Let’s first look at a definition, what does string theory mean? Let’s try to understand this theory simply later. In the most classical expression, string theory is referred to as “the theory in particle physics in an effort to unite quantum mechanics and Einstein’s general theory of relativity”.
So why did these theories need unification? What are the points that set them apart? I think we need to understand quantum mechanics and general relativity first to know this. Let’s just take a look at what they are saying.
Quantum mechanics is known as a science that studies matter at the atomic and subatomic levels. They simply go deep into the universe and study it at the level of particles smaller than atoms. Why do you think they needed to go this deep?
Of course, this is because classical mechanics is no longer sufficient. Classical mechanics has begun to fail to explain some situations (such as blackbody radiation, spectral lines, photoelectric effect), which has prompted scientists to do new studies. Well, what happened and they decided that?
There are different reasons for this, but let us explain this with a simple example for you to understand: Most of your readers actually know this; The double slit experiment, also known as the Young’s experiment. This experiment was first used by a physicist named Thomas Young to prove that light has wave properties. In the following years, scientists also used it to understand the movement of matter. Scientists use electrons as matter in this experiment. They first throw the electrons through one slit and get the result as they expected. In other words, a trace is formed as a single line on the back panel. Then they subtract the number of slits by two, and when they send the electrons back, an interesting situation happens.
Electrons move like waves. In the wave feature, when the waves pass through the slits, they hit each other again at the back and an interference pattern is formed on the panel. Electrons show the same property, surprising scientists. Thinking that the electrons are hitting each other, they change the process. So this time, they send the electrons one by one and try again and see that the result is the same.
To understand this, they consider examining the electrons by placing a sensor at the bottom of the slits. When they start the experiment again, the electrons show a grain feature this time and they only form two traces on the panel. This is one of the steps that scientists realize that they cannot understand the universe only through classical physics and that provides access to the quantum.
We said that our theory unites quantum mechanics and the theory of relativity. After explaining the quantum a little bit, it’s time for relativity. It is probably very, very few of you who have not heard of it.
We can say that general relativity is based on gravity. This theory explains the force of gravity in relation to space and time. According to the theory, time, space and matter are completely interdependent. One cannot be independent of the other.
We asked why quantum mechanics and general relativity need unification. According to string theory, the universe is made of vibrating threads at the subatomic level. While general relativity explains massive objects in space, quantum mechanics studies much smaller objects.
In other words, one examines the macro universe and the other examines the micro universe. Since we want to collect the entire universe under a single theory, we have to combine these two theories. In this way, we hope that we will be able to explain the entire universe with a single theory and understand it more comfortably.
We said we were trying to combine them with string theory. In the quantum world, things don’t happen with the logic we are used to. Although it goes against the logic of most people, Einstein’s theory of general relativity has a more prudent approach. He says that speed, time and bodies are interdependent and have logical explanations in a certain order.
Previously it was thought that the smallest subatomic building blocks of matter were dimensionless point particles. But in 1984, Michael Green of Queen Mary College and John Schwarz of the California Institute of Technology proposed that the universe was not made up of dimensionless point particles, but rather vibrating one-dimensional planck-length filaments.
In other words, “matter is made up of atoms, and atoms are made up of protons, neutrons and electrons. Protons and neutrons are made up of quarks. Quarks and electrons are made of strings (threads), ”says string theory.
The number of dimensions is quite high in string theory; There are 10 (9 spaces and 1 time) dimensions. 4 of them are 3 space and 1 time dimensions as we know them. This number can be increased or decreased according to the own approach of the scientist working on the theory. It is suggested that these “extra dimensions” are only discernible dimensions on string scales, that the strings vibrate within these dimensions and therefore we cannot observe.
Of course, it is not quite right to be precise in the world of science. For what we consider to be absolutely correct today may lose its accuracy within some limits or in general terms with a different approach or explanation tomorrow. Of course, there can be an infinite number of dimensions. It is also among the claims of “some” of string theory that these dimensions absorb most of the gravity and that the gravity is so weak because of this.
Let’s explain how weak the gravity is with a good example of Michio Kaku, one of the physicists of our time: Let’s consider the gravity of our world, which weighs 5.9722 × 1024 kg. We all know how comfortably we can beat him. At least for low mass objects. Of course, as the mass increases, the amount of force required will increase. I guess we all did it in primary school. We used to rub a comb or straw on our hair and pull out small pieces of paper. This is how weak the gravity of our world is.
Going back to our topic, it is suggested that some, even most, dimensions may be of string scale. Now, according to the theory, the building blocks of all matter are threads called strings, in this case the building blocks of every material are the same. So how do these make up different substances? It’s actually simple: We said that strings are one-dimensional threads that vibrate, so in order to form different substances, the strings must also vibrate at different vibration frequencies.
The one-dimensional thread concept can of course leave question marks in your mind. How about threads that have only one length (planck length) but no width and height? This seems a little counterintuitive to our perceptions. But if we consider this in string scales, I think we can understand that these threads are not one-dimensional as we think.
Just like understanding that microscopic-scale objects that seem two-dimensional are not two-dimensional as they actually thought when viewed with a microscope. Perhaps we can find new laws of physics at those scales. Who knows, maybe these are just inaccurate guesses. Although most of the things have been said according to mathematical models, it is not necessary to be precise as we said.
We should also make the following explanation for the part up to here:
String theory is not a theory with a general consensus, such as the theory of the Big Bang, the theory of evolution, the theory of relativity, and the electron theory, which are the theories we know today and can be tested in daily life. It is a collection of ideas, most of which are shaped as “toy theory”, that different scientists try to develop with different approaches. Most of the predictions of string theory cannot be tested, nor can they be presented with ideas as to how to test them. Theory M, which is often spoken of, is very similar.
While we have tried to explain this theory, which is already difficult and complex enough, simply a little, let’s not confuse you any more. After you realize this, the rest is now a bit up to your research. Later, we can discuss a more detailed topic by including M theory. Of course, when these theories are clarified and more accurate information is obtained.