 Hi, I'm Zor, welcome to Unisor Education. The purpose of today's lecture is basically to explain certain motivation which I have to start a completely new part, a new course actually, which I would like to present on the same website Unisor.com. Now I was talking before about the course, the first course which I put on this website was Math 14s, the second was Physics 14s. Now I consider both courses relatively complete, I mean I can add some problems maybe or exams in certain cases, but theoretical material is basically covered and I do recommend actually both of them. I am Mathematician so the first part Math 14s was kind of no problems for me. The Physics 14s I had to learn certain things myself in a little bit more detailed way than I knew it before, but my purpose was to explain certain physical concepts from the position of Mathematician. You see, people who are involved in Mathematics are usually fascinated with the way how Math was built. There are certain axioms in the very beginning and then we gradually built the whole building of theories logically deriving the new things from the previous ones. And obvious example is axioms of Euclidus. They put basically the base for geometry while the axioms can be expanded and they were actually expanded to make it a little bit more rigorous I would say. But in any case this build up from axioms to theorems and to more complicated theorems etc. is extremely fascinating way of building the theory. It seems to be the right way to do it. Physics not always was built this way. But I was trying to present the course Physics 14s in relatively the same fashion which means I had certain axioms like three laws of Newton for example for mechanics and then built the whole theories one after another using whatever has been already kind of covered in the future lectures. Now speaking about theory of relativities you see I was always fascinated with how Albert Einstein came up with certain ideas which seemed to me very strange but again very attractive like time is changing if we are switching from one observer to another who is moving relative to the first one. Lengths are changing, paradox of twins which we will cover as well. Even when I was in high school actually I was trying to read books about theory of relativity and it was interesting but I cannot say that I understood everything. So today my purpose is to bring to well relatively young audience some knowledge about theory of relativity as simple as I can but as mathematically rigorous as is possible. So I will always try to do it exactly the same fashion as mathematics was built like certain axioms and then you derive from these axioms whatever is necessary. There are different ways of derivation. You can do it simply, you can do it more sophisticated way. There are some fundamental articles by Einstein which he published in the beginning of 20th century in 1905 which basically explain his ideas about time, space and special theory of relativity. I read them and I cannot say that I kind of completely feel comfortable with how he explained it. So I was trying maybe to find a way to explain it maybe a little bit simpler or maybe a little bit more mathematically. So that's actually my purpose to start this course which is called special theory of relativity. I call it relativity for all because I hope that whatever I will try to convey will be understood by the reasonably educated person like good high school for example or if you wish on the level of my math 14th and physics 14th courses which I have on this website. So if people are familiar with these two courses I mean with material which is explained in these courses you can get it somewhere else whatever but if it's there this basic knowledge which I consider to be the knowledge of educated teenager I think it would be not very difficult to cover the material of special theory of relativity. The only thing is certain conclusions which we come up with might be strange like time is shrinking or length is shrinking or lengthening or something like this. These are kind of counterintuitive but mathematics supports it and people believe in it basically. Yes there were obviously experimental confirmations of theory of relativity and it's generally accepted as the true way to approach our nature but still it seems to be strange in certain circumstances it does contradict our common sense. Okay on this what else I wanted to say basically that's it this is kind of an introductory lecture and I will start starting from the next lecture I will start explaining certain concepts which are at the foundation of special theory of relativity and then we will see how it goes so thank you very much and good luck.