We are living in a 11-dimensional world?-String theory and M-theory

　　

　　We are all composed of particles,quarks(夸克) and electrons,which we called elementary particles. In physical theories, we always think these particles as points. Is this idea true? Although this idea had made great contributions, it still has limitation.(Because general relativity cannot combined with quantum mechanics)

　　String theory(弦論)thought all elementary particles are strings. The vibration modes(震動模式) form different kind of particles. In order to make string theory possible, it demand the world has 10 dimensions! We know that we have 3 space dimensions and 1 time dimensions. String theory contains another 6 space dimensions.

　　Where are the 6 space dimensions? They all curled up like small circle(called Calabi-Yau manifold(卡拉比-丘流形)). They are so small that we couldn’t see them.

 

　

　  There are five different string theories before 1995.(In fact,six,the other one called Supergravity(超重力)) Great physicist and mathematician Edward Witten(I think he is the greatest physicist nowadays!) connect these theories by a great idea called duality(對偶性). The five theories are all bases of a bigger theory called M-theory. The theory promote string to brane(膜,2-d),which means the world has 11 dimensions!

　String theory is a very beautiful and difficult physical theory.(perhaps the most difficult one) The ideas are abstract but simple. My introduction is oversimplified, but I hope you will like it. In fact, I want to dedicate my life to study string theory.