory called string theory. This theory says that the point-like particles of particle physics are replaced by one-dimensional objects called strings or membranes. These strings or membranes are always vibrating at different frequencies. Due to this vibration of these strings at different frequencies, different types of particles are created in this universe.
To understand the string theory, we need to have an idea about Fundamental Forces and Standard Model of Elementary Particles. So before starting let us know first about fundamental forces and the Standard Model of Elementary Particles.
Fundamental Forces
In this universe, there are various types of interactions are occurring between the particles. When we studied very closely the mechanism of the interactions between these particles, we find that these interactions can be divided into four fundamental forces.
These four fundamental forces are like this -
1. Gravitational force
2. Electromagnetic force
3. Strong nuclear force
4. Weak nuclear force
Gravitational force
If gravitational force is to be talked about, then it is the weakest force of the four fundamental forces, but its region is the most. For this gravitational force, the planets rotate around the sun and the satellites orbit the planets.
Electromagnetic force
Now if we talk about Electromagnetic force, it would not be too difficult for us to understand because now we are experiencing it in our daily life. Yes, I'm talking about electric and magnetic force.
For a long time, electric and magnetic forces were considered as two separate forces. But in 1864, James Clerk Maxwell has unified these two forces through his Maxwell equations. Then in 1940, it becomes part of quantum mechanics due to quantum electrodynamics.
Strong nuclear force
If we talk about the Strong nuclear force, then it is the strongest force among the four fundamental forces. This is because it holds the neutrons and protons in the nucleus of the atoms.
You can estimate its strength by helium (He) atom, which has two positively charged protons in the nucleus. positively charged particles naturally repel each other, so it takes an extreme amount of force to hold protons together.
The strong nuclear force overcomes the repulsion between protons to hold together atomic nuclei. Without the strong nuclear force, complex nuclear cannot form.
Weak nuclear force
The Weak nuclear force is also strong enough but its region is very small. Its mechanism of interaction occurs between subatomic particles that are responsible for the radioactive decay of atoms. For example, a phenomenon like beta decay is caused by this type of nuclear force.
Standard Model of Elementary Particle
The Standard Model of Elementary Particle Physics tells us a lot of things about how the composition of the universe or different types of forces work in the sub-atomic levels.
According to this theory, everything in this universe is made up of twelve basic building blocks. Of these twelve building blocks, six are Quark, to whom interesting names have been given, like - Up, Down, Charm, Strange, Top and Bottom. For example, the proton is made up of two up quark and one down quark.
The remaining six building blocks are called leptons, where there are three neutrinos with Electrons, Muon, and Tau.
Of the four fundamental forces we learned about, three forces (Electromagnetic force, Strong nuclear force, and Weak nuclear force) can be easily explained by the Standard Model of Elementary Particle Physics. Because the fundamental particles here are work as the carriers of these forces.
For example, if we try to understand the magnetic force, then the magnet attracts iron only because of the exchange of photons occurring between iron and magnet.
But the gravitational force is the only force that has not yet been explained at the microscopic level. In fact, no concept of gravity has been found at the microscopic level yet.
Now if we find a theory that proves quantum gravity then we will get a unified theory, through which we can easily explain all the forces.
Theories that have been given for decades, string theory is the only theory among them that claims to explain quantum gravity.
What does string theory say?
Suppose we have an object such as a candle. Now if we try to know what it is made of, then we will get atoms. Now if we go inside the atom we see that there are electrons and they are rotating around the nucleus. Inside this nucleus, there are neutrons and protons.
Now if we go inside the proton we get quarks through which proton is formed. Here the thought of Modern Physics ends. That is why we accept that quark is the smallest part of the matter and we can't break it anymore.
But the string theory says that inside the quark there is a kind of energy that always vibrates which makes it look like a string or a membrane.
It is not necessary that the strings are always in the closed state. In fact, they may be in the open state in both directions and also in the straight.
You may have noticed that when strings are vibrated in different patterns in a cello, different types of sounds are produced. Similarly, when strings are vibrated in different patterns, different types of particles have been formed.
