In the last issue I discussed a little about the history of string theory. I have also mentioned some of the successes of this theory there. In this episode, I have basically described the success story. One of the successes of the string theory I discussed in the last discussion was the prediction of graviton particles responsible for gravity and the determination of the dimensions of spacetime. As well as having a stable minimum energy state, this theory requires supersymmetry. This makes it possible to find fermions (i.e., elementary particles of the genus Quark and Lepton) in theory. As the Spacetime Dimensions are more than four, according to scientist Theodore Kaluza, gravity will give rise to other basic interactions as well. This is very promising, because we need to use different fields for each interaction in order to make the theory stand out according to the rules of quantum field theory.
Apparently theory contains many elements of the world we know, but how much reality does it actually contain? Let us give a small comparison: both goats and cows have four legs, hooves, horns and two animals are herbivores. But plowing cannot be done with goats like cows. Examination is the ultimate determinant of whether a theory is correct or not. In addition, this test must be such that this test can be done again. As we have heard, Galileo threw a wooden and iron ball from the Leaning Tower of Pisa and gave visual evidence that gravitational acceleration is the same for both. Whether he actually did that may be questionable but this test can be done anywhere, even in Antarctica. And we get the same result. Of course there is a huge exception. That is the creation of the universe. It is not possible for us to do it again and again. We have the same data for this. Anyway, let's see how successful that test string theory is when it comes to this question.
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The ambition for string theory dates back to the mid-1980s. Before formulating a quantum theory, we need to know the equivalent of its classical language in mechanics. Because, we do not measure using the language of quantum mechanics. Now if it so happens that there is no such thing as symmetry in classical theory in the quantum world, then we have to face a logical problem. That is, quantum is the world of small objects, and the Newtonian or traditional world is its collective counterpart. That is why if we look at any symmetry in the traditional theory, we must look at the quantum version of the same theory. If not, then we assume that there is anomaly in that theory. Our current most successful model, the Standard Model, has the same number of quarks and lepton families. Because if it weren't for that, there would be a difference between the traditional form of the model and the quantum form. From this we learn that there can be no such inconsistency between the quantum form of the correct theory. The reason behind saying so much is that when hyperbolicism was added to the string theory, two types of string theories, namely IIA and IIB, were found besides fermions. There is also the theory of open strings আমরা which we call type and.
Quantitating these superstring theories, it was found that if there is no symmetry of the SO (32) or E8 x E8 groups within the ten-dimensional theory of spacetime, then that theory is inconsistent. It created a huge stir at the time. Because, this is the first time any theory has determined its country-time-dimension as well as its internal symmetry. This is why since then, superstring theory has come to be called the Theory of Everything or ToE. And in the meanwhile many began to search for the last frontier of physics. Naturally, our expectations for this branch of theoretical physics have increased a lot due to 30 years of continuous research. In addition, Edward Witten's startling discovery of string theory in 1995 fueled this demand. There have been five types of superstring theories before, but there are some differences between them. Witten shows that each of the five theories can be transformed into another superstring theory through various transformations. Not only that, but 11 levels of supergravity, the existence of which was a mystery to theorists, was apparently not related to superstring, but was caught in the trap discovered by Witten. Note that the supergravity theories obtained from the superstring theory have a space-time-dimension of 10. From then on, many began to think that there was more to string theory than just basic fibers.

Scientist Theodore Kaluza
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The argument in favor of this idea was further strengthened when Joseph Polchinsky discovered an object called D-Brane in superstring theory in 1995. This led to the solution of an old puzzle in the middle of this theory. What is the puzzle, I will say a little. I mentioned in the previous issue that in the superstring theory, if the value of the string tension is infinite, only massless particle assembly is found there. These include Graviton with Spin Quantum Number-2 and Gravitino with Spin Quantum Number-3/2 with its supersymmetric partner. That is why we do not derive ordinary Einstein gravity from this theory. Rather its supersymmetric refinement, which we have termed supergravity above. An interesting thing here is that these supergravities also have black holes just like Einstein's theory. However, the difference is that all the black holes here have different types of charges besides mass and rotation (they are not just the electrical charges we know) and their dimensions are more than the three we know. The picture looks like this:
Superstring → Supergravity → Charged (high level) black holes
Now the puzzle is that the new charges are appearing because of what basic object? Superstring theory is where we started with one-dimensional objects like wires!
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Polchinski's discovery suggests that superstring theory describes objects of different dimensions and their combinations, not just strings. Theoretical physicists suffered the greatest shock of this result when Hawking gave the famous formula in his research for the entropy of black holes. Kamran Vafa and Andrew Strumminger gave his explanation in 1998 by calculating the combination of this U-Ithadhab. This suggests that string theorists have come very close to the quantum interpretation of the black hole.
Does that mean string theory has succeeded? Critics say the exact opposite. In their words, ‘Have we seen any direct evidence of hawking radiation and black hole entropy in the laboratory?’ We will analyze their statements in the next episode.
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