 One of the most important achievements of modern science is the realization that the world is made up of atoms or elementary particles. So electricity is made up of electrons or light is made up of photons. These are the quanta of matter, electrons and photons. And it is difficult to convey how deep and complete is our understanding. But based on the rules, quantum mechanical rules that govern the motion of these elementary particles, we can understand everything around us, including how mobile phone works, how atoms, nuclei, laser, everything really around us, we can understand in great detail. And this has been one of the major successes of quantum theory of matter and interactions between matter. But one thing that does not fit in this, and that's a force that we are all familiar with, namely gravity. So for gravity, we need to use another theory, which is Einstein's general theory of relativity, which is a generalization of Newton's law of gravity. And again, the relativity theory has been extremely successful to describe things like the expansion of the universe, black holes, pulsars, however solar system behaves. So it also is a very successful theory that it does not fit gel in this framework of quantum mechanics. And this has been one of the really outstanding puzzles of the 20th century physics. Now string theory imagines that instead of having point particles as the fundamental constituents, the world is made up made up of little strings, little loops of energy. That's why the name string theory. And everything can be understood from the motion of these elementary strings rather than elementary particles. Now this is a very innocent looking, almost childish looking idea. But it turns out that it has very profound consequences. In particular, in this picture, you can view all the elementary particles as little vibrations of the same string. So electron is the string vibrating in one way and the photon is the string vibrating in another way, rather like the musical notes of a violin string. So one note is one particle. One of the big surprises was that one of the musical notes of the string turns out to be graviton, which is a particle that carries the force of gravity. And therefore, for the first time, it seemed possible that you could treat gravity and the same footing as all other forces and all other particles of matter and in this way, unify general relativity with quantum mechanics. And this has been the reason why string theory has been a very active field of research for the last 50 years because this is an extremely promising idea. The two most important theories of nature we can describe in a unified framework. Of course, all this is very easy to say qualitatively, but to really get into the details and to extract all the information is not an easy task. And it's very demanding and it requires very sophisticated mathematics and deep physical ideas. So the work of these four Dirac medalists, they have really made pioneering contributions in developing both the formalism of string theory and also in extracting important physical consequences out of it. So for example, in particular, how do you understand the properties of elementary particles like electron and photon coming out of string theory? How can we construct this standard model of particle physics as it is called, which describes atoms or nuclei? So this is one of the questions that was addressed by one of the Dirac medalists, for example. But how do you understand the properties of black holes in the, that's within the framework of string theory? This was the main achievement of this Dirac medalist. But as a bonus, first of all, we were able to unify gravity with all the forces, but we also learned two very new important concepts. One of them is duality and the other is holography. And duality says that two very different descriptions of nature which look very different are somehow secretly the same. And this is something that I cannot explain in a minute, but this idea that two very different looking descriptions are secretly the same. So for example, a world living on a very large circle can be secretly the same as a world living on a very, very small circle. Now, this looks almost absurd, but this is possible because there are, in the string theory, there are additional modes like string winding around that circle. And because of the existence of these new modes of matter, it is possible that the two descriptions which look very different are actually the same. So this discovery of duality symmetries and discovery of holography is also one of the very important outcomes of string theory. And holography is even more bizarre. And it comes from the study of black holes because black holes, it looks like the black hole is like a black hole in space. And it looks like that everything that is happening inside the black hole is secretly encoded on the surface of the black hole. That's why the name holography. It's like a hologram. Everything that is some three dimensional image is stored on a film. It's a bit like the film on the surface of the black hole knows everything about what is happening inside the black hole. This is again a very deep, again, it sounds like a science fiction and too easy to state. But there have been very detailed and very beautiful and very non-trivial calculations which have gone into establishing that this actually is true. So I would summarize the work of these Dirac medalists who have made really very major contributions to string theory as in terms of their contribution to developing the formalism of string theory, making contact with the world of elementary particles, understanding the structure of black holes and understanding these two very new and very deep concepts of duality and holography which we still are struggling to fully understand.