That means the only difference between a stone and a human body is that the strings are vibrating in one way in the human body and another way in the stone.
Now if we had a microscope with which we could see the smallest objects in the universe, then our universe would look like this.
We will see that the energies are present around us are just look like the strings, that are always in vibrating at different frequencies. Due to the vibration of these strings at different frequencies, different types of particles are created in this universe, which is why it is so strange to see this universe.
Since everything in this universe and all the objects in this universe, as well as all the forces, are makes by these strings, so we can easily explain everything with it. That means we got a unified theory. But it is not as easy as it seems.
Multiple dimensions in string theory
Actually, when we look at the mathematical equations of string theory, we find that this theory does not work in a universe that has only 3 special dimensions. In order to work it needs a universe that has not five or six but has 10 space dimensions and also has a dimension of time.
Because till now we only know that our universe has 3 special dimensions and has one dimension of time so this theory should not work in this universe. But by the concept of string theory, we can derive mathematically the standard model of matter. This means that this theory can also be true.
Now the question arises that if this theory is correct, then where are the remaining seven dimensions. If it is present in this universe then why do we not see it?
String theory believers say that there are two types of dimensions, one is so large in size that we can easily see them while the other is so small that we can not see them.
For example, if we look at a single wire from a distance, we will find it look like one dimensional, but for ants, it will not look one dimensional because it can move around it. This means it is absolutely possible that many dimensions are in front of us but we are not able to see them.
Quantum gravity in string theory
Now let's talk about quantum gravity and know what it has to do with string theory. Actually, when string theory was in its early days, based on its mathematical equations it was predicted that there should be a massless particle inside the atom.
But even after many experiments, when scientists did not find any such particle in nature, then they stop taking the string theory seriously.
However, 4 years later, while Schwarz was trying to eliminate the complexities in the string theory, he found that this massless particle was actually describing to the gravity.
After that, the particle was named as graviton and it is believed that this graviton carries gravity at the quantum level. That is, if the string theory is correct, then by the quantum field theory, we will be able to understand all the fundamental forces. This means that we will get a unified theory.
However, it is still only a hypothetical particle i.e we have not yet found any such particle physically. String theory really makes interesting. But there are many forms of this theory.
Different people have created six different theories based on their understanding, the basic idea in this theory for everyone is the same but it is slightly different in terms of the behavior of strings. Five of them speak of ten space dimensions, whereas the sixth i.e the bosonic string theory talks about twenty-six space dimensions.
Since all these theories are derived from a single theory, the combination of these theories is also called M-theory.
What is the conclusion for string theory?
Now the next question arises whether the string theory is correct or not. Because string theory talks about such strings that we cannot prove experimentally so we do not consider this correct.
But it is not that scientists consider it completely wrong. In fact, most of the physicists consider it a philosophical theory more than physics.
String theory also predicts for another particle called Tachyon, whose speed is greater than the speed of light. Because physicists believe that no object in this universe can move faster than the speed of light, they refuse to believe this theory.
If we get graviton in some way, then this theory will be stamped, but even in the Large Hadron Collider (LHC), we have not found any such particle yet, due to which there is still a big question mark on this theory.
Those who believe in string theory say that this is absolutely true. But it's so complicated that we probably didn't fully understand it. Perhaps we will understand it better in the future. If this were to happen then our entire understanding of this universe would change.
All the theories of conventional physics fail in a black hole, in the same way, it is not even able to tell what was there before the Big Bang or why Big Bang happened. We get all the answers to these questions from the string theory.
If we talk about the Big Bang, so those who believe in string theory also believe that two huge size membranes existed before the Big Bang in which there were two different parallel universes which both were vibrating. Some parts of them collide with each other and our universe begins to form. This is what we call the Big Bang.
Those who believe in string theory also believe that the process of colliding with these membranes is always going on. That means in the future, it is certain that events like Big Bang can happen.
Maybe, the explanation that comes from Big Bang theory may not have satisfied you that much. Because many people do not agree with it but they believe that with the help of string theory we will get a satisfying answer.